CA4MG4CO3H19 AND YB4MG4CO3H19, CONTAINING ORIENTATIONALLY DISORDERED SQUARE-PYRAMIDAL [COH5](4-) ANIONS

The title hydrides and their deuterides were synthesized by a solid st ate reaction at 790-800 K and 120-155 bar hydrogen (deuterium) pressur e, and characterized by X-ray single-crystal (Ca compound) and neutron powder diffraction (Ca and Yb compounds). They crystallize with cubic symmetry, space group P (4) over bar 3m, Ca4Mg4Co3H19: a = 6.6953(2) Angstrom, deuteride: 6.6809(2) Angstrom; Yb4Mg4Co3H19: a = 6.6727(2) A ngstrom, deuteride: 6.6591(1) Angstrom (T = 295 K). The structures con tain tetrahedrally coordinated D- anions with bond distances [D3-Mg] = 1.912(5) Angstrom (Ca) and 1.902(7) Angstrom (Yb), [D3-3Ca)] = 2.355( 6) Angstrom and [D3-3Yb] = 2.354(5) Angstrom, and square-pyramidal [Co D5](4-) complex anions in which the equatorial ligands are ordered wit h bond distances [Co-4D1] = 1.546(3) (Ca). 1.535(5) Angstrom (Yb) and the apical ligands are disordered with bond distances [Co-D2] = 1.586( 9) (Ca), 1.60(1) Angstrom (Yb).