Studies on the thermal behavior and crystal chemistry of anhydrous phosphates .15. Synthesis, crystal structure, and properties of copper(II) ultraphosphate CuP4O11

CuP4O11 was synthesised from Cu2P4O12 and P4O10 (500 degrees 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 degrees C led to the formation of well developed, colourless, transparent crystals with edge-lengths up to 5 mm (deposition rate m approximate to 2 mg/h). The crystal structure of copper(II) ultraphosphate <(C(1)over bar ;> z = 8; a = 13.084(3) Angstrom, b = 13.024(2) Angstrom, c = 10.533(2) Angstrom, alpha = 89.28(2)degrees, beta = 118.42(2)degrees, gamma = 90.30(2)degrees) 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 2 theta less than or equal to 53.4 degrees; 291 variables; conventional residual (based on Fl R1 = 0.038, wR2 = 0.101 (based on F-2), 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 (-201) 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) approximate to 1.96 Angstrom; d(ax)(Cu-O) approximate to 2.34 Angstrom). The crystal g-tensor of CuP4O11 has been determined from powder samples to g(1) = 2.09, g(2) = 2.24, g(3) = 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 mu(exp) = 1.99 mu(B) is also reproduced nicely by this calculations.