Binuclear Homoleptic Copper Carbonyls Cu2(CO)x (x = 1−6): Remarkable Structures Contrasting Metal−Metal Multiple Bonding with Low-Dimensional Copper Bonding Manifolds

Binuclear homoleptic copper carbonyls Cu2(CO)x (x = 1−6) have been studied using four different density functional theory methods (DFT) in conjunction with a basis set of extended double-ζ plus polarization quality, labeled as DZP. For each homoleptic binuclear copper carbonyl compound, several stationary point structures are presented, and these structures are characterized in terms of their geometries, thermochemistry, and vibrational frequencies. The optimal unsaturated Cu2(CO)x (x = 1−6) structures are generated by joining 18-electron tetrahedral, 16-electron trigonal, 14-electron linear copper carbonyl building blocks, and/or bare copper atoms with copper−copper single bonds rather than by joining 18-electron copper carbonyl units with multiple copper−copper bonds. For Cu2(CO)6 the eclipsed and staggered ethane-like structure are virtually degenerate and lie significantly lower in energy than other possible structures. The eclipsed Cu−Cu single bond distance is predicted to be 2.61 A, while that for ...