Ba_n+2Zn_n(BO₃)_n(B₂O₅)F_n (n = 1, 2): new members of the zincoborate fluoride series with two kinds of isolated B–O units

Two new members of zincoborate fluoride series Ba_n+2Zn_n(BO₃)_n(B₂O₅)F_n (n = 1, 2), namely, Ba₃Zn(BO₃)(B₂O₅)F and Ba₄Zn₂(BO₃)₂(B₂O₅)F₂ were firstly synthesized as high-quality single crystals via a high-temperature solution method by adjusting the molar ratios of reactants. They were structurally determined by single-crystal X-ray diffraction and their structures can be regarded as three dimensional (3D) framework stacking of ²_∞[Zn₂B₆O₁₆]¹⁰⁻ layers for Ba₃Zn(BO₃)(B₂O₅)F and ²_∞[Zn₂B₄O₈O_5/2O_1/3]^17/3− layers for Ba₄Zn₂(BO₃)₂(B₂O₅)F₂. To the best of our knowledge, the two title compounds are the first examples of two kinds of isolated B–O groups that coexist in one zincoborate halide. The structure comparisons were carried out among all the available anhydrous-zincoborates, and it is interesting to conclude that about 80% of zincoborates contain isolated B–O clusters and notably the molar ratio of cation/boron (A/B) affects the polymerization of isolated B–O configuration. What's more, the first-principles calculations, infrared spectra, and UV-vis-NIR diffuse reflectance spectra of title compounds have also been performed.