1.Library Information Department,Beijing University of Posts and Telecommunications,Beijing,China;2.Key Laboratory of Applied Surface and Colloid Chemistry of Ministry of Education, School of Chemistry and Chemical Engineering,Shaanxi Normal University,Xi’an,China;3.Department of Chemistry and Center for Computational Chemistry,University of Georgia,Athens,USA
Abstract:
The geometries and thermochemistry of Re2(NO)4(CO)n (n?=?4, 3, 2, 1, 0) structures isovalent with the binuclear cobalt carbonyls Co2(CO)n+4 have been examined using density functional theory. Eight low-energy Re2(NO)4(CO)4 structures, all with formal Re–Re single bonds, lie within 6 kcal mol?1 of the global minimum. These eight structures include unbridged structures as well as structures with two bridging NO groups but no structures with bridging CO groups. Similarly, five low-energy Re2(NO)4(CO)3 structures, all with formal Re=Re double bonds, lie within 6 kcal mol?1 of the global minimum. Again these five structures include unbridged structures as well as structures with one or two bridging NO groups but no structures with bridging CO groups. The Re2(NO)4(CO)n (n?=?4, 3) appear to be fluxional systems similar to the well-known Co2(CO)8 for which doubly bridged and unbridged structures have approximately the same energies. The lowest energy Re2(NO)4(CO)2 structures have formal Re=Re double bonds including a structure with a five-electron donor bridging η2-μ-NO group. Isomeric Re2(NO)4(CO)2 structures with formal Re≡Re triple bonds lie approximately ～10 kcal mol?1 above the global minimum. For the more highly unsaturated Re2(NO)4(CO) and Re2(NO)4 systems, the lowest energy structures have formal Re≡Re triple bonds of length ～2.6 Å. Higher energy Re2(NO)4(CO) structures have shorter Re–Re distances of length ～2.5 Å suggesting formal quadruple bonds.
Graphical Abstract The geometries and thermochemistry of Re2(NO)4(CO)n (n?=?4, 3, 2, 1, 0) structures isovalent with the binuclear cobalt carbonyls Co2(CO)n+4 have been examined using density functional theory. A number of energetically closely spaced Re2(NO)4(CO)4 and Re2(NO)4(CO)3 structures are found, including unbridged and NO-bridged structures but no CO-bridged structures. The Re2(NO)4(CO)n (n?=?2, 1, 0) systems provide examples of Re–Re multiple bonds of orders ranging from 2 to 4.
