Coordination Complexes and Organometallic Compounds

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Questions and Answers

What is a key difference between coordination complexes and organometallic compounds?

Organometallic compounds are generally soluble in water.

Coordination complexes have fixed d-electron counts.

Organometallic compounds often resemble organic compounds. (correct)

Coordination complexes are usually neutral.

Which counting method is recommended for quickly determining electron counts in coordination complexes?

Neutral-ligand method (correct)

Oxidation number method

Charge balancing method

Donor-pair method

What is the total number of valence electrons in the complex [IrBr2(CH3)(CO)(PPh3)2]?

18 (correct)

What oxidation state is assigned to the Iridium in [IrBr2(CH3)(CO)(PPh3)2]?

+3 Signup and view all the answers

How many electrons does the η6-C6H6 ligand donate in the complex [Cr(η5-C5H5)(η6-C6H6)]?

6 Signup and view all the answers

Which of the following complexes does not obey the 18-electron rule?

[Cr(η5-C5H5)(η6-C6H6)] Signup and view all the answers

In the donor-pair method, why are some ligands treated as charged?

To simplify electron counting. Signup and view all the answers

How does the solubility of organometallic compounds compare to coordination complexes?

Organometallic compounds are soluble in organic solvents. Signup and view all the answers

What happens to the CO bond strength as the metal-carbon bond strength increases?

The CO bond strength decreases. Signup and view all the answers

Which complex exhibits the weakest CO bond strength among the following?

[Ti(CO)6]2- Signup and view all the answers

Which of the following statements about back-bonding is correct?

Back-bonding involves a filled d orbital of the metal donating electrons. Signup and view all the answers

Which of the following complexes follows the 18-electron rule?

Mn(CO)6 Signup and view all the answers

In the given complexes, which has the highest CO IR stretching frequency?

[Mn(CO)6]+ Signup and view all the answers

What contribution does the Group 6 Cr atom make to the electron count in a Cr(I) complex?

5 electrons Signup and view all the answers

Which of the following factors contributes to the stability of the organometallic complex known as Zeise's salt?

Strong-field ligands Signup and view all the answers

What is the oxidation number of the Pt center in Zeise’s salt?

+2 Signup and view all the answers

How many electrons does each CO ligand contribute in a complex?

2 electrons Signup and view all the answers

Which geometry is adopted by the stable complexes formed with a d8 metal ion?

Square planar Signup and view all the answers

What total valence electron count results in a stable Mn(-1) complex?

18 electrons Signup and view all the answers

What is the oxidation number of the metal atom in a complex that has a total charge of -1 and all neutral ligands?

-1 Signup and view all the answers

What is the total electron count in a complex formed by a d8 metal ion with four neutral ligands and three negative ligands?

16 electrons Signup and view all the answers

What is the oxidation number of the Ir center before the oxidative addition reaction occurs?

+1 Signup and view all the answers

What is the valence electron count required for the metal center to readily undergo oxidative addition?

16 Signup and view all the answers

During the bonding of dihydrogen to a metal atom, which component involves σ donation?

σ donation from H-H bond electrons Signup and view all the answers

After the oxidative addition reaction, what does the oxidation number of the Ir center become?

+3 Signup and view all the answers

What happens to the strength of the H-H bond as π backbonding from the metal increases?

It decreases. Signup and view all the answers

What is the oxidation state of the dihydrogen ligand after it has been added to the metal center?

-1 Signup and view all the answers

Which statement accurately describes the role of the lone pair on the carbon atom in the context of metal carbonyls?

Acts as a σ donor Signup and view all the answers

How does the molecular geometry of the complex relate to its valence electron count?

Higher electron count often leads to more complex geometries. Signup and view all the answers

Study Notes

Coordination Complexes vs. Organometallic Compounds

Coordination complexes are typically charged, have variable d-electron counts, and dissolve in water.
Organometallic compounds are often neutral, have fixed d-electron counts (18 or 16), and dissolve in organic solvents.
Organometallic compounds share properties with organic compounds, such as low melting points and some being liquid at room temperature.

18-Electron Rule

The 18-electron rule is a guideline for predicting the stability of organometallic complexes.
It states that a stable complex should have 18 valence electrons around the metal atom.

Calculating Valence Electrons

There are two methods for calculating valence electrons:
- Neutral-ligand method: ligands are treated as neutral
- Donor-pair method: ligands donate electrons in pairs
Neutral-ligand method is quicker for simple examples.
Donor-pair method reveals oxidation number of the metal.

Zeise's Salt

Zeise's salt, [Pt(C2H4)Cl3]-, is a stable ethene complex.
Its stability is attributed to strong-field ligands and a d8 metal ion.
The Pt atom has an oxidation number of +2, contributing 8 valence electrons.
The ligands (3 Cl- and ethene) donate 8 electrons via the donor-pair method.
This results in a total of 16 valence electrons, making the complex stable.

Dihydrogen as a Ligand

Dihydrogen can act as a neutral 2-electron donor ligand.
Bonding involves:
- σ donation from the H-H bond to the metal
- π backdonation from the metal to the σ* antibonding orbital of H2
As π backdonation increases, the H-H bond weakens and the structure trends towards a dihydride.

Oxidative Addition

Oxidative addition is a reaction where the metal center is formally oxidized.
The metal's oxidation number increases.
The reaction requires a metal center with 16 valence electrons.
The reaction results in 18 valence electrons for the metal.

Metal Carbonyls

Metal carbonyls feature a unique bonding interaction between the metal and CO.
The CO lone pair donates electrons to an empty metal d orbital (σ donation).
The metal d orbitals backdonate electrons to the empty antibonding CO orbitals (π backdonation).
Stronger metal-carbon bonds weaken the CO bond.

CO IR Stretching Frequencies

IR stretching frequencies of CO ligands reflect the strength of the CO bond.
Higher frequencies indicate stronger CO bonds.
The degree of π backdonation impacts CO bond strength.
More π backdonation weakens the CO bond, resulting in lower frequencies.

18-Electron Rule for 3d Metal Carbonyls

The 18-electron rule is obeyed by many 3d metal carbonyls:
- Cr(CO)6
- Mn2(CO)10
- Fe(CO)5
- Co2(CO)8
- Ni(CO)4
These complexes exhibit a stability in accordance with the 18-electron rule.

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Description

Explore the key differences between coordination complexes and organometallic compounds, focusing on their characteristics, stability guidelines like the 18-electron rule, and methods for calculating valence electrons. Also, learn about specific compounds such as Zeise's salt and how their properties relate to broader concepts in chemistry.