Ae3[TO3][SnOQ3] (Ae = Sr, Ba; T = Si, Ge; Q = S, Se) and Ba3[CO3][MQ4] (M = Ge, Sn; Q = S, Se): Design and Syntheses of a Series of Heteroanionic Antiperovskite-Type Oxychalcogenides

The heteroanionic materials (HAMs) have attracted more and more attention because they can better balance the functional properties of materials. However, their rational structural design is still a great challenge. Here, by using the antiperovskite Ba3S[GeS4] as a template and calculating the tolerance factor (t) as a reference, eight heteroanionic oxychalcogenides with balanced properties were finally synthesized by a partially group-substitution method. Among them, Ba3[CO3][MQ4] (M = Ge, Sn; Q = S, Se) are centrosymmetric (CS) crystals and realize optimization of band gaps and birefringence. For Ae3[TO3][SnOQ3] (Ae = Sr, Ba; T = Si, Ge; Q = S, Se), thanks to the novel [TO4SnQ3] polyanionic groups for the regulation to the antiperovskite structures and the contributions to the nonlinear optical (NLO) properties, they achieve the structural transition from CS to noncentrosymmetry and accomplish an excellent balance among the critical performance parameters as the potential candidates for the infrared NLO materials, including phase-matchable behavior, wide band gaps (Eg = 3.26-3.95 eV), high laser damage threshold (LDT = 3.2-4.4 × AgGaS2), suitable birefringence (Δn = 0.065-0.098@2090 nm) and sufficiently strong second-harmonic generation responses (about 0.6-0.9 × AgGaS2). Moreover, benefiting from crystallization in the polar space groups, they exhibit ferroelectricity and piezoelectricity at room temperature. As far as we know, this is the first reported fully inorganic antiperovskite ferroelectric. These demonstrate that our strategy is desirable and can provide some unique insights into the development of HAMs or antiperovskite materials with specific functions or structures.

Hydrazine-Assisted Synthesis, Structures, Photoelectricity, and Photocatalysis of Ternary Mercury-Tellurostannate Hybrids with Transition-Metal Complexes

Tellurostannates are traditionally prepared by multistep reactions using the tellurides SnTe, SnTe2, K4SnTe4, or A6SnTe6 (A = K, Rb, or Cs) as precursors, which are usually prepared by the molten reaction of alkali metals Sn and Te under harsh synthetic conditions. Differently, ternary Hg-tellurostannate hybrids [Mn(en)3]HgSnTe3(Te2) (1) (en = ethylenediamine), [Mn(dien)2]HgSnTe3(Te2) (2), and [Fe(dien)2]HgSnTe3(Te2) (3) (dien = diethylenetriamine) were synthesized by one-pot reactions using Sn and Te powders as starting materials in the presence of hydrazine under mild solvothermal conditions. In 1, HgTe3 and SnTe4 units are joined via Te-sharing to form a 1-D polymeric chain [HgSnTe3(Te2)]n2n-, while the [HgSnTe3(Te2)]n2n- chains in 2 and 3 are composed of HgTe4 and SnTe4 units. The common feature of the [HgSnTe3(Te2)2-]n chains in 1-3 is that they are constructed by both the telluride anion Te2- and the polytelluride anion Te22-. 1-3 exhibited strong photocurrent responses with current densities of 5.26, 3.38, and 3.94 μA cm-2, respectively. They showed effective photocatalytic activities for methylene blue degradation with degradation ratios in the range of 85.3-94.6% after light irradiation for 80 min. Investigation of the photocatalytic mechanism showed that •O2- radicals and h+ holes were the main active substances in the photodegradation.

Rational design via dual-site aliovalent substitution leads to an outstanding IR nonlinear optical material with well-balanced comprehensive properties

The acquisition of a non-centrosymmetric (NCS) structure and achieving a nice trade-off between a large energy gap (E g > 3.5 eV) and a strong second-harmonic generation (SHG) response (d eff > 1.0 × benchmark AgGaS2) are two formidable challenges in the design and development of infrared nonlinear optical (IR-NLO) candidates. In this work, a new quaternary NCS sulfide, SrCdSiS4, has been rationally designed using the centrosymmetric SrGa2S4 as the template via a dual-site aliovalent substitution strategy. SrCdSiS4 crystallizes in the orthorhombic space group Ama2 (no. 40) and features a unique two-dimensional [CdSiS4]2- layer constructed from corner- and edge-sharing [CdS4] and [SiS4] basic building units (BBUs). Remarkably, SrCdSiS4 displays superior IR-NLO comprehensive performances, and this is the first report on an alkaline-earth metal-based IR-NLO material that breaks through the incompatibility between a large E g (>3.5 eV) and a strong phase-matching d eff (>1.0 × AgGaS2). In-depth mechanism explorations strongly demonstrate that the synergistic effect of distorted tetrahedral [CdS4] and [SiS4] BBUs is the main origin of the strong SHG effect and large birefringence. This work not only provides a high-performance IR-NLO candidate, but also offers a feasible chemical design strategy for constructing NCS structures.

Two Nonlinear Optical Thiophosphates Cu5Hg0.5P2S8 and AgHg3PS6 Activated by Their Tetrahedra-Stacking Architecture

Infrared (IR) lasers are very critical in military and civil affairs, but it is also challenging and difficult to develop new infrared nonlinear optical (NLO) crystals. Herein, two new mixed-metal thiophosphates, Cu₅Hg_0.5P₂S₈ and AgHg₃PS₆ were discovered with the noncentrosymmetric (NCS) space group Pmn2₁ (No. 31) and Cc (No. 9). Cu₅Hg_0.5P₂S₈ displays a three-dimensional (3D) defective diamond-like structure stacked by _∞²[Cu_2.5Hg_0.25PS₈]^8- layers. AgHg₃PS₆ is characterized by a 3D framework consisting of distorted tetrahedrons. Moreover, the optical spectra show the band gaps of Cu₅Hg_0.5P₂S₈ and AgHg₃PS₆ are 2.12 and 1.85 eV, respectively, with a broad transparent range of 0.7-16.0 μm. In these two compounds, the dipole moments of nonlinear active units are strengthened due to the high-valence element P and the Hg-S bonds with large susceptibility. Therefore, AgHg₃PS₆ exhibits a moderate second harmonic generation (SHG) response that is half that of AgGaS₂ (AGS) at 30-45 μm, while Cu₅Hg_0.5P₂S₈ performs a phase-matching (PM) behavior with a good SHG signal of 0.8 × AGS at 150-200 μm. The origin of NLO performance and electronic structures were revealed by the calculated dipole moments of distorted tetrahedra and theoretical calculations on the basis of density functional theory.

Noncentrosymmetric Ba6In2Q10 (Q = S, Se): Structural Chemistry and Nonlinear-Optical Activity

The indispensable condition for laser frequency-doubling crystal materials is that they crystallize in the noncentrosymmetric (NCS) structures. Here, ternary NCS Ba₆In₂S₁₀ (1) and Ba₆In₂Se₁₀ (2) (P6₃) were synthesized via conventional solid-state reactions. Their zero-dimensional structures feature isolated InQ₄ tetrahedra and Q₂^2- (Q = S, Se) dimers that are separated by Ba²⁺ counter cations. The structural relevance and differences with the centrosymmetric Ba₁₂In₄S₁₉ and Ba₁₂In₄Se₂₀ are analyzed in detail. Both 1 and 2 show obvious laser frequency-doubling activity, and their optical band gaps are 3.72 and 1.78 eV, respectively. This work provides a new type of IR nonlinear-optical materials.

Copper(ii) complexes with tridentate halogen-substituted Schiff base ligands: synthesis, crystal structures and investigating the effect of halogenation, leaving groups and ligand flexibility on antiproliferative activities

To investigate the effect of different halogen substituents and leaving groups and the flexibility of ligands on the anticancer activity of copper complexes, sixteen copper(ii) complexes with eight different tridentate Schiff-base ligands containing pyridine and 3,5-halogen-substituted phenol moieties were synthesized and characterized by spectroscopic methods. Four of these complexes were also characterized by X-ray crystallography. The cytotoxicity of the complexes was determined in three different tumor cell lines (i.e. the A2780 ovarian, HCT116 colorectal and MCF7 breast cancer cell line) and in a normal primary fibroblast cell line. Complexes were demonstrated to induce a higher loss of cell viability in the ovarian carcinoma cell line (A2780) with respect to the other two tumor cell lines, and therefore the biological mechanisms underlying this loss of viability were further investigated. Complexes with ligand L₁ (containing a 2-pycolylamine-type motif) were more cytotoxic than complexes with L₂ (containing a 2-(2-pyridyl)ethylamine-type motif). The loss of cell viability in A2780 tumor cells was observed in the order Cu(Cl₂-L₁)NO₃ > Cu(Cl₂-L₁)Cl > Cu(Br₂-L₁)Cl > Cu(BrCl-L₁)Cl. All complexes were able to induce reactive oxygen species (ROS) that could be related to the loss of cell viability. Complexes Cu(BrCl-L₁)Cl and Cu(Cl₂-L₁)NO₃ were able to promote A2780 cell apoptosis and autophagy and for complex Cu(BrCl-L₁)Cl the increase in apoptosis was due to the intrinsic pathway. Cu(Cl₂-L₁)Cl and Cu(Br₂-L₁)Cl complexes lead to cellular detachment allowing to correlate with the results of loss of cell viability. Despite the ability of the Cu(BrCl-L₁)Cl complex to induce programmed cell death in A2780 cells, its therapeutic window turned out to be low making the Cu(Cl₂-L₁)NO₃ complex the most promising candidate for additional biological applications.

Experimental and theoretical studies of the ternary thiophosphate PbPS3 featuring ethane-like [P2S6]4- units

The ternary thiophosphate PbPS₃ was synthesized by a high-temperature solid-state reaction using PbS, P and S. Single-crystal X-ray diffraction analysis reveals that the compound crystallizes in the P2₁/c space group. It features a three-dimensional structure, which consists of [PbS₈] hendecahedra and isolated ethane-like [P₂S₆]^4- units. PbPS₃ can be easily obtained by different methods and shows high air stability, which is beneficial to its chemical synthesis and large-sized crystal growth. The crystal structure, optical properties and electronic structure of PbPS₃ have been researched by experimental methods and first-principles calculations. The results show that PbPS₃ has a moderate bandgap (E_{g. exp.} = 2.60 eV) and birefringence (Δn_cal. = 0.094@1064 nm), as well as a wide transparent range. Furthermore, to better understand the origin of the birefringence, structure comparisons and theoretical calculations were carried out. With a relatively high physicochemical stability and easy synthesis, PbPS₃ can be expected to be a prospective birefringent material.

EuHgGeSe4 and EuHgSnS4: Two Quaternary Eu-Based Infrared Nonlinear Optical Materials with Strong Second-Harmonic-Generation Responses

Metal chalcogenides play a critical role in the infrared (IR) nonlinear optical (NLO) field. However, Eu-based chalcogenide-type IR NLO materials are still scarce up to now. In this paper, two new quaternary Eu-based chalcogenides, EuHgGeSe₄ and EuHgSnS₄, containing the "NLO active groups" [HgQ₄]^6- (Q = S, Se) and [GeSe₄]^4-/[SnS₄]^4- were synthesized through traditional high-temperature solid-state reactions. They possess noncentrosymmetric structures, crystallizing in the Ama2 space group, and exhibit strong phase-matchable second-harmonic-generation (SHG) responses (3.1× and 1.77× that of AgGaS₂ for EuHgGeSe₄ and EuHgSnS₄, respectively). Meanwhile, the optical band gaps of EuHgGeSe₄ (1.97 eV) and EuHgSnS₄ (2.14 eV) were determined from UV-vis-NIR diffuse reflectance spectra. Differential scanning calorimetry (DSC) analyses reveal the congruent-melting behavior of EuHgGeSe₄. Furthermore, structural analysis and theoretical calculations verify the critical driving effects of [HgQ₄]^6- tetrahedra on the strong SHG activity. The overall results demonstrate that EuHgGeSe₄ and EuHgSnS₄ are potential IR NLO materials.

Static- and frequency-dependent NLO properties of dithienothiophene and thienothiophene bridges — A computational investigation

We have explored detailed linear and nonlinear optical properties of push-pull systems bearing thienothiophene and dithienothiophene spacers. By using density functional theory (DFT), frequency-dependent strategies were applied to examine the polarizability ([Formula: see text] and hyperpolarizability ([Formula: see text] and [Formula: see text]. The set of global and range-separated hybrid functionals with different Hartree–Fock (HF) exchange percentage at two basis sets cc-pVDZ and cc-pVTZ were used to evaluate the nonlinear optical (NLO) properties. The observed trends in the absorption maxima supported by perturbation potential analysis; as the absorption maxima increases, the respective amplitude potential decreases. For the investigated compounds, [Formula: see text]-conjugation along with the type of substituted acceptor plays a crucial role in the enhancement of NLO properties. The presence of acceptor group and length of conjugation increase between the D and A group; the first- and second-order intrinsic hyperpolarizability increases, leads to enhanced first- as well as second-order hyperpolarizability. Bond length alternation (BLA)/bond order alteration (BOA) exploration suggested that compounds attain cyanine limit. The trends in NLO properties for investigated compounds are supported by chemical reactivity descriptors, hardness and hyperhardness analysis. The polarizability is linearly correlated with the hyperpolarizability parameters ([Formula: see text] and [Formula: see text] and shows a good regression coefficient by figures of merit analysis.

Coordinated regulation on critical physiochemical performances activated from mixed tetrahedral anionic ligands in new series of Sr6A4M4S16 (A = Ag, Cu; M = Ge, Sn) nonlinear optical materials

Coordinated regulation on physiochemical performances activated from mixed anionic ligands in a new series of IR NLO materials was systematically investigated.

Non-centrosymmetric sulfides A2Ba6MnSn4S16 (A = Li, Ag): syntheses, structures and properties

Li₂Ba₆MnSn₄S₁₆ and Ag₂Ba₆MnSn₄S₁₆ are synthesized for the first time. By modulating disordered sites with Mn²⁺, they not only show strong SHG responses and wide band gaps (5.1, 2.7 × AgGaS₂; 2.88, 2.76 eV), but also possess paramagnetism.

New quaternary chalcogenide Ba4HgAs2S10 originating from the combination of linear [HgS2]2− and tetrahedral [AsS4]3− modules

A new quaternary chalcogenide Ba₄HgAs₂S₁₀ is constructed by combining linear HgS₂²⁻ and tetrahedral AsS₄³⁻ modules.

Two rare-earth-based quaternary chalcogenides EuCdGeQ4 (Q = S, Se) with strong second-harmonic generation

Two RE-based quaternary metal chalcogenides EuCdGeQ₄ (Q = S, Se) are discovered. They possess many attractive properties as preferred IR NLO materials including large band gaps, phase-matched intense SHG and congruent melting behavior.

Adjustable optical nonlinearity in d10 cations containing chalcogenides via dp hybridization interaction

The role of d¹⁰-cations on band gap and nonlinearity in Cd/Hg-containing metal chalcogenides was investigated using DFT.

Four new quaternary chalcogenides A2Ba7Sn4Q16 (A = Li, Na; Q = S, Se): syntheses, crystal structures determination, nonlinear optical performances investigation

Four new quaternary chalcogenides with interesting structures and potential nonlinear optical performances were synthesized for the first time.

Band gap tuning from an indirect EuGa2S4 to a direct EuZnGeS4 semiconductor: syntheses, crystal and electronic structures, and optical properties

Novel EuZnGeS₄, with a direct band gap, can be obtained via simple substitution from EuGa₂S₄, with an indirect band gap.

BaCu2MIVQ4(MIV= Si, Ge, and Sn; Q = S, Se): synthesis, crystal structures, optical performances and theoretical calculations

Structural changes and optical performances for title compounds were studied and BaCu₂SnS₄was verified as one promising IR NLO candidate.