Synthesis and crystal structure of two novel polymorphs of (NaCl)[Cu(HSeO3)2]: a further contribution to the family of layered copper hydrogen selenites

Crystals of two new polymorphic forms of the known compound (NaCl)[Cu(HSeO3)2], which we term polymorphs II and III, were formed after a ca. one-year dwelling of a crystalline precipitate under mother liquor and upon crystallization in the presence of K+, respectively. Both structures belong to the “layered copper hydroselenite” family. The polymorph II is a structural analog of (KCl)[Cu(HSeO3)2] with a fully ordered Na+ site; the main difference concerns the environment of Cu2+ which is more regular in (NaCl)[Cu(HSeO3)2]-II. In contrast to some expectations, crystallization from solutions containing KCl. NaCl, CuCl2, and H2SeO3 upon evaporation does not result in formation of mixed (Na1−x K x Cl)[Cu(HSeO3)2] crystals, but rather in a separate crystallization of (KCl)[Cu(HSeO3)2] and (NaCl)[Cu(HSeO3)2]-III which exhibits a complex structure with four ordered and one disordered Na+ sites. It is possible that longer crystallization times enhance formation of ordered structures.

AIn4S6Cl (A = Rb and Cs) and Pb5Sn3Q10Cl2 (Q = S and Se): quaternary chalcohalides with mixed anionic coordination exhibit photocurrent responses

Mixed-anionic compounds have caught considerable attention due to their flexible coordination manners and abundant physical properties. Four new chalcohalides RbIn₄S₆Cl (1), CsIn₄S₆Cl (2), Pb₅Sn₃S₁₀Cl₂ (3) and Pb₅Sn₃Se₁₀Cl₂ (4) were successfully obtained by the high-temperature halide salt flux method. Compounds 1 and 2 have layered structures that consist of octahedral InS₆ and aliovalent-anionic InS₃Cl units. Compounds 3 and 4 feature 3-D structural frameworks built by [Pb₄SnQ₈Cl₄]^6- and [PbSn₂Q₆]^2- (Q = S and Se) polyhedral chains, in which partial Pb²⁺ cations are coordinated by Q^2- and Cl^- anions. Compounds 1-4 have optical band gaps close to the wavelength range of visible light and exhibit significant photocurrent responses of 28.75 nA cm^-2, 55.12 nA cm^-2, 19.58 mA cm^-2, and 36.12 μA cm^-2 with on/off ratios 30.0, 2.5, 15.7 and 2.6, respectively, implying their potential for photovoltaic applications. To the best of our knowledge, compound 3 has the largest photocurrent response among all non-oxides. In addition, the activation energies of 1-4 are well below 0.3 eV, which makes these compounds interesting for potential applications in electrochemical devices. This work sheds light on the exploration of promising photocurrent response materials in the mixed-anionic compound system.

Lead Tellurite Crystals BaPbTe2O6 and PbVTeO5F with Large Nonlinear-/Linear-Optical Responses due to Active Lone Pairs and Distorted Octahedra

The exploration of nonlinear-/linear-optical crystal materials with high performance is an extremely difficult research project. Herein, the two new lead tellurite crystals BaPbTe₂O₆ and PbVTeO₅F were successfully obtained through a facile hydrothermal synthesis strategy. BaPbTe₂O₆ lies in the noncentrosymmetric (NCS) and chiral orthorhombic space group P2₁2₁2₁, featuring a unique _∞¹[PbTe₂O₆] chain consisting of the PbO₄ and TeO₃ building units, while PbVTeO₅F belonging to the centrosymmetric (CS) orthorhombic space group Pbca manifests a 2D layer made up of _∞¹[PbO₄F₂] chains and novel [V₂Te₂O₁₀F₂] clusters. Further, a systematic analysis of lead tellurites finds that the coordination geometries of the Pb atom exert a considerable influence on the connection modes of Pb-O and Te-O building units. BaPbTe₂O₆ shows a great second-harmonic-generation (SHG) effect of ∼5× the benchmark KH₂PO₄ (KDP) and a large optical birefringence of 0.086 at 590 ± 3 nm. PbVTeO₅F demonstrates a remarkably larger birefringence of 0.142 at 590 ± 3 nm, benefiting from the introduction of the VO₅F octahedral unit. Theoretical studies reveal that the large SHG and birefringence in BaPbTe₂O₆ can be attributed to TeO₃ and PbO₄ polyhedra with active lone pairs, while the remarkably enlarged birefringence in PbVTeO₅F is attributable to the highly distorted octahedral VO₅F. The functional orientations of active building units may offer a practical insight into the design of the desired optical functional materials.

A spin-1/2 gapped compound CdCu2(SeO3)2Cl2 with a ladder structure

The exploration of two-leg spin-ladder materials is a great challenge to the chemical community since it is one of the most ideal models for the study of low-dimensional magnetism and high-Tc superconductivity. Herein, we report on a successful synthesis of a new Cu2+-based two-leg ladder compound constructed by CuO4Cl2 octahedra along the [101] direction. The magnetic results exhibit a broad peak at Tmax ∼ 265 K, and suggest that CdCu2(SeO3)2Cl2 has a spin singlet ground state. The fitting of the isolated two-leg spin-ladder model shows J⊥/kB = 429 K and J‖/kB = 21 K, leading to a large spin gap of ∼409 K.

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).

Synthesis and structural variety of first Mn and Bi selenites and selenite chlorides

Single crystals of new Mn2[Bi2O](SeO3)4 (I), MnBi(SeO3)2Cl (II), MnIIMnIII(SeO3)2Cl (III), Mn5(SeO3)2Cl6 (IV), and Mn4(Mn5,Bi)(SeO3)8Cl5 (V) have been synthesized by chemical vapour transport and hydrothermal methods. They have been structurally characterized by single crystal X-ray diffraction analysis. The compounds II–V are the first Mn selenite chlorides, while the I, II and V compounds are the first Bi-containing Mn oxoselenites. Structural relationships of the new phases with other compounds are discussed. An overview of the mixed-ligand MnO m Cl n polyhedra in inorganic compounds is given.

Synthesis and characterization of a series of transition metal oxychlorides: MBi(SeO3)2(H2O)Cl (M = Co, Ni, Cu)

Three new transition metal oxychlorides MBi(SeO3)2(H2O)Cl (M = Co, Ni, Cu) have been firstly synthesized through a hydrothermal reaction method at 200 °C. They were structurally determined to be isostructural with the Pbca space group of the orthorhombic system. They feature a 3D framework topology with two-dimensional tunnels intersected and filled with Cl anions parallel to the crystallographic bc-plane. Two neighboring MO5Cl octahedra are connected by a sharing edge into a M2O8Cl2 dimer which serves as the structural knots to knit the 2D [Bi(SeO3)2]∞ layers in the ab-plane together into the total 3D crystal architecture. The optical band gaps of CoBi(SeO3)2(H2O)Cl (1), NiBi(SeO3)2(H2O)Cl (2) and CuBi(SeO3)2(H2O)Cl (3) were evaluated to be 3.7 eV, 3.5 eV and 3.2 eV, respectively, through extrapolating the UV-vis-NIR optical absorption spectra. Besides, the spin-allowed d-d transition absorption spectra of the transition ion centers are observed in three compounds exhibiting different colors. Compounds 1, 2 and 3 can stay thermally stable below 370 °C, 400 °C and 300 °C, respectively, as found from the results of thermal analysis based on the simultaneous thermogravimetry and differential scanning calorimetry techniques. 1, 2 and 3 exhibit antiferromagnetic properties below Néel temperatures 6 K, 18 K and 52 K, respectively. Above the Néel temperatures, Curie-Weiss behavior dominates in the M-T process for the three compounds. The cell parameters are listed: a = 14.056 Å, b = 7.582 Å, c = 14.996 Å, and Z = 8 for 1, a = 14.083 Å, b = 7.575 Å, c = 14.860 Å, and Z = 8 for 2, and a = 14.576 Å, b = 7.371 Å, c = 14.656 Å, and Z = 8 for 3.

Transition Metal Selenite Halides: A Fascinating Family of Magnetic Compounds

The problem of searching for low-dimensional magnetic systems has been a topical subject and has attracted attention of the chemistry and physics community for the last decade. In low-dimensional magnetic systems, magnetic ions are distributed anisotopically and form different groups such as dimers, chains, ladders, or planes. In 3D frameworks, the distances between magnetic ions are equal in all directions while in low-dimensional systems the distances within groups are different from those between groups. The main approach of searching for desired systems is a priori crystal chemical design expecting the needed distribution of transition metal ions in the resulting structure. One of the main concepts of this structural design is the incorporation of the p-element ions with stereochemically active electron pairs and ions acting as spacers in the composition. Transition metal selenite halides, substances that combine SeO32− groups and halide ions in the structure, seem to be a promising object of investigation. Up to now, there are 33 compounds that are structurally described, magnetically characterized, and empirically tested on different levels. The presented review will summarize structural peculiarities and observed magnetic properties of the known transition metal selenite halides. In addition, the known compounds will be analyzed as possible low-dimensional magnetic systems.

Magnetism of coupled spin tetrahedra in ilinskite-type KCu5O2(SeO3)2Cl3

Synthesis, thermodynamic properties, and microscopic magnetic model of ilinskite-type KCu5O2(SeO3)2Cl3 built by corner-sharing Cu4 tetrahedra are reported, and relevant magnetostructural correlations are discussed. Quasi-one-dimensional magnetic behavior with the short-range order around 50 K is rationalized in terms of weakly coupled spin ladders (tubes) having a complex topology formed upon fragmentation of the tetrahedral network. This fragmentation is rooted in the non-trivial effect of the SeO3 groups that render the Cu-O-Cu superexchange strongly ferromagnetic even at bridging angles exceeding 110°.

Pb3(SeO3)Br4: a new nonlinear optical material with enhanced SHG response designedviaan ion-substitution strategy

A new NLO material has been designedviaion-substitution from a similar structure. It shows an enhanced SHG response equalling to that of KH₂PO₄(KDP) and a high laser damage threshold of 67 MW cm⁻¹.

[NaCl][Cu(HSeO3)2], NaCl-intercalated Cu(HSeO3)2: synthesis, crystal structure and comparison with related compounds

Single crystals of [NaCl][Cu(HSeO3)2] have been prepared by the chemical vapor transport reactions. Its crystal structure (monoclinic, C2/c, a = 13.9874(7), b = 7.2594(4), c = 9.0421(5) Å, β = 127.046(2)°, V = 732.81(7) Å3) is based upon electroneutral [Cu(HSeO3)2] sheets formed by corner sharing between the [CuO4] squares and (HSeO3) groups that are parallel to the (100) plane. Each (SeO2OH)– group forms the Oh1...O2 hydrogen bond to an adjacent hydroselenite group to constitute a [(SeO2OH)2]2– dimer that provides additional stabilization of the copper diselenite sheet. The [Cu(HSeO3)2] sheets alternate with the sheets consisting of zigzag–Na–Cl–Na–Cl–chains formed by Cl atoms and disordered Na sites. The chains are parallel to the c axis. The linkage between the alternating electroneutral [Cu(HSeO3)2] and [NaCl] sheets is provided by the Cu–Cl and Na–O bonds. The coordination of Na is fivefold and consists of three O and two Cl atoms. [NaCl][Cu(HSeO3)2] is a new member of the group of compounds based upon the M(HSeO3)2 layers (M2+ = Cu, Co, Cd). The prototype structure for this group is [Cu(HSeO3)2] that does not have any chemical species separating the copper hydroselenite layers. In other compounds, the interlayer space between the [Cu(HSeO3)2]0 layers is occupied by structural units of different complexity. [NaCl][Cu(HSeO3)2] can be considered as [Cu(HSeO3)2] intercalated with the NaCl layers consisting of one-dimensional–Na–Cl–Na–Cl–chains.

Oxocentered Cu(II) lead selenite honeycomb lattices hosting Cu(I)Cl2 groups obtained by chemical vapor transport reactions

Chemical vapor transport (CVT) reactions were used to prepare three modular mixed-valent Cu(I)-Cu(II) compounds, (Pb2Cu(2+)9O4)(SeO3)4(Cu(+)Cl(2))Cl5 (1), (PbCu(2+)5O2)(SeO3)2(Cu(+)Cl2)Cl3 (2), and (Pb(x)Cu(2+)(6-x)O2)(SeO3)2(Cu(+)Cl2)K(1-x)Cl(4-x) (x = 0.20) (3). In their crystal structures chains of anion-centered (OCu(2+)4) and (OCu(2+)3Pb) tetrahedra form honeycomb-like double layers with cavities occupied by linear [Cu(+)Cl2](-) groups.

Nonfrustrated interlayer order and its relevance to the Bose-Einstein condensation of magnons in BaCuSi2O6

Han purple (BaCuSi2O6) is not only an ancient pigment, but also a valuable model material for studying Bose-Einstein condensation of magnons in high magnetic fields. Using precise low-temperature structural data and extensive density-functional calculations, we elucidate magnetic couplings in this compound. The resulting magnetic model comprises two types of nonequivalent spin dimers, in excellent agreement with the Cu63,65 nuclear magnetic resonance data. We further argue that leading interdimer couplings connect the upper site of one dimer to the bottom site of the contiguous dimer, and not the upper-to-upper and bottom-to-bottom sites, as assumed previously. This finding is verified by inelastic neutron scattering data and implies the lack of frustration between the layers of spin dimers in BaCuSi2O6, thus challenging existing theories of the two-dimensional-like Bose-Einstein condensation of magnons in this compound.