Thermal dehydration of the double salts K2Be(XO4)2.2H2O (X = S, Se) by M. P. Georgiev, D. G. Stoilova, D. M. Marinova, and V. A. Karadjova

Crystal Research and Technology

Cryst. Res. Technol. 42, 54 (2007) - Abstract -

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

M. P. Georgiev, D. G. Stoilova*, D. M. Marinova*, and V. A. Karadjova

Department of Inorganic Chemistry, University of Chemical Technology and Metallurgy, 8 Kliment Ohridski Str., 1756 Sofia, Bulgaria
*Institute of General and Inorganic Chemistry, Bulgarian Academy of Sciences, 1113 Sofia, Bulgaria

Keywords	potassium beryllium sulfate dihydrate, potassium beryllium selenate dihydrate, enthalpy of dehydration, anhydrous potassium beryllium sulfate and selenate, lattice parameters, vibrational spectra
PACS	81.70.Pg, 61.10.Hz, 07.57.Hm
DOI	10.1002/crat.200610770

The thermal dehydration of the title compounds was studied by TG, DTA and DSC methods and the enthalpies of dehydration were calculated (87.6 kJ mol^-1 and 167.5 kJ mol^-1 for the sulfate and selenate compound, respectively). The larger value of ΔH_deh of K₂Be(SeO₄)₂^.2H₂O 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 SeO₄^2- ions. The enthalpies of formation of the dihydrates are also calculated from the DSC measurements. The anhydrous double salt, K₂Be(SO₄)₂, forms tetragonal crystals with lattice parameters: a = 7.232(2) Å; c = 14.168(2) Å; V = 741.0 Å³, while the anhydrous salt, K₂Be(SeO₄)₂, forms monoclinic crystals with lattice parameters: a = 9.217(3) Å; b = 10.645(3) Å; c = 8.989(2) Å; β = 108.52(4)°; V = 836.2 Å³. Vibrational spectra (infrared and Raman) of both the dihydrates and the anhydrous compounds are also presented and discussed.

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