On the crystal structures of the transition-metal(II) dodecahydro-closo-dodecaborate hydrates Cu(H2O)(5.5)[B12H12]center dot 2.5H(2)O and Zn(H2O)(6)[B12H12]center dot 6H(2)O

By neutralization of an aqueous solution of the free acid (H3O)(2)[B12H12] with basic copper(II) carbonate or zinc carbonate, blue lath-shaped single crystals of the octahydrate Cu[B12H12]center dot 8H(2)O (= Cu(H2O)(5.5)[B12H12]center dot 2.5H(2)O) and colourless face-rich single crystals of the dodecahydrate Zn[B12H12] center dot 12 H2O (= Zn(H2O)(6)[B12H12]center dot 6H(2)O) could be isolated after isothermic evaporation. Copper(II) dodecahydro-closo-dodecaborate octahydrate crystallizes at room temperature in the monoclinic system with the non-centrosymmetric space group Pm (Cu(H2O)(5.5)[B12H12]center dot 2.5H(2)O: a = 768.23(5), b = 1434.48(9), c = 777.31(5) pm, beta = 90.894(6)degrees; Z = 2), whereas zinc dodecahydro-closo-dodecaborate dodecahydrate crystallizes cubic in the likewise non-centrosymmetric space group F23 (Zn(H2O)(6)[B12H12]center dot 6H(2)O: a = 1637.43(9) pm; Z = 8). The crystal Structure of Cu(H2O)(5.5)[B12H12]center dot 2.5H(2)O can be described as a rnonoclinic distortion variant of the CsCl-type arrangement. As characteristic feature the formation of isolated [Cu-2(H2O)(11)](4+) units as a condensate of two corner-linked Jahn-Teller distorted [Cu(H2O)(6)](2+) octahedra via an oxygen atom of crystal water can be considered. Since zeolitic water of hydratation is also present, obviously both classical H-O delta-center dot center dot center dot H+delta-O and non-classical B-H delta-center dot center dot center dot H+delta-O hydrogen bonds play a significant role for the stabilization of the structure. A direct coordinative influence of the quasi-icosahedral [B12H12](2-) anions on the Cu2+ cations has not been determined. The zinc Compound Zn(H2O)(6)[B12H12]center dot 6H(2)O crystallizesin a NaTl-type related structure. Two crystallographically different [Zn(H2O)(6)](2+) octahedra are present, which only differ in their relative orientation within the packing of the [B12H12](2-) anions. The stabilization of the crystal structure takes place mainly via H-O delta-center dot center dot center dot H+delta-O hydrogen bonds, since again the hydrogen atoms of the [B12H12](2-) anions have no direct coordinative influence on the Zn2+ cations.