Formed by combination of transition metals with carbon monoxide (CO).
Types of metal carbonyls cover non-metallic carbonyls and those combining with vacant metals.
Metal Carbonyl Formation
Transition metals combine with CO to form strong bonds.
CO acts as a ligand and donates a pair of electrons to the metal.
Synergic bonding: CO accepts and donates electrons, forming strong bonds with metals.
Characteristics of CO as a Ligand
CO binds with transition metals forming coordinate bonds.
Acts as a Lewis base but can form strong bonds due to synergic bonding.
COтАЩs bonding is usually stable and hard to oxidize or dissociate.
CO can form terminal (one metal) or bridging bonds (between two metals).
Classification of Metal Carbonyls
Based on Ligands: Carbonyl Compounds: CO as ligand forming stable complexes.
On the Basis of the Number of Metals
Mononuclear: One metal atom in the complex.
Polynuclear: More than one metal atom; subdivided into homonuclear (same metal atoms) and heteronuclear (different metal atoms).
Terminal Ligands: Only bind to one metal atom.
Bridging Ligands: Bind to multiple metal atoms.
Examples: Fe3(CO)12 highlights three metal atoms with CO as ligand.
Reactions and Stability
Metal carbonyls typically do substitution reactions rather than oxidation.
Stability factors include metal-CO bond strength, bond order, and electron density.
Infrared Spectroscopy of Metal Carbonyls
Usage: Identifies metal carbonyl compounds even in crowded regions with other ligands.
CO Stretching Frequencies: Vary based on bond strength and electron density.
Higher electron density decreases stretching frequency of the CO bond.
Examples and Practical Analysis
CO stretching frequencies generally follow trends based on ligand types and metalтАЩs oxidation state.
Example: Nickel carbonyl complexes like Ni(CO)_4 differ in frequency based on ligand attachment.
Questions: Determine the highest CO stretching frequency based on formal charges and ligand types.
Molecular Orbital Theory (MOT) of CO
COтАЩs electron configuration and bonding explained through MOT.\n- Anti-bonding and bonding orbitals play a crucial role in understanding the stability and reactivity of the CO-formed bonds.
Highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) of CO discussed for interaction with transition metals.
Metal Carbonyl Bridging and Terminal Bonding
Structural differences between bridging and terminal CO bonds.
Impact of metalтАЩs oxidation state on the CO bonding.
Example: CO bonding in Fe_3(CO)_12 firm due to bridging and terminal explanations.
Factors Affecting Metal CarbonylsтАЩ Stability
Electron density, oxidation state, and ligand types crucial for stability.
Infrared spectroscopic data aligns with bonding models and theoretical predictions.
Organometallic Chemistry Aspects
Transition metals and CO forming various organometallic compounds.
Application of molecular orbital theory and synergistic bonding in organometallic complexes.
Conclusion
CO binds strongly with transition metals due to synergistic behavior.
Metal carbonyl complexes exhibit distinct properties that align with spectroscopic and theoretical analyses.
Practical applications and examples reinforce concepts of metal carbonyl chemistry.