High-pressure synthesis of novel europium magnesium hydrides

Three new ternary metal hydrides of composition Eu2MgH6, Eu6Mg7H26 and Eu2Mg3H10 have been synthesised from mixtures of the binary hydrides in a multi-anvil press at quasi-hydrostatic pressures of up to 3.2 GPa and temperatures of up to 870 K. Crystal structures of the deuterides were determined by joint refinements of neutron and synchrotron powder diffraction data. All structures have alkaline earth and fluorine analogues. Eu2MgD6, K2GeF6 type structure, space group P3m1, a = 550.644(6) pm, c = 410.054(6) pm; Eu6Mg27D26, Ba6Zn7F26 type structure, 12/m, n = 1409.39(4) pm, b = 564.55(2) pm, c = 1150.90(3) pm, beta = 90.683(2)degrees; Eu2Mg3D10, Ba2Ni3F10 type structure, C2/m, a = 1748.41(5) pm, b = 572.31(2) pm, c = 736.47(2) pm, beta = 111.478(2)degrees. The coloured compounds are saline and show volume contractions of up to 7.3% upon formation from the binary hydrides. Eu2MgH6 shows Curie-Weiss paramagnetic behaviour (mu (eff) = 7.88 mu (B)) and orders ferromagnetic at T-C = 31.6 K. (C) 2001 Elsevier Science B.V. All rights reserved.