Cs2CdV2O6Cl2 and Cs3CdV4O12Br: two new non-centrosymmetric oxyhalides containing d0 and d10 cations and exhibiting second harmonic generation activity†
Two new oxyhalides including d0 and d10 cations, Cs4Cd2V4O12Cl4 (1) and Cs3CdV4O12Br (2), were successfully synthesized via a solid phase reaction. Their crystal structures have been determined by X-ray single crystal diffraction. Compound 1 crystallizes in space group Cm (no. 8), whereas compound 2 is found in space group Cmm2 (no. 35). The corner-shared V3O8 units and CdO2Cl4 units in the compound 1 bridge a three-dimensional network, whereas the corner-shared V4O11 polyhedron and CdO4Br2 octahedron in the compound 2 form a three-dimensional structure. All the polar groups align in one direction, which results in a favorable net polarization. Powder second harmonic generation, using 1064 nm incident radiation, indicates that they are phase-matchable with observable and strong SHG response (5 and 7 times KH2PO4, respectively). The UV-vis-NIR diffuse reflectance spectra indicate that the band gaps of the compound 1 and 2 are 3.00 eV (413 nm) and 3.13 eV (396 nm), respectively. Based on the IR and UV-vis-NIR data, the transparent range of both compounds is 0.4–10.4 μm. Furthermore, the electronic structure was also investigated by the first-principles calculations.