Effect of Hydrogen Atoms on the Structures of Trinuclear Metal Carbonyl Clusters: Trinuclear Manganese Carbonyl Hydrides

Abstract

The structures of the trinuclear manganese carbonyl hydrides H(3)Mn(3)(CO)(n) (n = 12, 11, 10, 9) have been investigated by density functional theory (DFT). Optimization of H(3)Mn(3)(CO)(12) gives the experimentally known structure in which all carbonyl groups are terminal and each edge of a central Mn(3) equilateral triangle is bridged by a single hydrogen atom. This structure establishes the canonical distance 3.11 A for the Mn-Mn single bond satisfying the 18-electron rule. The central triangular (mu-H)(3)Mn(3) unit is retained in the lowest energy structure of H(3)Mn(3)(CO)(11), which may thus be derived from the H(3)Mn(3)(CO)(12) structure by removal of a carbonyl group with concurrent conversion of one of the remaining carbonyl groups into a semibridging carbonyl group to fill the resulting hole. The potential energy surface of H(3)Mn(3)(CO)(10) is relatively complicated with six singlet and five triplet structures. One of the lower energy H(3)Mn(3)(CO)(10) structures has one of the hydrogen atoms bridging the entire Mn(3) triangle and the other two hydrogen atoms bridging Mn-Mn edges. This H(3)Mn(3)(CO)(10) structure achieves the favored 18-electron configuration with a very short MnMn triple bond of 2.36 A. The other low energy H(3)Mn(3)(CO)(10) structure retains the (mu-H)(3)Mn(3) core of H(3)Mn(3)(CO)(12) but has a unique six-electron donor eta(2)-mu(3) carbonyl group bridging the entire Mn(3) triangle similar to the unique carbonyl group in the known compound Cp(3)Nb(3)(CO)(6)(eta(2)-mu(3)-CO). For H(3)Mn(3)(CO)(9) a structure with a central (mu(3)-H)(2)Mn(3) trigonal bipyramid lies >20 kcal/mol below any of the other structures. Triplet structures were found for the unsaturated H(3)Mn(3)(CO)(n) (n = 11, 10, 9) systems but at significantly higher energies than the lowest lying singlet structures.

Edge‐Bridging and Face‐Bridging Hydrogen Atoms in Trinuclear Rhenium Carbonyl Hydrides

“…Whereas structure 11-2S is geometrically similar to the global minimum for H 3 Mn 3 (CO) 11 (311-1 in ref. [18] ), structure 11-1S is similar to a high-energy structure for H 3 Mn 3 (CO) 11 (311-4 in ref. [18] ).…”

“…[18] ), structure 11-1S is similar to a high-energy structure for H 3 Mn 3 (CO) 11 (311-4 in ref. [18] ). Nevertheless, these two H 3 Re 3 (CO) 11 gives all three Re atoms in 11-2S the favored 18-electron configuration, after considering the four-electron donor bridging carbonyl group.…”

“…The lowest energy H 3 Re 3 (CO) 9 structure with a central Re 3 (μ 3 -H) 2 trigonal bipyramid is of particular interest. Related structures exist for H 3 Mn 3 (CO) n (n = 12, 11, 10, 9), [18] however, the rhenium analogues are found experimentally to be significantly more stable.…”

“…[ 18] One of the Re···Re distances in 11-4S is very long at 4.099 Å (MPW1PW91) or 4.175 Å (BP86), indicating the absence of direct bonding between these two Re atoms. The other two Re-Re distances are 2.870 Å (MPW1PW91) or 2.892 Å (BP86), suggesting two formal Re=Re double bonds.…”

“…The H 3 Re 3 (CO) 10 global minimum 10-1S is predicted to have C s symmetry and to be geometrically similar to the global minimum for the analogous H 3 Mn 3 (CO) 10 (ref. [18] ). Structure 10-1S has one bridging carbonyl group and nine terminal CO groups.…”