Beiträge zum thermischen Verhalten und zur Kristallchemie von wasserfreien Phosphaten. XV. Darstellung,Kristallstruktur und Eigenschaften von Kupfer(II)-ultraphosphat CuP4O11 (≙ Cu2P8O22)

Synthesis, Crystal Structure, and Properties of Copper(II) Ultraphosphate CuP₄O₁₁ CuP₄O₁₁ was synthesised from Cu₂P₄O₁₂ and P₄O₁₀ (500°C, sealed silica ampoules) using iodine and a few mg of CuP₂ or phosphorus as mineraliser. Chemical transport reactions in a temperature gradient 600 → 500°C led to the formation of well developed, colourless, transparent crystals with edge-lengths up to 5 mm (deposition rate m ≈? 2 mg/h). The crystal structure of copper(II) ultraphosphate (C1 ; Z = 8; a = 13.084(3) Å, b = 13.024(2) Å, c = 10.533(2) Å, α = 89.28(2)°, β = 118.42(2)°, γ = 90.30(2)°) has been determined and refined from X-ray data obtained from a pseudo-merohedrally twinned crystal (twin element two-fold rotation axis // b; volume ratio: 17/3; 3063 independent reflections with 2θ ? 53.4°; 291 variables; conventional residual (based on F) R1 = 0.038, wR2 = 0.101 (based on F²), GooF = 1.10). The crystal structure of CuP₄O₁₁ is built from four crystallographically independent ten-membered polyphosphate rings of very similar conformation. These rings are linked to form two-dimensional nets parallel (?2 0 1) planes. There is a close topological relationship between these nets and those formed in polyphosphides CdP₄ and CuP₂. Copper on two crystallographic sites (Cu₂P₈O₂₂) is coordinated by oxygen thus forming elongated CuO₆] octahedra (d_eq(Cu? O) ≈? 1.96 Å; d_ax(Cu? O) ≈? 2.34 Å). The crystal g-tensor of CuP₄O₁₁ has been determined from powder samples to g₁ = 2.09, g₂ = 2.24, g₃ = 2.36. These values are in good agreement with molecular g-values from calculations within the framework of the angular overlap model on the two independent CuO₆ octahedra (Cu²⁺(1): g_x = 2.09, g_y = 2.10, g_z = 2.52; Cu²⁺(2): g_x = 2.08, g_y = 2.11, g_z = 2.52) assuming exchange coupling. The observed broad absorption band (7000 cm^?1 to 13000 cm^?1) from powder reflectance measurements (4000–28000 cm^?1) and the bulk magnetic susceptibility of μ_exp = 1.99 μ_B is also reproduced nicely by this calculations.