PbTeB4O9: a lead tellurium borate with unprecedented fundamental building block [B4O10] and large birefringence

Herein, the first lead tellurium borate, PbTeB4O9, with an unprecedented fundamental building block [B4O10] was successfully synthesized. The near-parallel alignment of [B4O10] groups and [TeO3] polyhedra resulted in a high birefringence (0.099@1064 nm). The structure-property relationship was discussed by using the first-principles calculations.

Three Polyborates with High-Symmetry [B12O24] Units Featuring Different Dimensions of Anion Groups

Three polyborates, namely, LiNa₁₁B₂₈O₄₈, Li_1.45Na_7.55B₂₁O₃₆, and Li₂Na₄Ca₇Sr₂B₁₃O₂₇F₉, were synthesized via the high-temperature solution method. All of them feature high-symmetry [B₁₂O₂₄] units, yet their anion groups exhibit distinct dimensions. LiNa₁₁B₂₈O₄₈ features a three-dimensional anionic structure of ³[B₂₈O₄₈]_∞ framework, which is composed of three units: [B₁₂O₂₄], [B₁₅O₃₀], and [BO₃]. Li_1.45Na_7.55B₂₁O₃₆ possesses a one-dimensional anionic structure of ¹[B₂₁O₃₆]_∞ chain consisting of [B₁₂O₂₄] and [B₉O₁₈] units. The anionic structure of Li₂Na₄Ca₇Sr₂B₁₃O₂₇F₉ is composed of two zero-dimensional isolated units, namely, [B₁₂O₂₄] and [BO₃]. The novel FBBs [B₁₅O₃₀] and [B₂₁O₃₉] are present in LiNa₁₁B₂₈O₄₈ and Li_1.45Na_7.55B₂₁O₃₆, respectively. The anionic groups in these compounds exhibit a high degree of polymerization, thereby augmenting the structural diversity of borates. And the crystal structure, synthesis, thermal stability, and optical properties were meticulously discussed to guide the synthesis and characterization of novel polyborates.

NaBa3[M2B7O16(OH)2]F2 (M = Ge, Si): Two Synthetic F Analogues of Garrelsite with [B7O16(OH)2]13- Polyanions and Deep-Ultraviolet Cutoff Edges

Two new borogermanate/borosilicate fluorides, namely, NaBa₃[M₂B₇O₁₆(OH)₂]F₂ (M = Ge, Si), have been successfully synthesized through a conventional mild hydrothermal method. They represent the first examples of mixed alkali and alkaline-earth borogermanate/borosilicate fluorides. NaBa₃[M₂B₇O₁₆(OH)₂]F₂ (M = Ge, Si) crystallize in the space group of C2/c, and their structures feature a unique 3D anionic framework composed of [B₇O₁₆(OH)₂]^13- polyanions corner-sharing with SiO₄ or GeO₄ tetrahedra, forming 1D 10-membered-ring tunnels along the b axis, which are filled by Na⁺, Ba²⁺, and F^- ions. UV-vis-near-IR absorption spectra identify the title compounds possessing short deep-ultraviolet absorption edges (below 200 nm), while their birefringences were calculated to be 0.021 and 0.016 at 1064 nm, respectively. Optical property, thermal stability, and theoretical calculations have also been conducted on NaBa₃[M₂B₇O₁₆(OH)₂]F₂ (M = Ge, Si).

MM'B3O4F3 (M = K; M' = Na, K, Cs): Alkali-Metal Fluorooxoborates with ∞1[B3O4F3] Chains and Deep-Ultraviolet Cutoff Edges

Three mixed-alkali-metal fluorooxoborates, KNaB₃O₄F₃ (I), K₂B₃O₄F₃ (II), and KCsB₃O₄F₃ (III), were acquired in a closed system. I-III are isomorphic and adopt orthorhombic structures [Pbcn (No. 60)] with wavy parallelly arranged pseudolayers composed of _∞¹[B₃O₄F₃] chains, which exhibit slight differences in the arrangement modes of the fundamental building blocks. First-principles calculations illustrate that they all have moderate birefringence and large band gaps on the order of 7.0 eV, suggesting deep-ultraviolet (DUV) cutoff edges. In order to investigate the main source of the optical properties, the electronic structure and anisotropy of the response electron distribution were analyzed. Experimental characterizations for I confirm the structure and DUV transparence ability.

A2B6O9F2 (A = NH4, K): new members of A2B6O9F2 family with deep-UV cutoff edges and moderate birefringence

Two new fluorooxoborates A2B6O9F2 (A = NH4, K) with different two-dimensional [B6O9F2]∞ layered structure constructed by the fundamental building block [B6O11F2] were obtained.