Linear and Bent Nitric Oxide Ligand Binding in an Asymmetric Butterfly Complex: CoMoCo'.

Two synthetic approaches to install metallodithiolate ligands on molybdenum centers using the synthons [Mo2(CH3CN)10]4+ and (N2S2)Co(NO) [N2S2 = N,N-bis(2-mercaptoethyl)-1,4-diazacycloheptane and NO = nitric oxide], or [Mo(NO)2(CH3CN)4]2+ (CH3CN = acetonitrile) and [(N2S2)Co]2 lead to a bis-nitrosylated, trimetallic dication, CoMoCo'. This unique asymmetric butterfly complex, with S = 1, has a bent NO within the small {Co(NO)}8 wing (denoted as Co), reflecting CoIII(NO-), and is S-bridged to a linear {Mo(NO)}6 diamagnetic unit. The latter is further S-bridged to a pentacoordinate (N2S2)CoIII(CH3CN) donor in the larger wing and is the origin of the two unpaired electrons, denoted as Co'. The asymmetry in Mo-Co distances, 3.33 Å in the Co wing and 2.73 Å in the Co' wing, indicated a Mo-Co' bonding interaction. The transfer of NO from (N2S2)Co(NO) in the former path is needed to cleave the strong quadruple bond in [Mo≣Mo]4+, with the energetic cost compensated for via a one-electron bond between Mo and Co', as indicated by natural bonding orbital analysis.