Homoleptic mononuclear and binuclear ruthenium carbonyls Ru(CO)n(n=3―5) and Ru2(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 D3h trigonal bipyramid.Similar to Os(CO)5,the distorted square pyramid isomer with C2v symmetry lies ～7 kJ·mol-1 higher in energy.For the unsaturated mononuclear ruthenium carbonyls Ru(CO)4 and Ru(CO)3,a singlet structure with C2v symmetry and a Cs bent Tshaped structure are the lowest-energy structures,respectively.The global minimum for the Ru2(CO)9 is a singly bridged(CO)4Ru(μ-CO)Ru(CO)4 structure.A triply bridged Ru2(CO)6(μ-CO)3 structure analogous to the known Fe2(CO)9 structure is predicted to lie very close in energy to the global minimum.For Ru2(CO)8,the doubly bridged C2 structure is predicted to be the global minimum.For the lowest-energy structures of M2(CO)n(M=Fe,Ru,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 Ru2(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 Ru2(CO)9 to give Ru2(CO)8.
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