AM3(P2O7)2 (A = ALKALINE-EARTH METALS - M = FE, CO, NI) - DIPHOSPHATES CONTAINING INFINITE CHAINS OF EDGE-SHARING MO6 OCTAHEDRA

Diphosphates of the stoichiometry AM3(P2O7)2 (A = alkaline-earth metal s; M = Fe, Co, Ni) have been synthesized and structurally characterize d by single-crystal X-ray diffraction. Crystal data: CaNi3(P2O7)2, mon oclinic, P2(1)/c, a = 7.330(3) angstrom, b = 7.589(3) angstrom, c = 9. 400(3) angstrom, beta = 11 1.90(3)-degrees, V = 485.1(3) angstrom3, Z = 2, and R = 0.026; CaCo3(P2O7)2, as above except a = 7.394(l) angstro m, b = 7.6266(9) angstrom, c = 9.444(2) angstrom, beta = 11 1.73(2)-de grees, V = 494.7(l) angstrom3, and R = 0.035; SrFe3(P2O7)2, as above e xcept a = 7.553(l) angstrom, b = 7.7477(8) angstrom, c = 9.5796(8) ang strom, beta = 112.11(1)-degrees, V = 519.4(l) angstrom3, and R = 0.029 . The three compounds are isostructural, consisting of zigzag infinite chains of MO6 octahedra sharing either trans or skew edges. The infin ite chains arc connected by P2O7 groups to form a three-dimensional ar chitecture with channels parallel to the b axis. Alkaline-earth metals are located in sites within the channels. The following isostructural compounds have also been prepared: AM3(P2O7)2 (A = Sr, Ba; M = Ni, Co ) and BaFe3(P2O7)2. A magnetic susceptibility study on SrFe3(P2O7)2 in dicates that the material is paramagnetic with an effective magnetic m oment of 5.07 mu(B) per Fe between 300 and 26 K. Below this temperatur e the magnetic susceptibility increases sharply to a maximum at 6 K an d then decreases rapidly. Mossbauer spectra also confirm the presence of Fe(II).