Hydrogen-Bond-Assisted Reinforcement of Interlayer Connections in ZnBOX·HO (X = Cl, Br): Two UV Nonlinear Optical Crystals with KBBF-Type Structure.

Two novel zinc borate halides named ZnBOX·HO (X = Cl, Br) were discovered through hydrothermal techniques. Both compounds are isomorphic and feature the layered structure similar to that of KBBF, consisting of the infinite planar [ZnBOX·OH] (X = Cl, Br) layers. Compared with the weak ionic bond between adjacent layers in KBBF, the strong interaction of hydrogen bonds between layers in ZnBOX·HO (X = Cl, Br) effectively enhances the interlayer force, contributing to eliminating the layering growth tendency. Optical measurements on these two NLO crystals revealed that they have a broad wavelength transparency window and a moderate NLO coefficient. Moreover, the theoretical calculations revealed that the linear and NLO properties primarily depended on the [BO] and [ZnOCl/Br] groups in both crystals.