CRYSTAL-GROWTH AND SINGLE-CRYSTAL STRUCTURAL REFINEMENT OF THE RHODIUM(III) PHOSPHATES RHPO4 AND RHP3O9

By means of chemical vapour transport reactions (transport agent: 1 atm Cl2 at room temperature) dark red, transparent crystals of RhPO4 (1323 K --> 1223 K) and orange crystals of RhP3O9 (1223 K --> 1123 K) were obtained with edge length up to 1 mm. The structures of both compounds were refined from x-ray single crystal data (RhPO4: alpha-CrPO4 structure type, Imma, Z = 12, a = 10.3967(8) angstrom, b = 13.1124(9) angstrom, c = 6.3929(5) angstrom, 1249 independent reflections with \F\ greater-than-or-equal-to 3sigma(F), 50 variables, R = 0.026; RhP3O9: C-MP3O9 structure type, Cc, Z = 12, a = 13.002(8) angstrom, b = 19.065(9) angstrom, c = 9.296(4) angstrom, beta = 127.04(3)-degrees, 4541 independent reflections with \F\ greater-than-or-equal-to 3sigma(F), 119 variables, R = 0.033). The crystal structures of RhPO4 and RhP3O9 are described and compared to isotypical compounds. Temperature dependent x-ray powder photographs gave no evidence for a phase transition for RhPO4 neither then for RhP3O9 UP to 1223 K.