Beiträge zum Koordinationsverhalten von Oxidionen in anorganischen Feststoffen. IV [1] Darstellung,Kristallstruktur und spektroskopische Charakterisierung von NiP4O11 und CaNiP2O7

Synthesis, Crystal Structures, and Spectroscopic Characterization of NiP₄O₁₁ and CaNiP₂O₇ From melts single crystals of NiP₄O₁₁ and CaNiP₂O₇ have been grown. These allowed refinement of the crystal structures (NiP₄O₁₁: C1¯, Z = 8, a = 12, 753(4)Å, b = 12.957(3)Å, c = 10.581(4)Å, α = 89.42(2)°, β = 116.96(2)°, γ = 90.20(2)°, R1 = 0.027, wR2 = 0.072 for 3058 I_o > 2σ (I_o), 3291 independent reflections, 290 parameters; CaNiP₂O₇: P1¯, Z = 2, a = 6.433(3)Å, b = 6.536(4)Å, c = 6.515(2)Å, α = 66.4(2)°, β = 87.5(2)°, γ = 82.7(2)°, R1 = 0.026, wR2 = 0.062 for 1624 I_o > 2σ (I_o), 2189 independent reflections, 101 parameter) and measurement of polarized electronic absorption spectra in the uv/vis/nir region (6000—32000 cm^—1). NiP₄O₁₁ is isotypic to the series of ultraphosphates MP₄O₁₁ (M = Mn, Fe, Co, Cu, Zn, Cd) that exhibit a two‐dimensional network formed from ten‐membered phosphate rings. CaNiP₂O₇ completes the series of diphosphates AMP₂O₇ (A: Ca, Sr, Ba; M = Cr — Zn) and is isotypic to CaCoP₂O₇. Ni²⁺ ions in both phosphates show distorted octahedral coordination. The electronic transitions associated with the chromophores Ni²⁺O₆] are nicely reproduced by calculations within the framework of the angular overlap model (AOM). The parametrisation scheme leads to e_{σ, norm}(2.0Å) = 3690 cm^—1 and B = 896 cm^—1 (C/B = 4.2) for CaNiP₂O₇ and e_{σ, norm}(2.0Å) = 4150 cm^—1 and B = 948 cm^—1 (C/B = 4.5) for NiP₄O₁₁ (Δ_o(CaNiP₂O₇) = 6800 cm^—1; Δ_o(NiP₄O₁₁) = 7100 cm^—1).