Syntheses, structures and optical properties of two B3O7 cluster-based borates

Abstract

Two new B₃O₇ cluster-based borates, [B₆O₉(OH)₂]·H₂dap (1, dap = 1,2-diaminopropane) and Li_0.5Ca_0.5[B₃O₅][BO(OH)₂]_0.5 (2), were solvothermally synthesized using different organic and inorganic templates, respectively. In 1, two different B₃O₇ clusters interconnect to construct a rare 2D fluctuant layer with 11-MR unclosed channels. Templating [H₂1,2dap]²⁺ located in the interlayers stabilizes the layers through H-bonds. 2 features an acentric 3D open framework with 17-MR large channels built by 4-connected B₃O₇ clusters. Guest Li-BO(OH)₂-Ca 1D chains intercalate in the 17-MR channels, directing the formation of the 3D open framework through host–guest symmetry and charge matching. 2 is a phase-matchable nonlinear optical (NLO) material with a second-harmonic generation (SHG) response ∼1.6 times that of KDP (KH₂PO₄). UV-vis absorption spectra reveal that 1 and 2 have short cut-off edges of 205 and 213 nm, respectively, indicating that 1 is a wide-band semiconductor and 2 is a UV NLO material.