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Combining Second-Order Jahn−Teller Distorted Cations to Create Highly Efficient SHG Materials: Synthesis, Characterization, and NLO Properties of BaTeM 2 O 9 (M = Mo 6+ or W 6+ )
Abstract
Two new oxides, BaTeMo2O9 and BaTeW2O9, have been synthesized, by standard solid-state techniques, that have strong SHG intensities of approximately 600 x SiO2, on the order of LiNbO3. Both materials contain cations susceptible to second-order Jahn-Teller (SOJT) distortions, resulting in asymmetric coordination environments. The SOJT distortion polarizes the M6+-O and Te4+-O bonds. Equally importantly, these polarizations constructively add, resulting in the large SHG responses. Powder SHG measurements on BaTeM2O9 (M = Mo6+ or W6+) indicated that both materials are phase-matchable and have a deffexp of 28 and 22 pm/V, respectively. Using bond hyperpolarizability values (beta's) of 130 x 10-40 and 305 x 10-40 m4/V for Te4+-O and Mo6+-O respectively, we calculate a deffcalc of 20pm/V for BaTeMo2O9. In addition, through the powder SHG measurements, we are able to give a more reasonable value for beta(W6+-O), 230 x 10-40 m4/V. This value is consistent with the smaller polarizability and magnitude of the intra-octahedral distortion of W6+ compared with Mo6+.
... The tellurite molybdenum/tungsten (A-Te-Mo/W-O) quaternary oxides are a highly intriguing class of nonlinear optical crystals with remarkable multifunctional properties [1][2][3][4][5] . Their diverse compositions-including ATeMoO 6 (A = Mg, Zn, Mn, Cd, Co, etc.), BaTe 2 MO 9 (M = Mo, W), Cs 2 TeM 3 O 12 (M = Mo, W) and others-typically possess non-centrosymmetric crystal structures, which give rise to their nonlinear optic, piezoelectric and electro-optical characteristics. ...
The discovery of ultraconfined polaritons with extreme anisotropy in a number of van der Waals (vdW) materials has unlocked new prospects for nanophotonic and optoelectronic applications. However, the range of suitable materials for specific applications remains limited. Here we introduce tellurite molybdenum quaternary oxides—which possess non-centrosymmetric crystal structures and extraordinary nonlinear optical properties—as a highly promising vdW family of materials for tunable low-loss anisotropic polaritonics. By employing chemical flux growth and exfoliation techniques, we successfully fabricate high-quality vdW layers of various compounds, including MgTeMoO6, ZnTeMoO6, MnTeMoO6 and CdTeMoO6. We show that these quaternary vdW oxides possess two distinct types of in-plane anisotropic polaritons: slab-confined and edge-confined modes. By leveraging metal cation substitutions, we establish a systematic strategy to finely tune the in-plane polariton propagation, resulting in the selective emergence of circular, elliptical or hyperbolic polariton dispersion, accompanied by ultraslow group velocities (0.0003c) and long lifetimes (5 ps). Moreover, Reststrahlen bands of these quaternary oxides naturally overlap that of α-MoO3, providing opportunities for integration. As an example, we demonstrate that combining α-MoO3 (an in-plane hyperbolic material) with CdTeMoO6 (an in-plane isotropic material) in a heterostructure facilitates collimated, diffractionless polariton propagation. Quaternary oxides expand the family of anisotropic vdW polaritons considerably, and with it, the range of nanophotonics applications that can be envisioned.
... They define two antiferroelectric ordering processes which are effectively electronic instabilities, the first occurring at some temperature above the sublimation point, described by q 1 , and the second arising at a much lower temperature, described by q 3 , with or without the hypothetical Γ-point instability. W 6 þ is not Jahn-Teller active but is susceptible to second-order-Jahn-Teller distortions, 71 and there is an obvious analogy also with the large shear strains that accompany martensitic transitions driven by a band Jahn-Teller distortion in Heusler compounds. [72][73][74][75] Anomalies in electrical conductivity accompany all the phase transitions at high temperatures, 4,76 but their magnitude is smaller than seen at the "Pc"-P 1 transition point. ...
Lattice parameter data from the literature have been used to provide a complete description of spontaneous strain variations across each of the six known phase transitions of WO3 in the temperature interval 5–1273 K. Analysis of strain/order parameter coupling reveals the character of each phase transition, a unified description of strain across the full temperature range, the relationship between strain and electronic effects, and new insights into the strain gradients likely to be present in each of the different domain walls that develop in four different ferroelastic phases. Tetragonal and orthorhombic shear strains have values of 4%–6% and 2%–3%, respectively, and are dominated by coupling with the order parameter for antiferroelectric-type displacements. Conversely, shear strains, e4, e5, and e6, of up to 2% are controlled by octahedral tilting. Changes in electronic structure and properties have been related back to the susceptibility of W6+ to develop cooperative second-order-Jahn–Teller distortions. Proximity to tilt instabilities along with group–subgroup relationships in the P4/nmm parent structure results in two overlapping sequences of structural phase transitions, which differ in the form of their electronic structure. The possibility of a ground state structure in space group P21/c can be rationalized in terms of the efficiency by which different combinations of shearing and tilting of the WO6 octahedra can reduce the unit cell volume and would imply that WO3 has a re-entrant phase transition. Gradients in up to three order parameters coupled with gradients in strain of up to 12% across ferroelastic domain walls indicate that the different ferroelastic phases of WO3 should have domain walls with varied and potentially exotic electronic properties for device applications such as in nanoelectronics and neuromorphic computing.
... Beyond the π-conjugated systems, introducing some polar distorted polyhedra were also favorable for a large SHG response and birefringence, including the polyhedra with the canter of d 10 cations (such as Zn 2+ , Cd 2+ , and Hg 2+ ) [11,17,39,40], d 0 cations (such as V 5+ , Mo 6+ , W 6+ , Ti 4+ , etc.) [41][42][43][44], and stereo-chemical active lone pair (SCALP) cations (such as, Bi 3+ , Te 4+ , Sn 2+ Pb 2+ , I 5+ , etc.) [18,35,42,[45][46][47]. These cations with second-order Jahn-Teller (SOJT) effects could enhance the birefringence and SHG effect of NLO materials. ...
A new noncentrosymmetric cadmium indium borate, Cd4InO(BO3)3 (CIBO) has been successfully developed via a standard solid-state reaction. Its crystal structure was confirmed by the single crystal X-ray diffraction, which shows that CIBO belongs to the non-centrosymmetric and polar space group Cm. Its structure contains the distorted InO6 and CdOn (n = 6, 8) polyhedra, which link together by sharing an edge or corner to build a three dimensions framework with BO3 triangles accommodated in tunnels. Benefiting from the approximately parallel configuration of BO3 triangles, CIBO exhibited a strong second harmonic generation (SHG) effect (3 × KDP), and moderate birefringence of 0.077@1064 nm. Further optical and thermal characterizations suggest that CIBO possesses a wide transparent window and good thermal stability. Theoretical calculation reveals that the macroscopic SHG coefficients of CIBO results from the synergistic effect of the parallel arrangement of BO3 groups and d10 Cd2+ cation.
... [19][20][21][22][23][24][25] In addition, d 0 asymmetric oxide-based coordination is favor of obtaining non-centrosymmetric (NCS) structures with large second-order susceptibilities and strong NLO response. [26][27] KTiOPO 4 (KTP) and LiNbO 3 family compounds consisting of distorted TiO 6 and NbO 6 octahedra are outstanding NLO and electro-optic (EO) crystals exhibiting wide applications in laser communication and laser industries. [28][29][30] On the other hand, d 0 asymmetric oxide-based coordination plays a crucial role in acquiring large birefringent materials. ...
Transition metal ions with d⁰ electronic states (Ti⁴⁺, Zr⁴⁺, Nb⁵⁺ and Ta⁵⁺) are widely investigated as functional materials. This work first illustrates that Sc³⁺ ion, long‐time ignored, displays a second‐order Jahn‐Teller (SOJT) effect similar to asymmetric oxide‐coordinated transition metal ions, thus providing a new ground to seek for asymmetric functional materials with enhanced performances. In Ba3Sc2(BO3)4, BO3 groups are parallelly arranged, satisfying the ideal arrangement to produce large birefringence. Importantly, distorted octahedral ScO6 with Sc³⁺ ion in its d⁰ electronic state enlarges birefringence unexpectedly up to 0.149 @ 550 nm, which is larger than previously reported borates containing solely BO3, even to B3O6 units. Subsequently, the SOJT influence of distorted ScO6 octahedra on birefringence is verified by a comparison between experimental data and theoretical calculations. In addition, Ba3Sc2(BO3)4 also displays a high transmittance in the range of 230 nm–3.5 μm with a UV cut‐off wavelength at 198 nm and a large laser induced damage threshold (2.7 GW/cm²), comparable to α‐BaB2O4. Above characteristics imply that the title compound may be a promising birefringent material.
... Eventually, spin canting in CAFM systems was shown to have the potential to trigger magnetoelectric coupling [10,[22][23][24]. In addition, the compounds having lone pair cations (Te 4+ , Se 4+ , etc.) and d 0 transition metals (W 6+ , Mo 6+ , etc.) are highly interesting for the second-order Jahn-Teller (SOJT) effect and for hosting multiferroicity [2,25]. Hence, the combination of the noncentrosymmetric crystal structure, the CAFM magnetic structure, and the existence of the lone pair and d 0 orbitals in CTMO renders it an interesting ...
The physical properties of the noncentrosymmetric and quasi-two-dimensional canted antiferromagnetic material CoTeMoO6 (CTMO) are studied. We unravel a spectrum of intriguing phenomena, including a correlated short-range-ordered Griffiths-like phase near TG∼64K, a sharp step-like metamagnetic behavior of isothermal magnetization induced by a spin-flop transition at a critical magnetic field Hc∼1.2T, a strong dielectric anomaly, a pronounced magnetodielectric effect, and the associated weak magnetoelectric coupling at its magnetic transition temperature, TN∼23.4K. The crucial roles played by spin canting in CTMO are revealed in the aforementioned strongly entangled behavior of the spin and dipolar order parameters. The observed magnetostriction effect coupled with spin-phonon coupling seems to be a key factor in influencing the observed magnetodielectric effect. In addition, our theoretical first-principles calculations predict an insulating state with a canted antiferromagnetic spin configuration that matches well with the experimental results.
Organic–inorganic metal halides (OIMHs) exhibit a rich structural diversity and excellent semiconductor properties, making them attractive candidates in the field of nonlinear optics (NLO). Second harmonic generation, as an important NLO property, imposes strict symmetry constraints, requiring noncentrosymmetric structures. Currently, a key task in the NLO field is to design noncentrosymmetric structures for OIMHs and explore the relationship between structure and NLO performance. This will help further optimize the application of OIMHs in NLO materials. The design of noncentrosymmetric structures for OIMHs can be facilitated by the use of chiral organic cations or distorted inorganic polyhedra, both of which induce structural features that favor noncentrosymmetry. The NLO properties of OIMHs are summarized the relationship between structure and performance is analyzed, and the research directions in the field of NLO for these materials are further elaborated.
Birefringent materials are of great interest because of their ability to manipulate light. The demand for smaller devices has driven the development of new birefringent materials with high levels of...
The novel NaVSeO5 birefringent crystals were successfully synthesized using a multifunctional group synergistic strategy, which combines a two-dimensional layered structure, consisting of stereochemically active lone pairs [SeO3], and anomalous [VO6]...
Employing functional building units with microscopic second‐order NLO response has been proposed to explore high performance NLO materials. Herein, structural, electronic and optical properties of non‐centrosymmetric molybdenyl carbonate Cs3MoO4(HCO3) with NLO active functional units have been examined based on density functional theory. Theoretical results are consistent with experimentally mentioned data, confirming the reliable method. Detailed geometric structure, electronic attributes, linear optical properties, and nonlinear optical properties of Cs3MoO4(HCO3) are provided. Analysis of structures, compositions of bands and plots of charge density suggest that asymmetric functional building units [MoO4] and [HCO3] exhibit varying degrees of second‐order Jahn‐Teller distortions, and therefore have a significant impact on the electronic structure and optical properties of Cs3MoO4(HCO3). Maximum absolute value of SHG coefficients at 1064 nm is 0.671 pm/V for d15, which is nearly twice as much as that of KDP. Further researches are needed in future to validate and enhance optical anisotropy characteristic of Cs3MoO4(HCO3) for satisfying the phase matching conditions. Analysis results indicate that microscopic origins of SHG response in Cs3MoO4(HCO3) are complicated, such as geometric environment, induced polar asymmetric functional building units, and electronic properties. Continuous research on structure‐property relationship of NLO materials is needed for exploring more competitive NLO materials.
Large birefringence is a crucial but hard‐to‐achieve optical parameter that is a necessity for birefringent crystals in practical applications involving modulation of the polarization of light in modern opto‐electronic areas. Herein, an oxyanion polymerization strategy that involves the combination of two different types of second‐order Jahn–Teller distorted units is employed to realize giant anisotropy in a covalent molybdenum tellurite. Mo(H2O)Te2O7 (MTO) exhibits a record birefringence value for an inorganic UV‐transparent oxide crystalline material of 0.528 @ 546 nm, which is also significantly larger than those of all commercial birefringent crystals. MTO has a UV absorption edge of 366 nm and displays a strong powder second‐harmonic generation response of 5.4 times that of KH2PO4. The dominant roles of the condensed polytellurite oxyanions [Te8O20]⁸⁻ in combination with the [MoO6]⁶⁻ polyhedra in achieving the giant birefringence in MTO are clarified by structural analysis and first‐principles calculations. The results suggest that polymerization of polarizability‐anisotropic oxyanions may unlock the promise of birefringent crystals with exceptional birefringence.
Structural dissymmetry and strong second‐harmonic generation (SHG) responses are key conditions for nonlinear optical (NLO) crystals, and targeted combinatorial screening of suitable anionic groups has become extremely effective. Herein, optimal combination of flexible SnSn (n = 5, 6) groups and highly electropositive cations (lanthanides (Ln³⁺) and alkaline earth (Ae²⁺: Sr, Ca) metals) affords the successful synthesis of 12 NLO thiostannates including Ln2Sr3Sn3S12 (Pmc21) and Ln2Ca3Sn3S12 (P‐62m); whereas 17 rigid GeS4 or SiS4 tetrahedra‐constructed Ln2Ae3Ge3S12 and Ln2Ae3Si3S12 crystallize in the centrosymmetric (CS) Pnma. This unprecedented CS to noncentrosymmetric (NCS) structural transformation (Pnma to P‐62m to Pmc21) in the Ln2Ae3MIV3S12 family indicates that chemical substitution of the tetrahedral GeS4/SiS4 units with SnSn breaks the original symmetry to form the requisite NCS structures. Remarkably, strong polarization anisotropy and hyperpolarizability of the Sn⁽⁴⁺⁾S5 unit afford huge performance improvement from the nonphase‐matching (NPM) SHG response (1.4 × AgGaS2 and Δn = 0.008) of La2Ca3Sn3S12 to the strong phase‐matching (PM) SHG effect (3.0 × AgGaS2 and Δn = 0.086) of La2Sr3Sn3S12. Therefore, Sn⁽⁴⁺⁾S5 is proven to be a promising “NLO‐active unit.” This study verifies that the coupling of flexible SnSn building blocks into structures opens a feasible path for designing targeted NCS crystals with strong nonlinearity and optical anisotropy.
Nonlinear optical (NLO) materials currently attract significant interest and hold paramount importance in the optoelectronic field. Nevertheless, the fabrication of NLO crystals capable of transmitting ultraviolet to mid-infrared wavelengths remains...
Second‐harmonic generation (SHG) is a fundamental optical property of nonlinear optical (NLO) crystals. Thus far, it has proved difficult to engineer large SHG responses, particularly in the mid‐infrared region, owing to the difficulty in simultaneously controlling the arrangement and density of functional NLO‐active units. Herein, a new assembly strategy employing functional modules only, and aimed at maximizing the density and optimizing the spatial arrangement of highly efficient functional modules, has been applied to the preparation of NLO crystals, affording the van der Waals crystal MoO2Cl2. This exhibits the strongest powder SHG response (2.1 × KTiOPO4 (KTP) @ 2100 nm) for a transition‐metal oxyhalide, a wide optical transparency window, and a sufficient birefringence. MoO2Cl2 is the first SHG‐active transition‐metal oxyhalide effective in the IR. Theoretical studies and crystal structure analysis suggest that the densely packed, optimally‐aligned [MoO4Cl2] modules within the two‐dimensional van der Waals layers are responsible for the giant SHG response.
Second‐harmonic generation (SHG) is a fundamental optical property of nonlinear optical (NLO) crystals. Thus far, it has proved difficult to engineer large SHG responses, particularly in the mid‐infrared region, owing to the difficulty in simultaneously controlling the arrangement and density of functional NLO‐active units. Herein, a new assembly strategy employing functional modules only, and aimed at maximizing the density and optimizing the spatial arrangement of highly efficient functional modules, has been applied to the preparation of NLO crystals, affording the van der Waals crystal MoO2Cl2. This exhibits the strongest powder SHG response (2.1×KTiOPO4 (KTP) @ 2100 nm) for a transition‐metal oxyhalide, a wide optical transparency window, and a sufficient birefringence. MoO2Cl2 is the first SHG‐active transition‐metal oxyhalide effective in the infrared region. Theoretical studies and crystal structure analysis suggest that the densely packed, optimally‐aligned [MoO4Cl2] modules within the two‐dimensional van der Waals layers are responsible for the giant SHG response.
A new mineral species, murphyite (IMA 2021-107), ideally Pb(TeO4), has been found from the Grand Central mine, Tombstone, Arizona, USA. It occurs as bladed or prismatic crystals on top of a quartz matrix. Associated minerals include chlorargyrite, emmonsite, ottoite, stolzite, scheelite, schieffelinite, quartz, and jarosite. Individual crystals of murphyite are up to 0.20 × 0.05 × 0.05 mm in size. Twinning is common on {100}. Murphyite is colorless to very pale yellow in transmitted light, transparent with white streak and adamantine luster. It is brittle and has a Mohs hardness of ∼3½, with perfect cleavage on {100}. The calculated density is 7.579 g/cm3. Murphyite is insoluble in water or hydrochloric acid. An electron microprobe analysis yielded the empirical formula (based on 4 O apfu): (Pb0.96Fe0.03Mn0.02)Σ1.01[(Te0.61W0.38)Σ0.99O4], which can be simplified to Pb[(Te,W)O4].
Murphyite is the Te-analogue of raspite, Pb(WO4), and represents the first mineral with Te6+ substituting for W6+ over 50%. It is monoclinic with space group P21/a and unit-cell parameters a = 13.6089(3), b = 5.01750(10), c = 5.5767(2) Å, β = 107.9280(10)°, V = 362.302(17) Å3, and Z = 4. Its crystal structure consists of distorted MO6 (M = Te + W) octahedra sharing edges to form zigzag chains running parallel to [010]. These chains are linked together by PbO7 polyhedra. Compared to raspite, the substitution of W6+ by Te6+, which has a smaller ionic radius, results in a noticeable structural change: a significant decrease in MO6 octahedral angle distortion, with a concomitant increase in both MO6 octahedral volume and average Pb–O bond length. The unit-cell volume increases from 358.72(4) Å3 for raspite to 362.302(17) Å3 for murphyite. Raman spectroscopic data show that the major peak ascribable to M–O symmetrical stretching vibrations within the MO6 octahedron is centered at 870 cm−1 for raspite but at 881 cm−1 for murphyite.
A series of oxides with high rare earth contents, RE3TeBO9 (RE = La, Pr, Nd, Sm-Dy), were synthesized, and they all crystallize in the noncentrosymmetric space group P63 resembling that of a previously reported Bi3TeBO9 (J. Am. Chem. Soc. 2016, 138, 14190-14193), which showed a very strong second harmonic generation (SHG) signal believed to come from all three structural units [BO3], [TeO6], and [BiO6]. Surprisingly, compared with the isostructural compound Bi3TeBO9, both theoretical calculations and powder SHG tests show that RE3TeBO9 has an abnormally small SHG effect (0.2 × KDP). Based on the group theory analysis, the possible reasons are attributed to the misalignments and lack of distortions of the [BO3], [TeO6], and [REO8] groups in the unit cell. The 21 symmetric operation (a subset operation of the 63-screw axis) of the [TeO6], [BO3], and [REO8] groups leads to complete cancellation of their contributions to the xy directions, while the absence of lone pair electrons in RE3+ and Te6+ results in small distortion in the c axis, hence small contributions to the SHG coefficients dijk involving the z axis. Diffuse reflectance spectra of RE3TeBO9 (RE = La, Pr, Nd, Sm-Dy) show typical absorption of different RE3+, and the similarity of their infrared spectra is due to the same crystal structure and same structural units of the [TeO6] and [BO3] groups. The strong fluorescence intensities of Eu3TeBO9 and Tb3TeBO9 show the characteristic emissions of Eu3+ and Tb3+, which may serve as luminescence materials with proper doping.
A potential, nonlinear optical alkaline borate crystal K2B4O5(OH)4·3·6H2O(KBOH) was crystallized from aqueous solution by slow evaporation method. In this asymmetric unit cell, BO4 the tetrahedral coordination geometries and the BO3 triangular planar coordination geometries are linked by common O atoms to form the isolated B4O7 group. Single crystal XRD was taken to know the structural parameters and revealed orthorhombic crystal system comprising a 3D network. UV–Vis absorption spectrum shows that crystal has wide optical transparency in 200–1100 nm range. The functional groups of the K2B4O5·(OH)4·3·6H2O crystal were analyzed by FT–IR spectrum. The mechanical strength and the luminescence response of the crystal have been tested by Vicker’s microhardness and photoluminescence study. The chemical stability was presented by HOMO–LUMO energy values. The intermolecular interaction is evident from the 3d-Hirshfeld surface and 2d-fingerprint plot. The dielectric property of the grown crystal was established by dielectric measurements. Thermal analyses reveal that the material has good thermal stability. The second harmonic generation of the borate hydrated structure material KBOH has been accomplished by Kurtz–Perry technique, and third-order nonlinear optical parameters Nonlinear Refractive Index NLR, Nonlinear Absorption Coefficient and third order susceptibility (χ⁽³⁾) were found by Z-scan closed and open aperture approach to explore its suitability in the field of NLO applications.
A novel mercury selenite sulfate named Hg3(SeO3)2(SO4) has been successfully synthesized under a mild hydrothermal method. Hg3(SeO3)2(SO4) crystallizes in a monoclinic space group P21 and features a unique three-dimensional (3D) frame structure formed by [Hg6O8(SeO3)4]∞ layers and SO4 tetrahedra, which enables it to exhibit a comprehensive performance of a moderate second-harmonic generation (SHG) response of approximately 1.3 times that of baseline KH2PO4 (KDP), a moderate birefringence (0.118@546 nm), and a wide band gap (4.70 eV), which indicates that it has potential for application as an ultraviolet (UV) nonlinear optical material. Detailed theoretical calculations show that the Hg2+-based polyhedra with large polarizability and deformability and the SeO3 groups with stereochemically active lone pair (SCALP) electrons are the main contributors to moderate optical properties.
Oxides are emerging candidates for mid‐infrared (mid‐IR) nonlinear optical (NLO) materials. However, their intrinsically weak second harmonic generation (SHG) effects hinder their further development. A major design challenge is to increase the nonlinear coefficient while maintaining the broad mid‐IR transmission and high laser‐induced damage threshold (LIDT) of the oxides. In this study, it is reported on a polar NLO tellurite, Cd2Nb2Te4O15 (CNTO), featuring a pseudo‐Aurivillius‐type perovskite layered structure composed of three types of NLO active groups, including CdO6 octahedra, NbO6 octahedra, and TeO4 seesaws. The uniform orientation of the distorted units induces a giant SHG response that is ≈31 times larger than that of KH2PO4, the largest value among all reported metal tellurites. Additionally, CNTO exhibits a large band gap (3.75 eV), a wide optical transparency window (0.33–14.5 µm), superior birefringence (0.12@ 546 nm), high LIDT (23 × AgGaS2), and strong acid and alkali resistance, indicating its potential as a promising mid‐IR NLO material.
Nonlinear optical (NLO) crystals assume an irreplaceable role in the development of laser science and technologies, yet the reasonable design of a high-performance NLO crystal remains difficult owing to the unpredictability of inorganic structures. In this research, we report the fourth polymorph of KMoO3(IO3), i.e., δ-KMoO3(IO3), to understand the effect of different packing patterns of basic building units on structures and properties. Among four polymorphs of KMoO3(IO3), the different stacking patterns of Λ-shaped cis-MoO4(IO3)2 units result in α- and β-KMoO3(IO3) featuring nonpolar layered structures, whereas γ- and δ-KMoO3(IO3) display polar frameworks. Theoretical calculations and structure analysis reveal that IO3 units can be regarded as the main source of its polarization in δ-KMoO3(IO3). Further property measurements show that δ-KMoO3(IO3) exhibits a large second-harmonic generation response (6.6 × KDP), a wide band gap (3.34 eV), and a broad mid-infrared transparency region (∼10 μm), which demonstrates that adjusting the arrangement of the Λ-shaped basic building units is an effective approach for rationally designing NLO crystals.
We report the synthesis and optical properties of noncentrosymmetric (NCS) γ-Cs2I4O11 that was obtained through IO4 polyhedral rearrangements from centrosymmetric (CS) β-Cs2I4O11. Trifluoroacetic acid (TFA) acts as a structure-directing agent and plays a key role in the synthesis. It is suggested that the function of TFA is to promote rearrangement reactions found in the organic synthesis of stereoisomers. γ-Cs2I4O11 crystallizes in the NCS monoclinic space group P21 (No. 4) and exhibits a strong second-harmonic-generation (SHG) response of 5.0 × KDP (KH2PO4) under 1064 nm laser radiation. Additional SHG experiments indicate that the material is type I phase matchable. First-principles calculations show that SHG intensity mainly comes from its d34, d21, and d23 SHG tensor components. The synthetic strategy of discovering γ-Cs2I4O11 provides a new way for designing novel NCS SHG materials.
The first examples of silver fluorotellurites, namely, AgTeO2F and Ag2(TeO2F2), as well as the first silver tellurite fluoride, Ag3F3(TeF6)(TeO2)12, have been obtained successfully under mild hydrothermal conditions. AgTeO2F displays a...
At multianvil high-pressure/high-temperature conditions of 10 GPa and 1273 K, the first ternary tungsten tellurate WTe2O7 is formed, starting from a stoichiometric mixture of WO3 and TeO2. The compound crystallizes triclinic in a hitherto unknown crystal structure type with the space group P1̄; (no. 2), and was refined from single-crystal X-ray diffractometer data: a = 538.3(1), b = 687.5(1), c = 802.3(1) pm, α = 72.4(1)°, β = 85.7(1)°, γ = 68.1(1)°, wR2 = 0.0323, GooF = 1.048, 3157 F2 values, and 106 variables. The main motifs of the crystal structure are pairs of edge-linked [WO6]6- octahedra and fourfold oxygen-coordinated Te4+ atoms. The oxidation state of W6+ and Te4+ was further verified by measuring the characteristic binding energy values for the W 4f and the Te 3d core levels via X-ray photoelectron spectroscopy (XPS). In addition, DFT calculations of the structure, the associated electron localisation functions (ELF) and vibrational spectra have been carried out. The theoretical data clearly demonstrates the impact of the residual electron density located at the Te4+ ions, which can be directly interpreted as the presence of lone electron pairs within the solid structure.
Noncentrosymmetric (NCS) structure is a prerequisite condition for nonlinear optical (NLO) crystals and searching for feasible design strategy on the discovery of new NCS compounds has become extremely important. For that reason, new series of rare-earth (Re) based NCS K3ReP2S8 (Re = Y, Ho, Er; P21 space group) and CS K3ReP2S8 (Re = Pr, Sm, Gd; P21/c) thiophosphates were successfully prepared and this interesting CS to NCS structural remodeling shows the interior relationship with cation-size effect of Re metals. Systematic structural analysis indicates that several of varying influence factors including Re's ionic radii, average Re–S bond lengths and distortion degrees of ReS8 units induce the born of local coordination asymmetry between ReS8 and PS4 units, which facilitates the transformation from CS to NCS structures in K3ReP2S8 system. Moreover, excellent performances including strong NLO responses (1.1–1.4 times that of commercial AgGaS2) and required phase-matching behavior in P21–K3ReP2S8 were determined. Note that P21–K3ReP2S8 can be viewed as first NLO examples in the quaternary rare-earth thiophosphates. Moreover, NCS K3ReP2S8 also satisfy the well-balance between large NLO effects (1.1–1.4 × AgGaS2) and high laser damage thresholds (2.5–7.0 × AgGaS2). Theoretical study demonstrates that synergetic contributions of ReS8 and PS4 units guarantee the intrinsic origin of NLO response and ReS8 units provide the major NLO contribution. Therefore, this work not only affords one effective pathway to design new NCS materials through breaking the local symmetry in CS structures based on the size-directing effect of Re cations, but also verifies that bridging ReSn units into thiophosphates is beneficial to the huge enhancement of intrinsic NLO performances.
A series of n = 3 Dion–Jacobson type perovskites, RbEu2-xBixTi2NbO10 (0 ≤ x ≤ 2) have been synthesized by high temperature solid-state reactions. The Rietveld refinements using powder X-ray diffraction data indicate that the reported materials crystallizing in the noncentrosymmetric (NCS) polar orthorhombic space group, Ima2 (No. 46) or centrosymmetric (CS) tetragonal space group, P4/mmm (No. 123) reveal solid-solution behaviors depending on the amount of Eu³⁺ and Bi³⁺ cations. Detailed structural analyses indicate that once more than 30% of A-site cations are occupied by Eu³⁺ cations in RbEu2-xBixTi2NbO10, the centricity of the solid solutions changes from NCS to CS. Powder second-harmonic generation (SHG) measurements suggest while RbBi2Ti2NbO10 reveals strong SHG (2.5 × KDP), the SHG intensity abruptly decreases as small amount of Eu³⁺ cations occupy the site of lone pair cation, Bi³⁺. The origin of the large SHG response of polar RbBi2Ti2NbO10 and the abrupt decrease of SHG for the Eu³⁺-doped RbEu2-xBixTi2NbO10 solid solutions are explained by a detailed structural analysis and dipole moment calculations along with the electron localization function diagrams. Detailed characterizations including infrared and ultraviolet–visible spectroscopy, thermogravimetric analysis, density functional theory calculations, energy dispersive X-ray analysis, and photoluminescence measurements are provided.
Based on the co-crystal engineering strategy, a new polar non-centrosymmetric compound, KNO3SO3NH3, was meticulously designed by introducing KNO3 into the centrosymmetric SO3NH3 crystal. It has an unexpected strong second-harmonic generation (SHG) response (10 × KDP), which is a new record among the inorganic nonlinear optical (NLO) materials without NLO-active cations. Theoretical calculations showed that the enhanced SHG response should be attributed to the effect of hydrogen bond. Meanwhile, it has the shortest absorption edge of 216 nm among the known materials with strong SHG responses (>8 × KDP). Besides, it possesses a large birefringence of [email protected] nm. Our results showed that KNO3SO3NH3 should be an excellent UV NLO crystal.
The introduction of the transition metal cations with d0 electron configurations and F in the iodate systems generates a new polar compound, Ba2[WO3F(IO3)][WO3F2], which features the first example of direct...
Infrared (IR) nonlinear optical (NLO) crystals are the major materials to widen the output range of solid-state lasers to mid-infrared regions, but they are still inadequate for application due to the difficulties in balancing the large band gaps and strong NLO response. The diamond-like structure is a potential structural template to explore IR NLO materials. Herein, a computational workflow is proposed for exploring compounds with diamond-like structures, a series of LiMgGaSe3 structures were predicted successfully through this workflow, and LiMgGaSe3-I-III exhibited good optical performances in a large band gap (2.75-2.92 eV), strong SHG response (1.2-1.3 × AGS), and suitable birefringence (0.0470-0.0783 at 1064 nm). The in-depth mechanism explorations strongly demonstrate that the synergistic effect of alkaline earth metal tetrahedral [MgSe4] and [GaSe4] units is the main origin of large SHG response. The foregoing results suggest that our workflow can accelerate the discovery of new mid-IR NLO materials with diamond-like structures.
Highly‐polarizable materials are favorable for photoelectric conversion due to their efficient charge separation, while precise design of them is still a big challenge. Herein a novel polar oxyselenide, Sr6Cd2Sb6O7Se10, is rationally designed. It contains lateral sublattices of polarizable [Sb2OSe4]4‐ chains and highly‐orientated [CdSe3]4‐ chains. The intense polarization was evaluated by significant second‐harmonic generation (SHG) signal (maximum: 12.6×AgGaS2) in broad spectrum range. The polarization was found to mainly improve the carrier separation with a much longer recombination lifetime (76.5 μs) than that of the nonpolar compound Sr2Sb2O2Se3 (18.0 μs), resulting in better photoelectric performance. The single‐crystal photoelectric device exhibited excellent response covering broad spectrum in 500‐1000 nm with stable reproducibility. This work provides some new insights into the structure design of highly‐polarizable heteroanionic materials for photoelectric conversion.
Highly‐polarizable materials are favorable for photoelectric conversion due to their efficient charge separation, while precise design of them is still a big challenge. Herein a novel polar oxyselenide, Sr6Cd2Sb6O7Se10, is rationally designed. It contains lateral sublattices of polarizable [Sb2OSe4]⁴⁻ chains and highly‐orientated [CdSe3]⁴⁻ chains. The intense polarization was evaluated by significant second‐harmonic generation (SHG) signal (maximum: 12.6×AgGaS2) in broad spectrum range. The polarization was found to mainly improve the carrier separation with a much longer recombination lifetime (76.5 μs) than that of the nonpolar compound Sr2Sb2O2Se3 (18.0 μs), resulting in better photoelectric performance. The single‐crystal photoelectric device exhibited excellent response covering broad spectrum in 500–1000 nm with stable reproducibility. This work provides some new insights into the structure design of highly‐polarizable heteroanionic materials for photoelectric conversion.
Molybdate oxide materials have attracted considerable academic interest owing to their multifunctional optoelectronic properties and applications. However, to date, studies on the intrinsic properties of multiple molybdates have rarely been implemented. Herein, a prospective triple molybdate crystal, Rb3LiZn2(MoO4)4, with high crystalline quality was successfully grown using top-seeded solution growth (TSSG) approaches. Intriguingly, it affords a cage-like structure with the I4̅3d space group, analogous to that of Ca12Al14O33 (C12A7). The Rb3LiZn2(MoO4)4 crystal exhibits excellent thermal stability up to 603 °C, accompanied by a congruent melting nature. Simultaneously, it preserves the optical merits of a large band gap of 4.10 eV and a wide transmission window of 0.29-5.4 μm, which are superior to those of most molybdate crystals. More importantly, Raman spectroscopic measurements demonstrated that the title compound possesses an intense Raman shift located at 925 cm-1 and narrow line width, facilitating a stimulated Raman laser. In addition, first-principles calculations were also implemented to elucidate the structure-property relationships of Rb3LiZn2(MoO4)4. These observations provide an empirical platform for intuitively comprehending the underlying properties of multiple molybdates and pave the way for exploiting Raman crystals.
Huge crystals of noncentrosymmetric (NCS) organic-inorganic hybrid niobium oxyfluorides, (R)-[C8H10NO3]2[NbOF5] [(R)-Nb] and (S)-[C8H10NO3]2[NbOF5] [(S)-Nb], have been easily grown via a slow evaporation method in high yields through the systematic driving...
Second-order nonlinear optical (NLO) materials have drawn enormous academic and technological attention attributable to their indispensable role in laser frequency conversion and other greatly facilitated applications. The exploration of new NLO materials with high performances thus has long been an intriguing research field for chemists and material scientists. However, an ideal NLO material should simultaneously satisfy quite a few fundamental yet rigorous criteria including a noncentrosymmetric structure, large NLO coefficients, desired transparent range, large birefringence, high laser damage threshold, and availability of a large-size single crystal. Therefore, the identification of promising compound systems, targeted design, and experience-based syntheses are crucial to discover novel NLO materials working in the spectral region of interest. As an important family of mixed-anion compounds, versatile metal oxyhalides containing metal-centered oxyhalide functional units ([MOmXn] (X = F, Cl, Br, and I)) are becoming a marvelous branch for interesting NLO materials. Especially, when the central metals are d0/d10 transition metals or heavy post-transition metals, a number of novel NLO materials with superior functionalities are expected. Our thorough review on the recent achievements of metal oxyhalides for NLO materials are divided into the fast-growing NLO metal oxyhalides with single type halogen anions and the newly identified NLO metal oxyhalides with mixed halogen anions. Here we mainly focus on the design strategy, structural chemistry, NLO-related properties, and structure–property correlation of the metal oxyhalides with relatively large NLO responses. We hope this review can provide an insight on the rational design and future development of emerging metal oxyhalides for NLO and other applications.
KPb 3 ( o -C 5 H 4 NCOO) 2 Cl 5 featuring a π-conjugated nicotinate group is simultaneously connected by a [PbO 2 Cl] trigonal pyramid and a distorted [PbNCl 3 ] polyhedron into an ordered arrangement, exhibits good comprehensive NLO performance.
A novel open-framework borate-rich cadmium borophosphate has been obtained by the boric acid reflux method. The compound exhibits a complicated network which is composed of CdO6 octahedra and interesting 1D...
Materials with multi‐stabilities controllable by external stimuli have potential for high‐capacity information storage and switch devices. Herein, we report the observation of pressure‐driven two‐step second‐harmonic‐generation (SHG) switching in polar BiOIO3 for the first time. Structure analyses reveal two pressure‐induced phase transitions in BiOIO3 from the ambient noncentrosymmetric phase (SHG‐high) to an intermediate noncentrosymmetric phase (SHG‐intermediate) and then to a centrosymmetric phase (SHG‐off). The three‐state SHG switching was inspected by in situ high‐pressure powder SHG and polarization‐dependent single‐crystal SHG measurements. Local structure analyses based on the in situ Raman spectra and X‐ray absorption spectra reveal that the SHG switching is caused by the step‐wise suppression of lone‐pair electrons on the [IO3]⁻ units. The dramatic evolution of the functional units under compression also leads to subtle changes of the optical absorption edge of BiOIO3. Materials with switchable multi‐stabilities provide a state‐of‐art platform for next‐generation switch and information storage devices.
An experimental technique using powders is described which permits the rapid classification of materials according to
(a) magnitude of nonlinear optical coefficients relative to a crystalline quartz standard and
(b) existence or absence of phase matching direction(s) for second-harmonic generation.
Results are presented for a large number of inorganic and organic substances including single-crystal data on phase-matched second-harmonic generation in HIO3, KNbO3, PbTiO3, LiClO4·3H2O, and CO(NH2)2. Iodic acid (HIO3) has a nonlinear coefficient d14∼1.5×d31 LiNbO3. Since it is readily grown from water solution and does not exhibit optical damage effects, this material should be useful for nonlinear device applications.
The synthesis and characterization of a noncentrosymmetric tellurium selenate, Te2SeO7, is reported. In addition, the powder second-harmonic-generating (SHG) properties of TeO2, Te2SeO7, Te2O5, and TeSeO4 have been measured, using 1064 nm radiation. Through the powder SHG experiments, we are able to determine that TeO2 is not phase-matchable, whereas Te2SeO7, Te2O5, and TeSeO4 are phase-matchable. Also, TeO2, Te2SeO7, Te2O5, and TeSeO4 have SHG efficiencies of 5, 200, 400, and 400 times SiO2, respectively. The relative SHG efficiencies may be understood by examining the structure of each material. Through the powder SHG measurements, we estimate the average nonlinear optical bond susceptibility, 〈d2ωijk〉, for each material.
The solid solution behavior and second-harmonic generating (SHG)
properties of SbSb xM1- xO 4 ( M=Nb
V or Ta V) ( x=0.0, 0.2, 0.4, 0.5, 0.6, 0.8, and
1.0) have been investigated by powder X-ray diffraction and nonlinear
optical (NLO) measurements. Both SbNbO 4 and SbTaO
4 form solid solutions with α-Sb 2O
4. All the materials crystallize in the non-centrosymmetric
space group Pna2 1, with Sb IIIO 4E
polyhedra linked to MVO 6 ( MV=Sb
V, Nb V, or Ta V) octahedra. SHG data
is presented for the solid solutions and α-Sb 2O
4, SbNbO 4, and SbTaO 4. With respect
to the SbSb xM1- xO 4 phases, NLO
measurements indicate a substantial decrease in SHG efficiency for
x≥0.6. This decrease is attributable to the "nonpolar" nature of the
Sb VO 6 octahedra compared with the polar nature
of Nb VO 6 or Ta VO 6.
The synthesis, structure, and characterization of a new noncentrosymmetric tellurite, Na2TeW2O9, is reported. The oxide exhibits a three-dimensional structure comprising distorted W6+O6 octahedra linked to asymmetric Te4+O3 groups. Both cations are in local acentric environments attributable to second-order Jahn−Teller effects. Single crystals of Na2TeW2O9 were synthesized through supercritical hydrothermal methods, utilizing NaOH(aq), WO3, and TeO2 as reagents. Polycrystalline Na2TeW2O9 was synthesized by combining stoichiometric amounts of Na2CO3, WO3, and TeO2 through standard solid-state methods. Na2TeW2O9 crystallizes in the noncentrosymmetric space group Ia (No. 9) with a = 13.1394(5) Å, b = 7.3202(3) Å, c = 31.4435(11) Å, and β = 95.0270(10)°. Powder SHG measurements, using 1064-nm radiation, on polycrystalline Na2TeW2O9 indicated a strong SHG intensity of approximately 500× SiO2. Additional SHG measurements revealed the material is phase-matchable (Type I).
It is demonstrated that second-order perturbation theory is useful in ; determining the manner in which the electron density present in a molecule is ; changed during a nuclear vibration. Furthermore, it is shown that one nuclear ; motion will lead to a particularly favorable electronic distortion such that this ; motion is energetically favored over the other possible motions of the molecule. ; This allows the theory to be employed to predict the symmetry of the reaction ; coordinate in both unimolecular and bimolecular reactions. The chemical ; implications of the electron density changes are discussed. (auth);
Bond-valence parameters which relate bond valences and bond lengths have been derived for a large number of bonds. It is shown that there is a strong linear correlation between the parameters for bonds from cations to pairs of anions. This correlation is used to develop an interpolation scheme that allows the estimation of bond-valence parameters for 969 pairs of atoms. A complete listing of these parameters is given.
Parameters for the calculation of bond valence (s) from bond length (r) have been determined for 750 atom pairs using the Inorganic Crystal Structure Database. In the relation s = exp((ro - r)/B), it is found that B = 0.37 was consistent with most of the refined values and the 141 most accurate values of ro for this value of B are tabulated. An algorithm for the calculation of ro in terms of position of the two atoms in the periodic table is given. Graphical bond-valence-bond-length correlations are presented for hydrogen bonds.-J.E.C.
Two novel, isostructural, one-dimensional tellurites of molybdenum(VI), (NHâ)âMoâTeOââ·2HâO and RbâMoâ-TeOââ·2HâO, have been synthesized by hydrothermal method. They contain linear (MoâTeOââ)â´â» anionic chains, parallel to one another and held together by NHâ{sup +}/Rb{sup +} ions. MoâOââ moieties, formed by edge-sharing of six MoOâ octahedra, are connected through tellurium resulting in the (MoâTeOââ)â´â» anionic chain. Tellurium is four-coordinated with SFâ geometry. The water of crystallization occupies the rest of the lattice. Both compounds have been structurally characterized by single-crystal X-ray diffraction studies. Hydrothermal syntheses, structure, powder X-ray diffraction, spectroscopy, and thermal studies of these compounds are described.
trans-Co(dien)2·Al3P4O16·3H2O (GTex3) (dien - bis-(2-aminoethyl)amine) was prepared hydrothermally using Co(dien)2Cl3as a structure-directing agent in an aluminophosphate gel. The structure of GTex3 was determined using single-crystal X-ray diffraction. It contains chiral layers distinct from, but related to, those previously found ind,l-Co(en)3·Al3P4O16·xH2O. They are stacked in a helical fashion with only one enantiomer of the aluminophosphate macroanion in any one crystal. Co(C4N3H13)2·Al3P4O16·3H2O,Mr= 780.1, hexagonal,P652 2,a=b= 8.457(3),c= 63.27(2) Å,V= 3920(2) Å3,Z= 6, ρx= 1.98 gcm−3, ρe= 1.95 gcm−3, λ(MoKα) = 0.71073 Å, μ = 10.99 cm−1,F(000) = 2396,T= 293 K,R1= 0.0954 for 2277 reflectionsF> 4σ(F).
The bond valence approach is used to model the characteristic out-of-center electronic distortions around d0 transition metal cations in octahedral coordination. The distortions are influenced not only by the electronic structure of the cation but also by the structure of the bond network, by lattice incommensurations, and by cation-cation repulsion. These latter effects often determine whether a distortion will occur and, if so, in what direction. Once the direction of an expected out-of-center distortion is known, its magnitude can be modeled using modified bond valence network equations, where certain bonds are weighted to take into account the intrinsic inequality of the bonds in such a distorted coordination. The arguments are illustrated by examples.
According to the Jahn-Teller theorem, symmetrical molecules with degenerate electronic states are unstable. Such molecules therefore take up a distorted shape. If there is near-degeneracy, the symmetrical shape may also be unstable. We have studied the distortion in some particular cases. The approach is to minimize the total electronic energy with respect to distortions of the nuclear framework, the latter being considered to be static. There are always several equivalent distortions of equal energy, so that a static distortion fails to remove the degeneracy. The discussion of dynamic effects is postponed to a subsequent paper. A linear molecule of formula BAB, for which two electronic states of opposite symmetry are sufficiently nearly degenerate, will be stable in a configuration with unequal A-B separations, and unstable when symmetrical. This example illustrates some of the main physical features of Jahn-Teller distortions in a simple manner. Although we know of no example where the symmetrical structure is actually unstable, there are examples where the tendency towards distortion noticeably reduces the force constant of the asymmetric vibration. Octahedral complexes AB6 with degenerate electronic states occur in many situations (e.g. paramagnetic crystals, F-centres, luminescent centres and exciton states in cubic crystals). The orbital degeneracy may be threefold (T1 and T2) or twofold. In the former case the stable distortion is found to be either of tetragonal symmetry about a [100] direction, or of trigonal symmetry about a [111] direction. The twofold degenerate situation leads to a more complicated situation. If one neglects anharmonic effects there appears to be an infinity of distortions minimizing the energy; a more detailed consideration of the anharmonic terms shows that the stable distortions are of elongated tetragonal character. This result has an important bearing on complexes involving the cupric ion.
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This paper examines the use of second-order perturbation theory in the interpretation and prediction of the signs of the interaction constants which are appended to the simple valence force potential functions. It is shown, for the large number of molecules considered here, that complete agreement with the observed signs can be obtained by expanding the electronic Hamiltonian in terms of the normal coordinates of motion and by then assuming that the lowest of the excited electronic states makes the most important contribution to the second-order sum in the expression for the energy. A knowledge of the symmetry of the transition density between the ground and the first excited electronic states is thus sufficient to determine which of the vibrations in a molecule is energetically favoured and thus to determine the sign of the interaction constant.
The nonlinear optical response of Li1-x(Nb,Ta)1-xWxO3 increases strongly with x. This is explained in terms of changing bond polarizabilities: W-0 bonds are more polarizable than Nb-O/Ta-0 bonds. A W-0 bond polarizability beta(parallel-to) of (570 +/- 130) 10(-40) m4/V is derived, neglecting beta(perpendicular-to). The luminescence properties depend also on x, and new emission and excitation bands are found.
Progress in the understanding of the relation betwen the structure and
properties of nonlinear optical (NLO) and electrooptical (EO) materials
is described. The structural and performance requirements of NLO and EO
devices and applications such as tunable coherent light sources for
spectroscopy, holography and optial phase conjugation, and integrated
optics and optical communications systems are discussed. Theoretical
explorations of the origin of the anharmonic potential in microscopic
structure are summarized, along with an anionic group theory for NLO
susceptibility in crystals and a charge-transfer theory of orgnaic NLO
crystals. Finally, state of the development of a molecular engineering
approach to identifying inorganic NLO materials is assessed.
Two families of molecular frameworks which grow as homochiral single crystals are described. Both consist of multiple interpenetration of the three-connected chiral (10,3)-a (Y*) network and result from the tridentate coordination of the 1,3,5-benzenetricarboxylate (btc) ligand to octahedral metal centers which act as linear connectors. The nature of the interpenetration is controlled by the auxiliary ligands bound in the equatorial plane of the metal center. Ethylene glycol (eg) binds in a unidentate fashion to form phase A which has 28% accessible solvent volume and contains four interpenetrating (10,3)-a networks. 1,2-Propanediol (1,2-pd) coordinates as a bidentate ligand to yield a phase B with a greatly enhanced 51% of solvent accessible volume, because only two (distorted) (10,3)-a‘ networks interpenetrate. Ligands in the void space and bound to the metal center can both be liberated thermally: the kinetics of this process allow isolation of microporous desolvated crystalline A and B. The porous phases lose crystallinity reversibly upon further loss of ligands bound to the equatorial metal: crystallinity is restored upon exposure to the vapors of simple alcohols, which can also effect conversion of B to A. Both phases present interpenetrating network topologies that are unique to chemistry and adopt space groups that are new for molecular solids: A crystallizes in P4232 and B adopts I4132. B can be grown homochirally from enantiomerically pure diol template. The stereochemistry of the alcohol bound to the metal controls the helicity of the chiral framework. The structure determination of the 1,2-propanediol phase represents the first demonstration that chiral molecules can specifically template helix handedness in a chiral porous framework solid.
The vapor-phase photochemistry of trans-crotonaldehyde has been studied at wavelengths longer than 2550 Å between 70 and 130°. The major photodecomposition products were CO and propylene. Small amounts of C2H4, allene, methylacetylene, cyclopropane, ethylketene, and enol-crotonaldehyde were also formed. The results are explained by a mechanism involving decomposition from, and multistage collisional deactivation of, a vibrationally excited upper singlet state, intersystem crossing to an unstable upper triplet state, and internal conversion to the ground state via isomerization of the upper singlet state to unstable intermediates.
Using the second-order Jahn-Teller effect as a basis of calculation, the stable structures of molecules XYn are predicted for n = 2-7. The symmetry argument is used that 〈ψ0/∂U/∂Q/ψk〉 is nonzero only if the direct product of the representations of ψ0 and ψk contains the representation of (∂U/∂U). Only the lowest lying one or two excited states are considered for ψk. In spite of this severe approximation, the results are remarkably good for a large variety of molecules and complex ions. The method provides a good test for molecular orbital calculations.
Noncentrosymmetric materials are of special interest in materials chemistry owing to their technologically important properties, such as ferroelectricity and second-order nonlinear optical behavior. Over 500 noncentrosymmetric oxides have been compiled and categorized by symmetry-dependent property and crystal class. In addition, the materials are described by their transition, or main group, metal coordination environment and grouped by element. Similarities within and between groups are discussed, as are noncentrosymmetric structure−property relationships.
Crystalline inorganic borates comprise a structurally intriguing, technologically important class of solid-state oxides. During the past 18 months, new and unique examples have been synthesized; enhanced performance characteristics have been realized; and improved descriptions of physical properties have been developed. Combined, these advances will likely increase the overall scope of applicability for these materials.
The second-order Jahn-Teller effect is an example of reactions proceeding by an interaction between the HOMO and the LUMO within the same molecule. The consequences can be decomposition of the molecule or a structural change. First the general theory is given, and then a number of examples are presented.
Linear M-X-M linkages in which X is a nitride, oxide, or halide commonly occur in dimers, square tetramers, one-dimensional polymers, and extended three-dimensional solids. For low d electron counts a second-order Jahn-Teller mixing of metal dπ and X pπ orbitals favors asymmetric M-X⋯M bridges. M-X σ bonding works against the distortion. Going to higher d electron counts also favors the symmetrical bridge by filling M-X π* levels. For the cyclic [ML4X]4 tetramer and ∞1[ML4X] chain, d electron counts greater than two favor a symmetric bridge; for perovskites, dn metals with n ≥ 1 are calculated to be symmetric. The extent of M-X bond length alternation can also be decreased by increasing the electronegativity difference between M and X to widen the HOMO-LUMO gap.
Crystal engineering, the ability to predict and control the packing of molecular building units in the solid state, has attracted much attention over the past three decades owing to its potential exploitation for the synthesis of technologically important materials. We present here the development of crystal-engineering strategies toward the synthesis of noncentrosymmetric infinite coordination networks for use as second-order nonlinear optical (NLO) materials. Work performed mainly in our laboratory has demonstrated that noncentrosymmetric solids based on infinite networks can be rationally synthesized by combining unsymmetrical bridging ligands and metal centers with well-defined coordination geometries. Specifically, coordination networks based on 3D diamondoid and 2D grid structures can be successfully engineered with a high degree of probability and predictability to crystallize in noncentrosymmetric space groups. We have also included noncentrosymmetric solids based on 1D chains and related helical structures for comparison.
Electronic effects and the bond network are the two factors that cause out-of-center distortions in octahedral d(0) transition metal oxide fluoride anions. Overlap between filled oxide p orbitals and vacant cation d orbitals results in strong, short metal-oxide bonds causing the metal ion to distort toward the oxide ligand. This primary, electronic distortion is not dependent on the extended structure. Smaller, secondary distortions of the anionic octahedra are caused by interactions with the bond network. [HNC(6)H(6)OH](2)[Cu(NC(5)H(5))(4)(NbOF(5))(2)], prepared with 5-hydroxy-2-methylpyridine that provides two coordination contact sites to the anion when protonated, exhibits distortions in the anion reflecting both factors. Crystal data for [HNC(6)H(6)OH](2)[Cu(NC(5)H(5))(4)(NbOF(5))(2)]: monoclinic, space group C2/c (No. 15), with a = 10.9427(8) A, b = 16.204(1) A, c = 21.396(2) A, beta = 93.263(1) degrees, and Z = 4. Conditions for detection of both distortion types are discussed with five additional examples.
Two novel copper(II) arsenates Na5ACu4(AsO4)4Cl2 (A = Rb, Cs) were synthesized by conventional solid-state methods using reactive molten salt media. These compounds are isostructural and crystallize in an orthorhombic lattice (Fmmm, No. 69; Z = 8). The cell constants are a = 14.632(3) A, b = 18.872(2) A, c = 14.445(3) A, V = 3989(1) A3, for A = Rb; a = 14.638(3) A, b = 18.990(4) A, c = 14.418(3) A, V = 4008(1) A3, for A = Cs. Single-crystal structure studies reveal a new composite framework consisting of alternating covalent and ionic lattices. The covalent lattice contains highly oriented oligomeric mu-oxo [Cu4O12]16- tetrameric units with a cyclo-S8-like Cu4O4 magnetic core that resembles the building block of layered cuprates. The ionic slab consists of a novel framework of mixed alkali metal chloride lattice and rarely seen Na6O8 clusters. Similar to organic-inorganic hybrid materials, the title compounds present a new class of host-guest chemistry via salt inclusion reactions.
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