HgBrI: a possible tecton for NLO molecular materials?

Mixed mercury(II) halogenides have been known for a long time as good NLO (non-linear optic) materials. The NLO properties are due to the halogen disposition in the solid state and the electron distribution among the bonds formed by soft elements. We investigated the possibility of using HgBrI as a asymmetric tecton in the preparation of noncentrosymmetric crystalline compounds, by exploiting the coordinating power of Hg(II) toward N-donor ligands, and seven coordination complexes have been obtained. To unravel the nature of these complex systems we combined the data from different techniques: Raman spectroscopy, SC-XRD and Second Harmonic Generation, supported by a periodic DFT computational approach. In HgBrI crystalline products with low symmetry, the presence of substitutional disorder leads to a lack of the inversion center conferring NLO activity, which is absent in analogous complexes of Hg(II) halogenides. These results indicate HgBrI as an interesting tecton to obtain metallorganic NLO materials.

Sn7Br10S2: The First Ternary Halogen-Rich Chalcohalide Exhibiting A Chiral Structure and Pronounced Nonlinear Optical Properties

Infrared nonliear optical (IR NLO) materials are significant in laser technology for civil and military uses. Here, we report the synthesis, structural chemistry and NLO properties of a halogen-rich chalcohalide Sn7Br10S2. Its noncentrosymmetric (NCS, P63) structure can be considered as partially aliovalent anion substitution of SnBr2 (P63/m) induced centrosymmetric (CS) to NCS structural transformation. The 3D ∞[Sn(1)6Sn(2)6Br6X6]6- (X = Br/S) channel framework is consisting of Sn(1)BrX2 and Sn(2)X3 trigonal pyramids. It exhibits excellent NLO performances, including strong phase-matchable NLO response 1.5 × AgGaS2 and high laser-induced damage threshold 6.3 × AgGaS2. Structure-NLO performance relationship investigation confirm that the effective arrangement of Sn(1)BrX2 and Sn(2)X3 units predominantly contribute to the large SHG response. These results indicate Sn7Br10S2 is a potential IR NLO candidate, and provide a new feasible system as promising NLO materials.

Helical {[HgS]}n Chain-Induced Balanced Nonlinear-Optical Performance for Trigonal Mercury Sulfide

Large second-harmonic-generation (SHG) response and enhanced laser-induced damage threshold (LIDT) compared with benchmark AgGaS₂ (AGS), together with a simple chemical composition and exclusion of the light-sensitive Ag element, are vital for exploration of superior IR nonlinear-optical (NLO) materials beyond AGS. Herein, we report trigonal HgS as a highly promising IR NLO material. It was obtained by a facile one-pot hydrothermal reaction, and its noncentrosymmetric P3₂21 structure features a unique dumbbell-shaped HgS₂ group and a neutral helical {[HgS]}_n chain, which first served as a SHG functional motif. Its polycrystalline powder sample exhibits a phase-matchable SHG response comparable to that of AGS and a LIDT value of 1.2 × AGS. Structural analysis and theoretical calculation suggest that the {[HgS]}_n chain plays an important role for excellent NLO performance. This work not only provides a strong candidate for IR NLO application but also introduces a new SHG functional motif for the design of future NLO materials.

Acentric Organic-Inorganic Hybrid Halide [N(CH3)4]2HgBr2I2 Featuring an Isolated [HgBr2I2]2- Tetrahedron and Second-Order Nonlinearity

A new hybrid compound [N(CH₃)₄]₂HgBr₂I₂, obtained by a hydrothermal reaction, crystallized in the noncentrosymmetric space group P2₁2₁2₁. Its structure contains an isolated asymmetric [HgBr₂I₂]^2- tetrahedron with net polarization, connected by hydrogen bonds to form pseudo-one-dimensional chain structures. Moreover, its optical band gap, nonlinear optical (NLO) property, fluorescence property, and thermal property were characterized in detail. A rare high-temperature phase transition was observed in the compound. In addition, theoretical calculations were performed to elaborate the relation between electronic state, band structure, and their nonlinear optical response. These results indicate that [N(CH₃)₄]₂HgBr₂I₂ is a new potential candidate for future photoelectronic applications in fluorescence and nonlinear optics.

Nonlinear organic–inorganic halide hybrids containing unprecedented linear [MIX2]− coordination units and quasi-two-dimensional lone pairs

A first example of monovalent-metal-based hybrid halides [N(CH₃)₄]MCl₂ (M = Ga⁺, In⁺) with zero-dimensional configuration containing unprecedented linear [GaCl₂]/[InCl₂] units have been designed and synthesized.

Synthesis, crystal structures and nonlinear optical properties of β-RbCdI3·H2O and CsCdI3·H2O

Searching for new IR nonlinear optical (NLO) crystals with a high laser damage threshold (LDT) is still a challenge. In this paper, two new halides, β-RbCdI₃·H₂O and CsCdI₃·H₂O, have been synthesized by a conventional solution reaction. Both of them crystallize in the monoclinic space group Pc (no. 7). In their crystal structures, all the corner-sharing [CdI₄] tetrahedra connect with each other to form 1D chains, which further connect with [Rb(H₂O)]⁺/[Cs(H₂O)]⁺ complexes to form three-dimensional (3D) frameworks. All the polar [CdI₄]^2- groups align in such a way that results in a favorable net polarization. Powder second-harmonic generation (SHG) measurements indicate that β-RbCdI₃·H₂O and CsCdI₃·H₂O show phase-matchable SHG responses of 2.7 and 2.6 times that of KH₂PO₄ (KDP). The infrared transmission range can reach 21 μm. The UV-vis diffuse reflectance spectra indicate that the band gaps of β-RbCdI₃·H₂O and CsCdI₃·H₂O are about 3.26 and 3.54 eV, respectively. A preliminary measurement indicates that the LDT of their powders is about 90 and 100 MW cm^-2, respectively, suggesting that β-RbCdI₃·H₂O and CsCdI₃·H₂O are two new promising IR NLO materials. Their band structure and optical property calculations based on DFT methods are carried out.

Theoretical perspectives on the structure, electronic, and optical properties of titanosilicates Li2M4[(TiO)Si4O12] (M = K+, Rb+)

The structure–property relationship of new transition-metal silicates, used as promising SHG materials, was unraveled using theoretical perspectives.

Computational design of inorganic nonlinear optical crystals based on a genetic algorithm

A theoretical method to design inorganic nonlinear optical crystals for second harmonic generation (SHG) is presented here.

Exploration of new second-order nonlinear optical materials of the Cs–Hg–Br–I system

A new compound, Cs₂Hg₂Br₂I₄·H₂O, was synthesized to achieve a better balance between nonlinear optical properties and its band gap.