Non-stoichiometric tubular nickel(II) hydroxyarsenates of the dumortierite family: crystal structure and topochemical thermal reduction of Ni12+xH6–x(AsO4)8(OH)6(x= 1.16 and 1.33)

Abstract

Arsenate derivatives of formula Ni_12+xH_6–2x(AsO₄)₈(OH)₆(1.16⩽x⩽1.33) have been synthesized. The structures of the two extreme compositions (x= 1.16 and x= 1.33) have been refined from X-ray powder diffraction data. Like the other members of this family, these hydroxyarsenates crystallize in the hexagonal P6₃mc space group (Z= 1) with a= 12.7018(2)Å and c= 5.03223(9)Å[V= 703.11(3)ų] and reliability factors R_F= 4.5%, R_p= 8.6%, R_wp= 11.1% for x= 1.16, and a=12.6953(2)Å and c= 5.0311(1)Å[V= 702.23(3)ų] and R_F= 3.7%, R_P= 6.4%, R_WP= 8.9% for x= 1.33. Thermal studies have shown that these tubular dumortierite-like solids remain unaltered, or only slightly modified, up to 700 °C.