Deuterium-induced copper pairing in Zr2CuD∼5

Deuteration of Zr2Cu leads to a reconstruction of its MoSi2-type metal atom arrangement. While the tetragonal alloy contains isolated copper atoms (Cu-Cu = 3.22 angstrom) in a cubic zirconium atom environment, the monoclinic deuteride Zr2CuD4.71 contains Cu-2 dumbbells (Cu-Cu = 2.39 angstrom), of which each copper atom has a trigonal-prismatic zirconium atom environment. Deuterium occupies five sites, of which four have tetrahedral metal configurations (two Zr-4-type and two Zr3Cu-type) and are fully occupied while one has a trigonal-bipyramidal metal configuration (Zr3Cu2-type) and is partially occupied (71 %). Copper is bonded to four deuterium atoms in a saddlelike configuration (Cu-D = 1.73-1.87 angstrom). Two of the ligands connect copper in a nearly linear Cu-D-Cu arrangement to partially interrupted dimeric [CU2D6], ribbons running perpendicular to the Cu-2 dumbbell direction. At the upper phase limit, the ribbons are presumably no longer interrupted and the deuteride can be described by the limiting ionic formula 2Zr(2+)[Cu+D3](2-)2D(-).