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

Abstract

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≤x<1 and 0≤y<0.5 homogeneity ranges. High quality single crystals of the γ(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 P21/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 Bi2−yAsyMoO6 phases crystallize with γ(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 BiIII, SbIII and AsIII, the latter adopting the one-sided coordination CN3, while the two former Sb and Bi can present CN4 and CN5 coordinations.