Recent advances in size-specific spectroscopy of metal carbonyl complexes

Metal carbonyl complexes provide unique platforms for probing metal–ligand bonding, electronic structures, and catalytic mechanisms. This review focusses on recent advances in a series of novel homometallic and heterobimetallic carbonyl complexes studied by infrared–vacuum ultraviolet spectroscopy, photoelectron spectroscopy, and quantum chemical calculations. This combined approach enables accurate determination of vibrational characteristics, electron detachment energies, and bonding motifs, allowing clear differentiation between σ-donation, π-back-donation, and metal–metal interactions. Investigations of group-3 homoleptic carbonyls identified the first neutral confinement-free species: Sc(CO) 7 and M(CO) 8 (M = Y, La). Spectroscopic observation of neutral OTiCCO(CO) ₙ ( n = 2–5) served as the fresh evidence for efficient C O cleavages and concomitant C C formations. Studies of heterobimetallic carbonyl complexes MFe(CO) 4 − (M = Ti, V , Cr, Si, Ge, Sn) and MNi( CO ) n − (M = Sc, Y, Ti, Zr, Hf, V; n = 3–5) indicated coordination preferences dictated by both cluster size and metal identity, along with associated charge redistribution and CO-activation pathways, all of which bear direct relevance to surface catalysis. Collectively, these studies established the well-defined clusters as functional molecular analogues of catalytically active sites, effectively bridging fundamental bonding concepts with applications in CO/CO 2 utilization, syngas chemistry, and energy-conversion processes. • Identifying the first interference-free neutral heptacarbonyl and octacarbonyls. • Observing C C coupling reactions in neutral transition-metal carbonyls. • Characterizing coordination preferences by cluster size and metal identity.