Crystallochemical classification scheme for molybdates

Abstract

The authors propose a classification scheme for molybdates of the type R/sub c/A/sub d/ (MoO4)/sub y/ based on analysis of crystallochemical formulas of the structural groups (A/sub d/(MoO3)/sub y/), in the composition of which there are high-valence cations of the complexing agent A and molybdate groups coordinated to them. It has been determined that the 84 studied molybdates are representatives of 32 crystallochemical groups of complexes, in which there are 13 different types of coordination between the tetrahedral MoO4S anions and the A atoms. They have considered the effect of the MoO4:A ratio and the nature of the A cations on the structure and dimensionality of the structural groups. On the basis of the proposed crystallochemical formulas, they have analyzed the interrelationship between the number of bridge oxygen atoms in the AO/sub n/ polyhedra and the method for joining the polyhedra; and they also discuss the reasons for differences in crystal structure between the considered molybdates and sulfates which are analogous in stoichiometric composition.