A I B 3 II C 2 III Q 6 VI X VIII : A Thioborate Halide Family for Developing Wide Bandgap Infrared Nonlinear Materials by Coupling Planar [BS 3 ] and Polycations.

Developing high-performance infrared (IR) nonlinear optical (NLO) materials is urgent but challenging due to the competition between NLO coefficient and bandgap in one compound. Herein, by coupling NLO-active [BS 3 ] planar units and halide-centered polycations, six new metal thioborate halides ABa 3 B 2 S 6 X (A = Rb, Cs; X = Cl, Br, I) composed of zero-dimensional [XBa m Rb n /Cs n ] polycations and [BS 3 ] units, belonging to a new A I B 3 II C 2 III Q 6 VI X VIII ${\mathrm{A}}^{\mathrm{I}}{\mathrm{B}}_{3}^{\mathrm{II}}{\mathrm{C}}_{2}^{\mathrm{III}}{\mathrm{Q}}_{6}^{\mathrm{VI}}{\mathrm{X}}^{\mathrm{VIII}}$ family, are rationally designed and fabricated. The compounds show an interesting structural transition from Pbcn (ABa 3 B 2 S 6 Cl) to Cmc2 1 (ABa 3 B 2 S 6 Br and ABa 3 B 2 S 6 I) driven by the clamping effect of polycationic frameworks. ABa 3 B 2 S 6 Br and ABa 3 B 2 S 6 I are the first series metal thioborate halide IR NLO materials, and the introduction of [BS 3 ] unit effectively widens the bandgap of planar unit-constructed chalcogenides. ABa 3 B 2 S 6 Br and ABa 3 B 2 S 6 I, exhibiting wide bandgaps (3.55-3.60 eV), high laser-induced damage thresholds (≈ 6 × AgGaS 2 ), and strong SHG effects (0.5-0.6 × AgGaS 2 ) with phase-matching behaviors, are the promising IR NLO candidates for high-power laser applications. The results enrich the chemical and structural diversity of boron chemistry and give some insights into the design of new IR NLO materials with planar units.