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Four new compounds of A(VO2F)(SeO3) (A = Sr 1, Ba 2) and Ba(MOF2)(TeO4) (M = Mo 3, W 4) oxyfluorides have been synthesized successfully by hydrothermal reactions. They represent the first examples of alkali-earth selenites or tellurites with a fluorinated d0-TM octahedron. Their crystal structures were determined by single-crystal X-ray diffraction. They exhibit two different types of structures. Compounds 1 and 2 are isostructural and crystallize in the orthorhombic crystal system with the space group of Pbca (no. 61). Their structures feature a 3D network composed of 0D [V2O4F2(SeO3)2]4− dimers which are further bridged by Sr2+ or Ba2+ cations. Isostructural compounds 3 and 4 are crystallized in the monoclinic crystal system with the space group of P21/c (no. 14). Their structures can be described as 2D [(MOF2)(TeO4)]2− (M = Mo, W) anionic layers separated by Ba2+ cations. Out-of-center distortion studies show that the magnitude of the distortion of the (MOxF6−x) octahedron is comparable to that of MO6 (M = d0 transition metal). Infrared spectroscopy, thermal stability, optical property studies and theoretical calculations based on density functional theory methods were also performed.

Two new alkali boroselenites RbSe3B2O9(OH) and CsSe3B2O9(OH) have been synthesized by traditional solid-state reactions. Single-crystal X-ray diffraction study indicated that they are isostructural and adopt a new type of structure, which crystallizes in the noncentrosymmetric space group P212121. Optical diffuse reflectance spectrum studies emphasized that both are indirect optical transitions with values of 3.79 and 4.17 eV for RbSe3B2O9(OH) and CsSe3B2O9(OH), respectively. Optical analysis revealed a broad transparency window in the 0.3-8.5 μm region for both compounds. In addition, RbSe3B2O9(OH) featured a relatively weak second-harmonic-generation response, and for CsSe3B2O9(OH), the response is 0.8-times that of KH2PO4. Theoretical calculations of band structure, density of state, and linear and nonlinear optical properties were also performed to get insight into the relationships between electronic structures and their optical properties.

Using hydrothermal reactions, three series of rare-earth borate-sulfates, namely, RE(SO4)[B(OH)4](H2O) (RE = La (1), Sm (2), Eu (3)), RE(SO4)[B(OH)4](H2O)2 (RE = Pr (4), Nd (5), Sm (6), Eu (7), Gd (8)), and RE(SO4)[B(OH)4](H2O)·H2O (RE = Tb (9), Dy (10), Ho (11), Er (12), Tm (13), Yb (14), Lu (15), Y (16)), have been synthesized, which represent the first rare-earth borate-sulfate mixed-anion compounds. All these compounds possess the same fundamental building anionic units of SO4 and B(OH)4 tetrahedra; however, they exhibit three different types of two-dimensional (2D) layered structures composed of 1D RE–B–O and RE–S–O chains. The rare-earth borate chains are similar in all compounds, while the rare-earth sulfate chains differ in each type of compound due to the various coordination modes of sulfate groups. On the basis of the measured UV–vis diffuse reflectance spectra, the optical band gaps of compounds 2, 3, 6, and 7 are estimated to be 4.66, 4.53, 4.62, and 4.50 eV, respectively. Luminescence studie...

Here, the combination of the strong electropositive lithium and the most electronegative fluorine with the TeO3 group afforded the first lithium fluoride tellurite, namely, Li7(TeO3)3F (P63), which was synthesized by solid-state reactions. Its structure features a novel three-dimensional anionic framework of [Li7O9F]12– composed of LiO3F and LiO4 tetrahedra with one-dimensional hexagonal tunnels of 12-membered rings along the c-axis, filled by the “isolated” ψ-TeO3 tetrahedra. Notably, this compound displays the largest band gap of 4.75 eV among all of the non-centrosymmetric metal-tellurites reported so far, as well as strong second harmonic generation (SHG) responses (3 × KH2PO4 @1064 nm, 0.2 × β-BaB2O4 @532 nm) and a large laser damage threshold (73 × AgGaS2). Furthermore, theoretical calculations reveal that the LiO4 and LiO3F tetrahedra also contribute significantly to the SHG response (∼30%).

Partial substitution of iodate anions in La(IO3)3 by OH- or NO3- anion led to acentric La3(IO3)8(OH) and chiral La(IO3)2(NO3). The structure of La3(IO3)8(OH) can be seen as a complex three-dimensional (3D) network composed of two-dimensional [La3(IO3)2(OH)]6+ cationic layers that are further bridged by remaining iodate anions, or alternatively as a 3D network composed of one-dimensional [La3(IO3)6(OH)]2+ cationic columns being further interconnected by additional iodate anions, while the structure of La(IO3)2(NO3) can be seen as a novel 3D structure with planar NO3 groups serving as linkage between the [La3(IO3)6]3+ triple layers. Compared to La(IO3)3, both compounds show considerably wide band gaps and enhanced thermal stability. La(IO3)2(NO3) shows a moderate second harmonic generation (SHG) response of ∼0.6 times that of KDP (KH2PO4), a wide band gap of 4.23 eV, and a high LDT value (22 × AgGaS2). Optical property measurements, thermal analysis, as well as theoretical calculations on SHG origin, were performed. It can be deduced that partial substitution of iodate anions can be a facile route to design new noncentrosymmetric metal iodates with novel structure and potential application.

The first series of metal phosphate iodates, namely, M(IO3)(HPO4)(H2O) (M = Sc 1, Fe 2, Ga 3, In 4), have been obtained through hydrothermal syntheses. The title compounds are isomorphic and crystallize in the monoclinic space group C2/c (No. 15). Their structures feature a three-dimensional (3D) network composed of 1D [M(HPO4)(H2O)]+ chains that are further bridged by IO3 groups, forming 1D tunnels based on eight-membered rings along the b-axis. Magnetic measurements revealed antiferromagnetic coupling interactions between magnetic centers in compound 2. The UV absorption spectra measurements revealed that compound 2 exhibits a broad absorption peak at about 427 nm. The TGA studies and IR spectra for compounds 1–4 were also performed.

To develop new mid-infrared (MIR) nonlinear optical (NLO) materials, which can overcome the low laser damage threshold (LDT) of the commercial MIR-NLO crystals (AgGaS2 , AgGaSe2 and ZnGeP2 ) and simultaneously keep the large NLO susceptibility, is necessary for high-power MIR laser frequency conversion technology. To improve the LDT, a new strategy of increasing lattice stability was adopted. Here, the strongly covalent structural unit of the PS4 tetrahedron was introduced into AgGaS2 (AGS), and that led to the isolation of the first compound in AgI -GaIII -PV -S system, namely, AgGa2 PS6 (Cc). It retains a large SHG efficiency (1.0×AGS) with phase-matchable ability, and also exhibits an improved LDT (5.1×AGS), indicating AgGa2 PS6 is a new promising MIR-NLO crystal. Moreover, a novel 3D framework of [Ga2 PS6 ]- , with triangular-shaped channels, as well as interesting single triangular geometry of AgS3 -both of which are very rare in reported sulfides-was discovered in AgGa2 PS6 . Furthermore, theoretical calculations, and lattice energy and thermal expansions analyses suggest that the PS4 group makes a large contribution to the large SHG efficiency and high LDT.

Two new phosphates, non-centrosymmetric (NCS) (H3O)Ca2Zn3.5(PO4)4 and centrosymmetric (CS) Ba2Cd3(PO4)2(HPO4)2 have been prepared by hydrothermal reactions. The single-crystal X-ray structural analyses have shown that they crystallized in space group P−421c and P21/c, respectively·(H3O)Ca2Zn3.5(PO4)4 features a three-dimensional (3D) network structure composed of ZnO4 and PO4 tetrahedra that are interconnected via corner-sharing, forming 1D channels of 6-MRs and 8-MRs which are filled by Ca2+ and H3O+ cations, respectively. Ba2Cd3(PO4)2(HPO4)2 features a layered [Cd3(PO4)2(HPO4)2]4- composed of 1D chain of edge-sharing CdO6 octahedra that are further bridged by PO4 tetrahedra with Ba2+ cations filling the interlayer spaces. Luminescent studies suggest that (H3O)Ca2Zn3.5(PO4)4 emits blue light. Optical diffuse reflectance spectra show the experimental band gaps for (H3O)Ca2Zn3.5(PO4)4 and Ba2Cd3(PO4)2(HPO4)2 are 5.67 eV and 5.68 eV, respectively. The UV cut-off edge of title compounds are around at 218 nm·(H3O)Ca2Zn3.5(PO4)4 exhibits a very weak SHG response.

Two new barium gold iodates, namely, BaAu(IO3)5 and HBa4Au(IO3)12, have been prepared. BaAu(IO3)5 crystallizes in the polar space group Pca21, whereas HBa4Au(IO3)12 crystallizes in the centrosymmetric space group P21/c. BaAu(IO3)5 consists of unique polar [Au(IO3)4]− anions whose four iodate groups are located at both sides of the AuO4 plane and the polarity points in the [001] direction. BaAu(IO3)5 displays strong second-harmonic-generation (SHG) effects about 0.6KTiOPO4 (KTP) and is phase-matchable. Thermal properties, optical spectra analyses, and theoretical calculations are also reported.

Two new vanadium tellurites, VTeO4(OH) (1) and Ba2V4O8(Te3O10) (2), have been synthesized successfully with the use of hydrothermal reactions. The crystal structures of the two compounds were determined by single-crystal X-ray diffraction. Compound 1 crystallizes in the polar space group Pca21 (No. 29) while compound 2 crystallizes in the centrosymmetric space group C2/c (No. 15). The topography of compound 1 reveals a two-dimensional, layered structure comprised of VO6 octahedral chains and TeO3(OH) zig-zag chains. Compound 2, on the contrary, features a three-dimensional [V4O8(Te3O10)]4- anionic framework with Ba2+ ions filled into the 10-member ring helical tunnels. The [V4O8(Te3O10)]4- anionic network is the first 3D vanadium tellurite framework to be discovered in the alkaline-earth vanadium tellurite system. Powder second harmonic generation (SHG) measurements indicate that compound 1 shows a weak SHG response of about 0.3×KDP (KH2PO4) under 1064 nm laser radiation. Infrared spectroscopy, elemental analysis, thermal analysis, and dipole moment calculations have also been carried out.

The first alkali-metal vanadium iodate fluoride, CsVO

The first divalent-metal iodate-phosphate, Pb

An excellent SHG iodate, LiMg(IO3)3, has been obtained via the aliovalent substitution of defect-containing MIV sites with ordered Mg2+., An excellent second harmonic generation (SHG) material, LiMg(IO3)3 (LMIO), has been elaborately designed from Li2MIV(IO3)6 (MIV = Ti, Sn, and Ge) by aliovalent substitution of the central MIV 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 MIV 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.

Two new indium sulfate tellurites, namely, In

A cesium bismuth germanate, Cs

A new ultraviolet nonlinear optical material, namely LiHgPO

By using hydrofluoric acid as a solubilizer, the first alkali-metal niobium iodate and an alkali-earth metal niobium iodate, i.e. (H3O)HCs2Nb(IO3)9 and SrNbO(IO3)5, have been obtained. An obvious cation-controlled polarity shift is observed in the Ae/A-Nb5+-IO3 system. (H3O)HCs2Nb(IO3)9 gives a strong second harmonic generation (SHG) signal about 6 times that of KH2PO4 (KDP), making it a promising nonlinear optical (NLO) material.

The first examples of rare-earth polyiodates, namely, REI

The first metal iodate fluoride, Bi(IO3)F2, with a strong second harmonic generation (SHG) effect has been prepared. Bi(IO3)F2 crystallizes in the polar space group C2 and features a three-dimensional [BiF2]+ cationic framework with IO3 groups capping the inner walls of the one-dimensional tunnels. This [BiF2]+ cationic framework acts as a template for the assembly of the polar IO3 units in a favorable superposed fashion, which leads to the polar structure of the material. Bi(IO3)F2 displays a rather wide transmittance window (0.3–11 μm) and exhibits a very strong SHG response that is about 11.5 times larger than that of KH2PO4 (KDP) under 1064 nm laser radiation and the same as that of KTiOPO4 (KTP) under 2.05 μm laser radiation. Preliminary investigations indicate that Bi(IO3)F2 is a promising nonlinear optical material in the visible and mid-IR region.

A series of lanthanide boroantimonates, namely, LnBSb2O8 (Ln = Sm 1, Eu 2, Gd 3, and Tb 4) have been successfully synthesized by high temperature solid-state reactions for the first time. They are isostructural and feature novel three-dimensional (3D) frameworks composed of 2D [Sb3O12]9– layers interconnected by 1D [SbBO7]6– chains with remaining BO3 groups hanging on the walls of the 1D 6-membered-ring (MR) tunnels along the a-axis, and the lanthanide ions filled in the voids of the anionic structure. They exhibit high thermal stability (up to 900 °C). Luminescent studies suggest that compounds 1, 2, and 4 have potential application as orange, red, and green light luminescent materials, respectively. Magnetic measurements reveal ferromagnetic coupling interactions in compound 3 and antiferromagnetic coupling interactions between magnetic centers in compounds 1, 2, and 4.

The first bismuth selenite fluoride, BiFSeO3, was obtained by aliovalent substitution of 2D BiOIO3. Its structure features a 3D network composed of 1D [BiF](2+) chains interconnected by SeO3 groups. BiFSeO3 exhibits a very strong second harmonic generation (SHG) effect of about 13.5 times that of KH2PO4 (KDP) under 1064 nm laser radiation and 1.1 times that of KTiOPO4 (KTP) under 2.05 μm laser radiation, which is the highest among all of the metal selenites reported. It has also very simple chemical composition and can be synthesized easily under mild hydrothermal conditions.

The first examples of mixed-anion lanthanide galloborates, namely, Ln2Ga[B3O6(OH)]2[B7O9(OH)2](CH3CO2)2 [Ln = Y (1), Sm (2), Eu (3), Gd (4), Dy (5)], have been obtained through hydrothermal synthesis. The title compounds are isomorphic and belong to monoclinic space group C2/c (No. 15). Their structures possess [B7O13(OH)2] borate layers further bridged with [B3O7] clusters to give a three-dimensional (3D) borate framework displaying two types of rhombus-like B14O14 14-membered-ring (14-MR) channels along the b axis. The Ga(3+) ions are octahedrally coordinated and located at one end of the B14O14 14-MR channels, forming small tunnels of B7Ga 8-MRs, which are filled by the Ln(III) ions. The Ln ions and Ga cations are further held together by bridging acetate anions. It is worth noting that in these compounds there are two different types of borate clusters and two types of anions that are uncommon in the borates reported. Luminescent studies revealed the characteristic emission bands of Ln ions for compounds 2-5, and the luminescent lifetimes are 3.6, 0.86, and 3.05 ns for compounds 2, 3, and 5, respectively. Magnetic measurements suggest that there are antiferromagnetic interactions between magnetic centers for compounds 2-5.

A series of vanadium selenites covalently bonded with metal-organic complex, namely, Ni(2,2-bipy)2V2O4(SeO3)2 (1), Cu(2,2-bipy)V2O4(SeO3)2·0.5H2O (2) and Cu2(2,2-bipy)2V5O12(SeO3)2 (3) (2,2-bipy=2,2-bipyridine) have been hydrothermally synthesized and structurally characterized. They exhibit three different structural dimensions, from 0D cluster, 1D chain to 2D layer. Compound 1 features a 0D {Ni(2,2-bipy)2V2O4(SeO3)2}2 dimeric cluster composed of two {Ni(2,2-bipy)2}2+ moieties connected by the {V4O8(SeO3)4}4- cluster. Compound 2 shows a 1D {Cu(2,2-bipy)V2O4(SeO3)2}n chain in which the {Cu2(2,2-bipy)2}4+ moieties are bridged by the {V4O8(SeO3)4}4− clusters. Compound 3 displays a 2D structure consisted of mixed valence vanadium selenites layers {VIVVV4SeIV2O18}n4− and {Cu(2,2-bipy)}2+ complex moieties. The adjacent layers are further interconnected via π-π interactions between the 2,2-bipy ligands exhibiting an interesting 3D supramolecular architecture. Both compound 1 and 2 contain a new {V4O8(SeO3)4}4− cluster and compound 3 exhibits the first 2D vanadate polyhedral layer in vanadium selenites/tellurites with organic moieties.

We reported the synthesis and crystal structures of alkali metal and alkali-earth metal phosphite, namely, CsV2(H3O)(HPO3)4 (1), and Ba3V2(HPO3)6 (2). Both compounds were prepared by hydrothermal reactions and feature unique new structures. They both exhibit 3D complicated frameworks based on VO6 octahedra which are connected by HPO3 tetrahedra via corner-sharing. Alkali or alkali earth metal cations are filled in the different channels of the frameworks. Topological analysis shows that the framework of CsV2(H3O) (HPO3)4 (1) is a new 3,3,3,4,5-connected network with the Schlafli symbol of {4.62}2{42.66.82}{63}{65.8}. The investigations of X-ray photoelectron spectroscopy (XPS) and magnetic measurement on CsV2(H3O)(HPO3)4 suggest a +3 oxidation state of the vanadium ions in compound 1. Photocatalytic performance was evaluated by photocatalytic H2 evolution and degradation of methylene blue, which shows that both compounds exhibit activity under visible-light irradiation. IR spectrum, UV–vis-NIR spectrum and thermogravimetric analysis (TGA) of compounds were also investigated.

Incommensurately modulated borate structures of a new type were studied in detail in the nonlinear optical (NLO) materials Cs2TB4O9(T= Ge, Si) using single-crystal X-ray diffraction techniques. The structures were solved by the charge-flipping algorithm in the superspace groupI2(αβ0)0. The refinement results strongly suggest that the main structure modulation feature of Cs2TB4O9is the ordering of the O atoms. With these modulated structure models, the unreasonable B—O distances in the average structures were explained as the ordering of BO4and BO3.

Semiconducting ferroelectricity is realized in hybrid perovskite-type compounds (cyclohexylammonium)2 PbBr4-4 x I4 x (x = 0-1). By adjusting the composition x, the bandgap is successfully tuned from previously reported 3.65 eV to as low as 2.74 eV, and the excellent ferroelectricity was kept intact. This finding may contribute to improving the photoelectronic and/or photovoltaic performance of hybrid perovskite-type compounds.

Three new isostructural mixed anionic tellurites, namely, Pb2Al3F3(Te6F2O16) (1), Pb2Ga3F3(Te6F2O16) (2) and Ba2Ga3F3(Te6F2O16) (3), have been synthesized successfully by hydrothermal reactions. Their structures feature a novel 3D framework composed of 1D GaO4F2/AlO4F2 octahedral chains joined together with isolated (Te6F2O16)10− anionic rings. The charge-balance cations of Pb2+ or Ba2+ are located at the six-member polyhedral ring tunnels of the structures. The 0D (Te6F2O16)10− coplanar anionic ring is first reported in fluorotellurites, formed by two TeO4 and four TeO3F groups via corner-sharing. Thermogravimetric analyses revealed that their thermostabilities are in the following order: Pb2Al3F3(Te6F2O16) (1), Ba2Ga3F3(Te6F2O16) (3) and Pb2Ga3F3(Te6F2O16) (2). Optical diffuse reflectance spectra showed that these solids are wide band gap semiconductors with Eg of 4.1, 4.2 and 4.4 ​eV for compounds 1–3 respectively. The band gaps of compounds 1 and 2 are determined by O, Te and Pb atoms while the band gap of compound 3 is determined by O and Te atoms based on the theoretical calculations.

Three new acentric Sc-based borates, K

The first examples of bismuth fluoride selenites with d

We adopted a chemical substitution strategy to design a particular anionic structure with large optical anisotropy in phosphate. Specifically, we replaced one O

Two mixed-metal gallium iodate fluorides, namely, α- and β-Ba2 [GaF4 (IO3 )2 ](IO3 ) (1 and 2), have been designed by the aliovalent substitutions of α- and β-Ba2 [VO2 F2 (IO3 )2 ](IO3 ) (3 and 4) involving one cationic and two anionic sites. Both 1 and 2 display large second-harmonic generation responses (≈6×KH2 PO4 (KDP)), large energy band gaps (4.61 and 4.35 eV), wide transmittance ranges (≈0.27-12.5 μm), and high relevant laser-induced damage thresholds (29.7× and 28.3×AgGaS2 , respectively), which indicates that 1 and 2 are potential second-order nonlinear optical materials in the ultraviolet to mid-infrared. Our studies propose that three-site aliovalent substitution is a facile route for the discovery of good NLO materials.

A new nonlinear optical material, the first fluoride selenite nitrate PbCdF(SeO

Systematic explorations of new phases in the Ag+–Ti4+/Zr4+/Nb5+/Ta5+–Se4+–O(F) system by hydrothermal syntheses or standard high temperature solid-state reactions resulted in four new mixed-metal silver selenites, namely, Ag3Ti3O3(SeO3)4F (1, P63), Ag2ZrF2(SeO3)2 (2, Cmca) and AgMO(SeO3)2 (M = Nb, 3; Ta, 4) in the space group Cmcm. Ag3Ti3O3(SeO3)4F features an interesting [Ti3O3(SeO3)4]2− 3D anionic framework composed of 1D chains of corner-sharing TiO6 octahedra which are further interconnected by tridentate bridging SeO32− anions, displaying 1D hexagonal channels of Ti6Se6 12-member rings (MRs) along the c-axis, filled by the Ag+ cations and isolated F− anions. More interestingly, it displays a moderate strong Second-Harmonic Generation (SHG) response about 2 times that of KH2PO4 (KDP). Compound 2 features a novel 1D [ZrF2(SeO3)2]2− anionic chain composed of edge-sharing ZrO4F4 polyhedra in which two neighboring Zr4+ cations are further bridged by a pair of selenite anions. Compounds 3 and 4 are isostructural and their structures feature 1D anionic chains of [MO(SeO3)2]− (M = Nb, Ta) which are separated by Ag+ cations, the 1D [MO(SeO3)2]− (M = Nb, Ta) chain is formed by 1D chains of corner-sharing MO6 (M = Nb, Ta) octahedra in which two neighboring metal centers are also bridged by a pair of selenite anions. Other characterizations including thermal analyses, optical and luminescence property measurements have also been performed.

Four new alkali metal boroantimonates, namely, A2SbB3O8 (A = Na, K, Rb) and β-RbSbB2O6, have been synthesized by high-temperature solid-state reactions. Isostructural A2SbB3O8 (A = Na, K, Rb) crystallizes in the monoclinic space group P21/c, with structures featuring a novel 3D anionic framework composed of SbO6 octahedra and linear B3O8 groups with 1D tunnels of Sb4B4 8-membered-rings (MRs) along the a-axis, which are filled by alkali metal ions. β-RbSbB2O6 crystallizes in the polar space group Cc, revealing novel 3D anionic networks composed of SbO6 octahedra chains and B2O5 groups with 1D tunnels of Sb4B2 6-MRs along the b-axis and 1D tunnels of Sb3B4 7-MRs along the c-axis. Studies on their optical properties and thermal stability, band structure calculations based on DFT methods and linear optical calculations have also been performed.

Large crystal of the nonlinear optical and polar oxide Cs2TeW3O12 with a size of 20×15×4 mm3 has been grown by the top-seeded solution growth (TSSG) method. This crystal can be thermally stable up to 808 °C and melts incongruently. It possesses a large transparent range of 0.415–5.250 μm. Thermal properties, including thermal expansion, specific heat, thermal diffusivity and thermal conductivity were investigated. The average linear thermal expansion coefficients were calculated based on the measurement in the temperature range of 30–390 °C. It exhibits strong anisotropic thermal expansion which was discussed according to the relationships between the structure and thermal properties. Furthermore, laser-induced damage threshold has been estimated to be 591.28 MW/cm2 with a laser wavelength of 1064 nm and pulse duration of 8 ns.

Here, we report the preparation and characterization of two lead(II) phosphites, namely, Pb 2 (HPO 3 ) 2 and Pb 2 (HPO 3 )(NO 3 ) 2 through hydrothermal reaction or simple solution synthesis, respectively. A new lead phosphite, namely, Pb 2 (HPO 3 ) 2 , crystallizes in the noncentrosymmetric space group C mc2 1 (no. 36), which features 3D framework formed by the interconnection of 2D layer of lead(II) phosphites and 1D chain of [Pb(HPO 3 ) 5 ] ∞ . The nonlinear optical properties of Pb 2 (HPO 3 )(NO 3 ) 2 have been studied for the first time. The synergistic effect of the stereo-active lone-pairs on Pb 2+ cations and π-conjugated NO 3 units in Pb 2 (HPO 3 )(NO 3 ) 2 produces a moderate second harmonic generation (SHG) response of ∼1.8×KDP (KH 2 PO 4 ), which is phase matchable (type I). IR, UV–vis spectra and thermogravimetric analysis (TGA) for the two compounds were also measured.

Two new cesium selenites containing TaO6 or TiO4F2 octahedra, namely, Cs(TaO2)3(SeO3)2 (1) and Cs(TiOF)3(SeO3)2 (2), have been prepared using standard high temperature solid-state method and hydrothermal reaction, respectively. Compound 1 crystallizes in P3̅m1 and features an unusual [(TaO2)3(SeO3)2](-) sandwich-like double layer in which two [Ta(1)O3(SeO3)](3-) layers are bridged by central Ta(2)O6 octahedra via corner-sharing, whereas Cs(TiOF)3(SeO3)2 with a polar space group P63mc features an interesting hexagonal tungsten oxide (HTO) layered topology and presents a strong second harmonic generation (SHG) of about 5 × KDP (KH2PO4), which is much larger than those of A(VO2)3(QO3)2 (A = K, Tl, Rb, Cs, or NH4; Q = Se, Te) with a similar HTO layered structure. Cs(TiOF)3(SeO3)2 is also type-I phase matching. The SHG of above-mentioned HTO materials can be enhanced greatly with the replacement of VO6 octahedra by TiO4F2 octahedra. Furthermore, thermal stabilities, UV-vis diffuse reflectance spectra, infrared spectra, relationship between crystal structure and SHG, and theoretical calculations were also reported.

Metal iodates with a lone-pair containing I(V) in an asymmetric coordination geometry can form a diversity of unusual structures, including non-centrosymmetric (NCS) structures with promising second-order nonlinear optical (NLO) properties. They have wide transparent wavelength regions (0.4–12 μm), large second harmonic generation (SHG) coefficients (>10 × KDP for many iodates) and high optical-damage thresholds (4–50 GW cm −2 ) as well as good thermal stability (usually >400 °C). In this review, the structures and second-order NLO properties of metal iodates will be discussed. Under reaction media with a high concentration of iodic acid, the iodate groups can be condensed into binuclear or polynuclear iodate anions, these compounds are able to display large SHG responses. The introduction of other lone pair containing cations into the iodate system is also an effective strategy to design new NCS materials. The combination of d 0 transition-metal cations with iodate groups afforded a large number of NCS metal iodates with anionic structures ranging from 0D clusters, 1D chains, 2D layers to 3D networks. These NCS materials can display excellent second-order NLO properties when the polarizations from both types of the asymmetric units are aligned properly. As for the iodates of d 8 -transition metal ion with a square planar TMO 4 geometry, the cis TM(IO 3 ) 4 unit in which the four iodate groups are located at the same side of the TMO 4 plane favors the formation of NCS structures whereas the trans - one in which the four iodate groups being located at both sides of the TMO 4 square plane prefers to a centrosymmetric structure. NCS structures with good SHG properties can also be found in other mixed metal iodate systems.

Four new compounds of A(VO

Three new transition metal copper(II) selenites or tellurites, namely, CdCu(SeO3)2 (1), HgCu(SeO3)2 ()2, and Hg2Cu3(Te3O8)2 (3), have been obtained by conventional hydrothermal reactions of CdO (or Hg2Cl2), CuO and SeO2 (or TeO2). Compounds 1 and 2 are isostructural and crystallize in P2(1)/c. Their structures feature a 3D anionic framework of Cu(SeO3)2(2-) with 1D channels of eight-membered rings (MRs) along the c-axis and a-axis, respectively, which are filled by Cd(2+) or Hg(2+) cations. Compound 3 crystallizes in a tetragonal system of space group P42(1)2. Its structure is characterized by a [Cu3(Te3O8)2](2-) honeycomb layer composed of [Te3O8](4-) anions interconnected by Cu(2+) ions with 1D channels of 8-MRs along the c-axis. TOPOS analysis indicates that the copper(ii) tellurite layer exhibits a new topological structure with a Schläfli symbol of {4(6)·8(9)}(2){4(6)}(3). The above anionic copper(II) tellurite layers are further linked by dumbbell Hg2(2+) cations to form a novel 3D framework. Magnetic measurements based on magnetic susceptibility and heat capacity indicate that compounds 1 and 2 show a spin-singlet ground state with a spin gap based on the [Cu2O8](12-) dimeric model, whereas compound e3 xhibits a 2D spin-system with an antiferromagnetic ordering around 25 K correlated with its honeycomb [Cu3(Te3O8)2](2-) layer. Furthermore, crystalline structures, thermal stabilities, IR spectra and UV-Vis diffuse reflectance spectra have also been studied.

Three novel lead(II) borate–nitrates were obtained through a facile hydrothermal reaction by adjusting the concentrations of the starting materials, namely, [Pb6(μ4-O)4(BO3)](NO3) (1), H[Pb6(μ3-O)2(BO3)2](NO3)3 (2) and H[Pb8(μ4-O)3(μ3-O)(BO3)2](NO3)3 (3). All three compounds feature lead(II) oxo borate layers that are separated by nitrate anions. The 2D [Pb6(μ4-O)4(BO3)]+ layer parallel to the ab plane in 1 is built from 1D [Pb6(μ4-O)4]4+ chains along the a axis and bridging borate anions. The 2D H[Pb6(μ3-O)2(BO3)2]3+ layer in 2 which is perpendicular to the b axis is composed of “isolated” Pb2+ and tetranuclear [Pb4(μ3-O)2]4+ clusters interconnected by bridging BO3 groups. The [Pb8(μ4-O)3(μ3-O)(BO3)2]2+ (011) layer in 3 is composed of two types of lead(II) oxo chains, namely, 1D chains of [Pb4(μ4-O)2]4+ and 1D chains of [Pb4(μ4-O)(μ3-O)]4+, both elongated along the a axis, which are further interconnected by bridging borate anions. This study also demonstrates that a small change in the concentration of the starting materials could result in a product with a different density of the π-conjugated planar units.

The development of artificial photosynthesis systems that can efficiently catalyze water oxidation to generate oxygen remains one of the most important challenges in solar energy conversion to chemical energy. In photosystem II (PSII), the Mn4CaO5 cluster adopts a distorted coordination geometry and every two octahedra are linked by di-μ-oxo (edge-shared) or mono-μ-oxo (corner-shared) bridges, which is recognized as a critical structure motif for catalytic water oxidation. These structural features provide guidance on the design and synthesis of new water oxidation catalysts. Herein we synthesized a new layered organic cobalt phosphonate crystal, Co3(O3PCH2–NC4H7–CO2)2·4H2O (1) and demonstrate it as a heterogeneous catalyst for water oxidation. Its catalytic activity was compared to those of cobalt phosphonates with different structures (2–4) in terms of O2 evolution rate and O2 yield under the same reaction conditions. The compound with both mono- and di-μ-oxo bridged octahedral cobalt displays superior catalytic activity. In contrast, the presence of only mono-μ-oxo bridged cobalt in the structure results in lower O2 yield and O2 evolution rate. Further structural analysis reveals that the presence of a longer Co–N bond induces a distorted dissymmetry coordination geometry, and consequently facilitates water oxidation. These results provide important insight into the design of water oxidation catalysts.

Using hydrothermal reactions, three series of rare-earth borate-sulfates, namely, RE(SO

Here, the combination of the strong electropositive lithium and the most electronegative fluorine with the TeO

Partial substitution of iodate anions in La(IO