YB4MG3H14 WITH CA4MG3H14-TYPE STRUCTURE

Yb4Mg3H14 and its deuteride were prepared from Yb4Mg3 alloys at 731(5) K (708(10) K) under 89(5) bar hydrogen (95(5) bar deuterium) pressure and characterized by X-ray and neutron powder diffraction. The compound crystallizes with hexagonal symmetry - space group P62mBAR (No. 189). The lattice parameters at 298 K are a = 6.2649(6) angstrom and c = 6.8307(9) angstrom for the hydride and a = 6.2479(5) angstrom and c = 6.8173(9) angstrom for the deuteride, with Z = 1. It contains an ordered array of four symmetry-independent deuterium atoms which have tetrahedral (D1 - [3 Yb, Mg], D2: [4 Yb]), trigonal bipyramidal (D3 - [2 Yb, 3 Mg]) and triangular (D4 - [3 Mg]) metal coordinations. The enthalpy of desorption was determined from pressure-composition isotherms to be DELTAH(des) = 103(5) kJ (mol H-2)-1.