The fact that the stable mononuclear vanadium carbonyl V(CO)
6 fails to satisfy the 18-electron rule has led to aninvestigation of the binuclear vanadium carbonyls V
2(CO)
n (
n = 10-12) using methods from density functionaltheory. There are several important experimental studies of these homoleptic binuclear vanadium carbonyls. Theglobal minimum for V
2(CO)
12 is a singlet structure having two V(CO)
6 units
linked by a long V-V single bond (3.48Å by B3LYP or 3.33 Å by BP86) without any bridging CO groups. For V
2(CO)
11 the global minimum is a singletstructure V
2(CO)
10(
2-
-CO) with a four-electron
-donor bridging CO group. For V
2(CO)
10 the global minimum isan unsymmetrical singlet (OC)
4V
V(CO)
6 structure with three semibridging CO groups and a V-V distance of2.54 Å (B3LYP) or 2.51 Å (BP86), suggesting a V
V triple bond. The theoretical
(CO) frequencies of this V
2(CO)
10 isomer agree approximately with those assigned by Ishikawa et al. (
J. Am. Chem. Soc. 1987,
109, 6644)to a V
2(CO)
10 isomer produced in the photolysis of gas-phase V(CO)
6. In contrast, the laboratory bridging
(CO)frequency assigned to V
2(CO)
12 by Ford et al. (
Inorg. Chem. 1976,
15, 1666) seems more
likely to arise from thelowest-lying triplet isomer of V
2(CO)
11.