Hydrothermal syntheses and crystal structures of two new iron phosphates [C2N2H10](2+)[Fe(HPO4)(2)(OH)](2-)center dot H2O and KFe3(OH)(2)(PO4)(2)center dot 2H(2)O

Two new iron phosphates have been prepared hydrothermally and characterized by single crystal X-ray diffraction. [C2N2H10](2+) [Fe(HPO4)(2)(OH)](2-) . H2O (I) crystallizes in tri-clinic space group P-1, a = 8.526(2) Angstrom, b = 9.796(2) Angstrom, c = 7.232(2) Angstrom, alpha = 90.25(2)degrees, bet a = 92.72(2)degrees, gamma = 65.20(1)degrees, Z = 2, R, R-w = 0.040, 0.044. The structure is composed of isolated anionic chains of the tancoite type, [Fe(HPO4)(2)OH](n), consisting of vertex-sharing Fe-O octahedra, The chain s are isotypic with those in the iron fluorophosphate ULM-14, but in that c ase the vertex-sharing is via an F- link rather than an OH- link, KFe3(OH)( 2)(PO4)(2) . 2H(2)O (II) adopts the orthorhombic space group Pmc2(1), a = 6 .410(2) Angstrom, b = 7.329(3) Angstrom, c = 9.868(4) Angstrom, Z = 2, R, R -w = 0.053, 0.090. In this case the structure was solved from microcrystal diffraction data at a synchrotron source (crystal size 60 x 15 x 5 pm), The structure is isotypic with the mineral olmsteadite, KFe2NbO2(PO4)(2) . 2H( 2)O, with Fe3+ on the Nb5+ site and charge-balancing OH- groups replacing O 2-. This compound has a three-dimensional framework structure with small ch annels running parallel to a and c in which the K+ ions sit, (C) 1999 Acade mic Press.