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.