Non-centrosymmetric Space Group Research Articles

One-Dimensional Chiral Copper Iodide Chain-Like Structure Cu4 I4 (R/S-3-quinuclidinol)3 with Near-Unity Photoluminescence Quantum Yield and Efficient Circularly Polarized Luminescence.

Chiral organic-inorganic hybrid metal halide materials have shown great potential for circularly polarized luminescence (CPL) related applications for their tunable structures and efficient emissions. Here, this work combines the highly emissive Cu4 I4 cubane cluster with chiral organic ligand R/S-3-quinuclidinol, to construct a new type of 1D Cu-I chains, namely Cu4 I4 (R/S-3-quinuclidinol)3 , crystallizing in noncentrosymmetric monoclinic P21 space group. These enantiomorphic hybrids exhibit long-term stability and show bright yellow emission with a photoluminescence quantum yield (PLQY) close to 100%. Due to the successful chirality transfer from the chiral ligands to the inorganic backbone, the enantiomers show intriguing chiroptical properties, such as circular dichroism (CD) and CPL. The CPL dissymmetry factor (glum ) is measured to be ≈4×10-3 . Time-resolved photoluminescence (PL) measurements show long averaged decay lifetime up to 10 µs. The structural details within the Cu4 I4 reveal the chiral nature of these basic building units, which are significantly different than in the achiral case. This discovery provides new structural insights for the design of high performance CPL materials and their applications in light emitting devices.

Electronic band structure and optical properties of Li2In2GeSe6 crystal

We present results of a complex experimental and theoretical study of peculiarities of the electronic structure and optical constants of Li2In2GeSe6 compound crystallizing in monoclinic non-centrosymmetric space group Cc. In particular, we have measured the XPS spectra of core-level and valence electrons of atoms composing a high optical quality Li2In2GeSe6 crystal for both pristine and treated with middle-energy Ar+ ions surfaces. Furthermore, the XPS spectrum as measured for the valence-band range of the Li2In2GeSe6 crystal is compared with the total density of states (DOS) theoretically calculated within a density functional theory (DFT) framework as implemented in the augmented plane wave plus local orbitals (APW+lo) method. The present theoretical APW+lo results reveal a very good agreement regarding the shapes and energy positions of main features of the theoretical total DOS curve and the experimental XPS spectrum when the first-principles DFT calculations are made using the modified Becke-Johnson (mBJ) functional in the form of Tran-Blaha and involving the Hubbard correction parameter U treated for highly correlated In 4d electrons (TB-mBJ+U approach). This technique gives also band gap value of 2.26 eV, which is in good agreement with that experimentally measured for this compound. The present TB-mBJ calculations indicate that, at the top and in the upper region of the valence band, Se 4p states make the biggest contributions; the central region is formed mainly by Ge 4p states, while In 5s states dominate at the bottom and in the lower portion of the Li2In2GeSe6 valence band. With respect to peculiarities of filling the valence band by Se(Ge) 4p states, the present calculations are verified experimentally. Furthermore, the optical properties of Li2In2GeSe6 are studied theoretically in detail employing the TB-mBJ+U technique.

Praziquanamine enantiomers: Crystal structure, Hirshfeld surface analysis, and quantum chemical studies

In this work, we report a microwave–assisted method to perform an acid hydrolysis using 2–6 praziquanamides as substrate to produce both praziquanamine (1) enantiomers: (R)–(–)–praziquanamine (1a) or (S)–(+)–praziquanamine (1b). This method provides very good yields and short reaction times (twenty minutes). A structural characterization of praziquanamine and its enantiomers was performed by using X–ray diffraction, spectroscopic and spectrometric techniques, thermal analysis, and powder X–ray diffraction. Computational calculations were also carried out, such as density functional theory (DFT), as it yields suitable geometries for the optimized structures. We also performed frontier molecular orbital (LUMO–HOMO) and electrostatic potential (ESP) analyses. Theoretical values were calculated for electronic transitions, vibration frequencies, and chemical shifts for nuclear magnetic resonances (NMR), and they were later compared to the experimental results. Additionally, the Hirshfeld Surface Analysis was performed to evaluate intermolecular interactions. Crystal structures of both 1a and 1b enantiomers were obtained as an orthorhombic system in the non-centrosymmetric P212121 space group. Conversely, the 1 compound crystallized as a monoclinic system in the centrosymmetric P21/n space group. The following interactions define the crystal packing: N–H···O, N–H···N, C–H···O, C–H···N, C–H···π, and π–π. They all establish an infinite one-dimensional chain. The crystal architectures of praziquanamine enantiomers may be used as resolution agents to discriminate chiral topologies.

Intermetallics La4M3Al3 and La4M5Al2 (M = Co, Ni) with M/Al slabs as building blocks

New compounds were obtained by arc-melting and characterized by X-ray diffraction on single crystal or on powder sample. The compounds crystallize with own types of structure: iso-structural La4Co3Al3 and La4Ni3Al3 with non-centrosymmetric space group Amm2 and Z ​= ​2 (a ​= ​4.148(5), b ​= ​10.111(7), c ​= ​10.601(7) Å for La4Co3Al3 and a ​= ​4.1895(7), b ​= ​10.0465(15), c ​= ​10.6538(16) Å for La4Ni3Al3). In contrast, iso-stoichiometric La4Co5Al2 and La4Ni5Al2 are not iso-structural. La4Co5Al2 crystallizes in space group Pnnm, Z ​= ​2, a ​= ​8.2997(11), b ​= ​13.5982(15), c ​= ​4.1160(6) Å. La4Ni5Al2 adopts a site exchange variant of Ca4Ni4Ge3 structure: Cmcm, Z ​= ​4, a ​= ​4.1848(6), b ​= ​10.3177(13), c ​= ​21.033(2) Å. Structural peculiarity of all the compounds are infinite corrugated M/Al layers between which La atoms are situated.

Nonlinear Optical and Magnetic Properties of FeII-SCN-HgII Isomers: Centrosymmetric Layers and Chiral Networks

Research on isomers is highly desirable due to their prospective role in better understanding of physicochemical properties of similar systems and further development of multifunctional molecular materials. Iron(II) and tetra(thiocyanato)mercury(II) ions self-assembled in the presence of 2-acetylpyridine (2-acpy) excess to form two {[Fe(2-acpy)][Hg(μ-SCN)4]}n isomers: two-dimensional (2D) centrosymmetric layers with folded ring structural motifs (1) and three-dimensional (3D) chiral networks with right- or left-handed {···Fe-NCS-Hg-SCN···}∞ helixes (2). New methods of designing and synthesizing functional thiocyanate-bridged materials have been proposed. In addition, the similarity between 1 and 2 allowed for the description of subtle changes in IR and UV-visible spectra. Moreover, 2 shows spontaneous resolution, and it crystallizes in the noncentrosymmetric space group P21, leading to the occurrence of nonlinear optical activity in circular dichroism studies and second harmonic generation (SHG). At room temperature, the SH susceptibility for powder sample 2 reached 6.0 × 10-11 esu. Ab initio calculations indicated the electric polarization vector and the crystallographic twofold screw axis pass through the aromatic ring. Magnetic studies for 1 and 2 revealed high-spin iron(II) with zero-field splitting at low temperatures. Analysis of magnetic data gave |D| = 37.45 cm-1, |E/D| = 5.59 cm-1, and ⟨g⟩ = 2.15 for 1, |D| = 36.78 cm-1, |E/D| = 4.92 cm-1, and ⟨g⟩ = 2.18 for 2, and information about the orientation of magnetic anisotropy vectors for both compounds.

Noncentrosymmetric Supramolecular Hydrogen-Bonded Assemblies Based on Achiral Pyrazine-Bridged Zinc(II) Coordination Polymers with Pyrazinedione Derivatives

Reaction of M(OAc)2·xH2O (M, x = Zn, 2 and Co, 4), 1,4-dihydro-5,6-dicyano-2,3-pyrazinedione (H2CN2pyzdione), and pyrazine (pyz) affords two compounds of the same molecular formula {[M(H2O)6][M(CN2pyzdione)2(pyz)]·6H2O}n (M = Zn for 1 and Co for 2) in which discrete units of [M(H2O)6]2+ are linked to one-dimensional chains of [M(CN2pyzdione)2(pyz)]2– via multiple O–H···O hydrogen-bonding interactions and M2+-bound H2O molecules in [M(H2O)6]2+ also serve as linkers of hydrogen-bonded interstitial H2O molecules. Remarkably, 1 crystallizes in the monoclinic crystal system, the similar crystal system and unit cell parameters as 2, but with a space group distinct from 1 and 2, i.e., 1 is the noncentrosymmetric space group C2, whereas 2 is the centrosymmetric space group C2/m. This polar structure for 1 is induced by the presence of alternating arrangements of distinguishable two axial Zn–N bonds within [Zn(CN2pyzdione)2(pyz)]2– chains. Indeed, solid-state circular dichroism spectra of 1 exhibit significant Cotton effects, as evidenced by the polar space group C2. Moreover, these Cotton effects show clear temperature-dependence depending on contents of H2O molecules of 1.

Small Changes, Big Impact: Tungsten Bronzes with Extremely Large Second Harmonic Generation Achieved by the Transition Metal Doping on the B‐Site

AbstractTwo novel transition metal‐doped tungsten bronze oxides, Pb2.15Li0.85Nb4.85Ti0.15O15 (PLNT) and Pb2.15Li0.55Nb4.85W0.15O15 (PLNW), are synthesized by high‐temperature solid‐state reactions. The Rietveld method using the high‐resolution synchrotron radiation indicates that PLNT and PLNW crystallize in the orthorhombic polar noncentrosymmetric space group, Pmn21 (no. 31). As a class of tungsten bronze oxide, PLNT and PLNW retain a unique rigid framework composed of d0 transition metal cation (Ti4+ or W6+)‐doped highly distorted NbO6 octahedra along with the subsequently generated Pb/LiO12 and PbO15 polyhedra. Interestingly, the d0 transition metal‐doped tungsten bronzes, PLNT and PLNW, exhibit extremely large second‐harmonic generation (SHG) responses of 56 and 67 × KH2PO4, respectively. The observed immeasurably strong SHG is mainly attributed to a net polarization originating from the alignment of highly distorted NbO6 octahedra with doped transition metals in the frameworks. It is believed that doping transition metal cations at the B‐site of the tungsten bronze structures should be an innovative strategy to develop novel high‐performance nonlinear optical materials.

Synthesis, crystal structure and dielectric properties of a hybrid dihydrogen arsenate salt: (C9H11N4)H2AsO4

The use of the organic aromatic amine molecule 5-amino-3-methyl-1-phenyl-1H-1,2,4-triazole to synthesize a dihydrogen arsenate hybrid salt leads to a supramolecular structure type. Single crystals of (C9H11N4)H2AsO4 were grown through slow evaporation in solution. The synthesized compound crystallizes in the monoclinic system with the non-centrosymmetric P21 space group according to the following parameters; a = 9.655 (3) Å, b = 4.7090 (15) Å, c = 14.022 (4) Å, β = 108.147 (5)° and Z = 4. The mineral part building from dihydrogen arsenate anions [H2AsO4]− is linked together and to the organic cations [C9H11N4]+ by hydrogen bonds only. The results of Hirshfeld’s analysis show that in all possible molecular contacts, the hydrogen–hydrogen and the oxygen–hydrogen are the most important interaction in the crystal (37.5 and 31.9%, respectively). The Fourier transform infrared (FT-IR) confirms the existence of vibrational modes corresponding to the organic amine molecule and mineral arsenate tetrahedron. The optimized molecular structure and the vibrational spectra were calculated by the density functional theory DFT methods and the semi-empirical PM3 calculations. Dielectric study of this compound has been measured in order to determine the electrical conductivity type giving rise to an activation energy of ΔEσ = 0.17 eV.

K2CdGe3S8: A New Infrared Nonlinear Optical Sulfide

A quaternary metal chalcogenide, namely K2CdGe3S8 (I), is obtained through a high-temperature solid-state approach. Compound I crystallizes with the non-centrosymmetric space group P212121. It features a 2D layer structure with [CdGe3S8] layers consisting of tetrahedral GeS4 and CdS4 units, and counter K+ embedded between the layers. The compound exhibits a powder second-harmonic generation (SHG) response of ~0.1 times that of KH2PO4 (KDP) with phase-matchable character at the laser wavelength of 1064 nm. Remarkably, it has a wide band gap (3.20 eV), which corresponds to a favorable high laser-induced damage threshold of 6.7 times that of AgGaS2. In addition, the calculated birefringence (Δn) is 0.039 at the wavelength of 1064 nm, which satisfies the Δn criteria for a promising infrared NLO material.

Three-Dimensional Perovskite Phase Transition Materials with Switchable Second Harmonic Generation Properties Introduced by Homochiral (1S,4S)-2,5-Diazabicyclo[2.2.1]-heptane.

Switchable second harmonic generation (SHG) materials have potential applications in information storage, signal processing, and so on because they can switch between SHG-on and SHG-off states. In this work, we designed and synthesized three organic-inorganic hybrid Rb halide three-dimensional (3D) perovskite materials [1S,4S 2,5-2.2.1-H2dabch]RbX3·0.5H2O (X = Cl, 1; Br, 2; I, 3) based on the chiral 1S,4S-2,5-diazabicyclo[2.2.1]heptane (1S,4S-2,5-2.2.1-dabch). The selection of homochiral organic cations ensures that the compounds 1∼3 crystallize in the noncentrosymmetric and chiral space group P212121, which further leads to reversible SHG responses of the three compounds. Through differential scanning calorimetry (DSC) and dielectric measurements, it revealed that the phase transition point of the compounds 1∼3 increased with RbCl, RbBr, and RbI. This is because the hydrogen interaction H···X between the inorganic framework [RbX3]n and the organic cation [1S,4S-2,5-2.2.1-H2dabch]2+ is increased with the order of I > Br > Cl. This study can provide an effective molecular design strategy for the exploration and construction of temperature-tunable SHG switching materials.

Energy Level, Crystal Morphology and Fluorescence Emission Tuning in Cocrystals via Molecular-Level Engineering.

Organic donor-acceptor complexes as new organic semiconductor class have attracted wide attention, due to their potential applications in functional optoelectronics. Herein, we present two new charge transfer cocrystals of di-cyanodiazafluorene -perylene (DCPE) and di-cyanodiazaflfluorene-pyrene (DCPY) through a rational cocrystal-engineering strategy. Although they are both 1 : 1 mixed stacking cocrystals with similar chemical structures, the DCPE cocrystal possesses a non-centrosymmetric space group and narrower band gap compared to DCPY cocrystal, because of the non-covalent bonding variation. The electrostatic potential accumulated in the lateral facets leads to highly twisted DCPE nanobelts, and the small band gap causes near infrared fluorescence. Meanwhile, the DCPY crystals with centrosymmetric space groups and weaker intermolecular interactions exhibited an untwisted morphology and red emission. This study will be helpful for the design and understanding of functional cocrystal materials that can be used in flexible micro/nano-mechanics, mechanical energy, and optical devices.

Rational Design of Non-Centrosymmetric Hybrid Halide Perovskites.

Structural non-centrosymmetry in semiconducting organic-inorganic hybrid halide perovskites can introduce functionalities like anomalous photovoltaics and nonlinear optical properties. Here we introduce a design principle to prepare Pb- and Bi-based two- and one-dimensional hybrid perovskites with polar non-centrosymmetric space groups. The design principle relies on creating dissimilar hydrogen and halogen bonding non-covalent interactions at the organic-inorganic interface. For example, in organic cations like I-(CH2)3-NH2(CH3)+ (MIPA), -CH3 is substituted by -CH2I at one end, and -NH3+ is substituted by -NH2(CH3)+ at the other end. These substitutions of two -H atoms by -I and -CH3 reduce the rotational symmetry of MIPA at both ends, compared to an unsubstituted cation, for example, H3C-(CH2)3-NH3+. Consequently, the dissimilar hydrogen-iodine and iodine-iodine interactions at the organic-inorganic interface of (MIPA)2PbI4 2D perovskites break the local inversion symmetries of Pb-I octahedra. Owing to this non-centrosymmetry, (MIPA)2PbI4 displays visible to infrared tunable nonlinear optical properties with second and third harmonic generation susceptibility values of 5.73 pm V-1 and 3.45 × 10-18 m2 V-2, respectively. Also, the single crystal shows photocurrent on shining visible light at no external bias, exhibiting anomalous photovoltaic effect arising from the structural asymmetry. The design strategy was extended to synthesize four new non-centrosymmetric hybrid perovskite compounds. Among them, one-dimensional (H3N-(CH2)3-NH(CH3)2)BiI5 shows a second harmonic generation susceptibility of 7.3 pm V-1 and a high anomalous photovoltaic open-circuit voltage of 22.6 V.

A new series of magnetic and luminescent layered hybrid materials obtained from thianthrene phosphonic acid: M(H2O)PO3-S2C12H7 (M = Cu, Zn) and M(H2O)2(PO2OH-S2C12H7)2 (M = Mn, Co).

Four new metallophosphonates with the chemical formulae M(H2O)PO3-S2C12H7 (M = Cu, Zn) and M(H2O)2(PO2OH-S2C12H7)2 (M = Mn, Co) were synthesized using a hydrothermal route from the original bent rigid thianthrene-2-ylphosphonic acid (TPA). This organic precursor crystallizes in a non-centrosymmetric space group P212121 and presents a unique bent geometry due to the presence of two sulfur atoms in its rigid platform architecture. Obtained as single crystal and polycrystalline powders, the structures of the four hybrid materials were solved using X-ray diffraction on single crystals in a monoclinic P21/c space group. These compounds adopt a lamellar structure consisting of one inorganic subnetwork alternating with a 'sawtooth' double organic -S2C12H7 subnetwork. The inorganic layers of these compounds are made of (PO3C) or partially deprotonated (PO2OHC) tetrahedra connected by the apices to isolated ZnO3(H2O) tetrahedra, Cu2O6(H2O)2 copper dimers and cobalt and manganese MO4(H2O)2 octahedra, where the latter two exhibit an isotype structure. Thermogravimetric analysis was performed to confirm the amount of water molecules present in the formula, to track the dehydration process of the structures, and to evaluate their thermal stability. The magnetic properties of the copper, cobalt, and manganese-based materials were investigated from 2 K to 300 K by using a SQUID magnetometer revealing dominant antiferromagnetic interactions with Weiss temperatures of -8.0, -10, and -1 K, respectively. These magnetic behaviors were further corroborated by first-principles simulations based on Density Functional Theory (DFT). Finally, the absorption and photoluminescence properties of both the ligand and hybrid materials were investigated, revealing diverse excitation and recombination mechanisms. The organic moiety based on thianthrene significantly influenced the absorption and emission, with additional peaks attributed to transition metals. Singlet and triplet states recombination were observed, accompanied by an unidentified quenching mechanism affecting the triplet state lifetime.

Синтез производных N-(5-(метилсульфанил)- 4H-1,2,4-триазол-3-ил)пиридин-2-амина и их 1,2,4-триазиновых предшественников

A solvent-free interaction between 5-cyano-1.2.4-triazines and 5-methylsulfanyl-4H-1,2,4-triazol-3-amines has been studied. The structure of the product of ipso-substitution of cyano-group with the corresponding heterocyclic amine residue has been proven by 1Н NMR and ESI-MS data. Thus, in the 1Н NMR spectra a three-proton singlet at 2.61 ppm is present, which can be interpreted as the signal of the methylsulfanyl group protons. Subsequent transformation of 1,2,4-triazine scaffold of the resulting product into a pyridine one has been successfully per-formed under autoclave conditions. It has been found that methylsulfanyl group undergoes no transformations in both stages of synthesis. This fact is also proven by X-Ray crystallography data of the obtained functionalised bypyridines. According to the X-Ray crystallography data, compound 4 crystallizes as two crystallographically independent molecules in non-centrosymmetric space group P-1 with triclinic system. The crystal structure is formed by numerous intermolecular N∙∙∙H contacts between two crystallographically independent molecules of triazolylpyridine-2-amine. The 1Н NMR spectra of compound 4 contain two doublets of the new pyridine cycle at 7.37 and 7.61 ppm. Thus, properties of 5-methysulfanyl-4H-1,2,4-triazol-3-amine are different from these of its analogue with mercaptogroup at C5 position. Namely, in accordance to our previous results ipso-substitution of C5-cyanogroup of 1,2,4-triazine with moiety of the latter amine is accompanied by desulfurization reaction.

A pair of ionic 1D Cu(II) chain enantiomers simultaneously displaying large second- and third-harmonic generation responses.

By employing enantiomerically pure mono-bidentate N-donors (LR/LS) as chiral bridging ligands to react with Cu(ClO4)2(H2O)6 in CH3CN-DMF mixed solvent, respectively, a pair of ionic one-dimensional (1D) Cu(II) chain enantiomers formulated as {[CuLR(CH3CN)(DMF)H2O](ClO4)2}n/{[CuLS(CH3CN)(DMF)H2O](ClO4)2}n (D-1/L-1) were isolated and structurally characterized, where LR/LS = (-)/(+)-4,5-pinenepyridyl-2-pyrazine. They crystallize in the noncentrosymmetric (NCS) P212121 space group of an orthorhombic system due to the introduction of chiral LR/LS, and the ClO4- groups as counteranions reside in crystal lattices, thus leading to charge separation with large dipole moments in their molecular structures. Based on crystal samples, investigation on their nonlinear optical (NLO) behaviors showed that D-1 and L-1 display simultaneously much larger second- and third-harmonic generation (SHG and THG) responses than their analogues based on the same chiral N-donors (LR/LS) and Cu(NO3)2(H2O)3 with NO3- acting as the coordination group to bind Cu(II) ions. The SHG intensities of D-1/L-1 are 0.62/0.60 × KDP (KH2PO4), and THG intensities of D-1/L-1 are 238/228 × α-SiO2. Our finding indicates that coordination polymers (CPs) with charge separation and NCS structures, i.e., ionic CPs with NCS arrangements are the ideal NLO crystalline materials for the simultaneous observation of large SHG and THG responses, thus providing a new approach to obtain NLO-active CP crystalline materials with high-performance SHG and THG responses.

Temperature and pressure dependence of the Yb valence state in YbMn∼0.17Si∼1.89

Single crystals of the non-stoichiometric YbMn∼0.17Si∼1.89 intermetallic compound were investigated by room-temperature x-ray diffraction as well as by temperature and pressure-dependent x-ray absorption experiments at the Yb L3 edge. The crystal structure can be described in the orthorhombic space group Cmcm or in the non-centrosymmetric P21 monoclinic space group. In both cases, the cell comprises two Yb sites of identical multiplicity with close coordination numbers and interatomic distances. The average Yb valence is found independent of temperature νav ∼ 2.42. Such a low Yb valence is hardly compatible with the occurrence of local magnetism on Yb inferred from a previous study. The pressure dependence of the Yb valence at 10 K does not reveal any first-order transition. The average Yb valence increases continuously under pressure but remains far from trivalency (νav ∼2.63) even under the highest external pressure used of 37 GPa.

Local Polarity-Induced Assembly of Second-Order Nonlinear Optical Materials.

ConspectusSecond-order nonlinear optical (NLO) materials, producing coherent light by the cascaded frequency conversion, are current hot topics in material chemistry and optics, as they play an important role in diverse fields, such as laser technology, precision measurements, and quantum information as well as future space propulsion. The prerequisite for a second-order NLO material is that it must crystallize in a noncentrosymmetric space group, but it tends to be centrosymmetric in terms of thermodynamical stability. Furthermore, it should simultaneously satisfy strict requirements on second-order NLO coefficients, birefringence, optical transmittance windows, crystal growth, and so on. Therefore, it is still an urgent challenge to rationally assemble high-performance second-order NLO materials. In this Account, we first review the significance and background of second-order NLO materials and some strategies to design new second-order NLO materials controllably. After that, we mainly present our recent studies on the rational assembly of second-order NLO materials by the so-called strategy of "local polarity-induced assembly", including: (1) making use of the coordination habit between specific cations like Li+ or Mg2+ and tetrahedral (PO4)3-, (P2O7)4-, and (SO4)2- units to generate the local polarity, and further inducing the assembly of second-order NLO materials of superb optical properties; (2) by virtue of self-condensation of weakly polarizable units, condensation of different weakly polarizable units and partial substitution of O atoms by F or S atoms in weakly polarizable units of tetrahedral MO4 or octahedral MO6 configuration, enhancing the local polarity to induce the assembly of second-order NLO materials; and (3) introducing strongly polarizable units of stereoactive lone pair electrons into π-conjugated systems to afford the local polarity and inducing second-order NLO materials with enhanced NLO responses. Based on this strategy, we successfully assembled a variety of excellent second-order NLO materials and expanded new sources of second-order NLO materials, like fluorooxosilicophosphates, thiosulfates, and borosulfates. Finally, we will conclude the topic and give some prospects for exploring new excellent second-order NLO materials. We believe that the "local polarity-induced assembly" strategy will not only be useful for understanding the structure-property relationships of second-order NLO materials but also provide researchers with insights into obtaining noncentrosymmetric structures that are essential to other functional materials in piezoelectricity, ferroelectricity, and pyroelectricity, etc.

Linear and nonlinear optical properties of trigonal borate crystals K7MIn2−xYbx(B5O10)3 (M = Ca, Sr, Ba; x = 0…2) with isolated B5O10 units

Noncentrosymmetric borates K7MIn2−xYbx(B5O10)3 (M = Ca, Sr, Ba; x = 0…2) were synthesized by the solid state reaction and the crystals were successfully grown by the top seeded solution growth method using the K2O-B2O3-MF2 flux. According to Rietveld refinement, the crystal structure belongs to the noncentrosymmetric R32 space group. Also, the octahedrally coordinated In atoms are located at wide ranges ∼8 Å which may be promising for phosphor and laser applications. Samples with ytterbium show a characteristic emission band in the range of 950–1050 nm related to the 2F5/2 → 2F7/2 transition of Yb3+ ions that is commonly used for laser generation. IR, Raman and absorption spectra were obtained for the samples as well. The short cut edge of UV absorption, SHG intensity comparable with KDP and low concentration quenching of luminescence suggest that the K7MIn2−xYbx(B5O10)3 borates are promising self-frequency doubling materials.

New Insights on the Electronic-Structural Interplay in LaPdSb and CePdSb Intermetallic Compounds.

Multifunctional physical properties are usually a consequence of a rich electronic-structural interplay. To advance our understanding in this direction, we reinvestigate the structural properties of the LaPdSb and CePdSb intermetallic compounds using single-crystal neutron and X-ray diffraction. We establish that both compounds can be described by the non-centrosymmetric space group P63mc, where the Pd/Sb planes are puckered and show ionic order rather than ionic disorder as was previously proposed. In particular, at 300 K, the (h, k, 10)-layer contains diffuse scattering features consistent with the Pd/Sb puckered layers. The experimental results are further rationalized within the framework of DFT and DFT+ embedded DMFT methods, which confirm that a puckered structure is energetically more favorable. We also find strong correspondence between puckering strength and band topology. Namely, strong puckering removes the bands and, consequently, the Fermi surface pockets at the M point. In addition, the Pd-d band character is reduced with puckering strength. Thus, these calculations provide further insights into the microscopic origin of the puckering, especially the correspondence between the band's character, Fermi surfaces, and the strength of the puckering.

Investigation on growth, growth kinetics and characterization of L-valine L-valinium perchlorate monohydrate single crystal

The ultimate focus of this paper is on nucleation and growth kinetics, structural and dielectric behavior of l-valine l-valinium perchlorate monohydrate (LVPM) single crystal. LVPM single crystals were grown by conventional slow evaporation technique at room temperature. Salient nucleation parameters, essential for the growth of good quality crystal were estimated with the help of solubility curve and Classical Nucleation Theory (CNT). Single Crystal X-ray Diffraction (SC-XRD) analysis reveals that the synthesized crystal (LVPM) possesses monoclinic structure with lattice parameters as a = 11.227 Å, b = 5.82 Å, c = 13.08 Å, α = γ = 90º and β = 91º. The above results were also confirmed by powder XRD study. The structure of the grown crystal was analyzed by using SHELXT-2014/7 program. It is found that grown crystal belongs to non-centrosymmetric space group P21. All the functional groups and also carboxyl and amino functional groups of LVPM crystal were identified and confirmed by Fourier Transform Infra-red (FTIR) spectroscopy. The molecular structure of the grown crystal and in particular, the presence of amino group was discussed by using 1H and 13C Nuclear Magnetic Resonance (NMR) spectra. The low values of dielectric constant and dielectric loss at higher frequencies indicate that the grown crystal enhances the Second Harmonic Generation (SHG) efficiency. The activation energy of the grown crystal was estimated as 0.1433 eV from AC conductivity study. Kurtz and Perry powder experiment was performed to explore the Nonlinear Optical (NLO) properties of LVPM and its SHG efficiency was found 1.5 times of KDP (1.5’ KDP). The grown material was also found possessing SHG efficiency nearly five times higher than most of the l-arginine compounds. Since the grown material belongs to non-centrosymmetric group and exhibits improved structural, NLO and dielectric behavior, the material will be useful in optoelectronic devices, fiber optic communication, computing, optical switching, image reconstruction, optical storage technology, 3D-images, etc.