Bimetallic Nickel–Cobalt Hexacarbido Carbonyl Clusters [H6–nNi22Co6C6(CO)36]n− (n = 3–6) Possessing Polyhydride Nature and Their Base-Induced Degradation to the Monoacetylide [Ni9CoC2(CO)16–x]3– (x = 0, 1)

The reaction of [Ni10C2(CO)16]2– with Co3(μ3-CCl)­(CO)9 results in the new bimetallic Ni–Co hexacarbido carbonyl clusters [H6–nNi22Co6C6(CO)36]n− (n = 3–6), which possess polyhydride nature and can be interconverted by means of acid–base reactions. The tetra-anion [H2Ni22Co6C6(CO)36]4– and the hexa-anion [Ni22Co6C6(CO)36]6– have been isolated in a crystalline state and structurally characterized via X-ray crystallography. The six carbide atoms are lodged into Ni7CoC square antiprismatic cages. Addition of strong bases to [Ni22Co6C6(CO)36]6– affords mixtures of the monoacetylides [Ni9CoC2(CO)16]3– and [Ni9CoC2(CO)15]3–, which have been cocrystallized as [NEt4]3[Ni9CoC2(CO)16–x] (x = 0.58–0.84) salts, displaying tightly bonded interstitial C2 units.