The crystal chemistry of AM2O4 oxometallates

This review summarizes the crystal chemistry of oxometallates with composition AM(2)O(4), which indicates that more than 50 individual structure types regarding the formulae AM(2)O(4) or A(2)MO(4) exist. The spectrum of reported structures includes spinels, spineloids, compounds with closed and interrupted octahedra layers, tunnel structures, as well as square-planar polygons and dumb-bells. Irregular polyhedra around large metal ions have been estimated by calculations of effective coordination numbers (ECoN). Calculations of the Coulomb terms of the lattice energy (MAPLE) lead to the centers of stereochemically active lone pairs in AM(2)O(4) compounds containing s(2) cations. The positions of lone pairs and their crystal chemical function are pointed out in the corresponding figures. (C) 2002 Elsevier Science B.V. All rights reserved.