How Lewis acidity of the cationic framework affects KNaNbOF(5) polymorphism.

The valence matching principle is used to explain the loss of inversion symmetry in the noncentrosymmetric (NCS) polymorph of KNaNbOF5 in comparison to its centrosymmetric (CS) polymorph. The [NbOF5](2-) anion has five contacts to both potassium and sodium in the NCS polymorph, whereas in the CS polymorph there are only four contacts to potassium and six contacts to sodium. The lower average Lewis acidity of the cationic framework in the NCS polymorph relative to the CS polymorph reflects the loss of inversion symmetry.

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.

Structure and magnetic properties of Pb2Cu3B4O11: a new copper borate featuring [Cu3O8]10- units.

Pb2Cu3B4O11 crystallizes in the monoclinic space group P2/n (No. 13) with a = 6.8016(15) A, b = 4.

Synthesis, crystal structure, and nonlinear optical properties of Li6CuB4O10: a congruently melting compound with isolated [CuB4O10]6- units.

Single crystals of Li(6)CuB(4)O(10) have been synthesized, and its crystal structure has been determined. Li(6)CuB(4)O(10) crystallizes in the non-centrosymmetric triclinic space group P1 (No. 1).