Synthesis and crystal structure of cadmium dodecahydro closo-dodecaborate hexahydrate, Cd(H2O)(6)[B12H12]

Through neutralization of the aqueous free acid (H3O)(2)[B12H12] with cadmium carbonate (CdCO3) and after isothermic evaporation of the resulting solution, colourless lath-shaped single crystals of Cd(H2O)(6)[B12H12] are obtained. Cadmium dodecahydro closo-dodecaborate hexahydrate crystallizes at room temperature in the monoclinic system (space group: C2/m) with the lattice constants a = 1413.42(9), b = 1439.57(9), c = 749.21(5) pm and beta = 97.232(4)degrees (Z = 4). The crystal structure of Cd(H2O)(6)[B12H12] can be regarded as a monoclinic distortion variant of the CsCl-type structure. Two crystallographically different [Cd(H2O)(6)](2+) octahedra (d(Cd-O) = 227-230 pm) are present which only differ in their relative orientation. The intramolecular bond lengths for the quasi-icosahedral [B12H12](2-) cluster anions range in the intervals usually found for dodecahydro closo-dodecaborates (d(B-B) = 177-179 pm, d(B-H) = 103-116 pm). The hydrogen atoms of the [B12H12](2-) clusters have no direct coordinative influence on the Cd2+ cations. Due to the fact that no zeolitic crystal water molecules are present, a stabilization of the lattice takes place mainly via the B-H delta-center dot center dot center dot H-delta-O hydrogen bonds.