Crystal structures of rubidium scandium bis(hydrogenphosphate), RbSc(HPO4)2, and ammonium scandium bis(hydrogenphosphate), NH4Sc(HPO4)2

Abstract

H2O8P2RbSc, monoclinic, P121/c1 (no. 14), a = 5.3214(6) A, b = 8.9221(7) A, c = 14.758(1) A, = 94.967(5)°, V = 698.0 A, Z = 4, Rgt(F) = 0.060, wRref(F) = 0.180, T = 295 K. H6NO8P2Sc, monoclinic, P121/c1 (no. 14), a = 5.3211(5) A, b = 8.8660(7) A, c = 14.791(1) A, = 95.266(4)°, V = 694.8 A, Z = 4, Rgt(F) = 0.092, wRref(F) = 0.287, T = 295 K. Source of material The isotypic compoundsMSc(HPO4)2 (M = Rb, NH4) were prepared under mild hydrothermal conditions. For RbSc(HPO4)2, a mixture of 0.5000 g Sc2O3 (Abcr, 99.9 %), 0.3715 g RbOH (Alfa Aesar, 99 %), and 2.5079 g H3PO4 (Merck, 85 %) was heated at 363 K after addition of deionized water (10 ml) with continuous stirring until the components were completely dissolved (molar ratio Sc : Rb : P = 1 : 1 : 6). The clear solution (pH = 1) was then transferred into a 20 ml Teflon-lined autoclave (filling degree 40 %) and heated at 443 K for seven days. NH4Sc(HPO4)2was synthesized fromamixture of 0.5000 gSc2O3 (Abcr, 99.9%), 0.2241 g H3BO3 (Alfa Aesar, 99.9 %) and 3.8302 g (NH4)2HPO4 (Merck, 99 %) in the molar ratio NH4 : Sc : P = 1 : 1 : 8. 10 ml of deionized water were added, and the systemwas stirred at 373 K. The pH value was adjusted to 1 by the addition of 3.0 ml HCl (37 %). The mixture was then filled into a 10 ml Teflon-lined autoclave (filling degree 30%) and heated under autogenous pressure at 443 K for 24 days. The obtained reaction products were separated by filtration, washed with hot water/acetone and dried in air at 333 K. The products consisted of needle-shaped transparent crystalswith dimensions ranging from0.05 to 0.1mm.The chemical compositionMSc(HPO4)2 (M=Rb,NH4) was confirmed by EDXS and chemical analyses. IR spectra and the loss of water during TG analyses confirm the presence of P−OH groups. Experimental details The crystals of both compounds were affected by reticular merohedry twinning. The positions of Rb, Sc, P, O for RbSc(HPO4)2 and Sc, P, O, N for NH4Sc(HPO4)2 were obtained from structural data of the isotypic compound CsSc(HPO4)2 [1]. Subsequent introduction of the twinmatrix [−1 0 0 0 −1 0 0.5 0 1] and simultaneous refinement of the twin ratio together with the atomic coordinates and anisotropic thermal parameters led to reasonable structural models and residuals. The positions of the protons could not be determined from Fourier difference map analyses for both compounds MSc(HPO4)2 (M = Rb, NH4).