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

Abstract

Key words 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.HmThe 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 ∆H deh of K 2 Be(SeO 4 ) 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 2ions. The enthalpies of formation (∆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, K 2 Be(SO 4 ) 2 , forms tetragonal crystals with lattice parameters: a = 7.232(2) Å; c = 14.168(2) Å; V = 741.0 Å 3 , while the anhydrous salt, K 2 Be(SeO 4 ) 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 Å 3 . Vibrational spectra (infrared and Raman) of both the dihydrates and the anhydrous compounds are also presented and discussed.

Infrared spectroscopic study of SO42− ions included in M′2M′′(SeO4)2⋅6H2O (Me′=K, NH4+; M′′=Mg, Co, Ni, Cu, Zn) and NH4+ ions included in K2M(XO4)2⋅6H2O (X=S, Se; M′′=Mg, Co, Ni, Cu, Zn)

“…Recently, the value of the ratio Dm as /m c (where m c is the centro-frequency value of the asymmetric modes) has been proposed to calculate the relative splitting of dopant ions [9]. Continuing our study on the vibrational behavior of matrixisolated ions in different matrices [17][18][19][20][21][22][23] 6 ], (three crystallographically different water molecules are coordinated to the M 00 ions) and tetrahedra XO 4 . These polyhedra are linked by hydrogen bonds.…”

Comparative study of ionic interactions of 1 : 1 and 1 : 2 electrolytes of nitrates salts solutions with water analysed with physicochemical data

“…In the case of a pure electrolyte, the interaction between the two ions based on ion-ion interactions [13] is a long-range arrangement of water used as solvent where energy E is inversely related to a distance r between the two ions (E / 1/r). When an ionic compound is dissolved in a polar solvent like water, the stronger electrostatic interaction between ions and the solvent molecules noted as ion-dipole interaction takes place [13][14][15][16][17][18][19][20][21]. It is similar to the ionion interaction except the latter are more sensitive to the distance with E / 1/r 2 relation.…”