Cation-anion interactions and polar structures in the solid state.

Complicated structures where oxygen and fluorine are found together in one framework, where deviations from Pauling's second crystal rule (PSCR) are expected, often result in structures with important physical properties. The [NbOF5]2- anion and therefore all the individual Nb-O and Nb-F bonds are ordered in noncentrosymmetric KNaNbOF5 and centrosymmetric CsNaNbOF5. The Na/K- and Na/Cs-O/F interactions in these phases, in particular the expected deviations from PSCR and the bond valence model, reveal the essential role of the small potassium cations in the acentric packing of the [NbOF5]2- anion.

New layered uranium phosphate fluorides: syntheses, structures, characterizations, and ion-exchange properties of A(UO2)F(HPO4).xH2O (A = Cs+, Rb+, K+; x = 0-1).

Single crystals of three new layered uranium phosphate fluorides, A(UO2)F(HPO4).xH2O (A = Cs+, Rb+, and K+; x = 0-1) have been synthesized by hydrothermal reactions using UO3, H3PO4, HF, and corresponding alkali metal halides as reagents. Although all three new materials have layered structures, each of them contains different structural motifs within the layer.