Synthesis, crystal structure, NMR studies, and thermal stability of mixed iron-indium phosphates with quasi-one-dimensional frameworks

The hydrothermal synthesis, single-crystal structure analysis, spectroscopi c studies, and thermal stability of the compounds Ca-2(In1-xFex)(PO4)(HPO4) (2). H2O (0 less than or equal to x less than or equal to 1) are reported. The framework of these new phases is based on linear chains (//[101]) forme d by (MO6) octahedra and (PO4)/(HPO4) tetrahedra sharing centers. The (HPO4 ) groups and water molecules link the chains through hydrogen bonding to fo rm layers stacked perpendicular to the c axis. The calcium cations are loca ted between the layers and are coordinated by nine oxide anions. Crystal da ta: Ca2In(PO4)(HPO4)(2). H2O, space group C2/c (No. 15), a = 7.573(1) Angst rom, b = 15.838(1) Angstrom, c = 9.3126(7) Angstrom, beta = 113.55(1)degree s; Ca-2(In0.5Fe0.5) (PO4)(HPO4)(2). H2O, C2/c (No. 15), a = 7.548(2) Angstr om, b = 15.670(3) Angstrom, c = 9.241(2) Angstrom, beta = 113.62(3)degrees; Ca2Fe(PO4)(HPO4)(2) H2O, C2/c (No. 15); a = 7.503(2) Angstrom, b = 15.477( 2) Angstrom, c = 9.142(1) Angstrom. beta = 113.60(2)degrees. The phases los e two water molecules between 350 and 600 degrees C to form the series Ca-2 (In1-xFex)(PO4)(P2O7) (0 less than or equal to x less than or equal to 1), which are isostructural with Ca2V(PO4)(D2O7). Solid state magic angle spinn ing (MAS) P-31 NMR of Ca2In(PO4)(HPO4)(2). H2O confirms two phosphorous moi eties in roughly a 2:1 ratio. A CP-MAS buildup study yielded polarization t ransfer rates (T-IS(-1)) of 2128 and 1597 s(-1) for the HPO4 (-2.4 ppm) and PO4 (-0.9 ppm) sites, respectively. A H-1-P-31 WISE experiment indicates t he presence of motional narrowing and hydrogen exchange between the water m olecules and hydroxyl protons.