Crystal structures of the new diphosphates,K2NiP2O7 and K6Sr2Ni5(P2O7)5

Crystalline K₂NiP₂O₇ (I): monoclinic, P2₁,a=9.230(2),b=17.540(8),c=8.319(9)Å, =91.44(2)°,Z=8,d_calc=3.067 g cm^–3, MoK=0.71069Å,R/R_w=6.5/9.4%, is characterized by the existence of face sharing NiO₆ octahedra with Ni–Ni separation of 2.827 Å (Ni–O; 1.93(2)–2.17(2)Å). K⁺ is seen in sites of seven, six, and fivefold coordination (K–O, averages; 2.83(2), 2.81(2), and 2.77(2)Å, respectively) P₂O₇^4– groups are observed in semieclipsed conformation. K₆Sr₂Ni₅(P₂O₇)₅ (II) crystallizes in monoclinic space group P2₁/c;a=11.038(7),b=9.533(13),c=7.438(2)Å, =100.13(4)°,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 =0 and =0.5. On the planes, =0, Ni²⁺ ions form successive linked trimers of edge sharing NiO₆ octahedra (Ni–Ni, 3.018(1), 3.008(1)Å; Ni–O, av 2.07(2)Å). The intermediate planes (=0.5) contain isolated and six coordinate Ni²⁺ ions (Ni–O av. 2.09(2)Å). Seven-coordinate potassium ions (K–O, av. 2.74(2)Å) are located on intermediate planes at =0.25 and 0.75. P₂O₇^4– 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)Å).