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

Sodium manganese(II) phosphate bis(hydrogenphosphate), NaMn3(PO4)(HPO4 )(2), has been prepared hydrothermally and its structure has been dete rmined 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) Angstro m, and beta = 114.616(7)degrees. The structure consists of a complex n etwork of edge-sharing Mn(II)O-6 octahedral chains that are linked tog ether by both corner-sharing PO4 tetrahedra and O-H...O bonds, forming channels along which Na atoms reside. The structure thus represents a n unoxidized variant of the alluaudite structure type, containing Mn a toms in only the single oxidation state of +Pi. The structure is embel lished by the presence of hydrogen bonds, evidence for which was obtai ned from bond-valence calculations, infrared spectroscopy, and thermal measurements which suggest the loss of one H2O molecule per formula u nit. Magnetic susceptibility measurements confirm the assignment of hi gh-spin Mn2+ in the title compound, as well as in its dehydrated form. (C) 1995 Academic Press, Inc.