A structural study of lithium, beryllium, magnesium, strontium, barium, and lanthanum alkoxotantalates

The crystal structures of LiTa(OMe) 6 (I), LiTa(OEt) 6 (II), BeTa 2 (OPr-iso) 1 2 (III), MgTa 2 (OEt) 1 2 . 2EtOH (IV), SrTa 2 (OPr-iso) 1 2 .2iso-PrOH (V), BaTa 2 (OPr-iso) 1 2 .2iso-PrOH (VI), and LaTa 2 (OPr-iso) 1 3 (VII) were studied. Structure I is composed of infinite chains of alternating LiO 4 tetrahedra and TaO 6 octahedra with shared edges parallel to one of the crystallographic axes. In the linear structure III, the central BeO 4 tetrahedron shares edges with two TaO 6 octahedra. Molecules IV-VII contain chains of three edge-sharing octahedra; in linear molecule IV, the magnesium atom coordinates two solvation molecules of alcohol trans to each other, whereas in angular isomorphous molecules V and VI, they are cis to each other. In asymmetric molecule VII, the central LaO 6 octahedron shares a face with one peripheral TaO 6 octahedron and an edge with the other. All alkoxotantalates under consideration are isomorphous with corresponding alkoxoniobates. The mutual arrangement of three metal atoms in the chains as a function of the structure of the coordination polyhedron of the central atom is discussed. Complex III was obtained for the first time by the exchange reaction of BeO 2 .THF with NaTa(OPr-iso) 6 in an isopropanol solution, and its mass spectrum was measured.