K2 Na3 [{B6 O10 (OH)}{B3 O4 (OH)3 }] ⋅ H2 O: A Layered Borate Built by Mixed Oxoboron Clusters with Nonlinear-Optical Property

NaRbB10O14(OH)4 and Na3CsB10O16(OH)2: Two Cases of Hydroxyborates with [B5Om(OH)n] Units and Deep Ultraviolet Cutoff Edges

Two deep ultraviolet (DUV) hydroxylated-alkali-metal borates, NaRbB10O14(OH)4 (I) and Na3CsB10O16(OH)2 (II), have been successfully synthesized by a high-temperature solution and solvothermal method. Both of them feature [B5Om(OH)n] units, which form chains for (I) and bilayers with nine-membered boron rings for (II). It is worth noting that both compounds exhibit very wide theoretical band gaps of 7.33 and 6.55 eV for (I) and (II), respectively, which denotes that they should have desirable DUV transmittance ability. Moreover, the title compounds have moderate birefringence owing to the π-conjugated [BO3], [BO2(OH)] groups, corresponding to 0.070 for (I) and 0.054 for (II) at 1064 nm. The structure characteristics and optical properties were also investigated and discussed. The results make it beneficial for exploring novel DUV hydroxylated borate optical crystals.

LiCs3AlB7O14: achieving enhanced optical anisotropy via [AlO4] tetrahedron introduction to rearrange the anionic framework

Borate has become a hot topic because of its rich structural chemistry and excellent properties for functional materials fields. The rearrangement of π-conjugated B-O units is key to enhancing the optical anisotropy, but it remains a challenge. Herein, by introducing [AlO₄] tetrahedra, a new congruent melting aluminoborate LiCs₃AlB₇O₁₄ with [B₇O₁₄] clusters was discovered. This work confirms that the introduction of [AlO₄] tetrahedra can lead to the rearrangement of anionic framework of the borate system and thereby enhance the birefringence of LiCs₃AlB₇O₁₄. The birefringence is about 4.1 times higher than that of its congener Li₄Cs₃B₇O₁₄ with the same [B₇O₁₄] clusters. Similarly, the effects of [AlO₄] tetrahedra on the rearrangement of the B-O anionic framework are also demonstrated in other known borates.

Rational Design of the First Ammonium Magnesium Borate with Deep-Ultraviolet Cutoff Edge and Moderate Birefringence and Further Investigation into the Nature of Ammonium in the Borate System

Through the rational design of the experimental method, the first combination of ammonium and magnesium in the borate system was successfully achieved. In this paper, a case of ammonium magnesium borate, (NH₄)₂{Mg(H₂O)₂[B₆O₇(OH)₆]₂}·2H₂O, was successfully synthesized by a mild hydrothermal method at a relatively low temperature. A brief review was performed to show the participation of NH₄⁺ in the recent development of optical materials. By discussing the optimum synthesis method of ammonium-containing borates and the main factors affecting the dimensionality of B-O anionic groups in their structures, the design strategy for synthesizing ammonium-containing borate and adjusting its structure has been put forward. Relevant experimental measurement results and the first-principles calculation results show that the title compound has a deep-UV cutoff edge (<200 nm) and moderate birefringence (Δn_cal. = 0.064 @546 nm), which indicates its potential application in the deep-UV region.

Finding a Deep-UV Borate BaZnB4 O8 with Edge-sharing [BO4 ] Tetrahedra and Strong Optical Anisotropy

The polarization modulation of deep-UV light is an important process that incorporates functionality to selectively respond to light-mater interaction. Typically, optical anisotropy is foremost to the use efficiency of deep-UV birefringent crystals. Herein, a new congruently melting polyborate with extremely large birefringence (Δn₍₀₀₁₎ =0.14@589.3 nm) and band gap (6.89 eV) is discovered as a high performance birefringent crystal, which breaks the current deadlock of deep-UV polyborates that usually show small birefringence. The rigid tetrahedra, including [ZnO₄ ] and edge-sharing [BO₄ ] tetrahedra, make all the planar [BO₃ ] triangles in the lattice adopt preferential arrangement and thereby lead to an extraordinary large birefringence that is larger than all the deep-UV borates with experimentally measured values. Structural analyses with the additional theoretical calculations were used to study the origin of strong optical anisotropy in BaZnB₄ O₈ .

CsB3O4(OH)2: a new deep-ultraviolet birefringent crystal with [B3O4(OH)2] anionic group

A new cesium hydroxyborate CsB₃O₄(OH)₂, was designed and synthesized by a hydrothermal method. Remarkably, CsB₃O₄(OH)₂ presents novel [B₃O₄(OH)₂]_∞ chains formed by [B₃O₄(OH)₂] fundamental building blocks (FBBs). The report of less common [B₃O₄(OH)₂] FBBs and [B₃O₄(OH)₂]_∞ chains in CsB₃O₄(OH)₂ enriches the structural diversity of hydroxyborates. In addition, CsB₃O₄(OH)₂ has a wide transparent window in the DUV spectral range and a large birefringence.

Two New Nonaborates with {B9} Cluster Open-Frameworks and Short Cutoff Edges

Two new nonaborates, Na₂Ba_0.5[B₉O₁₅]·H₂O (1) and Na₄Ca_1.5[B₉O₁₆(OH)₂] (2), have been solvothermally made with mixed alkali and alkaline-earth metal cationic templates. 1 and 2 are constructed by two different types of nonaborate clusters. In 1, the [B₉O₁₉]¹¹⁻ cluster is composed of three corner-sharing [B₃O₇]⁵⁻ clusters, of which two of them interconnect to the 1D B₃O₇-based chains and are further bridged to the 3D framework with 7 types of 10-MR channels by another [B₃O₇]⁵⁻ bridging cluster. The [B₉O₁₈(OH)₂]¹¹⁻ cluster in 2 is made of four BO₄-sharing [B₃O₈]⁷⁻ clusters. As a 4-connected node, the interconnections of [B₉O₁₈(OH)₂]¹¹⁻ construct the unpreceded 2D layer with large 14-MR windows, which are further joined by H-bonds to the 3D supramolecular framework. UV–Vis absorption spectra reveal that both 1 and 2 have short cutoff edges below 190 nm, exhibiting bandgaps of 6.31 and 6.39 eV, respectively, indicating their potential applications in deep UV (DUV) regions.

Rearrangement of [B2O5] Dimers within [B7O14] Clusters Enables Enhanced Optical Anisotropy in Li3Cs6Al2B14O28F

Borates with tunable structure and property currently provide a new rich source for solid-state chemistry and materials science. Realization of property improvement via simple structural regulation is a rising hot spot of borate-based research. Herein, a new aluminoborate fluoride, Li₃Cs₆Al₂B₁₄O₂₈F, with [B₇O₁₄] clusters was discovered, and it was found to melt congruently. The optimally aligned [B₂O₅] dimers within [B₇O₁₄] clusters make Li₃Cs₆Al₂B₁₄O₂₈F an enhanced birefringence, which is about 4.3× higher than its congener compound Li₄Cs₃B₇O₁₄ with same [B₇O₁₄] clusters. Structural analysis and additional theoretical calculations have revealed the origin of enhanced optical anisotropy.

Double-Modification Oriented Design of a Deep-UV Birefringent Crystal Functionalized by [B12 O16 F4 (OH)4 ] Clusters

Polarization modulation of deep-UV light is of significance to current technologies, and to this end, the birefringent crystal has emerged as an invaluable material as it allows for effective light modulation. Herein, a double-modification strategy driven by F and OH anions that makes double effects towards the critical property enhancement of deep-UV birefringent crystals is proposed. This leads to a new hydroxyborate (NH₄ )₄ [B₁₂ O₁₆ F₄ (OH)₄ ] with giant cluster as a deep-UV birefringent crystal with large birefringence (Δn_exp. =0.12@546.1 nm). This birefringence is a record among inorganic hydroxyborates with experimentally measured birefringence. Structural analysis shows that the near-plane arrangement of [B₁₂ O₁₆ F₄ (OH)₄ ] cluster is responsible for the large optical anisotropy. Theoretical calculations indicate that its π-conjugated [BO₃ ] and [BO₂ OH] units are the main source of this large optical anisotropy.

Syntheses, structures and optical properties of two B3O7 cluster-based borates

1 is a 2D fluctuant layered borate made from two different B3O7 clusters. 2 features a 3D open framework with large 17-MR channels filled with Li-BO(OH)2-Ca chains.