Zu den Kristallstrukturen der Übergangsmetall(II)‐Dodekahydro‐closo‐Dodekaborat‐Hydrate Cu(H2O)5,5[B12H12]·2,5 H2O und Zn(H2O)6[B12H12]·6 H2O

On the Crystal Structures of the Transition‐Metal(II) Dodecahydro‐closo‐Dodecaborate Hydrates Cu(H₂O)_5.5B₁₂H₁₂]·2.5 H₂O and Zn(H₂O)₆B₁₂H₁₂]·6 H₂O By neutralization of an aqueous solution of the free acid (H₃O)₂B₁₂H₁₂] with basic copper(II) carbonate or zinc carbonate, blue lath‐shaped single crystals of the octahydrate CuB₁₂H₁₂]·8 H₂O (≡ Cu(H₂O)_5.5B₁₂H₁₂]·2.5 H₂O) and colourless face‐rich single crystals of the dodecahydrate ZnB₁₂H₁₂]·12 H₂O (≡ Zn(H₂O)₆B₁₂H₁₂]·6 H₂O) 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)_5.5B₁₂H₁₂]·2.5 H₂O: a = 768.23(5), b = 1434.48(9), c = 777.31(5) pm, β = 90.894(6)°; Z = 2), whereas zinc dodecahydro‐closo‐dodecaborate dodecahydrate crystallizes cubic in the likewise non‐centrosymmetric space group F23 (Zn(H₂O)₆B₁₂H₁₂]·6 H₂O: a = 1637.43(9) pm; Z = 8). The crystal structure of Cu(H₂O)_5.5B₁₂H₁₂]·2.5 H₂O can be described as a monoclinic distortion variant of the CsCl‐type arrangement. As characteristic feature the formation of isolated Cu₂(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^δ?···^+δH–O and non‐classical B–H^δ?···^+δH–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)₆B₁₂H₁₂]·6 H₂O crystallizes in 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^δ?···^+δH–O hydrogen bonds, since again the hydrogen atoms of the B₁₂H₁₂]^2? anions have no direct coordinative influence on the Zn²⁺ cations.