An Antimony(III) Fluoride Oxalate with Large Birefringence

Birefringent materials play a key role in modulating the polarization of light and thus in optical communication as well as in laser techniques and science. Designing new, excellent birefringent materials remains a challenge. In this work, we designed and synthesized the first antimony(III) fluoride oxalate birefringent material, KSb₂C₂O₄F₅, by a combination of delocalized π-conjugated [C₂O₄]²⁻ groups, stereochemical active Sb³⁺ cations, and the most electronegative element, fluorine. The [C₂O₄]²⁻ groups are not in an optimal arrangement in the crystal structure of KSb₂C₂O₄F₅; nonetheless, KSb₂C₂O₄F₅ exhibits a large birefringence (Δn=0.170 at 546 nm) that is even better than that of the well-known commercial birefringent material α-BaB₂O₄, even though the latter features an optimal arrangement of π-conjugated [B₃O₆]³⁻ groups. Based on first-principles calculations, this prominent birefringence should be attributed to the alliance of planar π-conjugated [C₂O₄]²⁻ anions, highly distorted SbO₂F₂ and SbOF₃ polyhedra with a stereochemically active lone pair. The combination of lone-pair electrons and π-conjugated systems boosts the birefringence to a large extent and will help the development of high-performance birefringent materials.     

Hierarchical Modulation of Optical Anisotropy Driven by Metal Cation Polyhedra in Fluorooxoborates MIIB4O6F2 (MII=Be,Mg, Pb,Zn, Cd)

The enhancement mechanism of birefringence is very important to modulate optical anisotropy and materials design. Herein, the different cations extending from alkaline-earth to alkaline-earth, d¹⁰ electron configuration, and 6s² lone pair cations are highlighted to explore the influence on the birefringence. A flexible fluorooxoborate framework from AEB₄O₆F₂ (AE=Ca, Sr) is adopted for UV/deep-UV birefringent structures, namely, M^IIB₄O₆F₂ (M^II=Be, Mg, Pb, Zn, Cd). The maximal enhancement on birefringence can reach 46.6 % with the cation substitution from Ca, Sr to Be, Mg (route-I), Pb (route-II), and Zn, Cd (route-III). The influence of the cation size, the stereochemically active lone pair, and the binding capability of metal cation polyhedra is investigated for the hierarchical improvement on birefringence. Significantly, the BeB₄O₆F₂ structure features the shortest UV cutoff edge 146 nm among the available anhydrous beryllium borates with birefringence over 0.1 at 1064 nm, and the PbB₄O₆F₂ structure has the shortest UV cutoff edge 194 nm within the reported anhydrous lead borates that hold birefringence larger than 0.1 at 1064 nm. This work sheds light on how metal cation polyhedra modulate birefringence, which suggests a credible design strategy to obtain desirable birefringent structures by cation control.     

Lead-strontium borate halides with hilgardite-type structure and their SHG properties

Lead-containing members of the hilgardite family of borate halides, M₂B₅O₉X (M=Ca, Sr, Ba, Pb; X=Cl, Br) exhibit an abnormally large nonlinear optical response. In order to establish any underlying crystal-chemical rationale for this we have carried out detailed crystallographic characterisations of the representative members of this series, Sr₂B₅O₉Cl and Pb₂B₅O₉Cl, using powder neutron diffraction. Both adopt the orthorhombic hilgardite structure type, in space group Pnn2. The full solid solution range Pb_2−xSr_xB₅O₉Cl has also been prepared, and studied by X-ray Rietveld and second harmonic generation (SHG) measurements. The SHG response shows a linear decrease with increasing x, whereas the unit cell shows an increasing orthorhombic distortion. However, the crystallographic results suggest no significant or systematic changes in the nature of the borate sublattice between Sr₂B₅O₉Cl and Pb₂B₅O₉Cl. We conclude that the enhanced SHG response in Pb-containing hilgardites is due predominantly to the presence of the polarizable nature of Pb²⁺, in particular the presence of a stereochemically active lone pair.     

Lanthanide Inorganic Solids Based on Main Group Borates and Oxyanions of Lone Pair Cations

Lanthanide 硼酸盐包含柱子转变金属主要的组元素,包括的 Ga ( III ), Ge ( IV ), Sb (V)和 Te ( VI ),以及孤独的对阳离子的 oxyanions 的 lanthanide 盐,例如我(V), Se ( IV )和 Te ( IV ),被考察。柱子转变金属在 lanthanide 硼酸盐的主要的组元素仅仅采用八面或有四面的几何学。在 lanthanide galloborates 的结构,当两八面的 GeO ₆ 和有四面的 GeO ₄ 出现在 borogermanates 时,仅仅八面的高 ₆ 被发现。第五时期元素 Sb (V) 和 Te (VI ) 在 lanthanide 硼酸盐系统比较喜欢八面的协作几何学。介绍给孤独的对的 lanthanide oxyanions 的第二个组主要那么集中于 d ⁰ TM 单位,例如 WO ₄ 四面体, VO ₅ 平方金字塔或哞 ₆ 八面体,和象硫酸盐一样的僵硬的有四面的组 ₄, 硅石 SiO ₄ 或硒酸盐 SeO ₄ 单位。象 Pb (II ) 和 Cu (II ) 或 Mn (II ) 的磁性的离子一样的二价的阳离子也被包括。在这些系统的 lanthanide 离子的结构化学是富有的。从六～十的协作数字被发现,产出包括五角的 bipyramid 的大量协作几何学,方形的 antiprism, metabidiminished 二十面体, tricapped 三角的棱柱,盖住的三角形的小圆屋顶,等等。在行 polyhedra 之间的连接模式是其他的,从 3D 网络,到 2D 层, 1D 链, tetramer,更整齐,更暗淡并且最后单体。很多混合物显示 NCS 结构和强壮的 SHG 反应,和许多 lanthanide 混合物展出好光性质在可见并且红外区域。     

Thermal expansion and structural complexity of strontium borates

Thermal expansion of four strontium borates has been studied by high-temperature powder X-ray diffraction. Strong anisotropy of thermal expansion is observed for the structures of Sr₃B₂O₆ (0D) and SrB₂O₄ (1D) based on triangles BO₃ only: The high expansion occurs perpendicular to the BO₃ plane, i.e. along the direction of the less strong bonds in the crystal structure. The monoclinic Sr₂B₁₆O₂₆ (3D) borate expands dramatically due to shear deformations in monoclinic plane: Monoclinic β′ angle changes significantly because it is not fixed by symmetry. In contrast to these borates, SrB₄O₇ (3D) borate built up from tetrahedra only expands almost isotropically. Average value of volume expansion is 36 × 10^?6 K^?1 for studied Sr-borates. Tendency of slight decrease in the volume thermal expansion and sharp decrease in the melting points is observed with an increase in B₂O₃ content as a result of the degree of polymerization increase. As the B₂O₃ content grows in Sr-borates, the structural complexity increases in the SrO–B₂O₃ system due to more complex anionic structure. Inverse “melting temperature decrease—structural complexity increase” correlation is revealed.     

Lead Mixed Oxyhalides Satisfying All Fundamental Requirements for High-Performance Mid-Infrared Nonlinear Optical Materials

To design high-performance mid-infrared (mid-IR) nonlinear optical (NLO) materials, we have focused on the combination of a heavy metal lone pair cation, Pb²⁺ and mixed oxyhalides. A systematic investigation in PbO-PbCl₂-PbBr₂ system led us to discover the first examples of NLO lead mixed oxyhalides, namely, Pb₁₃O₆Cl₄Br₁₀, Pb₁₃O₆Cl₇Br₇, and Pb₁₃O₆Cl₉Br₅. All the reported materials have remarkably comprehensive properties including broad IR transparency (up to 14.0 μm), qualified second harmonic generation (SHG) responses (0.6–0.9×AgGaS₂), wide band gaps (3.05–3.21 eV), and ease of crystal growth. Interestingly, a centimeter-sized single crystal (2.9×1.3×0.5 cm³) of Pb₁₃O₆Cl₉Br₅ revealing a wide transparent range (0.384–14.0 μm) and high laser damage threshold (LDT) (14.6×AgGaS₂) has been successfully grown in an open system. The study suggests that all the reported mixed oxyhalides are outstanding candidates for mid-IR NLO materials.     

Cooperation of Three Chromophores Generates the Water‐Resistant Nitrate Nonlinear Optical Material Bi3TeO6OH(NO3)2

Nitrates have long been ignored for practical uses as nonlinear optical (NLO) materials because they are usually very easy to dissolve in water; despite this, the π‐conjugated [NO₃]⁻ is among the most desirable NLO‐active structural units. The cooperation of three structural chromophores, namely, Bi₃O₆OH short chains with 6s² lone pair electrons, distorted TeO₆ octahedra with d¹⁰ electrons, and π‐conjugated [NO₃]⁻ triangles, generates a new nitrate NLO material, Bi₃TeO₆OH(NO₃)₂, which exhibits an enhanced phase‐matchable NLO response of three times that of KH₂PO₄ (3×KH₂PO₄), exceeding those of most nitrate NLO materials. Remarkably, the new material did not show obvious weight loss and degeneration of NLO response after being dipped in de‐ionized water for 24 h, indicating that it is highly resistant to water. Theoretical calculations reveal that foreign water molecules cannot stably stay in the crystal lattice of Bi₃TeO₆OH(NO₃)₂. These findings highlight the introduction of diverse chromophores into the nitrate systems as an effective approach for developing practical nitrate NLO materials that are of high water‐resistance and good optical performance.     

SrB5O7F3 Functionalized with [B5O9F3]6− Chromophores: Accelerating the Rational Design of Deep‐Ultraviolet Nonlinear Optical Materials

Fluorooxoborates, benefiting from the large optical band gap, high anisotropy, and ever‐greater possibility to form non‐centrosymmetric structures activated by the large polarization of [BO_xF_4?x]^(x+1)? building blocks, have been considered as the new fertile fields for searching the ultraviolet (UV) and deep‐UV nonlinear optical (NLO) materials. Herein, we report the first asymmetric alkaline‐earth metal fluorooxoborate SrB₅O₇F₃, which is rationally designed by taking the classic Sr₂Be₂B₂O₇ (SBBO) as a maternal structure. Its [B₅O₉F₃]^6? fundamental building block with near‐planar configuration composed by two edge‐sharing [B₃O₆F₂]^5? rings in SrB₅O₇F₃ has not been reported in any other borates. Solid state ¹⁹F and ¹¹B magic‐angle spinning NMR spectroscopy verifies the presence of covalent B?F bonds in SrB₅O₇F₃. Property characterizations reveal that SrB₅O₇F₃ possesses the optical properties required for deep‐UV NLO applications, which make SrB₅O₇F₃ a promising crystal that could produce deep‐UV coherent light by the direct SHG process.     

Sb6O7(SO4)2: A Promising Ultraviolet Nonlinear Optical Material with an Enhanced Second-Harmonic-Generation Response Activated by SbIII Lone-Pair Stereoactivity

The stereochemical activity of lone pairs (SCALP) in a cation favors the formation of acentric materials and can enhance the second-harmonic-generation (SHG) response and/or the birefringence. By introducing functional Sb^III into sulfates, an anhydrous sulfate of Sb₆O₇(SO₄)₂ ( 1 ) is explored. Sb³⁺ cations are in seesaw configurations and in-phase aligned in a 3D asymmetric dense structure. Compound 1 exhibits an enhanced phase-matching SHG response, a moderate birefringence, a wide transparency window, and considerable environmental stabilities, which result in it being a promising UV nonlinear optical (NLO) material. Theoretical studies reveal that the stereoactive lone pairs on Sb³⁺ cations make the predominant contribution to the SHG effect. This work will attract more interest from scientists for research into SCALP-cation-based NLO materials.     

Structure Cristalline de Na3H(C2O4)2SbOF, 2 H2O. Existence de la Bipyramide à Base Pentagonale SbO5FE

Crystal Structure of Na₃H(C₂O₄)₂SbOF, 2 H₂O. On the Existence of the Pentagonal Bipyramid SbO₅FE The crystal structure of Na₃H(C₂O₄)₂SbOF, 2H₂O shows SbOF(C₂O₄)₂^4? anions where oxalat units are bidendate chelates on the antimony (III). Antimony coordination is seven; five oxygen atoms are situated on the plane of the pentagonal bipyramid, distorded by the electronic lone pair of Sb^III, situated in an axial position; the fluorine atom of the oxofluoride occupies the other axial position. The existence of an oxonium ion is discussed.     

New oxyfluorotellurates(IV): MTeO3F (M = FeIII,GaIII and CrIII)

The crystal structures of the new isomorphous compounds iron(III) oxyfluorotellurate(IV), FeTeO₃F, gallium(III) oxyfluorotellurate(IV), GaTeO₃F, and chromium(III) oxyfluorotellurate(IV), CrTeO₃F, consist of zigzag chains of MO₄F₂ distorted octahedra alternately sharing O–O and F–F edges and connected via TeO₃ trigonal pyramids. A full O/F anionic ordering is observed and the electronic lone pair of the Te^IV cation is stereochemically active.     

Lead Mixed Oxyhalides Satisfying All Fundamental Requirements for High‐Performance Mid‐Infrared Nonlinear Optical Materials

To design high‐performance mid‐infrared (mid‐IR) nonlinear optical (NLO) materials, we have focused on the combination of a heavy metal lone pair cation, Pb²⁺ and mixed oxyhalides. A systematic investigation in PbO‐PbCl₂‐PbBr₂ system led us to discover the first examples of NLO lead mixed oxyhalides, namely, Pb₁₃O₆Cl₄Br₁₀, Pb₁₃O₆Cl₇Br₇, and Pb₁₃O₆Cl₉Br₅. All the reported materials have remarkably comprehensive properties including broad IR transparency (up to 14.0 μm), qualified second harmonic generation (SHG) responses (0.6–0.9×AgGaS₂), wide band gaps (3.05–3.21 eV), and ease of crystal growth. Interestingly, a centimeter‐sized single crystal (2.9×1.3×0.5 cm³) of Pb₁₃O₆Cl₉Br₅ revealing a wide transparent range (0.384–14.0 μm) and high laser damage threshold (LDT) (14.6×AgGaS₂) has been successfully grown in an open system. The study suggests that all the reported mixed oxyhalides are outstanding candidates for mid‐IR NLO materials.     

Lower main-group element complexes with a soft scorpionate ligand: the structural influence of stereochemically active lone pairs

The syntheses and structures of complexes of the fifth period elements indium and antimony, and the sixth period element bismuth with the soft scorpionate ligand, hydrotris(methimazolyl)borate (Tm(Me)) are reported. A considerable variety of structural motifs were obtained by reaction of the main-group element halide and NaTm(Me). The indium(III) complexes took the form [In(kappa(3)-Tm(Me))(2)](+). This motif could not, however, be isolated for antimony(III), the dominant product being [Sb(kappa(3)-Tm(Me))(kappa(1)-Tm(Me))X] (X = Br, I). An iodo-bridged species [Sb(kappa(3)-Tm(Me))I(mu(2)-I)](2), analogous to a previously reported bismuth complex, was also isolated. Reaction of antimony(III) acetate with NaTm(Me) results in a remarkable species in which three different ligand binding modes are observed. In each antimony complex the influence of the nonbonded electron pair is observed in the structure. Bismuth halides form complexes analogous to those of antimony, with directional lone pairs, but in addition, reaction of Bi(NO(3))(3) with NaTm(Me) results in a complex with a regular S(6) coordination sphere and a nonstereochemically active lone pair. Comparisons are drawn with known Tm(Me) complexes of As, Sn, and Bi in which the stereochemical influence of the lone pairs is negligible and with Tm(Me) complexes of Te and Bi in which the lone pairs are stereochemically active. This study highlights the ability of Tm(Me) to coordinate in a variety of modes as dictated by the metal centre with no adverse effects on the stability of the complexes formed.     

Deep‐Ultraviolet Nonlinear Optics in a Borate Framework with 21‐Ring Channels

A new borate LiBa₃(OH)[B₉O₁₆][B(OH)₄], which combines the uniform porosity of open‐frameworks with the extraordinary NLO properties of borates, has been obtained under hydrothermal conditions by using mixed lithium and barium ions as templates. The framework displays an acs‐type net with large 21‐ring channels. The second harmonic generation (SHG) measurement shows that it is a type I phase‐matchable material with a strong SHG signal intensity about 3.1 times that of KDP (KH₂PO₄). UV/Vis–NIR diffuse reflectance analysis indicates that the compound has a wide transparency range with the short‐wavelength absorption edge below 200 nm. These characteristics reveal that the compound is a promising deep‐UV nonlinear optical material.     

K2Sb(P2O7)F: Cairo Pentagonal Layer with Bifunctional Genes Reveal Optical Performance

Discovering new functional genes, designing perfect crystal structures, and developing high-performance materials are the goals being pursued by scientists. Herein, the first antimony pyrophosphate, K₂Sb(P₂O₇)F, possessing an optimal layered structure, is reported, where the perfect structural arrangement induces excellent optical properties. K₂Sb(P₂O₇)F not only displays a sharply enhanced birefringence (0.157@546 nm) compared to the existing phosphate optical materials, but also exhibits a strong second-harmonic generation response (4.0×KDP). Remarkably, a new bifunctional gene, the square-pyramidal SbO₄F group, was discovered, and a unique two-dimensional arrangement of Cairo pentagonal tiling units was observed in inorganic compounds for the first time.     

High‐Pressure Synthesis of Cd(NH3)2[B3O5(NH3)]2: Pioneering the Way to the Substance Class of Ammine Borates

To date, the access to the substance class of borates containing nitrogen, for example, nitridoborates, oxonitridoborates, or amine borates, was an extreme effort owing to the difficult starting materials and reaction conditions. Although a number of compounds containing boron and nitrogen are known, no adduct of ammonia to an inorganic borate has been observed so far. A new synthetic approach starting from the simple educts CdO, B₂O₃, and aqueous ammonia under conditions of 4.7 GPa and 800 °C led to the synthesis of Cd(NH₃)₂[B₃O₅(NH₃)]₂ as the first ammine borate. We thoroughly characterized this compound on the basis of low‐temperature single‐crystal and powder X‐ray diffraction data, IR and Raman spectroscopy, and by quantum theoretical calculations. This contribution shows that the adduct of NH₃ to the BO₃ group of a complex B–O network can be stabilized, opening up a fundamentally new synthetic route to nitrogen‐containing borates.     

[Sb(12-Krone-4)2(CH3CN)][SbCl6]3 und [Bi(12-Krone-4)2(CH3CN)][SbCl6]3, die ersten Trikationen von Antimon(III) und Bismut(III)

[Sb(12-Crown-4)₂(CH₃CN)][SbCl₆]₃ and [Bi(12-Crown-4)₂(CH₃CN)][SbCl₆]₃, first Trications of Antimony(III) and Bismuth(III) The crown ether complexes [M(12-crown-4)₂(CH₃CN)][SbCl₆]₃ with M = Sb and Bi are formed by the reaction of antimony trichloride and bismuth trichloride, respectively, with antimony pentachloride in acetonitrile solution in the presence of 12-crown-4. They form colourless, moisture sensitive crystals, which were characterized by X-ray structure determinations and by IR spectroscopy. The complex with M = Sb was also characterized by ¹²¹Sb Mössbauer spectroscopy. Both complexes crystallize isotypically in the orthorhombic space group Pbcn with four formula units per unit cell. M = Sb: 3 483 observed unique reflections, R = 0.038. M = Bi: 2 958 observed unique reflections, R = 0.036. The compounds consist of SbCl₆^? ions and trications [M(12-crown-4)₂(CH₃CN)]³⁺, in which the M³⁺ ions are ninefold coordinated by the eight oxygen atoms of the crown ether molecules and by the nitrogen atom of the acetonitrile molecule. The lone pair of the M³⁺ ions has no steric effect.     

Synthese,Kristallstruktur und 121Sb-Mößbauer-Spektrum von [SbCl2(18-Krone-6)]+SbCl6−

Synthesis, Crystal Structure, and ¹²Sb-Mössbauer Spectrum of [SbCl₂(18-Crown-6)]⁺SbCl₆^? The title compound, which has been prepared by the reaction of antimony trichloride and antimony pentachloride in the presence of 18-crown-6 in acetonitrile solution, is characterized by its ¹²¹Sb-Mössbauer spectrum and by an X-ray structure determination. Space group P2₁, Z = 2, 2439 observed unique reflections, R = 0.045, wR = 0.043. Lattice dimensions at ?80°C: a = 780.6(7), b = 1297.5(9), c = 1 278.5(10) pm, β = 100.56(7)°. The structure of [SbCl₂(18-crown-6)]⁺SbCl₆^? contains cations in which the antimony atom in the first coordination sphere is surrounded in a ?-trigonal-bipyramidal fashion by two oxygen atoms of the crown ether in axial position as well as in the equatorial position by the two chlorine atoms and the lone electron pair.     

Two‐Orbital Three‐Electron Stabilizing Interaction for Direct Co2+?As3+ Bonds involving Square‐Planar CoO4 in BaCoAs2O5

The quest for new oxides with cations containing active lone‐pair electrons (E) covers a broad field of targeted specificities owing to asymmetric electronic distribution and their particular band structure. Herein, we show that the novel compound BaCoAs₂O₅, with lone‐pair As³⁺ ions, is built from rare square‐planar Co²⁺O₄ involved in direct bonding between As³⁺E and Co²⁺ d_z2 orbitals (Co As=2.51 Å). By means of DFT and Hückel calculations, we show that this σ‐type overlapping is stabilized by a two‐orbital three‐electron interaction allowed by the high‐spin character of the Co²⁺ ions. The negligible experimental spin‐orbit coupling is expected from the resulting molecular orbital scheme in O₃AsE–CoO₄ clusters.     

Two‐Orbital Three‐Electron Stabilizing Interaction for Direct Co2+As3+ Bonds involving Square‐Planar CoO4 in BaCoAs2O5

The quest for new oxides with cations containing active lone‐pair electrons (E) covers a broad field of targeted specificities owing to asymmetric electronic distribution and their particular band structure. Herein, we show that the novel compound BaCoAs₂O₅, with lone‐pair As³⁺ ions, is built from rare square‐planar Co²⁺O₄ involved in direct bonding between As³⁺E and Co²⁺ d_z2 orbitals (Co? As=2.51 Å). By means of DFT and Hückel calculations, we show that this σ‐type overlapping is stabilized by a two‐orbital three‐electron interaction allowed by the high‐spin character of the Co²⁺ ions. The negligible experimental spin‐orbit coupling is expected from the resulting molecular orbital scheme in O₃AsE–CoO₄ clusters.