Influence of the Cation Size on the Framework Structures and Space Group Centricities in AMo2O5(SeO3)2 (A = Sr, Pb, and Ba)

Two new quaternary mixed-metal selenites, SrMo2O5(SeO3)(2) and PbMo2O5(SeO3)(2), have been synthesized as crystals and pure polycrystalline phases by standard solid-state reactions using SrMoO4, PbO, MoO3, and SeO2 as reagents. The crystal structures of the reported materials have been determined by single-crystal X-ray diffraction. SrMo2O5(SeO3)(2) and PbMo2O5(SeO3)(2) are isostructural and crystallized in the triclinic centrosymmetric space group P (1) over bar (No. 2). The reported materials exhibit chain structures consisting of MoO6 octahedra and asymmetric SeO3 polyhedra. Complete characterizations including IR spectroscopy and thermal analyses for the compounds are also presented, as are dipole moment calculations. In addition, the powder second-harmonic-generating (SHG) properties of noncentrosymmetric polar BaMo2O5(SeO3)(2) have been measured using 1064 nm radiatior. Through powder SHG measurement, we are able to determine that BaMo2O5(SeO3)(2) has a SHG efficiency of approximately 80 times that of alpha-SiO2. Additional SHG measurements reveal that the material is phase-matchable (type 1). A detailed cation size effect on the symmetry and framework structure is discussed.