Pb2GaF2(SeO3)2Cl: Band Engineering Strategy by Aliovalent Substitution for Enlarging Bandgap while Keeping Strong Second Harmonic Generation Response

Giant Second-Harmonic Generation Response and Large Band Gap in the Partially Fluorinated Mid-Infrared Oxide RbTeMo2O8F

Strong second-harmonic generation (SHG) and a wide band gap are two crucial but often conflicting parameters that must be optimized for practical nonlinear optical (NLO) materials. We report herein the first d⁰-transition-metal (TM) tellurite with half of the d⁰-TM-octahedra partially fluorinated, namely, quinary RbTeMo₂O₈F, which exhibits giant SHG responses (27 times that of KH₂PO₄ (KDP) and 2.2 times that of KTiOPO₄ (KTP) with 1064 and 2100 nm laser radiation, respectively), the largest SHG values among all reported metal tellurites. RbTeMo₂O₈F also possesses a large band gap (3.63 eV), a wide optical transparency window (0.34-5.40 μm), and a significant birefringence (Δn = 0.263 at 546 nm). Theoretical calculations and crystal structure analysis demonstrate that the outstanding SHG responses can be definitively attributed to the uniform alignment of the polarized [MoO₅F]/[MoO₆] octahedra and the seesaw-like [TeO₄], and the consequent favorable summative polarization of the three distinct SHG-active polyhedra, both induced by partial fluorine substitution on the [MoO₆] octahedra.

NaGaI3O9F: a new alkali metal gallium iodate combined with IO3- and IO3F2- units

Birefringent crystals are very important optical materials, which are widely used in the fields of optics and communication. In this work, we reported a new iodate, NaGaI₃O₉F, synthesized by mild hydrothermal method. NaGaI₃O₉F crystallized in the monoclinic space group P2₁/c (No. 14) and it featured a novel _∞[Ga₂(IO₃F)₂(IO₃)₄]^2- layer stacked with Na⁺ cations located in the void maintaining charge balance. Notably, IO₃^- and IO₃F^2- anionic units appeared in the same time in the A-Ga-I-O/F (A = alkali metal) system. According to the experimental characterization and theoretical calculations, NaGaI₃O₉F showed a wide bandgap (4.27 eV) and large birefringence (Δn_exp∼ 0.203, Δn_cal = 0.197 at 1064 nm), indicating its potential use as a birefringent material.

A Congruent-Melting Mid-Infrared Nonlinear Optical Vanadate Exhibiting Strong Second-Harmonic Generation

Study of mid-infrared (mid-IR) nonlinear optical (NLO) materials is hindered by the competing requirements of optimized second-harmonic generation (SHG) coefficient d_ij and laser-induced damage threshold (LIDT) as well as the harsh synthetic conditions. Herein, we report facile hydrothermal synthesis of a polar NLO vanadate Cs₄ V₈ O₂₂ (CVO) featuring a quasi-rigid honeycomb-layered structure with [VO₄ ] and [VO₅ ] polyhedra aligned parallel. CVO possesses a wide IR-transparent window, high LIDT, and congruent-melting behavior. It has very strong phase-matchable SHG intensities in metal vanadate family (12.0 × KDP @ 1064 nm and 2.2 × AGS @ 2100 nm). First-principles calculations suggest that the exceptional SHG responses of CVO largely originate from virtual electronic transitions within [V₄ O₁₁ ]_∞ layer; the excellent optical transmittance of CVO arises from the special characteristics of vibrational phonons resulting from the layered structure.

From thiophosphate to chalcohalide: mixed-anion AgSxCly ligands concurrently enhancing nonlinear optical effects and laser-damage threshold

In this study, we propose a new design strategy that introduces unique mixed-anion AgS_xCl_y ligands into thiophosphate to afford a successful synthesis of a promising Ag₅PS₄Cl₂ IR NLO chalcohalide. Compared with chlorine-free Ag₃PS₄, Ag₅PS₄Cl₂ undergoes overall performance enhancement and achieves a good balance between large NLO effect (2.0 × Ag₃PS₄) and high laser damage threshold (3.8 × Ag₃PS₄). Theoretical analysis further indicates that AgS_xCl_y groups are the new superior NLO-active units since they can maintain the wide bandgap while concurrently making a great contribution to the origin of NLO effects. Therefore, the incorporation of AgS_xCl_y groups into the crystal structure can be expected to be one feasible way to design new IR NLO candidates with excellent performance.

[GaF(H2O)][IO3F]: a promising NLO material obtained by anisotropic polycation substitution

A novel salt-inclusion fluoroiodate [GaF(H2O)][IO3F] derived from CsIO2F2 was ingeniously obtained through anisotropic polycation substitution. Because the catenulate [GaF(H2O)]2+ framework serves as a template for the favorable assembly of the polar [IO3F]2- groups and contributes to the nonlinear coefficient, [GaF(H2O)][IO3F] exhibits a greatly improved second-harmonic generation (SHG) effect of 10 times that of KH2PO4 (KDP) and a considerable band gap of 4.34 eV compared to the parent compound CsIO2F2 (3 × KDP, 4.5 eV). Particularly, to the best of our knowledge, [GaF(H2O)][IO3F] has the largest laser-induced damage threshold (LDT) of 140 × AgGgS2 of the reported iodates. All these results signify that [GaF(H2O)][IO3F] is a promising nonlinear optical (NLO) crystal. This work also proposes that anisotropic polycation substitution is an effective approach to optimize the SHG effect and develop excellent NLO materials.

AgBi(SO4)(IO3)2: aliovalent substitution induces structure dimensional upgrade and second harmonic generation enhancement

A new 3D noncentrosymmetric mixed-metal sulfate iodate, AgBi(SO₄)(IO₃)₂, has been designed based on a 2D iodate of AgBi(IO₃)₄via the aliovalent substitution of [IO₃]^- groups by [SO₄]^2- groups. Enhancement of the second harmonic generation response (3.0 × KDP to 3.9 × KDP) has been achieved while retaining a favorable NLO framework. This is a novel strategy to upgrade structural dimensions.

Unexpected aliovalent cation substitution between two NLO materials LiBa3Bi6(SeO3)7F11 and Ba3Bi6.5(SeO3)7F10.5O0.5

One new combination, alkali-metal and alkaline earth-metal selenite fluoride, LiBa₃Bi₆(SeO₃)₇F₁₁ (LBBSF) and its analogue Ba₃Bi_6.5(SeO₃)₇F_10.5O_0.5 (BBSF) were reported here for the first time. Unusual aliovalent cation substitution between them affected the layer thickness and made the bond strains of [SeO₃] enhanced, thereby inducing greater distortions and affecting the SHG efficiencies. This work may provide thoughts for exploring new NLO materials.

Hydrogen-Bond-Assisted Alignment of [MCu(SeO3)4Cl(H2O)]4- (M = Fe, Ga) Anionic Layers to Form Two Polar Oxychlorides: Pb2MCu(SeO3)4Cl(H2O)

Two novel selenite oxychlorides Pb₂MCu(SeO₃)₄Cl(H₂O) (M = Fe, Ga) were hydrothermally synthesized and structurally characterized. They are isostructural and crystallize in the two-dimensional [MCu(SeO₃)₄Cl(H₂O)]^4- anionic layer structure mediated with hydrogen bonds and aligned between neighboring layers which assist in building the three-dimensional framework with a polar space group. Optical properties measurements revealed that the optical band gaps are 2.61 and 3.22 eV for Pb₂FeCu(SeO₃)₄Cl(H₂O) (1) and Pb₂GaCu(SeO₃)₄Cl(H₂O) (2) and the SHG responses are about 0.12 and 0.18 times that of KDP, respectively. Furthermore, 1 exhibits an interesting metamagnetic phenomenon under varied applied fields from around 1 to 4 T at 2 K, and 2 behaves with potential ferromagnetic ordering at low temperature.

In situ hydrothermal synthesis of polar second-order nonlinear optical selenate Na5(SeO4)(HSeO4)3(H2O)2

An alkali–metal selenate nonlinear optical (NLO) crystal, Na₅(SeO₄)(HSeO₄)₃(H₂O)₂, which possesses good second-order nonlinear optical properties, has been obtained by mild in situ hydrothermal synthesis.

Y2(Te4O10)(SO4): a new sulfate tellurite with a unique Te4O10 polyanion and large birefringence

Y₂(Te₄O₁₀)(SO₄), featuring a unique (Te₄O₁₀)⁴⁻ polyanion, exhibits a large birefringence (0.124@1064), wide energy band gap (4.1 eV) and high thermal stability (>700 °C), which make it a potential birefringent material.

First chiral fluorinated lead vanadate selenite Pb2(V2O4F)(VO2)(SeO3)3 with five asymmetric motifs and large optical properties

The first fluorinated lead vanadate selenite Pb2(V2O4F)(VO2)(SeO3)3 (PVOFS) was successfully synthesized via a mild hydrothermal method. This compound crystallizes in the chiral space group P212121 of the orthorhombic system and it is the first noncentrosymmetric structure in the PbII-VV-SeIV-O-F system. PVOFS is composed of five kinds of second-order Jahn-Teller susceptible asymmetric motifs, including three distinct types of vanadium-centered polyhedral units ([VO5F], [VO6] and [VO5]), [SeO3] pyramids and Pb2+ cations. It features a unique three-dimensional open framework structure displaying three types of tunnels (10-, 8- and 7-membered rings), which enriches the structural diversity for fluorinated vanadate selenite systems. Optical property studies revealed that PVOFS shows a second-harmonic generation response of 0.3 times that of the commercial KH2PO4 with phase matching behavior, a wide transparent region covering IR windows, an optical band gap of 2.35 eV, a high laser damage threshold of 61 times that of AgGaS2, and a large birefringence of 0.105 at 1064 nm. Theoretical calculations have been performed to clarify the correlation between the molecular structure and the optical properties of PVOFS.

Selenite bromide nonlinear optical materials Pb2GaF2(SeO3)2Br and Pb2NbO2(SeO3)2Br: synthesis and characterization

Two new isomorphic selenite bromides, namely Pb2GaF2(SeO3)2Br (1) and Pb2NbO2(SeO3)2Br (2), were synthesized by mild hydrothermal reactions. These two compounds crystallize in the noncentrosymmertric space group P21 and feature 3D structures consisting of 1D (Pb2Br)3+ cationic chains and 2D [Ga2F4(SeO3)4]6-/[Nb2O4(SeO3)4]6- anonic chains. As measured, 1 and 2 are phase-matchable and exhibit excellent second harmonic generation (SHG) responses of 4.5 and 1.4 times that of KDP, respectively. Moreover, these two compounds possess wide bandgaps (>3.17 eV) and high thermal stabilities (>425 °C), indicating their suitable performances as potential nonlinear optical materials. First-principle density functional theory (DFT) calculations were also performed to explicate the structure-property relationship.

A6Sb4F12(SO4)3 (A = Rb, Cs): Two Novel Antimony Fluoride Sulfates with Unique Crown-like Clusters

Two new antimony fluoride sulfates named A₆Sb₄F₁₂(SO₄)₃ (A = Rb, Cs) with unique crown-like clusters have been successfully synthesized by introducing Sb³⁺ with a stereochemically active lone pair in the sulfate system through a facile hydrothermal method. The structure regulation induced by the cation sizes results in the symmetry difference in these two title compounds, i.e., Rb₆Sb₄F₁₂(SO₄)₃ crystallizing in the polar noncentrosymmetric (NCS) space group of P3 and Cs₆Sb₄F₁₂(SO₄)₃ in the centrosymmetric (CS) space group of P1̅. Detailed characterizations, including XRD, thermal behaviors, optical properties, and the theoretical calculations, for these two compounds have been performed. The discovery of the unique crown-like clusters observed in A₆Sb₄F₁₂(SO₄)₃ (A = Rb, Cs) enriches the diversity of structures for antimony sulfates systems. Simultaneously, a summary and comparison for all reported antimony halide sulfates has been made to illustrate the synergistic effect of the stoichiometric ratio and cation sizes on the macroscopic centricity and the framework structure, which will guide the systematical discovery of antimony(III)-based functional materials in future.

AxCe9(IO3)36 (A = K, La): the effects of a change in the intermediate valence on the second-harmonic generation response

Two new isostructural non-centrosymmetric cerium iodates K_xCe₉(IO₃)₃₆ (x≈ 3) and La_xCe₉(IO₃)₃₆ (x≈ 0.3) were synthesized via a hydrothermal method and systematically characterized. They are intermediate valence compounds with the same band gap, showing similar microscopic net dipole moments per unit volume, but different macroscopic second-harmonic generation (SHG) responses under 1064 nm laser irradiation. This research gives a new view for understanding the effects of electronic structure on the SHG response.

Gd(NO3)(Se2O5)·3H2O: a nitrate-selenite nonlinear optical material with a short ultraviolet cutoff edge

The first example of a rare-earth metal nitrate-selenite nonlinear optical (NLO) crystal, Gd(NO₃)(Se₂O₅)·3H₂O (1), was synthesized by hydrothermal reaction. This compound crystallizes in the noncentrosymmetric space group P2₁2₁2₁, and its structure features two-dimensional (2D) [Gd(NO₃)(Se₂O₅)]_∞ layers, extending to a pseudo-3D framework linked by hydrogen bonds. 1 exhibits a phase-matchable SHG efficiency about 0.2 times that of KH₂PO₄ (KDP) and a large laser damage threshold of 236.26 MW cm^-2. The UV-Vis-NIR diffuse reflectance spectroscopy study shows that the UV cutoff edge of 1 is 224 nm, which is the shortest value observed among selenite-based NLO materials. The birefringence of 1 is 0.109@1064 nm based on density functional theory calculations. These optical properties make 1 a potential UV NLO material. Theoretical studies using density functional theory have been implemented to further understand the relationship between its optical properties and band structures.

A Series of Chalcogenide Borates RE6Ta2MgQB8O26 (RE = Sm, Eu, Gd; Q = S, Se) Featuring a B4O10 Cluster

New compounds with multiple anions are receiving increasing interest in view of their diverse structures and physical properties. Here we report four isostructural hexanary RE₆Ta₂MgQB₈O₂₆ (RE = Sm, Eu, Gd; Q = S, Se), belonging to the rare chalcogenide borates. Their structures feature an unprecedented [B₄O₁₀]^8- unit comprised of one BO₄ and three BO₃ units. Their 3D structures are constructed by the connection between QRE₆ octahedra and the _∞{[Mg(TaB₄O₁₃)₂]^16-} polyanionic layer. Density functional theory calculations on the electronic structure and a birefringence of 4 are also performed.

First-Principles Design and Simulations Promote the Development of Nonlinear Optical Crystals

A hot topic in materials science is to search for nonlinear optical (NLO) crystals, which are indispensable in current laser technology, future optical information, and precision measurements. In the period of the 1980s and 1990s, the anionic group theory proposed by Prof. Chuangtian Chen has greatly promoted the inventions of BaB₂O₄ (BBO), LiB₃O₅ (LBO), and KBe₂BO₃F₂ (KBBF) which are widely applied in the ultraviolet (UV) spectral region today. From the beginning of this century, the rapid development of laser science and technology urgently demands new NLO crystals for wider application ranges. However, commercial NLO crystals in deep-UV and mid-infrared (mid-IR) regions are scarce. The challenge arises from the stringent criteria at various wavelengths and inefficient exploration strategy. As such, more comprehensive and quantitative theoretical guidance is necessary to improve and supplement the NLO structure-property understandings. Benefiting from high-performance computing resources, first-principles design and simulations came into being, which is more applicable to the understanding of mid-IR NLO mechanism and suitable for the efficient design of new NLO structures for current needs. In the past decade, a complete set of computational research programs based on first-principles simulations have been developed, which have promoted the development of NLO crystals in the deep-UV and mid-IR regions, and guided the subsequent and further experimental explorations. Based on our developed first-principles materials design system, the discoveries of NLO materials have ranged from basic theoretical design to rapid-prototyping and final experimental synthesis. In this Account, we will concisely summarize our ab initio guided and forward-looking studies on NLO crystals, which are our original contributions to this field and can be consulted by other material fields. First, we will review the development of NLO crystals and the important features of NLO materials. Second, we will summarize the important role of computer-aided design in advancing the NLO material field and our developed NLO material design system based on the first-principles simulations. Third, we will introduce the first-principles design for new deep-UV NLO crystals using two novel design proposals, i.e., interlayer cationic replacement and intralayer anionic substitution. Meanwhile, we will illustrate the hierarchical molecular engineering optimizations for mid-IR NLO crystals by illustrating an extended mid-IR NLO family pedigree, from which many promising mid-IR NLO systems were predicted theoretically and confirmed experimentally. Finally, we will give an outlook to explore new functional NLO crystals guided by our first-principles design and simulations. We believe that the computer-assisted exploration for new functional NLO materials is useful for understanding structure-property relationships and can provide researchers with a new approach to cost-effective and data-driven materials design.

Two-stage evolution from phosphate to sulfate of new KTP-type family members as UV nonlinear optical materials through chemical cosubstitution-oriented design

KTiOPO4 (KTP) is a classic commercial nonlinear optical (NLO) crystal, but its narrow bandgap (3.52 eV) prevents its practical application in the ultraviolet (UV) region. Many trials to widen the narrow bandgap of KTP have failed in the past few decades. A chemical cosubstitution strategy was implemented to design new members of the KTP-type family as potential UV NLO materials. First, a novel centrosymmetric KTP-type compound NH4SbFPO4·H2O with a sharply enlarged bandgap (5.01 eV) was obtained through three-site aliovalent substitution. Second, the noncentrosymmetric NH4SbF2SO4 was synthesized by the introduction of more F- anions to destroy the crystal symmetry and SO42- to replace PO43- for balancing the charge in NH4SbFPO4·H2O, which realized the transformation from a visible phosphate system to solar blind UV sulfate system for KTP-type family NLO materials. The preliminary experimental results indicated that NH4SbF2SO4 is a promising solar blind UV NLO material. The first-principles calculations revealed that the sharply enlarged bandgap resulted from the substitution of the transition metal cations with the main group metal cations and the introduction of F- anions with high electronegativity.

Hexagonal tungsten oxides with large bandgaps synthesized by a chemical substitution method

A novel hexagonal tungsten oxide designed by a chemical substitution method, NH₄(GaF₂)₃(SeO₃)₂, exhibits the largest bandgap among all known phase-matchable NLO selenite compounds.

Recent progress in selenite and tellurite based SHG materials

Fluorination and bandgaps have attracted more attention than d⁰ TM and SHG efficiency recently in metal selenites and tellurites.

In[Ba3Cl3F6]: a novel infrared-transparent molecular sieve constructed by halides

A new metal halide molecular sieve In[Ba₃Cl₃F₆] has been synthesized by the hydrothermal method. It possesses a wide transparent window from 0.366 to 22 μm and can exhibit the good adsorption–desorption property.

“Old dog, new tricks”: the lone pair effect inducing divergent optical responses in lead cyanurates containing π-bonds

The stereochemically active lone pair effect of Pb²⁺ and induced narrower bandgaps were elaborated in Pb₃(HC₃N₃O₃)₂(OH)₂ for the first time.

LiMg(IO3)3: an excellent SHG material designed by single-site aliovalent substitution

An excellent second harmonic generation (SHG) material, LiMg(IO₃)₃ (LMIO), has been elaborately designed from Li₂M^IV(IO₃)₆ (M^IV = Ti, Sn, and Ge) by aliovalent substitution of the central M^IV cation followed by Wyckoff position exchange. The new structure sustains the ideal-alignment of (IO₃)^- groups. Importantly, LMIO exhibits an extremely strong SHG effect of roughly 24 × KH₂PO₄ (KDP) under 1064 nm laser radiation or 1.5 × AgGaS₂ (AGS) under 2.05 μm laser radiation, which is larger than that of α-LiIO₃ (18 × KDP). The replacement of M^IV with Mg²⁺ without d-d electronic transitions induces an obviously larger band gap (4.34 eV) with a short absorption edge (285 nm). This study shows that single-site aliovalent substitution provides a new synthetic route for designing SHG materials.

LiGaP2O7: A Potential UV Nonlinear-Optical Crystal

A new noncentrosymmetric pyrophosphate, LiGaP₂O₇, is designed and synthesized by a reasonable energy-band regulation engineering strategy with isovalent substitution. The title compound crystallizes in the monoclinic space group P2₁ (No. 4) with lattice parameters a = 4.7593(10) Å, b = 7.9586(16) Å, c = 6.8940(14) Å, and Z = 2, which is the isomorphic compound of LiMP₂O₇ (M = Fe, Cr). Compared with LiMP₂O₇, LiGaP₂O₇ exhibits a wide band gap of 4.56 eV due to no d-d electronic transitions. Meanwhile, good phase-matching ability and a moderate second-harmonic-generation (SHG) response in LiGaP₂O₇ are maintained. First-principles calculations of the band structure and nonlinear-optical performance were also performed in order to gain insight into the role of the Ga-O groups in the band gap and SHG effect source.

Exploration of New Birefringent Crystals in Bismuth d0 Transition Metal Selenites

The first examples of bismuth fluoride selenites with d⁰ -TM/Te^VI polyhedrons, namely, Bi₄ TiO₂ F₄ (SeO₃ )₄ (1), Bi₄ NbO₃ F₃ (SeO₃ )₄ (2), Bi₄ TeO₄ F₂ (TeO₃ )₂ (SeO₃ )₂ (3), Bi₂ F₂ (MoO₄ )(SeO₃ ) (4) and Bi₂ ZrO₂ F₂ (SeO₃ )₂ (5) have been successfully synthesized under hydrothermal reactions by aliovalent substitution. The five new compounds feature three different types of structures. Compounds 1-3, containing Ti^IV , Nb^V and Te^VI respectively, are isostructural, exhibiting a new 3D framework composed of a 3D bismuth oxyfluoride architecture, with intersecting tunnels occupied by d⁰ -TM/Te^VI octahedrons and selenite/tellurite groups. Interestingly, compound Bi₄ TeO₄ F₂ (TeO₃ )₂ (SeO₃ )₂ (3) is the first structure containing Se^IV and mixed-valent Te^IV /Te^VI cations simultaneously. Compound 4 features a new 3D structure formed by a 3D bismuth oxyfluoride network with MoO₄ tetrahedrons and selenites groups imbedded in the 1D tunnels. Compound 5 displays a novel pillar-layered 3D open framework, consisting of 2D bismuth oxide layers bridged by the [ZrO₂ F₂ (SeO₃ )₂ ]^6- polyanions. Theoretical calculations revealed that the five compounds displayed very strong birefringence. The birefringence values of compounds 1-3, especially, are above 0.19 at 1064 nm, which are larger than the mineral calcite. Based on the structure and property analysis, it was found that the asymmetric SeO₃ groups (and TeO₃ in compound 3) displayed the largest anisotropy, compared with the bismuth cations and the d⁰ -TM/Te polyhedra, which is beneficial to the birefringence.

Pb2Cd(SeO3)2X2 (X = Cl and Br): two halogenated selenites with phase matchable second harmonic generation

The second harmonic generation (SHG) efficiencies of Pb₂Cd(SeO₃)₂X₂ (X = Cl and Br) are higher than that of commercial KDP (KH₂PO₄) and their laser damage thresholds are 30 times more than that of AGS (AgGaS₂).

From centrosymmetric to noncentrosymmetric: cation-directed structural evolution in X3ZnB5O10 (X = Na, K, Rb) and Cs12Zn4(B5O10)4 crystals

A new Cs₁₂Zn₄(B₅O₁₀)₄ compound exhibits a short DUV cutoff edge (lower than 185 nm) and contains a 3D [ZnB₅O₁₀]_∞ network.

Cs2CdV2O6Cl2 and Cs3CdV4O12Br: two new non-centrosymmetric oxyhalides containing d0 and d10 cations and exhibiting second harmonic generation activity

Two new non-centrosymmetric oxyhalides containing d⁰ and d¹⁰ cations and exhibiting strong second harmonic generation activity.

Pb7F12Cl2: a promising infrared nonlinear optical material with high laser damage threshold

This study reports, for the first time, the second-harmonic generation (SHG) property of Pb₇F₁₂Cl₂ as a promising infrared nonlinear optical (NLO) material.

Synthesis and structure of a new mixed metal iodate Ba3Ga2(IO3)12

Due to the pseudo-2D arrangement of the [IO₃] units, Ba₃Ga₂(IO₃)₁₂ exhibits a relatively strong optical anisotropy with a calculated birefringence of about 0.103 at 1064 nm.

LiO4 tetrahedra lock the alignment of π-conjugated layers to maximize optical anisotropy in metal hydroisocyanurates

The “lock-in effect” of LiO₄ tetrahedra contributes to the alignment of π-conjugated layers to maximize optical anisotropy in metal hydroisocyanurates.

M2(SeO3)F2 (M = Zn, Cd): understanding the structure directing effect of [SeO3]2− groups on constructing ordered oxyfluorides

The structure directing effect of [SeO₃]²⁻ anionic groups play a crucial role in the configuration of ordered [MO₃F₃] octahedral and its large anisotropy.

A rich structural chemistry in π-conjugated hydroisocyanurates: layered structures of A2B(H2C3N3O3)4·nH2O (A = K, Rb, Cs; B = Mg, Ca; n = 4, 10) with high ultraviolet transparency and strong optical anisotropy

Mixed alkali/alkali-earth metal hydroisocyanurates A₂B(H₂C₃N₃O₃)₄·nH₂O (A = K, Rb, Cs; B = Mg, Ca, n = 4, 10) with strong optical anisotropy were grown.