Borates: A Rich Source for Optical Materials

Abstract

The primary goal of this review is to present a clear chemical perspective of borates in order to stimulate and facilitate the discovery of new borate-based optical materials. These materials, which exhibit structures as varied as they are complex, are needed to meet the urgent technological milestones. In the current period of rapid sociotechnological breakthroughs, the need for the rational design and discovery of novel borates with superior performance is greater than ever before. Through the sustained efforts of chemists and material scientists, more than 3900 boron-containing compounds, including borate minerals and synthetic borates, have been documented in the scientific literature. This review provides a survey of all the reported anhydrous borates and an analysis of their complex structural chemistry. State-of-the-art progress related to technological advances in borate-based nonlinear optical, birefringent, and self-frequency-doubling materials is surveyed, with special emphasis on the relationships between structural architectures and optical properties. More importantly, this review serves both as a scientific introduction for graduates and post-doctoral researchers to the chemical richness of solid-state borates and as a comprehensive reference for researchers interested in borate-based optical materials.

Strong Lewis and Brønsted Acidic Sites in the Borosulfate Mg3[H2O→B(SO4)3]2

“…Their sulfate tetrahedra lead to rather weak coordination behaviour [3] and might even give rise to high Brønsted acidity, as tetra(hydrogensulfato)boric acid H[B(HSO 4 ) 4 ] is known to be a superacid [4] . Furthermore, boron incorporation enables an even larger structural variety due to the possible presence of planar BO 3 moieties next to the BO 4 tetrahedra [5] . Moreover, such triangular coordinated boron atoms can serve as Lewis acidic centre as in the strong Lewis acids BF 3 , BCl 3 , B(C 6 F 5 ) 3 , or B(OSO 2 CF 3 ) 3 , which are important catalysts for various organic reactions such as Friedel–Crafts acylation or olefin polymerisation [6, 7] …”

RbMT3(BO3)2O3 (M=Ba, Sr; T=Al, Ga): New Double‐Layered Oxyborates Constructed from [BO3] Triangles and [TO4] Tetrahedra

“…Structurally, the vacant 2p orbitals of B atom can construct sp, sp 2 , and sp 3 hybridized orbitals, which can further link with different nucleophiles to form the [BO 2 ] units, [BX 3 ] triangles, and [BX 4–x F x ] (X=O, OH, etc.) tetrahedra, respectively [1b] . These basic units can share corners or edges to construct anionic framework with various dimensions, like zero dimensional (0D) isolated clusters, 1D chains, 2D layers, and 3D frameworks [1b,4,5] .…”

“…tetrahedra, respectively [1b] . These basic units can share corners or edges to construct anionic framework with various dimensions, like zero dimensional (0D) isolated clusters, 1D chains, 2D layers, and 3D frameworks [1b,4,5] . Among them, layered borates with unique structures and properties have attracted much attention.…”

Starke Lewis‐ und Brønsted‐saure Zentren im Borosulfat Mg3[H2O→B(SO4)3]2

“…Ihre Sulfattetraeder führen zu einem eher schwachen Koordinationsverhalten [3] und könnten sogar zu einer hohen Brønsted‐Azidität führen, weil die Tetra(hydrogensulfato)borsäure H[B(HSO 4 ) 4 ] eine Supersäure ist [4] . Darüber hinaus ermöglicht der Einbau von Bor eine noch größere strukturelle Vielfalt durch die mögliche Realisierung planarer BO 3 ‐Einheiten neben den BO 4 ‐Tetraedern [5] . Außerdem können solche trigonal‐planar koordinierten Boratome als Lewis‐Säure‐Zentren dienen; so sind die starken Lewis‐Säuren BF 3 , BCl 3 , B(C 6 F 5 ) 3 oder B(OSO 2 CF 3 ) 3 wichtige Katalysatoren für verschiedene organische Reaktionen wie Friedel‐Crafts‐Acylierung oder Olefinpolymerisation [6, 7] …”