The incommensurately modulated scheelite-like KSm(MoO4)2 structure has been refined in the monoclinic superspace group I2/b(αβ0)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 {KMoO4} to {SmMoO4} observed in the ab structure projection along q. The specific features of KSm(MoO4)2 and degree of the A-cation ordering are discussed in comparison with the previously reported structure of KNd(MoO4)2.

Hydrothermally synthesized dipotassium gallium {hydrogen bis[hydrogenphosphate(V)]} difluoride, K2Ga[H(HPO4)2]F2, is isotypic with K2Fe[H(HPO4)2]F2. The main features of the structure are ([Ga{H(HPO4)2}F2]2−)n columns consisting of centrosymmetric Ga(F2O4) octahedra [average Ga—O = 1.966 (3) Å and Ga—F = 1.9076 (6) Å] stacked above two HPO4 tetrahedra [average P—O = 1.54 (2) Å] sharing two O‐atom vertices. The charge‐balancing seven‐coordinate K+ cations [average K—O,F = 2.76 (2) Å] lie in the intercolumn space, stabilizing a three‐dimensional structure. Strong [O...O = 2.4184 (11) Å] and medium [O...F = 2.6151 (10) Å] hydrogen bonds further reinforce the connections between adjacent columns.

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