Crystalline K2NiP2O7 (I): monoclinic, P2(1), a = 9.230(2), b = 17.540(8), c = 8.319(9)Angstrom, beta = 91.44(2)degrees, Z = 8, d(calc) = 3.067 g cm(-3), lambda MoKalpha 0.71069 Angstrom, R/R(w) = 6.5/9.4%, is characterized by the existence of face sharing NiO6 octahedra with Ni-Ni separation of 2.827 Angstrom (Ni-O; 1.93(2) - 2.17(2)Angstrom). K+ is seen in sites of seven, six, and fivefold coordination (K-O, averages; 2.83(2), 2.81(2), and 2.77(2)Angstrom, respectively). P2O74- groups are observed in semieclipsed conformation. K6Sr2Ni5(P2O7)(5) (II) crystallizes in monoclinic space group P2(1)/c; a = 11.038(7), b = 9.533(13), c = 7.438(2)Angstrom, beta = 100.13(4)degrees, D-calc = 3.309 g cm(-3) Z = 2, R/R(w) = 6.4/8.1%. Nickel atoms are distributed on planes parallel to the crystallographic (100) plane at x = 0 and x = 0.5. On the planes, x = 0, Ni2+ ions form successive linked trimers of edge sharing NiO6 octahedra (Ni-Ni, 3.018(1), 3.008(1)Angstrom; Ni-O, av 2.07(2)Angstrom). The intermediate planes (x = 0.5) contain isolated and six coordinate Ni2+ ions (Ni-O av. 2.09(2)Angstrom). Seven-coordinate potassium ions (K-O, av. 2.74(2)Angstrom) are located on intermediate planes at x = 0.25 and 0.75. P2O74- groups are found in eclipsed conformation. Strontium atoms are located between nickel and potassium planes and are surrounded by seven oxygen atoms(Sr-O, av. 2.586(2)Angstrom).
