Ba3 (BO3 )(CO3 )F: The First Borate Carbonate Fluoride Synthesized by the High-Temperature Solution Method

Cd8(BO3)4SiO4: Metal Cation Inducing the Formation of Isolated [BO3] and [SiO4] Units in Borate Silicate

The first compound of cadmium-borate silicate Cd8(BO3)4SiO4, crystallizing in space group P42/n (no. 86), has been successfully synthesized by the conventional high-temperature solution method and melts congruently. The zero-dimensional anionic groups of Cd8(BO3)4SiO4 are isolated [BO3] triangles and isolated [SiO4] tetrahedra which are filled in the framework formed by [CdO6] polyhedra. It has a moderate birefringence (Δn = 0.053 at 546 nm), which is measured by experiment and evaluated by first-principles calculations; meanwhile, the source of birefringence is revealed through the response electronic distribution anisotropy method. The UV-vis-NIR diffuse reflectance spectrum indicates that Cd8(BO3)4SiO4 possesses a wide optical transparency range, with a UV cutoff edge at about 254 nm. This work enriches the structure chemistry of borate silicates, and we discussed the possible methods for the exploration and synthesis of novel optical crystals possessing zero-dimensional anionic groups in the borate silicate system.

Optically Anisotropic Mixed-Metal Fluoroiodate Ba2[GaF5(IO3F)] with a Wide Optical Transparent Window and a Moderate Birefringence

An optically anisotropic alkali-earth-metal gallium fluoroiodate, Ba2[GaF5(IO3F)] (1), was ingeniously obtained by integrating fluoride and fluoroiodate functional units under moderate hydrothermal conditions. It features a three-dimensional (3D) structure constructed by the highly polarizable fluoroiodate unit [IO3F] and the fluoride groups [GaOF5] and [BaO3Fx] (x = 6, 7). The compound is stable at temperatures up to 500 °C. With the synergistic interaction between [IO3F] and the fluoride groups, the mixed-metal fluoroiodate induces a short ultraviolet cutoff edge at about 230 nm, a medium measured birefringence of 0.068 @ 550 nm, and a wide optical transparent window (0.34-11.9 μm), indicating that 1 has potential applications as a birefringent material from near-UV to mid-infrared. Theoretical calculations prove that the optical characteristics of the compound are mainly attributed to [IO3F] and the fluoride functional groups. This work demonstrates that the presence of various specific functional groups in compounds will help to develop promising inorganic functional materials possessing good optical performance.

Na2SrB16O26: a new borate with independent interpenetrating B-O networks and deep-ultraviolet cutoff edge

A new borate, Na₂SrB₁₆O₂₆, was synthesized by the high-temperature solution method. It exhibits complicated interpenetrating 3D B-O frameworks composed of the functional building block (FBB) [B₈O₁₆]. The UV-vis-NIR diffuse reflectance spectroscopy shows that it has a deep-ultraviolet (DUV) cutoff edge (<200 nm). The relationship between the structures and optical properties was uncovered by theoretical calculations. By the first-principles calculation, the birefringence is estimated to be 0.07 at 1064 nm. The response electron distribution anisotropy (REDA) analysis indicates that the [BO₃] units contribute mainly to the generation of the moderate birefringence.

Ba2.5Pb1.5B12O22: structural transformation from a centrosymmetric to a noncentrosymmetric space group by introducing Pb into Ba2B6O11

A new congruent-melting lead barium borate, Ba_2.5Pb_1.5B₁₂O₂₂, was synthesized via a high-temperature solid-state reaction under atmospheric pressure. It crystallizes in the noncentrosymmetric space group Cmc2₁ with a unit cell of a = 19.051(8) Å, b = 10.726(3) Å, c = 8.612(3) Å, and Z = 4. It features a new functional building block (FBB), [B₁₂O₂₆]^16-, that is made up of five [B₃O₈]^7- and one [BO₃]^3- connected by sharing vertex O atoms. It is derived by introducing Pb into Ba₂B₆O₁₁, which leads to a structural transformation from a centrosymmetric to a noncentrosymmetric space group. Its second harmonic generation response (SHG) is approximately 0.9 times that of KDP at the fundamental wavelength of 1064 nm and is also phase-matchable. It has a wide transparent region with a UV cutoff edge of about 250 nm according to the reflectance spectra and high thermal stability, which illustrates that it is a potential candidate for ultraviolet nonlinear optical materials.

Na6 MQ4 (M=Zn, Cd; Q=S, Se): Promising New Ternary Infrared Nonlinear Optical Materials

Four sodium-based ternary IR nonlinear optical (NLO) materials, Na₆ MQ₄ (M=Zn, Cd; Q=S, Se), were prepared through a high-temperature flux method. The crystal structure of the compounds is built up of isolated [MQ₄ ] tetrahedra and a 3D framework formed by the NaQ_n (n=4, 5) units. The two selenides, Na₆ MSe₄ (M=Zn, Cd), as promising IR NLO materials, show moderate second-harmonic generation (SHG) responses (0.9 and 0.5×AgGaS₂ ) with good phase-matching behavior, as well as high laser damage thresholds (2 and 1.9×AgGaS₂ ). The two sulfides, Na₆ MS₄ (M=Zn, Cd), exhibit higher laser damage thresholds (13 and 4×AgGaS₂ ), but smaller SHG responses (0.3 and 0.2×AgGaS₂ ). Theoretical calculations and statistical analyses indicate that the SHG effect and band gap in the compounds originate mainly from the distorted NaQ₄ NLO-active units with a short Na-S bond length, which provides a new insight into the design of novel IR NLO materials.

Three mixed-alkaline-metal borates with {Li@B12Ox(OH)24−x} (x = 18, 22) clusters: from isolated oxoboron cluster to unusual layer

The isolated {Li@B12O18(OH)6} clusters are extended to the {Li@B12O22(OH)2} layer through condensation reactions for the first time.