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GNDU Question Paper-2022

Ba/Bsc 5

Semester

CHEMISTRY

(Inorganic Chemistry-IV)

Time Allowed: Three Hours Maximum Marks: 35

Note: Attempt Five questions in all, selecting at least One question from each section.

The Fifth question may be attempted from any section. All questions carry equal marks.

SECTION-A

1. (a) Discuss the crystal field splitting in octahedral and square planar complexes. S

(b) What is CFSE? Calculate CFSE for [Cr(H₂O)

)]

and [Cr(CN) complexes.

2. (a) Discuss the factors affecting the magnitude of crystal field by taking examples of

complexes.

(b) What is Jahn Teller Effect? Which out of following configurations does not show this

effect: d

(High Spin), d

(High Spin) and d

(High Spin)?

SECTION-B

1.(a) What is magnetic susceptibility ? How can it be measured by Gouy's method?

Explain.

(b) Why Chromium (II) acetate dihydrate is diamagnetic in nature? 2

4. (a) What is the difference between thermodynamic and kinetic stability? What are the

factors which affect stability of complexes? Explain.

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(b) Discuss rate law in nucleophilic substitution reactions in square planar complexes,

SECTION-C

5.(a) Define term symbol. Derive the term symbols for an ion with d ^ 2 configuration.

(b) What are Mulliken symbols? Write these symbols for spectroscopic terms D and F is

tetrahedral field.

6.(a) Discuss selection rules for d-d transitions. Explain electronic spectra of [Ti (H

]

(b) What are Orgel diagrams ? Discuss Orgel diagram for V ^ 3 ion in Octahedral field.

SECTION-D

7.(a) What do you mean by homogeneous hydrogenation? Explain three catalysts used for

homogeneous hydrogenation of alkenes.

(b) What is E.A.N. rule? Calculate E.A.N. for the following:

(i) Fe (pi – C

)

(ii) Cr (CO)

8. (a) What are metal olefin complexes ? Give one method for the preparation of an

important metal olefin complex. Discuss the bonding in these complexes. 5

(b) Give the structure of organometallic compounds formed by 5, 6 and 8 donor

unsaturated molecules.

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GNDU Answer Paper-2022

Ba/Bsc 5

Semester

CHEMISTRY

(Inorganic Chemistry-IV)

Time Allowed: Three Hours Maximum Marks: 35

Note: Attempt Five questions in all, selecting at least One question from each section.

The Fifth question may be attempted from any section. All questions carry equal marks.

SECTION-A

1. (a) Discuss the crystal field splitting in octahedral and square planar complexes. S

(b) What is CFSE? Calculate CFSE for [Cr(H₂O)

)]

and [Cr(CN) complexes.

Ans: Crystal Field Splitting in Octahedral and Square Planar Complexes

(a) Crystal Field Splitting in Octahedral Complexes

In an octahedral complex, a central metal ion is surrounded by six ligands that are

symmetrically arranged. The interaction between the ligands and the d-orbitals of the metal

ion causes a phenomenon called crystal field splitting. The five degenerate (equal energy) d-

orbitals in the free metal ion split into two different energy levels when the ligands

approach.

• Higher energy level (eg level): This consists of the d

and d

−y

. These orbitals

experience more repulsion because the ligands approach directly along the axes

where these orbitals are concentrated.

• Lower energy level (t2g level): The d

, and _{y

} orbitals form the lower energy

group because they lie between the axes and thus experience less repulsion from

the ligands.

The energy difference between the two sets of orbitals is denoted by ΔoΔ_oΔo (octahedral

splitting energy). The magnitude of this splitting depends on factors such as the metal ion's

charge and the nature of the ligands. Strong-field ligands (like CN⁻) cause large splitting,

while weak-field ligands (like H₂O) cause smaller splitting.

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Crystal Field Splitting in Square Planar Complexes

In square planar complexes, the metal ion is surrounded by four ligands arranged in a

square plane. This geometry can be viewed as a distorted version of the octahedral

geometry, where the ligands along the z-axis have been removed, allowing the remaining

ligands in the xy-plane to exert greater repulsion on the metal’s d-orbitals.

• Highest energy level (dx²-y²): The d

−y

d orbital experiences the highest repulsion

because it lies in the xy-plane, directly along the ligand positions.

• Intermediate energy level (dxy, dz²): The dxyd_{xy}dxy orbital is also in the plane

but experiences slightly less repulsion compared to dx2−y2d_{x^2-y^2}dx2−y2, while

the orbital is perpendicular to the plane and experiences lower repulsion.

• Lowest energy level (dxz, dyz): These orbitals lie between the axes and thus

experience the least repulsion.

The energy difference between these orbitals is larger in square planar complexes

compared to octahedral complexes, denoted as Δsp and is about 1.3 times ΔoThis is why

square planar complexes are generally low-spin, strong-field complexes.

(b) What is CFSE?

Crystal Field Stabilization Energy (CFSE) refers to the energy stabilization that occurs when

the d-electrons of a metal ion occupy the lower energy orbitals after crystal field splitting.

CFSE is calculated based on the number of electrons in the t2g and eg orbitals and the

splitting energy.

CFSE = (number of electrons in t2g orbitals)×(−0.4Δo) orbitals}) \times

(number of electrons in eg orbitals)×(0.6Δo

This formula applies to octahedral complexes. For square planar complexes, the orbital

splitting is different, but the concept remains the same.

. Chromium in this complex is in the 3+3^+3+ oxidation state with a

d3d^3d3 configuration. Water is a weak-field ligand, meaning the splitting energy ΔoΔ_oΔo

is relatively small, leading to a high-spin complex. The three electrons will occupy the lower-

energy t2g orbitals. CFSE can be calculated as follows:

This indicates a moderate stabilization due to the weak-field ligand water.

• [Cr(CN)6]3−[Cr(CN)₆]^{3-}[Cr(CN)6]3−: In this complex, chromium is also in the

3+3^+3+ state with a d3d^3d3 configuration. However, CN⁻ is a strong-field ligand,

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causing a larger splitting energy ΔoΔ_ The electrons will still occupy the t2g orbitals,

but due to the larger ΔoΔ_the stabilization is greater:

However, because ΔoΔ_oΔo is larger for CN⁻ ligands compared to H₂O, the overall

stabilization is much greater.

Conclusion

Crystal field splitting is a crucial concept for understanding the electronic structure and

stability of transition metal complexes. Octahedral complexes exhibit a splitting into two

levels, while square planar complexes have a more significant splitting with the highest

energy for the d

−y

orbital. CFSE is used to quantify the stabilization energy resulting from

electron placement in the split orbitals, and the nature of the ligands plays a significant role

in determining the magnitude of this energy

2. (a) Discuss the factors affecting the magnitude of crystal field by taking examples of

complexes.

(b) What is Jahn Teller Effect? Which out of following configurations does not show this

effect: d

(High Spin), d

(High Spin) and d

(High Spin)?

Ans: (a) Factors Affecting the Magnitude of Crystal Field in Complexes

In chemistry, specifically in coordination chemistry, the Crystal Field Theory (CFT) helps us

understand how metal ions interact with surrounding ligands. When ligands approach a

metal ion, the orbitals in the metal ion, especially the ddd-orbitals, experience splitting due

to electrostatic interactions. This splitting creates what is called a crystal field. The

magnitude of this crystal field splitting (Δ\DeltaΔ) is crucial because it affects the overall

stability, color, and magnetic properties of the complex. Let’s dive deeper into the factors

affecting this splitting, or the magnitude of the crystal field.

1. Nature of the Ligand (Spectrochemical Series)

The type of ligand surrounding the metal ion plays a major role in determining the crystal

field splitting. Ligands are arranged in what is known as the Spectrochemical Series, which

lists them from weak-field ligands (causing small splitting) to strong-field ligands (causing

large splitting). Here’s the general order:

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Weak-Field Ligands (small Δ\DeltaΔ):

I−^-− < Br−^-− < S

− < Cl−^-< OH−^-− < H

O (neutral)

Intermediate Ligands:

Strong-Field Ligands (large Δ

en (ethylenediamine) < bipy (2,2'-bipyridine) < phen (1,10-phenanthroline) < NO

−< CO

• Weak-field ligands cause smaller splitting of the ddd-orbitals. Hence, the energy

difference between the split orbitals is lower, and the electrons can more easily

occupy higher-energy orbitals (which contributes to high-spin configurations).

• Strong-field ligands, on the other hand, create a large energy gap between the

orbitals, forcing electrons to pair up in the lower-energy orbitals (resulting in low-

spin configurations).

For example, in an octahedral complex with water as a ligand water

is a weak-field ligand, so the crystal field splitting is small. However, if cyanide (CN-) were

the ligand, the splitting would be larger because it’s a strong-field ligand.

2. Oxidation State of the Metal Ion

The oxidation state of the metal ion also significantly affects the magnitude of the crystal

field. As the oxidation state of the metal increases, the positive charge on the metal ion

increases, making the electrostatic attraction between the metal ion and ligands stronger.

This stronger interaction leads to greater splitting of the ddd-orbitals.

For example:

• iron is in the +2 oxidation state, and the splitting is relatively

small.

• iron is in the +3 oxidation state, and the splitting is larger

because the higher charge on the metal ion increases the ligand-metal interaction.

3. Geometry of the Complex

The geometry or arrangement of the ligands around the metal ion also affects the crystal

field splitting. The most common geometries are:

• Octahedral (six ligands)

• Tetrahedral (four ligands)

• Square planar (four ligands)

In an octahedral field, where six ligands surround the metal ion, the splitting of ddd-orbitals

is larger compared to the tetrahedral field. This is because, in an octahedral arrangement,

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the ligands directly approach the dz2d_{z^2}dz2 and dx2−y2d_{x^2-y^2}dx2−y2 orbitals,

causing them to experience greater repulsion and hence a greater energy difference

between the split orbitals. In contrast, in a tetrahedral field, the ligands approach between

the axes, causing less splitting.

Tetrahedral splitting is typically about half the size of octahedral splitting. Square planar

complexes, on the other hand, often have very large splitting due to the direct interaction of

ligands with the metal's ddd-orbitals.

4. Size of the Metal Ion (Atomic Number)

As we move down a group in the periodic table, the size of the metal ion increases, but

more importantly, so does the extent of ddd-orbital overlap with the ligands. For transition

metals in the same group, the splitting increases as we move from 3d to 4d and 5d metals

because the orbitals are larger and more diffuse, allowing for stronger interactions with

ligands.

For example, the crystal field splitting in complexes of Ru (Ruthenium, 4d) or Ir (Iridium, 5d)

is much larger than in complexes of Fe (Iron, 3d).

5. Nature of Metal-Ligand Bonding

If the metal-ligand bond has covalent character, the crystal field splitting can be affected.

For example, ligands like CO and CN−^-− form strong π\piπ-backbonding interactions with

the metal, where electrons are donated from the metal ddd-orbitals into the ligand’s empty

π∗\pi^*π∗-orbitals. This strengthens the metal-ligand bond, increasing the splitting of the

ddd-orbitals.

In contrast, if the bonding is purely ionic, the splitting would primarily depend on the

electrostatic interactions and might be smaller compared to complexes with covalent

interactions.

6. Coordination Number

The coordination number refers to how many ligands are bound to the metal ion. Higher

coordination numbers (e.g., octahedral complexes with 6 ligands) generally lead to greater

crystal field splitting compared to lower coordination numbers (e.g., tetrahedral complexes

with 4 ligands). This is because more ligands exert a greater total electrostatic influence on

the metal’s ddd-orbitals.

(b) Jahn-Teller Effect

The Jahn-Teller Effect occurs in certain coordination complexes where there is an

asymmetry in the electron distribution, leading to a distortion of the molecular geometry.

This effect is most prominent in octahedral complexes and is particularly noticeable in

complexes with certain electron configurations in their ddd-orbitals.

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What Causes the Jahn-Teller Effect?

The Jahn-Teller Theorem states that "any non-linear molecule with a degenerate electronic

state will undergo a distortion to remove the degeneracy and lower the overall energy of

the system." In simpler terms, if electrons are unevenly distributed in degenerate (same-

energy) orbitals, the molecule will distort its shape to lower the energy by removing this

degeneracy.

When Does the Jahn-Teller Effect Occur?

The Jahn-Teller effect is most commonly seen in octahedral complexes when there are

unevenly filled ege_geg orbitals. Here are the configurations that typically exhibit the Jahn-

Teller effect:

• d

: Seen in Cu

+ complexes.

• Low-spin d

• High-spin d

in an octahedral field.

Example of Jahn-Teller Distortion

In an octahedral d

complex, like [Cu(H

_O)

_]^{2+}, the ege_geg orbitals (d

and −y

) are

unevenly filled. To lower the overall energy, the complex distorts, elongating along the z-

axis. This elongation reduces the repulsion between the ligands and the dz

orbital,

stabilizing the complex.

Configurations That Do Not Show Jahn-Teller Effect

Now, let's examine the given configurations: d

, d

, and d

(all in high-spin).

1. d

(High Spin):

This configuration does show the Jahn-Teller effect because there are unevenly filled

ege_geg orbitals.

2. d

(High Spin):

This configuration does not show the Jahn-Teller effect in most cases. In high-spin

d5d^5d5, the ddd-orbitals are evenly filled, so there’s no need for the complex to

distort.

3. d

(High Spin):

This configuration does not show the Jahn-Teller effect. In high-spin d6d^6d6, the

ege_geg orbitals are evenly filled, which means there’s no degeneracy in the

electronic configuration to cause distortion.

Conclusion

• Jahn-Teller distortion occurs when there’s an asymmetry in the distribution of

electrons in degenerate orbitals, causing the complex to distort to achieve a lower

energy state.

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• The high-spin d

configuration shows the Jahn-Teller effect, while the high-spin d

and high-spin d

configurations do not.

SECTION-B

1.(a) What is magnetic susceptibility ? How can it be measured by Gouy's method?

Explain.

(b) Why Chromium (II) acetate dihydrate is diamagnetic in nature? 2

Ans: (a) What is Magnetic Susceptibility?

Magnetic susceptibility (χ) is a measure of how much a material becomes magnetized when

it is exposed to an external magnetic field. It indicates whether a substance is attracted to or

repelled from a magnetic field. Mathematically, it is defined as the ratio of the

magnetization MMM (magnetic moment per unit volume) to the applied magnetic field

strength H:

Materials can be classified based on their magnetic susceptibility:

1. Diamagnetic Materials: These materials have a small negative susceptibility (χ < 0).

They create a weak repulsion in the presence of an external magnetic field. Examples

include copper, water, and bismuth.

2. Paramagnetic Materials: These have a small positive susceptibility (χ > 0). They are

weakly attracted by a magnetic field and do not retain magnetization in the absence

of the field. Examples include aluminum, platinum, and oxygen.

3. Ferromagnetic Materials: These materials exhibit a strong positive susceptibility and

can become permanently magnetized. Examples include iron, cobalt, and nickel.

Magnetic susceptibility is a key property in understanding the magnetic behavior of

materials and is used in fields like solid-state physics, chemistry, and material science.

Measuring Magnetic Susceptibility: Gouy's Method

One of the traditional methods to measure magnetic susceptibility is Gouy's method, which

is simple and widely used in laboratories.

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Principle of Gouy's Method

In this method, a sample is placed in a magnetic field, and the force it experiences due to

the field is measured. The fundamental principle is based on the fact that a paramagnetic

substance is attracted into a magnetic field, while a diamagnetic substance is repelled.

Experimental Setup

The Gouy balance consists of a non-magnetic balance where a sample is suspended

between the poles of a magnet. The upper end of the sample is placed in a zero or weak

magnetic field, while the lower end is exposed to a strong magnetic field. The force exerted

on the sample due to the magnetic field is proportional to the material's magnetic

susceptibility.

Procedure

1. The sample is weighed using the balance when there is no magnetic field.

2. The magnetic field is applied, and the change in weight is measured.

3. The change in weight indicates the force acting on the sample due to the magnetic

field.

4. The force FFF on the sample is related to the volume susceptibility χχχ and the

magnetic field HHH as:

Where:

o H is the magnetic field strength,

o A is the cross-sectional area of the sample,

o is the field gradient.

5. Using a standard substance with known susceptibility, the calibration constant is

determined, which helps calculate the susceptibility of the unknown sample.

Advantages of Gouy's Method

• Simple equipment is required, which is cost-effective.

• A relatively large sample can be used, allowing easy measurement even with

ordinary balances.

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Disadvantages

• Requires a large sample size.

• The packing of the sample needs to be uniform and compact to avoid errors in

measurement.

This method remains a popular technique for determining the magnetic susceptibility of

various materials, especially in educational and research laboratories(

(b) Why Chromium (II) Acetate Dihydrate is Diamagnetic

Chromium(II) acetate dihydrate, also known as Cr₂(OAc)₄(H₂O)₂, is an interesting compound

due to its magnetic properties. Chromium in its +2 oxidation state typically has a

configuration of [Ar]3d

, which would suggest it to be paramagnetic because of unpaired

electrons. However, in this compound, it exhibits diamagnetic behavior. This is due to the

nature of the metal-metal bonding in the structure.

Explanation

In the structure of chromium(II) acetate, there are pairs of Cr²⁺ ions that form a direct Cr-Cr

bond. The formation of this bond leads to the pairing of the unpaired electrons between the

two chromium atoms. This electron pairing removes the paramagnetism that would

typically be present in a d⁴ system.

This bond leads to the effective cancellation of the magnetic moments, and as a result, the

compound behaves as diamagnetic rather than paramagnetic. In simple terms, the

chromium atoms form a bond that effectively "locks" the electrons into pairs, so the

material does not exhibit magnetism in the presence of a magnetic field.

This diamagnetic nature of chromium(II) acetate dihydrate is an excellent example of how

molecular structure and bonding can influence the magnetic properties of a material(

4. (a) What is the difference between thermodynamic and kinetic stability? What are the

factors which affect stability of complexes? Explain.

(b) Discuss rate law in nucleophilic substitution reactions in square planar complexes,

Ans: A) Difference Between Thermodynamic and Kinetic Stability

1. Thermodynamic Stability:

Thermodynamic stability refers to the stability of a compound or complex in terms of its

energy. A thermodynamically stable complex is one that has a lower energy state compared

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to its reactants, meaning it is more favorable for it to exist in that state. This concept is often

assessed using the Gibbs free energy (ΔG) of the reaction.

• Lower Gibbs Free Energy: If the ΔG of a reaction is negative, it indicates that the

products (including complexes) are more stable than the reactants. Thus, the

reaction is likely to proceed spontaneously toward the products.

• Equilibrium: Thermodynamic stability also involves reaching an equilibrium state

where the concentrations of reactants and products remain constant over time. At

this point, the rates of the forward and reverse reactions are equal.

• Examples: The formation of stable coordination complexes from transition metals

with ligands is a thermodynamic process. A complex formed with a strong field

ligand like CN⁻ will have lower energy and thus higher thermodynamic stability

compared to a complex formed with a weaker field ligand like H₂O.

2. Kinetic Stability:

Kinetic stability, on the other hand, relates to the rate at which a reaction occurs. A

kinetically stable complex is one that may have a relatively high energy state (and thus is not

thermodynamically stable), but the rate of decomposition or reaction to convert it to

another state is slow.

• Activation Energy: Kinetic stability is heavily influenced by the activation energy

required for a reaction to proceed. Even if a complex is thermodynamically unstable,

it can be kinetically stable if the activation energy for its decomposition is high.

• Reaction Rate: Kinetic stability is observed when a complex does not easily break

down into its components or reactants despite being thermodynamically

unfavorable.

• Examples: The stability of certain organometallic complexes, like ferrocene, can be

attributed to their kinetic stability, as they can remain intact for long periods despite

being in a higher energy state compared to the products of their decomposition.

3. Summary of Differences:

Aspect

Thermodynamic Stability

Kinetic Stability

Definition

Stability based on free energy

Stability based on reaction rate

Gibbs Free Energy

(ΔG)

Negative ΔG indicates stability

High activation energy indicates

stability

Equilibrium

Involves equilibrium

concentrations

May not reach equilibrium

quickly

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Aspect

Thermodynamic Stability

Kinetic Stability

Example

Formation of stable coordination

complexes

Long-lived organometallic

complexes

Factors Affecting the Stability of Complexes

The stability of coordination complexes is influenced by several factors, including:

1. Nature of the Metal Ion:

• Oxidation State: Higher oxidation states generally lead to stronger complexes due to

increased positive charge attracting the ligands more effectively. For example,

transition metals in a +3 oxidation state are typically more stable than in a +2 state.

• Size and Charge: Smaller, highly charged metal ions tend to form more stable

complexes. For example, Fe

+ forms more stable complexes than Fe

due to its

higher charge density.

2. Nature of the Ligand:

• Ligand Field Strength: Strong field ligands (e.g., CN⁻, CO) create greater crystal field

splitting, leading to more stable complexes compared to weak field ligands (e.g.,

H₂O, NH₃).

• Bidentate vs. Monodentate: Bidentate ligands, which can bind through two donor

atoms, often form more stable complexes due to the chelate effect. For example,

ethylenediamine (en) forms very stable chelates with transition metals.

3. Coordination Number:

• The coordination number of the metal ion, which indicates the number of ligand

donor atoms bonded to it, can affect stability. For instance, coordination numbers of

4 and 6 are commonly found in stable complexes.

4. Geometry:

• The spatial arrangement of ligands around the metal ion (e.g., octahedral, square

planar, tetrahedral) can impact stability. Square planar complexes, for instance, may

exhibit unique stabilities based on ligand interactions and electronic factors.

5. Solvent Effects:

• The nature of the solvent can significantly affect the stability of complexes. Polar

solvents tend to stabilize charged complexes, while non-polar solvents may favor

neutral complexes.

6. Temperature and Pressure:

• Changes in temperature and pressure can influence the stability of complexes.

Higher temperatures may lead to greater kinetic energy, potentially breaking down

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complexes, while changes in pressure can affect the formation of gaseous ligands or

products.

7. Electronic Factors:

• The electronic configuration of the metal ion and the nature of its interactions with

the ligands can play a crucial role. Metal-ligand bonding interactions can be ionic or

covalent, influencing stability.

8. Steric Hindrance:

• Bulky ligands may hinder the approach of other ligands to the metal center, affecting

complex stability.

B) Rate Law in Nucleophilic Substitution Reactions in Square Planar Complexes

Nucleophilic substitution reactions are critical in coordination chemistry, especially in

square planar complexes, commonly found in transition metals like Ni

+ Pd

+and Pt2+.

1. Mechanisms of Nucleophilic Substitution:

• Two main mechanisms are observed in nucleophilic substitution reactions of square

planar complexes: S_N1 and S_N2 mechanisms.

S_N1 Mechanism:

• This mechanism involves the formation of a stable intermediate (usually a square

planar complex) before the nucleophile attacks. The first step is usually slow and

rate-determining, leading to a racemization of the product due to the planar

structure of the intermediate.

S_N2 Mechanism:

• The S_N2 mechanism involves a direct attack of the nucleophile on the square planar

complex, resulting in a concerted reaction where bond formation and bond breaking

occur simultaneously. This mechanism is typically favored in complexes with less

steric hindrance.

2. Rate Law Expression:

• The rate law for nucleophilic substitution reactions can generally be expressed in

terms of the concentrations of the reactants. For example, consider a square planar

complex [ML

]+Nu−→[ML

Nu]+L\ where M is the metal, L is a ligand, and Nu− is the

nucleophile).

• For the S_N2 mechanism, the rate law is expressed as:

Rate=k[ML

][Nu

For the S_N1 mechanism, where the rate depends only on the square planar complex:

Rate=k[ML

]

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Summary of Nucleophilic Substitution in Square Planar Complexes:

• Kinetics: Kinetics is determined by the nature of the nucleophile, the metal center,

and the ligands attached to it.

• Substituents and Steric Effects: The nature of the substituents around the metal

affects the substitution reaction. Bulky ligands may slow down substitution reactions

due to steric hindrance.

• Polarization: The polarization of bonds within the complex can facilitate or hinder

the nucleophilic attack.

Conclusion

Understanding the difference between thermodynamic and kinetic stability is crucial in

coordination chemistry as it influences how complexes form and react. Thermodynamic

stability deals with energy favorability, while kinetic stability focuses on reaction rates.

Various factors, including the nature of metal ions and ligands, coordination number, and

geometrical arrangements, significantly influence the stability of complexes.

Nucleophilic substitution reactions, particularly in square planar complexes, can be well

described through specific rate laws and mechanisms, which are essential for predicting

how these complexes will behave under various conditions.

Overall, this topic showcases the intricate balance between stability, reactivity, and the

mechanisms that govern chemical transformations in coordination complexes, providing a

rich area for study and exploration in inorganic chemistry.

SECTION-C

5.(a) Define term symbol. Derive the term symbols for an ion with d ^ 2 configuration.

(b) What are Mulliken symbols? Write these symbols for spectroscopic terms D and F is

tetrahedral field.

Ans: a) Term Symbols:

Term symbols are a way to describe the electronic state of an atom or ion. They provide

information about the total angular momentum and spin of the electrons in a particular

configuration. Think of them as a shorthand code that tells us important details about how

the electrons are arranged and behaving in an atom or ion.

A term symbol typically looks like this: ^(2S+1)L_J

Where:

• S is the total spin quantum number

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• L is the total orbital angular momentum quantum number

• J is the total angular momentum quantum number

1. The superscript (2S+1) is called the "spin multiplicity." It tells us how many possible

orientations the total spin can have in a magnetic field.

2. L is represented by a letter: S = 0, P = 1, D = 2, F = 3, G = 4, and so on. This comes

from old spectroscopic terms: Sharp, Principal, Diffuse, Fundamental.

3. J is the subscript, representing the total angular momentum.

Now, let's derive the term symbols for a d^2 configuration:

Step 1: Determine possible microstates In a d orbital, we have 5 possible ml values: -2, -1, 0,

1, 2 With 2 electrons, we need to consider how they can be distributed among these ml

values, keeping in mind the Pauli exclusion principle.

Step 2: Calculate ML and MS values ML is the sum of individual ml values MS is the sum of

individual ms values (each electron can have ms = +1/2 or -1/2)

Step 3: Group microstates with the same ML and MS values

Step 4: Identify the terms The largest ML value in a group determines L: ML(max) = 4 → G

term ML(max) = 3 → F term ML(max) = 2 → D term ML(max) = 1 → P term ML(max) = 0 → S

term

Step 5: Determine multiplicities For d^2, we can have either paired spins (S = 0) or unpaired

spins (S = 1) So we'll have singlet (2S+1 = 1) and triplet (2S+1 = 3) terms

Step 6: Apply Hund's rules to determine the ground state

After going through this process, we find that the possible term symbols for a d^2

configuration are:

^1S, ^1D, ^1G (singlet terms) ^3P, ^3F (triplet terms)

The ground state, according to Hund's rules, is ^3F.

b) Mulliken Symbols:

Mulliken symbols are a way to describe the symmetry of electronic states in molecules or

complexes. They're particularly useful when dealing with molecules in specific symmetry

environments, like tetrahedral or octahedral fields.

Mulliken symbols consist of a capital letter indicating the degeneracy of the state, followed

by a subscript indicating the symmetry in the point group of the molecule:

A: singly degenerate (1 state) E: doubly degenerate (2 states) T: triply degenerate (3 states)

G: quadruply degenerate (4 states)

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Subscripts can be: 1 or g: symmetric with respect to inversion 2 or u: antisymmetric with

respect to inversion ' : symmetric with respect to horizontal plane " : antisymmetric with

respect to horizontal plane

Now, let's consider the D and F terms in a tetrahedral field:

In a tetrahedral field, the symmetry operations are different from those in a free ion. This

change in symmetry causes the degenerate states to split.

For a D term:

• In a free ion, a D term is 5-fold degenerate.

• In a tetrahedral field, it splits into: E + T2 So, the Mulliken symbols for a D term in a

tetrahedral field are E and T2.

For an F term:

• In a free ion, an F term is 7-fold degenerate.

• In a tetrahedral field, it splits into: A2 + T1 + T2 So, the Mulliken symbols for an F

term in a tetrahedral field are A2, T1, and T2.

To understand why this splitting occurs, we need to consider group theory and how the

symmetry operations of a tetrahedral field interact with the angular momentum states of

the D and F terms. The tetrahedral field has lower symmetry than the spherical symmetry of

a free ion, which causes the degeneracy to be partially lifted.

It's important to note that this splitting is not just a theoretical concept – it has real,

observable effects on the spectroscopic properties of compounds. For example, in transition

metal complexes with tetrahedral geometry, these splittings contribute to the colors we

observe and the magnetic properties of the compounds.

To further illustrate these concepts, let's consider some practical examples:

1. The compound [CoCl4]^2- is a tetrahedral complex with a d^7 configuration. The

ground state of a d^7 ion is ^4F (using the term symbol notation we discussed

earlier). In the tetrahedral field of the chloride ligands, this ^4F term splits into ^4A2,

^4T1, and ^4T2 states (using Mulliken symbols). This splitting is responsible for the

intense blue color of this complex.

2. Another example is the [MnCl4]^2- ion, which has a d^5 configuration. The ground

state for a d^5 ion is ^6S, which doesn't split in a tetrahedral field (it becomes ^6A1

in Mulliken notation). This is why many tetrahedral Mn(II) complexes are pale pink or

nearly colorless – the d-d transitions are spin-forbidden and thus very weak.

3. In the case of [CuCl4]^2-, which has a d^9 configuration, the ground state is ^2D. In a

tetrahedral field, this splits into ^2E and ^2T2 states. The transitions between these

states give rise to the characteristic green color of many tetrahedral Cu(II)

complexes.

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These examples show how the concepts of term symbols and Mulliken symbols are not just

abstract ideas, but tools that help us understand and predict the properties of real chemical

compounds.

It's worth noting that while we've focused on tetrahedral complexes here, similar principles

apply to octahedral complexes and other symmetries. The specific splittings and Mulliken

symbols would be different, but the general idea of how symmetry affects electronic states

remains the same.

In conclusion, term symbols and Mulliken symbols are powerful tools in inorganic chemistry

and spectroscopy. They allow us to succinctly describe complex electronic states and predict

how these states will behave in different environments. By understanding these symbols,

chemists can gain insights into the color, magnetism, and reactivity of compounds,

particularly transition metal complexes.

While these concepts can seem abstract at first, they're based on fundamental principles of

quantum mechanics and group theory. With practice, they become invaluable tools for any

chemist working with transition metals or studying spectroscopy.

Remember, these symbols are not just theoretical constructs – they have real, practical

applications in understanding and predicting the behavior of chemical compounds. Whether

you're analyzing the color of a solution, interpreting a complex spectrum, or designing a

new catalyst, a solid understanding of term symbols and Mulliken symbols will serve you

well.

6.(a) Discuss selection rules for d-d transitions. Explain electronic spectra of [Ti (H

]

(b) What are Orgel diagrams ? Discuss Orgel diagram for V ^ 3 ion in Octahedral field.

Ans: D-d transitions are a type of electronic transition that occurs in transition metal

complexes. These transitions involve the movement of electrons between different d

orbitals within the same metal ion. To understand this better, imagine the d orbitals as

different energy levels or "floors" in a building, and the electrons as people moving between

these floors.

Now, let's discuss the selection rules for d-d transitions:

Selection rules are like guidelines that tell us which transitions are allowed and which are

not. They help us predict which transitions we might see in a spectrum. There are two main

selection rules for d-d transitions:

1. Spin selection rule: This rule states that transitions between states with different

spin multiplicities are forbidden. In simpler terms, electrons prefer to keep their spin

the same during a transition. If we think of electron spin as the direction an electron

is spinning (either up or down), this rule says that an electron doesn't want to

change its spinning direction during a transition.

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2. Laporte selection rule: This rule states that transitions between states with the same

parity are forbidden in centrosymmetric molecules. Parity refers to whether the

wave function changes sign when inverted through the center of symmetry. In

simpler terms, this rule says that in molecules with a center of symmetry (like

octahedral complexes), transitions between orbitals of the same type (like d to d) are

not allowed.

However, there are ways these "forbidden" transitions can still occur:

1. Spin-orbit coupling: This is a phenomenon that can mix states with different spin,

allowing some spin-forbidden transitions to occur weakly.

2. Vibronic coupling: This involves the interaction between electronic and vibrational

states. It can cause temporary loss of the center of symmetry, making some Laporte-

forbidden transitions weakly allowed.

Now, let's look at the electronic spectra of [Ti(H2O)6]³⁺:

The [Ti(H2O)6]³⁺ complex is an octahedral complex of titanium(III). Titanium(III) has a d¹

electron configuration, meaning it has one electron in its d orbitals.

In an octahedral field, the d orbitals split into two sets:

• t2g orbitals (dxy, dyz, dxz): These are lower in energy

• eg orbitals (dx²-y², dz²): These are higher in energy

The difference in energy between these two sets is called the crystal field splitting

parameter, often denoted as Δo.

In the [Ti(H2O)6]³⁺ complex, the single d electron occupies one of the t2g orbitals in the

ground state. The electronic spectrum of this complex shows a single broad absorption band

corresponding to the transition of this electron from the t2g to the eg level.

This transition is written as ²T2g → ²Eg. Here's what this notation means:

• The "2" superscript indicates that the spin multiplicity is 2 (there's one unpaired

electron).

• T2g and Eg are the symmetry labels for the ground and excited states, respectively.

This transition is both spin-allowed (the spin doesn't change) and Laporte-forbidden (it's a d-

d transition in an octahedral complex). However, it still occurs due to vibronic coupling,

which is why we can see it in the spectrum.

The energy of this transition corresponds to the crystal field splitting parameter Δo. By

measuring the wavelength of the absorption maximum, we can calculate Δo for this

complex.

The spectrum of [Ti(H2O)6]³⁺ typically shows a single broad band with a maximum around

20,000 cm⁻¹ (500 nm), which appears purple-pink to our eyes. This is why solutions of Ti³⁺

often have a distinctive purple color.

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b) Orgel diagrams and the diagram for V³⁺ in an octahedral field

Orgel diagrams are a type of energy level diagram used to visualize the electronic states of

transition metal ions in different crystal field environments. They're named after Leslie

Orgel, who developed them in the 1950s.

Here's what Orgel diagrams show:

1. The ground state and excited states of a metal ion

2. How these states change as the crystal field strength increases

3. The possible electronic transitions between these states

Orgel diagrams are particularly useful for understanding the spectra of transition metal

complexes with d¹ to d⁹ electron configurations.

Now, let's look at the Orgel diagram for V³⁺ in an octahedral field:

V³⁺ has a d² electron configuration, meaning it has two electrons in its d orbitals.

In a weak octahedral field (left side of the diagram):

• The ground state is ³F, which splits into ³T1g, ³T2g, and ³A2g states as the field

strength increases.

• There's also a higher energy ³P state, which becomes a ³T1g state in the octahedral

field.

As we move from left to right on the diagram, we're increasing the strength of the

octahedral field. This causes the energy levels to change:

• The ³T1g(F) level (from the ³F state) increases in energy

• The ³T2g level increases more slowly

• The ³A2g level decreases in energy

• The ³T1g(P) level (from the ³P state) initially decreases, then increases in energy

The Orgel diagram for V³⁺ shows three main transitions:

1. ³T1g(F) → ³T2g: This is the lowest energy transition, often labeled ν1

2. ³T1g(F) → ³T1g(P): This is a higher energy transition, often labeled ν2

3. ³T1g(F) → ³A2g: This is the highest energy transition, often labeled ν3

These transitions correspond to the absorption bands we see in the electronic spectrum of

V³⁺ complexes.

The Orgel diagram helps us understand several important points:

1. How the energy levels change with crystal field strength

2. Which transitions are possible

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3. The relative energies of these transitions

For V³⁺ in a strong octahedral field, the ground state is ³T1g(F), and the two electrons

occupy the t2g orbitals with parallel spins (following Hund's rule).

The actual spectrum of [V(H2O)6]³⁺ shows three main absorption bands:

• ν1 at about 17,000 cm⁻¹ (590 nm, yellow-orange)

• ν2 at about 25,000 cm⁻¹ (400 nm, violet)

• ν3 at about 38,000 cm⁻¹ (263 nm, ultraviolet)

The colors we see are the complementary colors to those absorbed. So, [V(H2O)6]³⁺

solutions often appear pale blue or green.

Understanding Orgel diagrams and selection rules helps us interpret the electronic spectra

of transition metal complexes. This is crucial in fields like inorganic chemistry, materials

science, and even some areas of biology where metal ions play important roles.

For example:

• In catalysis, understanding the electronic structure of metal complexes helps in

designing more effective catalysts.

• In materials science, these concepts are used to develop materials with specific

optical or magnetic properties.

• In biochemistry, they help explain the function of metalloproteins like hemoglobin.

It's important to note that while Orgel diagrams are very useful, they have limitations. For

more complex systems or for very accurate calculations, more advanced methods like

Tanabe-Sugano diagrams or computational chemistry techniques are often used.

In conclusion, d-d transitions, selection rules, and Orgel diagrams are fundamental concepts

in understanding the electronic structure and spectroscopic properties of transition metal

complexes. They provide a framework for interpreting experimental results and predicting

the behavior of new compounds. As you continue your studies in inorganic chemistry, you'll

find these concepts appearing again and again, forming a foundation for understanding

more advanced topics in the field.

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SECTION-D

7.(a) What do you mean by homogeneous hydrogenation? Explain three catalysts used for

homogeneous hydrogenation of alkenes.

(b) What is E.A.N. rule? Calculate E.A.N. for the following:

(i) Fe (pi – C

)

(ii) Cr (CO)

Ans: Homogeneous Hydrogenation

Let's start with homogeneous hydrogenation. To understand this, we need to break down the

term:

•

"Homogeneous" means that everything is in the same phase or state. In chemistry, this

usually refers to everything being dissolved in the same solution.

•

"Hydrogenation" is a chemical reaction where hydrogen (H2) is added to another

molecule.

So, homogeneous hydrogenation is a process where hydrogen is added to a molecule, and both

the catalyst and the reactants are in the same phase - usually dissolved in the same liquid

solution.

This is different from heterogeneous hydrogenation, where the catalyst is typically a solid and

the reactants are gases or liquids. In homogeneous hydrogenation, everything - the catalyst, the

hydrogen, and the molecule being hydrogenated - is mixed together in the same solution.

A common example of homogeneous hydrogenation is adding hydrogen to an alkene (a

molecule with a carbon-carbon double bond) to create an alkane (a molecule with only single

bonds between carbons). This process is important in many industries, including the food

industry for making margarine from vegetable oils, and in the pharmaceutical industry for

making certain medicines.

Catalysts for Homogeneous Hydrogenation of Alkenes

Now, let's talk about three important catalysts used for the homogeneous hydrogenation of

alkenes. Catalysts are substances that speed up chemical reactions without being consumed in

the process.

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a) Wilkinson's Catalyst:

Wilkinson's catalyst, named after the chemist Geoffrey Wilkinson, is one of the most famous

catalysts for homogeneous hydrogenation. Its chemical formula is RhCl(PPh3)3, where:

•

Rh is rhodium, a transition metal

•

Cl is chlorine

•

PPh3 is triphenylphosphine, a common ligand in organometallic chemistry

This catalyst is particularly good at hydrogenating alkenes under mild conditions. It works by

first attaching to the alkene, then helping hydrogen molecules split and attach to the carbons of

the alkene.

b) Crabtree's Catalyst:

Crabtree's catalyst, named after Robert H. Crabtree, is another important homogeneous

hydrogenation catalyst. Its formula is [Ir(cod)(PCy3)(py)]PF6, where:

•

Ir is iridium, another transition metal

•

cod is cyclooctadiene, an organic molecule

•

PCy3 is tricyclohexylphosphine, another ligand

•

py is pyridine, a nitrogen-containing ring compound

•

PF6 is hexafluorophosphate, a counterion

This catalyst is particularly good at hydrogenating "difficult" alkenes - ones that are sterically

hindered (have bulky groups around them) or are not very reactive.

c) Noyori's Catalyst:

Noyori's catalyst, named after Ryoji Noyori, is actually a family of catalysts used for asymmetric

hydrogenation - a process that creates specific 3D arrangements of atoms. One example is

RuCl2[(S)-binap], where:

•

Ru is ruthenium, another transition metal

•

Cl is chlorine

•

(S)-binap is a special organic ligand that gives the catalyst its asymmetric properties

This catalyst is important because it can create molecules with specific 3D structures, which is

crucial in the pharmaceutical industry where the 3D shape of a molecule can determine its

effectiveness as a drug.

How These Catalysts Work

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These catalysts all work in a similar general way:

First, they bind to the alkene molecule.

Then, they help split a hydrogen molecule (H2) into two separate hydrogen atoms.

These hydrogen atoms are then added to the carbons of the alkene, one at a time.

Finally, the newly formed alkane is released, and the catalyst is ready to start the

process again with a new alkene molecule.

The specific details of how each catalyst does this vary, which is why different catalysts are

better for different types of reactions or different types of alkenes.

The E.A.N. Rule

Now, let's move on to the E.A.N. rule. E.A.N. stands for Effective Atomic Number. This rule is

used in inorganic chemistry, particularly when dealing with organometallic compounds

(compounds that have metal-carbon bonds).

The E.A.N. rule states that in stable organometallic compounds, the metal atom often has an

effective atomic number equal to that of the next noble gas in the periodic table.

To calculate the E.A.N., you:

Start with the number of electrons in the neutral metal atom

Subtract the oxidation state of the metal (because positive oxidation state means the

metal has lost electrons)

Add the number of electrons donated by the ligands

The result should typically equal the number of electrons in the nearest noble gas.

Let's calculate the E.A.N. for the compounds you mentioned:

a) Fe(π-C5H5)2 (Ferrocene):

Fe (Iron) has 26 electrons in its neutral state

In ferrocene, iron is in the +2 oxidation state, so we subtract 2 electrons

Each C5H5 (cyclopentadienyl) ring donates 6 electrons (it's an aromatic system)

So, the calculation is: 26 - 2 + (6 x 2) = 36

The E.A.N. of iron in ferrocene is 36, which is the same as the next noble gas, krypton.

b) Cr(CO)6 (Chromium hexacarbonyl):

Cr (Chromium) has 24 electrons in its neutral state

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In this compound, chromium is in the 0 oxidation state, so we don't subtract any

electrons

Each CO (carbon monoxide) ligand donates 2 electrons

So, the calculation is: 24 + (2 x 6) = 36

Again, the E.A.N. is 36, matching krypton.

Why is the E.A.N. Rule Important?

The E.A.N. rule helps chemists understand and predict the stability of organometallic

compounds. Compounds that follow this rule often have a complete set of electrons in their

outermost shell, similar to noble gases, which makes them particularly stable.

However, it's important to note that while the E.A.N. rule is useful, it's not absolute. There are

stable compounds that don't follow this rule, and unstable ones that do. It's best thought of as a

helpful guideline rather than a strict law.

Applications of Homogeneous Hydrogenation and Organometallic Compounds

Understanding homogeneous hydrogenation and organometallic compounds is crucial for many

areas of chemistry and industry:

•

In the pharmaceutical industry, hydrogenation is used to synthesize many drugs. The

ability to control the 3D structure of molecules through asymmetric hydrogenation is

particularly important.

•

In the food industry, hydrogenation is used to convert liquid vegetable oils into solid

fats, like in the production of margarine.

•

In the petrochemical industry, hydrogenation is used to remove sulfur from fuels,

making them cleaner-burning.

•

Organometallic compounds like ferrocene have applications in materials science. For

example, some ferrocene derivatives are used in making fire-resistant materials.

•

Some organometallic compounds are used as catalysts themselves, enabling a wide

range of industrial processes.

The Bigger Picture

These concepts - homogeneous hydrogenation, catalysis, and the E.A.N. rule - are part of the

broader field of inorganic chemistry. Inorganic chemistry deals with the synthesis and behavior

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of compounds that don't primarily involve carbon-carbon bonds (though organometallic

compounds, which do have carbon-metal bonds, are generally considered part of inorganic

chemistry).

Understanding these concepts helps chemists design new catalysts, create new materials, and

synthesize complex molecules more efficiently. This knowledge has far-reaching implications,

from developing new medicines to creating more efficient industrial processes to designing new

materials for technologies like solar cells or batteries.

In conclusion, while these topics might seem abstract, they're fundamental to much of the

chemistry that shapes our modern world. From the food we eat to the medicines we take to the

materials in our smartphones, the principles of inorganic chemistry, including homogeneous

hydrogenation and organometallic compounds, play a crucial role.

Remember, chemistry is a vast and complex field, and while these explanations aim to simplify

the concepts, there's always more depth to explore. If you're interested in learning more, don't

hesitate to ask for clarification or dive deeper into any of these topics!

8. (a) What are metal olefin complexes ? Give one method for the preparation of an

important metal olefin complex. Discuss the bonding in these complexes. 5

(b) Give the structure of organometallic compounds formed by 5, 6 and 8 donor

unsaturated molecules.

Ans: Metal Olefin Complexes:

Metal olefin complexes are a type of organometallic compound where a metal atom or ion

is bonded to an olefin (alkene) molecule. In simpler terms, it's when a metal hooks up with a

molecule that has a carbon-carbon double bond.

Olefins are hydrocarbons (molecules made of carbon and hydrogen) that contain at least

one carbon-carbon double bond. Examples include ethene (C2H4), propene (C3H6), and

butene (C4H8).

When these olefins attach to a metal, they form what we call metal olefin complexes. These

complexes are important in various chemical processes, especially in catalysis (helping

chemical reactions occur more easily).

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2. Preparation of an Important Metal Olefin Complex:

One of the most famous and important metal olefin complexes is called Zeise's salt. It's

named after William Christopher Zeise, who first prepared it in 1827. Let's look at how it's

made:

Zeise's salt has the formula K[PtCl3(C2H4)]·H2O. Here's a simple method to prepare it:

a) Start with potassium tetrachloroplatinate (K2PtCl4) dissolved in water. b) Bubble ethene

gas (C2H4) through this solution. c) Add a bit of hydrochloric acid (HCl) to the mixture. d)

The Zeise's salt will form as yellow crystals that you can filter out.

The reaction can be written as: K2PtCl4 + C2H4 + HCl → K[PtCl3(C2H4)]·H2O + KCl

This process demonstrates how a simple olefin (ethene) can attach to a metal (platinum) to

form a complex.

3. Bonding in Metal Olefin Complexes:

The bonding in metal olefin complexes is fascinating and a bit complicated. It involves two

types of bonding working together:

a) Sigma (σ) bonding: The electrons in the pi (π) bond of the olefin (the double bond) form a

sigma bond with empty orbitals on the metal. This is like the olefin sharing its electrons with

the metal.

b) Pi (π) back-bonding: At the same time, filled d-orbitals on the metal can overlap with

empty anti-bonding orbitals on the olefin. This allows the metal to share some of its

electrons back with the olefin.

• This two-way sharing of electrons is called synergic bonding. It's like the metal and

the olefin are helping each other out – the olefin gives electrons to the metal, and

the metal gives some back to the olefin.

• This bonding changes the olefin a bit. The carbon-carbon bond gets a bit longer and

weaker because some of its electron density is now shared with the metal. Also, the

hydrogen atoms on the carbons tend to bend back, away from the metal.

• Scientists use a model called the Dewar-Chatt-Duncanson model to describe this

bonding. It helps explain why these complexes are stable and why they're useful in

various chemical reactions.

4. Structures of Organometallic Compounds with 5, 6, and 8 Donor Unsaturated

Molecules:

Now, let's look at some organometallic compounds formed by larger unsaturated

molecules. These molecules can donate multiple electrons to the metal, forming more

complex structures.

a) 5-donor unsaturated molecules: A common example is the cyclopentadienyl anion

(C5H5-). It's a ring of five carbon atoms with five hydrogen atoms attached. This molecule

can donate five electrons to a metal.

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Structure: The cyclopentadienyl ring usually bonds to the metal in a way that all five carbon

atoms are equidistant from the metal. This forms a structure that looks a bit like an

umbrella, with the metal as the handle and the ring as the canopy.

Example: Ferrocene, Fe(C5H5)2, where two cyclopentadienyl rings sandwich an iron atom.

b) 6-donor unsaturated molecules: Benzene (C6H6) and its derivatives can act as 6-electron

donors. These form what we call "piano-stool" complexes because of their shape.

• Structure: The benzene ring sits flat (or nearly flat) above the metal, with other

ligands attached to the metal below. It looks a bit like a piano stool, with the

benzene as the seat and the other ligands as the legs.

• Example: Chromium tricarbonyl complex, (C6H6)Cr(CO)3, where a benzene ring sits

atop a chromium atom with three carbonyl (CO) groups below.

c) 8-donor unsaturated molecules: Cyclooctatetraene (C8H8) can act as an 8-electron donor

when it's in its dianion form (C8H82-).

• Structure: The cyclooctatetraene dianion forms a flat ring that bonds to the metal

from one side. The metal sits either above or below the plane of the ring.

• Example: Uranocene, U(C8H8)2, where two cyclooctatetraene rings sandwich a

uranium atom, similar to the structure of ferrocene but with larger rings.

• These structures show how versatile organometallic chemistry can be. The metal can

bond with these large, unsaturated molecules in various ways, creating compounds

with unique properties and reactivities.

5.Importance and Applications:

Metal olefin complexes and these larger organometallic compounds are not just interesting

from a theoretical perspective – they have many practical applications:

• Catalysis: Many of these compounds are excellent catalysts. They can help speed up

chemical reactions or make them more selective. For example, some are used in the

production of plastics, in pharmaceutical synthesis, and in the petroleum industry.

• Material Science: Some organometallic compounds have interesting electronic or

magnetic properties, making them useful in materials science. They might be used in

creating new types of sensors or electronic components.

• Organic Synthesis: These complexes can be used to create new carbon-carbon

bonds in ways that might be difficult with traditional organic chemistry methods.

• Understanding Bonding: Studying these compounds helps chemists understand

more about chemical bonding in general, which can lead to the development of new

theories and new types of compounds.

• Green Chemistry: Some of these complexes are being explored for use in more

environmentally friendly chemical processes, as they can sometimes allow reactions

to occur under milder conditions or with less waste.

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6. Historical Context and Development:

The field of organometallic chemistry, which includes metal olefin complexes, has a rich

history:

• In the 19th century, scientists were just beginning to understand that metals could

form stable compounds with organic molecules. Zeise's salt, discovered in 1827, was

one of the first such compounds.

• The true nature of the bonding in these compounds wasn't understood until the

20th century, with the development of quantum mechanics and more advanced

spectroscopic techniques.

• The discovery of ferrocene in 1951 by Kealy and Pauson was a major breakthrough.

Its unusual stability and sandwich structure challenged existing theories about

chemical bonding.

• Throughout the latter half of the 20th century, chemists discovered more and more

types of organometallic compounds, including those with 5-, 6-, and 8-donor

unsaturated molecules.

• The 2005 Nobel Prize in Chemistry was awarded to Yves Chauvin, Robert Grubbs,

and Richard Schrock for their work on olefin metathesis, a reaction where carbon-

carbon double bonds are rearranged with the help of metal catalysts. This

highlighted the ongoing importance of metal olefin chemistry.

7. Challenges and Future Directions:

While metal olefin complexes and related organometallic compounds have proven

extremely useful, there are still challenges and areas for future research:

• Stability: Some of these compounds are sensitive to air or moisture, which can make

them difficult to work with. Developing more stable versions is an ongoing area of

research.

• Selectivity: In catalysis, improving the selectivity of reactions (making sure you get

the product you want and not unwanted side products) is always a goal.

• Sustainability: There's a push to develop catalysts using more abundant, less

expensive metals. Many current catalysts use precious metals like platinum or

palladium.

• New Applications: Researchers are always looking for new ways to use these

compounds, such as in energy storage, in new types of polymers, or in medical

applications.

• Theoretical Understanding: Even with all we know, there's still more to learn about

the exact nature of the bonding in some of these complexes, especially with some of

the more unusual metals or ligands.

In conclusion, metal olefin complexes and the broader field of organometallic chemistry

represent a fascinating intersection of inorganic and organic chemistry. They challenge our

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understanding of chemical bonding, provide powerful tools for synthetic chemistry, and

continue to find new applications in various fields of science and technology. From the

relatively simple bonding in Zeise's salt to the more complex interactions in compounds with

larger unsaturated molecules, this area of chemistry demonstrates the incredible diversity

and utility of metal-carbon interactions.

As our understanding of these compounds grows and as new analytical and synthetic

techniques are developed, we can expect to see even more exciting developments in this

field. Whether it's creating new materials with unique properties, developing more efficient

and environmentally friendly catalysts, or pushing the boundaries of what we thought was

possible in chemical bonding, metal olefin complexes and their relatives will likely continue

to play a crucial role in the advancement of chemistry and related fields.

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