HYDROTHERMAL SYNTHESIS AND STRUCTURES OF NA3IN2(PO4)(3) AND NA3IN2(ASO4)(3) - SYNTHETIC MODIFICATIONS OF THE MINERAL ALLUAUDITE

Two indium-containing analogs of the mineral alluaudite, Na3In2(PO4)(3 ) and Na3In2(AsO4)(3), have been synthesized hydrothermally and struct urally characterized by single-crystal and powder X-ray diffraction, r espectively. Crystal data: Na3In2(PO4)(3), a=12.450(1), b=12.786(1), c =6.5920(7) Angstrom, beta = 114.174(2)degrees, V = 957.38 Angstrom(3), Z = 4; Na3In2(AsO4)(3), as above except a = 12.6037(2), b=13.1711(2), c=6.8342(1) Angstrom, beta = 113.743(1)degrees, V=1038.48 Angstrom(3) . The two compounds are isostructural, The main structural feature is the presence of infinite chains of edge-sharing In2O10 dimers and NaO6 octahedra, which are linked together by PO4 or AsO4 tetrahedra to for m a framework structure, enclosing two types of tunnels where Na+ cati ons reside. The X(1) site of the alluaudite structure is occupied by N a+, whereas the X(2) site is empty. Instead, a site which is shifted f rom the X(2) site by +/-1/4 along z is occupied by Na+. (C) 1997 Acade mic Press.