Thermal dehydration of the double salts K2Be(XO4)2•2H2O (X = S, Se)

The thermal dehydration of the title compounds was studied by TG, DTA and DSC methods and the enthalpies of dehydration were calculated (87.6 0 mol(-1) and 167.5 0 mol(-1) for the sulfate and selenate compound, respectively). The larger value of Delta H-deh of K2Be(SCO4)(2)(.)2H(2)O is due to the stronger hydrogen bonds formed in the selenate as compared to those formed in the respective sulfate owing to the stronger proton acceptor capabilities of the SeO(4)(2-)ions. The enthalpies of formation (Delta H-f(0)) of the dihydrates are also calculated from the DSC measurements (-4467.4 kJ mol(-1) and -3447.1 kJ mol(-1) for the sulfate and selenate compound, respectively). The anhydrous double salt, K2Be(SO4)(2), forms tetragonal crystals with lattice 3 parameters: a = 7.232(2) angstrom; c = 14.168(2) angstrom; V = 741.0 angstrom(3), while the anhydrous salt, K2Be(SeO4)(2), forms monoclinic crystals with lattice parameters: a = 9.217(3) angstrom; b = 10.645(3) angstrom; c = 8.989(2) angstrom; beta= 108.52(4)degrees; V = 836.2 angstrom(3). Vibrational spectra (infrared and Raman) of both the dibydrates and the anhydrous compounds are also presented and discussed. (c) 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.