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What is a key difference between coordination complexes and organometallic compounds?
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?
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]?
What is the total number of valence electrons in the complex [IrBr2(CH3)(CO)(PPh3)2]?
- 19
- 17
- 18 (correct)
- 16
What oxidation state is assigned to the Iridium in [IrBr2(CH3)(CO)(PPh3)2]?
What oxidation state is assigned to the Iridium in [IrBr2(CH3)(CO)(PPh3)2]?
How many electrons does the η6-C6H6 ligand donate in the complex [Cr(η5-C5H5)(η6-C6H6)]?
How many electrons does the η6-C6H6 ligand donate in the complex [Cr(η5-C5H5)(η6-C6H6)]?
Which of the following complexes does not obey the 18-electron rule?
Which of the following complexes does not obey the 18-electron rule?
In the donor-pair method, why are some ligands treated as charged?
In the donor-pair method, why are some ligands treated as charged?
How does the solubility of organometallic compounds compare to coordination complexes?
How does the solubility of organometallic compounds compare to coordination complexes?
What happens to the CO bond strength as the metal-carbon bond strength increases?
What happens to the CO bond strength as the metal-carbon bond strength increases?
Which complex exhibits the weakest CO bond strength among the following?
Which complex exhibits the weakest CO bond strength among the following?
Which of the following statements about back-bonding is correct?
Which of the following statements about back-bonding is correct?
Which of the following complexes follows the 18-electron rule?
Which of the following complexes follows the 18-electron rule?
In the given complexes, which has the highest CO IR stretching frequency?
In the given complexes, which has the highest CO IR stretching frequency?
What contribution does the Group 6 Cr atom make to the electron count in a Cr(I) complex?
What contribution does the Group 6 Cr atom make to the electron count in a Cr(I) complex?
Which of the following factors contributes to the stability of the organometallic complex known as Zeise's salt?
Which of the following factors contributes to the stability of the organometallic complex known as Zeise's salt?
What is the oxidation number of the Pt center in Zeise’s salt?
What is the oxidation number of the Pt center in Zeise’s salt?
How many electrons does each CO ligand contribute in a complex?
How many electrons does each CO ligand contribute in a complex?
Which geometry is adopted by the stable complexes formed with a d8 metal ion?
Which geometry is adopted by the stable complexes formed with a d8 metal ion?
What total valence electron count results in a stable Mn(-1) complex?
What total valence electron count results in a stable Mn(-1) complex?
What is the oxidation number of the metal atom in a complex that has a total charge of -1 and all neutral ligands?
What is the oxidation number of the metal atom in a complex that has a total charge of -1 and all neutral ligands?
What is the total electron count in a complex formed by a d8 metal ion with four neutral ligands and three negative ligands?
What is the total electron count in a complex formed by a d8 metal ion with four neutral ligands and three negative ligands?
What is the oxidation number of the Ir center before the oxidative addition reaction occurs?
What is the oxidation number of the Ir center before the oxidative addition reaction occurs?
What is the valence electron count required for the metal center to readily undergo oxidative addition?
What is the valence electron count required for the metal center to readily undergo oxidative addition?
During the bonding of dihydrogen to a metal atom, which component involves σ donation?
During the bonding of dihydrogen to a metal atom, which component involves σ donation?
After the oxidative addition reaction, what does the oxidation number of the Ir center become?
After the oxidative addition reaction, what does the oxidation number of the Ir center become?
What happens to the strength of the H-H bond as π backbonding from the metal increases?
What happens to the strength of the H-H bond as π backbonding from the metal increases?
What is the oxidation state of the dihydrogen ligand after it has been added to the metal center?
What is the oxidation state of the dihydrogen ligand after it has been added to the metal center?
Which statement accurately describes the role of the lone pair on the carbon atom in the context of metal carbonyls?
Which statement accurately describes the role of the lone pair on the carbon atom in the context of metal carbonyls?
How does the molecular geometry of the complex relate to its valence electron count?
How does the molecular geometry of the complex relate to its valence electron count?
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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 (Ï€ 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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