SYNTHESIS AND STRUCTURE OF NAMN3(PO4)(HPO4)(2), AN UNOXIDIZED VARIANT OF THE ALLUAUDITE STRUCTURE TYPE

Sodium manganese(II) phosphate bis(hydrogenphosphate), NaMn3(PO4)(HPO4)(2), has been prepared hydrothermally and its structure has been determined from single-crystal diffraction data. It crystallizes in space group C2/e of the monoclinic system with Z = 4 in a cell of dimensions a = 12.179(2) Angstrom, b = 12.405(1) Angstrom, c = 6.6602(8) Angstrom, and beta = 114.616(7)degrees. The structure consists of a complex network of edge-sharing Mn(II)O-6 octahedral chains that are linked together by both corner-sharing PO4 tetrahedra and O-H...O bonds, forming channels along which Na atoms reside. The structure thus represents an unoxidized variant of the alluaudite structure type, containing Mn atoms in only the single oxidation state of +Pi. The structure is embellished by the presence of hydrogen bonds, evidence for which was obtained from bond-valence calculations, infrared spectroscopy, and thermal measurements which suggest the loss of one H2O molecule per formula unit. Magnetic susceptibility measurements confirm the assignment of high-spin Mn2+ in the title compound, as well as in its dehydrated form. (C) 1995 Academic Press, Inc.