Sr4B10O18(OH)2•2H2O: a new UV nonlinear optical material with a [B10O23]16- building block

A new ultraviolet (UV) nonlinear optical (NLO) crystal Sr4B10O18(OH)2 center dot 2H(2)O has been synthesized using the hydrothermal method. It crystallizes in the triclinic space group P1 (no. 1) with lattice constants a = 6.4991(6) angstrom, b = 6.5059(6)angstrom, c = 11.3175(11)angstrom, alpha = 88.458(6)degrees, beta = 86.019(5)degrees, gamma = 61.351(5)degrees, Z = 1. The fundamental building block of the structure is a [B10O23](16-) unit which consists of two stereo-isomeric configurations of [B5O12](9-) groups. The structure exhibits a (infinity)[B10O18](6-) three dimensional network with 9-membered tunnels along the b-axis where the Sr cation, OH anion and H2O molecule are located. Powder second harmonic generation (SHG) measurements indicate that Sr4B10O18(OH)(2)center dot 2H(2)O is type-I phase-matchable and displays a SHG response of about 2 x KH2PO4. The UV-Vis-NIR diffuse reflectance spectrum shows that its cutoff edge is lower than 190 nm. Density functional theory (DFT) calculations on electronic structures and SHG coefficients confirm the experimental results.