Synthesis and structure of the novel octalithium-dipotassium mixed oxide-alkoxide cage complex [Li8K2(O)((BuO)-O-t)(8)center dot 2TMEDA]

The title compound crystallises as a hexane hemisolvate from 1 : 1 : 1 or 2: 1 :2 reaction mixtures of the lithium primary amide (BuN)-N-t(H)Li, potassium t-butoxide (BuOK)-O-t, and the diamine TMEDA in hexane solution. An X-ray crystallographic study reveals that it exists as a discrete cage species with a central oxo (O2-) anion, coordinated to the eight cations of a surrounding 16-vertex (Li8O8) polyhedron, two opposing sides of which are each bridged by a TMEDA-chelated K+ cation. Made up of mu(3)O-Li-3 and mu(2)O-Li-2 interactions, the Li8O8 polyhedron can be regarded in common terminology for alkali metal based structures, as an incomplete stack arrangement of two tetrameric (Li-O)(4) cyclic rings. The eight Li+ cations form a distorted dodecahedron and the eight alkoxide O atoms form a distorted square antiprism. (C) 1998 Elsevier Science Ltd. All rights reserved.