Binuclear homoleptic rhodium carbonyls: Structures, energetics, and vibrational spectra†
Abstract
The binuclear homoleptic rhodium carbonyls Rh2(CO)n (n = 8, 7, 6, 5) have been examined theoretically. Three energetically low-lying equilibrium structures of Rh2(CO)8 were found, i.e., one doubly bridged C2v singlet structure and two unbridged singlet structures with D3d and D2d symmetry. The doubly bridged structure is the global minimum predicted to lie 3.4 kcal/mol below the D2d structure and 6.4 kcal/mol below the D3d structure. For Rh2(CO)7 the global minimum is either a singlet C2v unbridged structure or a singlet doubly bridged Cs structure within 1.8 kcal/mol depending upon the theoretical method. For Rh2(CO)6, the global minimum is either a singlet doubly bridged D2 structure or a singlet unbridged D2d structure depending upon the method. Triplet structures for Rh2(CO)7 and Rh2(CO)6 are predicted to be of high energies relative to the low energy singlet structures. For Rh2(CO)5 the C2v singlet singly bridged structure lies below the C2 or C2v triplet structures.