Mixed-metal assemblies based on cyanide-bridged cubane-type Mo(3)CuS(4)/Mo(3)S(4) clusters and molybdenum carbonyls

The substitutional lability of Mo-Cl and Cu-Cl bonds in cubane-type Mo(3)CuS(4) and incomplete cubane-type Mo(3)S(4) clusters is exploited in an attempt to prepare cyanide-terminated complexes, namely [Mo(3)S(4)(CuCN)(dmpe)(3)Cl(3)]PF(6) ([2]PF(6)) and [Mo(3)S(4)(dmpe)(3)(CN)(3)]PF(6) ([5]PF(6)), and to subsequently use them as precursors in low-dimensional linking reactions. Mixed-metal assemblies formulated as [Mo(3)S(4)(Cu-muCN...Mo(CO)(5))(dmpe)(3)Cl(3)](+) ([3](+)) and [Mo(3)S(4)(dmpe)(3)(muCN...Mo(CO)(5))(3)](+) ([6](+)) are obtained by reaction of tetrahydrofuran solutions of [2]BPh(4) and [5]BPh(4) with the complex (THF)Mo(CO)(5). The intrinsic stability of the (M'-muCN...Mo(CO)(5)) linkages (M' = Cu in 3(+) and Mo in 6(+)) in solution and in the gas phase is investigated through a combination of variable-temperature (31)P NMR, IR, UV-vis spectroscopies, and electrospray ionization tandem mass spectrometry. The spectroscopic and electrochemical consequences of CN coordination as well as Mo(CO)(5) ligation either at the Cu or the Mo site in Mo(3)CuS(4) and Mo(3)S(4) clusters are reported. Replacement of Cl by CN or CN...Mo(CO)(5) at the Cu site does not affect the redox potentials, whereas analogous substitution at Mo sites exerts a profound anodic shift of 220 and 500 mV upon Cl to CN and Cl to CN...Mo(CO)(5) replacement, respectively.