Zn11Rh18B8 and Zn10MRh18B8 with M = Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Al, Si, Ge, Sn -: New ternary and quaternary zinc rhodium borides

Zn11Rh18B8 and Zn10MRh18B8 with M = Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Al, Si, Ge and Sn are obtained by reaction of the elemental components in sealed tantalum tubes at 1500 K. They crystallize tetragonally with Z = 2 in the spacegroup P4/mbm with lattice constants a = 1771.2(2) pm, c = 286.40(4) pm for Zn11Rh18B8 and in the range a = 1767.65(9) pm, c = 285.96(3) pm (Zn10NiRh18B8) to a = 1774.04(9) pm, c = 286.79(2) pm (Zn10SnRh18B8) for the quaternary compounds. According to powder photographs all compounds are isotypic. Struture determinations based on single crystal X-ray data were performed with Zn11Rh18B8, Zn10FeRh18B8 and Zn10NiRh18B8. The structure of Zn11Rh18B8 is related to the Ti3Co5B2 type. Along the short axis planar nets of rhodium atoms composed of triangles, squares, pentagons and elongated hexagons alternate with layers containing the boron and zinc atoms. The rhodium atoms form trigonal prisms centered by boron atoms, two kinds of tetragonal and pentagonal prisms centered by zinc atoms and elongated hexagonal prisms containing pairs of zinc atoms. In the quaternary compounds Zn10MRh18B8 the zinc atoms in one sort of tetragonal prisms are replaced by M atoms.