Single-crystal X-ray investigations of the structures of γ(H)Bi2MoO6 and its partially substituted As3+ and Sb3+ homologues

In order to establish the possible existence of the solid solutions Bi2-xSbxMoO6 and Bi2-yAsyMoO6, solid state syntheses were realized and single phases obtained with 0 less than or equal to x < 1 and 0 <less than or equal to> y < 0.5 homogeneity ranges. High quality single crystals of the <gamma>(H)-Bi2MoO6 prototype structure were grown for the first time and carefully refined (R = 0.048) by X-ray single-crystal techniques. This phase crystallizes in the monoclinic system, space group P2(1)/c; the observed general atomic architecture confirms a previous neutron diffraction investigation on a powder sample. A detailed description of the structure is given showing the imbrication of three different module types: A: {Bi12O14}(n) column, B: {Bi2Mo2O10}(n) and C: {BiMo3O12}(n) ribbons. Both Bi2-xSbxMoO6 and Bi(2-gamma)As(gamma)AoO(6) phases crystallize with gamma (H) structure and the fine structural analysis performed for several values of x and y indicate that Sb and As atoms are preferentially located in specific Bi sites at the periphery of the typical A and B modules. These results are discussed in the light of the typical coordination of the lone pair cations Bi-III, Sb-III and As-III, the latter adopting the one-sided coordination CN3, while the two former Sb and Bi can present CN4 and CN5 coordinations. (C) 2000 Editions scientifiques et medicales Elsevier SAS. All rights reserved.