An Unprecedented [BO 2 ]-Based Deep-Ultraviolet Transparent Nonlinear Optical Crystal by Superhalogen Substitution.

Solid-state structures with the superhalogen [BO 2 ] - have thus far only been observed with a few compounds whose syntheses require high reaction temperatures and complicated procedures, while their optical properties remain almost completely unexplored. Herein, we report a facile, energy-efficient synthesis of the first [BO 2 ]-based deep-ultraviolet (deep-UV) transparent oxide K 9 [B 4 O 5 (OH) 4 ] 3 (CO 3 )(BO 2 ) ⋅ 7H 2 O (KBCOB). Detailed structural characterization and analysis confirm that KBCOB possesses a rare four-in-one three-dimensional quasi-honeycomb framework, with three π-conjugated anions ([BO 2 ] - , [BO 3 ] 3- , and [CO 3 ] 2- ) and one non-π-conjugated anion ([BO 4 ] 5- ) in the one crystal. The evolution from the traditional halogenated nonlinear optical (NLO) analogues to KBCOB by superhalogen [BO 2 ] - substitution confers deep-UV transparency (<190 nm), a large second-harmonic generation response (1.0×KH 2 PO 4 @ 1064 nm), and a 15-fold increase in birefringence. This study affords a new route to the facile synthesis of functional [BO 2 ]-based oxides, paving the way for the development of next-generation high-performing deep-UV NLO materials.