Mixed-Metal Assemblies Based on Cyanide-Bridged Cubane-Type Mo3CuS4/Mo3S4 Clusters and Molybdenum Carbonyls

The substitutional lability of Mo−Cl and Cu−Cl bonds in cubane-type Mo3CuS4 and incomplete cubane-type Mo3S4 clusters is exploited in an attempt to prepare cyanide-terminated complexes, namely [Mo3S4(CuCN)(dmpe)3Cl3]PF6 ([2]PF6) and [Mo3S4(dmpe)3(CN)3]PF6 ([5]PF6), and to subsequently use them as precursors in low-dimensional linking reactions. Mixed-metal assemblies formulated as [Mo3S4(Cu-μCN···Mo(CO)5)(dmpe)3Cl3]+ ([3]+) and [Mo3S4(dmpe)3(μCN···Mo(CO)5)3]+ ([6]+) are obtained by reaction of tetrahydrofuran solutions of [2]BPh4 and [5]BPh4 with the complex (THF)Mo(CO)5. The intrinsic stability of the (M′-μCN···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 31P 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 Mo3CuS4 and Mo3S4 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