Theoretical study on homoleptic mononuclear and binuclear ruthenium carbonyls Ru(CO)n (n=3-5) and Ru2(CO)n (n=8, 9)

Homoleptic mononuclear and binuclear ruthenium carbonyls Ru(CO)(n) (n=3-5) and Ru-2(CO)(n) (n=8,9) have been investigated using density functional theory. Sixteen isomers are obtained. For Ru(CO)(5), the lowest-energy structure is the singlet D-3h trigonal bipyramid. Similar to Os(CO)(5), the distorted square pyramid isomer with C-2v symmetry lies similar to 7 kJ-mol(-1) higher in energy. For the unsaturated mononuclear ruthenium carbonyls Ru(CO)(4) and Ru(CO)(3), a singlet structure with C-2v symmetry and a C-s bent T-shaped structure are the lowest-energy structures, respectively. The global minimum for the Ru-2(CO)(9) is a singly bridged (CO)(4)Ru(mu-CO)Ru(CO)(4) structure. A triply bridged Ru-2(CO)(6)(mu-CO)(3) structure analogous to the known Fe-2(CO)(9) structure is predicted to lie very close in energy to the global minimum. For Ru-2(CO)(8), the doubly bridged C-2 structure is predicted to be the global minimum. For the lowest-energy structures of M-2(CO)(n) (M = Fe, Flu, Os, n = 9,8), it is found that both iron and ruthenium are favored to form structures containing more bridging carbonyl groups, while osmium prefers to have structures with less bridging carbonyl groups. The study of dissociation energy shows that the dissociation of Ru-2(CO)(9) into the mononuclear fragments Ru(CO)(5) + Ru(CO)(4) is a less energetically demanding process than the dissociation of one carbonyl group from Ru-2(CO)(9) to give Ru-2(CO)(8).