ABSTRACT
The incommensurately modulated scheelite-like KSm(MoO(4))(2) structure has been refined in the monoclinic superspace group I2/b(alphabeta0)00 by the Rietveld method on the basis of synchrotron radiation powder diffraction data. The systematic broadening of satellite reflections has been accounted for by applying anisotropic microstrain line-broadening. The microstructure has been studied by transmission electron microscopy (TEM). The partial disorder of the K and Sm cations in the A position is best approximated by a combination of harmonic and complex crenel functions with (0.952Sm + 0.048K) and (0.952K + 0.048Sm) atomic domains. This combination yields a compositional wave distribution from {KMoO(4)} to {SmMoO(4)} observed in the ab structure projection along q. The specific features of KSm(MoO(4))(2) and degree of the A-cation ordering are discussed in comparison with the previously reported structure of KNd(MoO(4))(2).
ABSTRACT
Hydrothermally synthesized dipotassium gallium {hydrogen bis[hydrogenphosphate(V)]} difluoride, K(2)Ga[H(HPO(4))(2)]F(2), is isotypic with K(2)Fe[H(HPO(4))(2)]F(2). The main features of the structure are ([Ga{H(HPO(4))(2)}F(2)](2-))(n) columns consisting of centrosymmetric Ga(F(2)O(4)) octahedra [average Ga-O = 1.966 (3) Angstrom and Ga-F = 1.9076 (6) Angstrom] stacked above two HPO(4) tetrahedra [average P-O = 1.54 (2) Angstrom] sharing two O-atom vertices. The charge-balancing seven-coordinate K(+) cations [average K-O,F = 2.76 (2) Angstrom] lie in the intercolumn space, stabilizing a three-dimensional structure. Strong [O...O = 2.4184 (11) Angstrom] and medium [O...F = 2.6151 (10) Angstrom] hydrogen bonds further reinforce the connections between adjacent columns.
