Synthesis and characterization of ASnOAsO(4) (A=K and Rb)

Crystals of two alkali-metal tin(IV) arsenates, KSnOAsO4 and RbSnOAsO4, were grown from a flux and structurally characterized by single-crystal X-ray diffraction. Crystal data: KSnOAsO,, orthorhombic, Pna2(1) (No. 33), a = 13.406(3) Angstrom, b = 6.678(1) Angstrom, c = 10.921(2) Angstrom, Z = 8, R = 0.037 for 1173 independent reflections with I > 2.5 sigma(I); RbSnOAsO4, as above except a = 13.567(3) Angstrom, b = 6.791(1) Angstrom, c = 10.891(2) Angstrom, R = 0.035 for 1958 independent reflections. The two compounds are isostructural with the nonlinear optical material KTiOPO4. The oxygen frameworks of both tin compounds approximate closely to a centrosymmetric arrangement, as indicated from the analysis of atomic coordinates. Second harmonics were generated in powdered RbSnOAsO4 to confirm the absence of a center of symmetry in the structure.