A powder diffraction study of the crystal structure and the dehydration process of yttrium potassium oxalate tetrahydrate

YK(C2O4)(2). 4H(2)O crystallises with the tetragonal symmetry, space group I4(1)/a (Z = 4), with the unit cell dimensions a = 11.4612(8) Angstrom, c = 8.9040(8) Angstrom and V = 1169.6(2) Angstrom(3). Its structure was solved ab initio by direct methods from conventional X-ray powder diffraction data and refined by the Rietveld method (R-F = 0.037, R-wp = 0.125). The yttrium atoms are eight-fold coordinated to the bidentate oxalate groups and the resulting opened framework exhibits tunnels in several directions. The water molecules are located in the vacancies and are slightly bonded to the potassium atoms. Zeolitic properties of some water molecules have been evidenced from X-ray diffraction and thermogravimetric measurements.