Hydrothermal Syntheses and Crystal Structures of Two New Iron Phosphates [C2N2H10]2+[Fe(HPO4)2(OH)]2-·H2O and KFe3(OH)2(PO4)2·2H2O

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 triclinic space groupP-1,a=8.526(2) ?,b=9.796(2) ?,c=7.232(2) ?,=90.25(2)°,= 92.72(2)°,=65.20(1)°,Z=2,R,Rw=0.040, 0.044. The structure is composed of isolated anionic chains of the tancoite type, [Fe (HPO4)2OH]n, consisting of vertex-sharing Fe-O octahedra. The chains are isotypic with those in the iron fluorophosphate ULM-14, but in that case the vertex-sharing is via an F-link rather than an OH-link. KFe3(OH)2(PO4)2·2H2O (II) adopts the orthorhombic space groupPmc21,a=6.410(2) ?,b=7.429(3) ?,c=9.868(4) ?,Z=2,R,Rw=0.053, 0.090. In this case the structure was solved from microcrystal diffraction data at a synchrotron source (crystal size 60×15×5 m). The structure is isotypic with the mineral olmsteadite, KFe2NbO2(PO4)2·2H2O, with Fe3+on the Nb5+site and charge-balancing OH-groups replacing O2-. This compound has a three-dimensional framework structure with small channels running parallel toaandcin which the K+ions sit.