Space Group Pna21 Research Articles

PbCN2 – an elucidation of its modifications and morphologies

Abstract Concerning the crystal structure of PbCN2 there exist two different descriptions in the literature, one based on the non-centrosymmetric structure, space group Pna21, another one on the centrosymmetric one in space group Pnma. To elucidate the conditions for their appearance, comprehensive preparative and structural investigations have been conducted which proved the existence of two distinct modifications of PbCN2. A detailed comparison of the two phases is provided. The growth conditions and crystallization processes of the two PbCN2 structures are reported with focus on the influence of the pH value on the products. Depending on the growth conditions several different morphologies arise, namely PbCN2 in needle-shaped and platelet-shaped crystals, as well as pompon-shaped and lance-shaped crystals.

Magnetic structure of magnetoelectric multiferroic HoFeWO6

The polar magnetic oxide, HoFeWO6, is synthesized, and its crystal structure, magnetic structure, and thermodynamic properties are investigated. HoFeWO6 forms the polar crystal structure (space group Pna21 (#33)) due to the cation ordering of W6+ and Fe3+. An antiferromagnetic transition at TN = 17 K is accompanied by a significant change in magnetic entropy with a value of ≈ 5 J kg−1 K−1 in a 70 kOe applied field. Temperature dependent neutron diffraction and magnetization data indicate that the Fe sublattice orders in a strongly non-collinear and non-coplanar arrangement below TN. The Fe ordering initially leads to induced ordering of the Ho spins such that the Ho spins also show behavior of long-range ordering that is evident from the neutron diffraction measurements. Below T ≈ 4 K, the Ho spins order independently and pull the Fe spins toward the direction of Ho spins. A comparison with the magnetic structures and corresponding ferroelectric properties of other members of RMWO6 (R = Y, Sm-Tm, M = Cr, Fe, V) family indicate that the spontaneous polarization is due to the magnetic structure specific to the Fe sublattice through magnetoelectric coupling whereas the polarization is independent of the Ho sublattice.

Thermal anomalies and phase transitions in Pb2Sc2Si2O9 and Pb2In2Si2O9

Abstract Pb2Sc2Si2O9 and Pb2In2Si2O9, respectively, the scandium and indium containing structural analogues of the mineral kentrolite are grown by spontaneous crystallization from a PbO flux. The corresponding polycrystalline powder samples are synthesized by conventional solid-state approach. The compounds are thoroughly characterized using temperature-dependent single crystal and powder X-ray diffraction, heat capacity measurements, second harmonic generation experiments and Raman spectroscopy. At ambient conditions, both compounds crystallize in the non-centrosymmetric Pna21 space group and undergo phase transitions to the centrosymmetric Pbcn space group at elevated temperatures. The Pbcn into Pna21 phase transitions are complemented by the signals of the temperature-dependent second harmonic generation. The specific heat capacity exhibits distinct cusp, supporting the λ-type second-order phase transition. The temperature dependency of some selective Raman modes further complements the findings, showing softening and hardening of the phonons across the phase transitions.

Crystal growth, spectroscopic and theoretical investigation of nonlinear optical 2‑bromo-4-nitroaniline single crystals for NLO and optoelectronic applications

The non-centrosymmetric space group, organic NLO single crystal of 2‑bromo-4-nitroaniline (2B4NA) was prosperously developed by slow evaporation method at 40 °C. Grown 2B4NA was orthorhombic structure with Pna21 space group was recognised by single crystal XRD analysis. An intermolecular contact of 2B4NA was visually analysed by Hirshfeld surface analysis. Active functional groups were confirmed by vibrational FT-IR, FT-Raman spectral analysis. An electron delocalization, hydrogen bond interactions and charge transfer during the chemical reactions of 2B4NA molecule were theoretically studied by NBO and Natural population charge analysis. Electronic transition and optical property were evaluated by UV-Visible spectral analysis and the theoretical spectrum was computed by TD-DFT level with CAM B3LYP approach. HOMO-LUMO and MESP analysis was visualised the chemical reactivity of the molecule. Thermal TG/DTA and mechanical micro hardness analyses were revealed the thermal and mechanical properties of the 2B4NA crystal. Laser beam irradiated LDT analysis was expressed the laser utility limitation of the 2B4NA crystal. The NLO second harmonic generation efficiency was tested by Kurtz Perry powder method.

Polar Lanthanide Anthracene Complexes Exhibiting Magnetic, Luminescent and Dielectric Properties

AbstractMultifunctional molecular materials combining magnetic, luminescent and dielectric properties are attractive for potential applications in spintronics and molecular devices. Herein we report three isostructural mononuclear lanthanide phosphonates, namely, Ln(NO3)3(2‐deap)3 [Ln=Dy (1Dy), Er (2Er), Yb (3Yb), 2‐deap=diethyl anthrancen‐2‐ylphosphonate] which crystallize in polar space group Pna21. Magnetic studies revealed field‐induced slow magnetization relaxation for 1Dy and 3Yb, but not for 2Er down to 1.8 K. Theoretical calculations were conducted to rationalize the magneto‐structural relationship. The photoluminescent properties are also dependent on the lanthanide ion. For 1Dy, luminescence was observed only in the visible region mainly originating from the ligand. For 2Er, luminescence was observed only in the near‐infrared (NIR) region due to a complete energy transfer from the ligand to the ErIII ion. Regarding to 3Yb, luminescence was observed in both visible and NIR regions suggesting a partial energy transfer from the ligand to YbIII ion. Dielectric and piezoelectric measurements were performed on single crystals of 3Yb, which confirmed the presence of high dielectric anisotropy and weak piezoelectric response.

Synthesis, crystal structure, DFT analysis, and DNA studies of a binuclear copper(II) complex with 2,2′-bipyridine and 4-aminobenzoate

A complex containing two discrete molecules, [Cu2(bpy)2(4-Ab)2(NO3)(H2O)] and [Cu2(bpy)2(4-Ab)2(H2O)2] and the lattice including three NO3 anions, one 4-Ab, and three H2O molecules (bpy = 2,2′-bipyridine, 4-Ab = 4-aminobenzoate), was prepared and structurally determined using elemental analyses, IR, EPR, UV-visible, and single-crystal X-ray crystallography. X-ray single-crystal structural studies indicated that the [Cu2(bpy)2(4-Ab)2] unit was present in both the crystallographic units. The complex crystallized in an orthorhombic crystal system with space group Pna21, a = 35.004(3) Å, b = 18.4134(16) Å and c = 12.8659(12) Å. In both crystallographic units, the geometry of the Cu(II) ions is distorted square-pyramidal, where both nitrogen atoms from one bpy and two oxygen atoms from two different p-aminobenzoate ions constitute the square plane and the apical positions are occupied by solvent or nitrate oxygen atoms. The geometry optimization of both units of the binuclear complex was carried out by taking the coordinates of the respective X-ray structures using DFT. The binding studies of the copper(II) complex with calf thymus DNA (CT-DNA) were explored by UV-Vis absorption, fluorescence spectroscopic, and cyclic voltammetric techniques. Also, the cleavage of pBR322 DNA with the binuclear copper(II) complex was studied using the gel electrophoresis method.

Metal–organic frameworks based on a benzimidazole flexible tetracarboxylic acid: Selective luminescence sensing Fe3+, magnetic behaviors, DFT calculations, and Hirshfeld surface analyses

AbstractFour novel metal–organic frameworks constructed from benzimidazole flexible tetracarboxylic acid ligand, 1‐(3,5‐dicarboxylbenzyl)‐1H‐benzimidazole‐5,6‐dicarboxylic acid (H4L), have been prepared by a solvothermal method in the presence of N‐donor ancillary ligands (1,10‐phen = 1,10‐phenanthroline monohydrate, 4,4′‐bibp = 1,4‐di[pyridine‐4‐yl]benzene), namely, [Co2(L)(H2O)3]n (1), {[Cd2(L)(1,10‐phen)(H2O)]·2H2O}n (2), {[Co4(L)2(4,4′‐bibp)2(H2O)7]·4H2O}n (3), and {[Ni4(L)2(4,4′‐bibp)2(H2O)7]·4H2O}n (4). Complexes 1 and 2 show a 3D supramolecular structure and crystallize in monoclinic space group P21/c. Complexes 3 and 4 are isomorphous and crystallize in monoclinic space group Pn, and the respective metals exhibit a similar coordination environment. The H4L ligand behaved in different coordinated modes in Complexes 1–4, namely, μ6‐η1:η1:η1:η0:η1:η1:η1:η1:η1 in 1, μ6‐η1:η1:η1:η1:η1:η1:η2:η1:η1 in 2, there are two coordination modes (μ5‐η0:η1:η1:η0:η1:η1:η1:η0:η1 and μ5‐η1:η1:η1:η0:η1:η1:η1:η0:η1) in 3 and 4. Furthermore, photoluminescence and magnetic properties have been studied. The results indicate that Complexes 3 and 4 show strong antiferromagnetic and ferromagnetic coupling through M–O–C–O–M interactions, respectively. In particular, Complex 2 can sensitively and selectively detect Fe3+ in aqueous systems, and the limit of detection (LOD) values of Fe3+ is ∼0.19 mM.

Preparation, structural, optical and thermal behavior of nonlinear Potassium DL-malato borate hydrate (C8H8BKO10H2O) single crystal

The solvent evaporation technique was adopted for growing a single crystal of potassium DL-malato borate. The crystalline behavior of the grown material was confirmed due to the formation of the distinct sharp peak in the powder XRD spectrum. The material crystallizes into the orthorhombic system with space group Pna21. The structural analysis confirms the occurrence of potassium and boron in the grown crystal. FTIR analysis was carried out to know about various functional groups present in the grown crystal. The cut-off wavelength and bandgap energy of the material were 212 nm and 5.27 eV, respectively. The thermogravimetric analysis was used to analyze the thermal stability of the compound and the material was thermally stable up to 96°C. The second-order nonlinear efficiency of the material was found to be 0.85 times that of KDP crystal.

SnPQ3 (Q = S, Se, S/Se): A Series of Lone-Pair Cationic Chalcogenophosphates Exhibiting Balanced NLO Activity Originating from SnQ8 Units.

Two chalcogenophosphates, SnPS2.86Se0.14 (1) and SnPSe3 (2), are isostructural and crystallize in the monoclinic noncentrosymmetric space group Pn. Their three-dimensional (3D) structures are constructed by [Sn(1)Q8] hendecahedra and [Sn(2)Q8] dodecahedra by sharing Q vertices and edges, leaving cavities for isolated [P2Q6] (Q = S/Se, Se) dimers. A second-harmonic-generation (SHG) measurement indicates that 1 is phase-matchable with a response of approximately 1.2 × AgGaS2 (AGS), which is verified by the theoretical calculation result. The powder sample of 1 exhibits a high laser-induced damage threshold of 3.9 × AGS. For comparison, the known SnPS3 (3) was also synthesized and evaluated using the same method. The chemical composition-NLO performance relationship of 1-3 is also discussed. Dipole moment calculation results suggest that [SnQ8] polyhedra make the main contribution to their excellent nonlinear optical (NLO) performance.

Optical Control of Polarization Switching in a Single-Component Organic Ferroelectric Crystal.

The optical control of polarization switching is attracting tremendous interest because photoirradiation stands out as a nondestructive, noncontact, and remote-control means beyond an electric or strain field. The current research mainly uses various photoexcited electronic effects to achieve the photocontrol polarization, such as a light-driven flexoelectric effect and a photovoltaic effect. However, since photochromism was discovered in 1867, the structural phase transition caused by photoisomerization has never been associated with ferroelectricity. Here, we successfully synthesized an organic photochromic ferroelectric with polar space group Pna21, 3,4,5-trifluoro-N-(3,5-di-tert-butylsalicylidene)aniline, whose color can change between yellow and orange via laser illumination. Its dielectric permittivity and spontaneous polarization can be switched reversibly with a photoinduced phase transition triggered by structural photoisomerization between the enol form and the trans-keto form. To our knowledge, this is the first photoswitchable ferroelectric crystal to achieve polarization switching through a structural phase transition triggered by photoisomerization. This finding paves the way toward photocontrol of smart materials and biomechanical applications in the future.

Spectroscopic characterization of 4,5-diphenyl-2-(2,4,5-trimethoxyphenyl)-1H-imidazole obtained from the condensation of benzyl. Experimental and DFT approach

An experimental and theoretical study of the 4,5-diphenyl-2-(2,4,5-trimethoxyphenyl)-1H-imidazole [DiPhTMImz] spectroscopic properties were carried out. The molecular structure of compound DiPhTMImz was determined by SCXRD; the compound crystallized in the orthorhombic system and Pna21 space group with Z = 4. Fourier transform infrared (FT-IR) spectroscopy, proton, carbon NMR chemical shift, and absorption wavelength analysis have been performed using the DFT/B3LYP method with a 6–311+G(d,p) basis set. The assignments of main vibrational modes were computed with the scaled quantum mechanism (SQM) method. At the same time, the 13C and 1H isotropic chemical shifts were calculated using the gage-invariant atomic orbital (GIAO) method. Besides, the ultraviolet-visible spectrum was predicted by the time-depend DFT approach. On the other hand, mapped molecular electrostatic potential surfaces (MEPS) were performed to estimate the nucleophilic and electrophilic sites in the molecules. The non-covalent intermolecular interactions energies of several molecular pairs were quantified using the PIXEL method and Hirshfeld surface analysis to evaluate the relative contributions of different interactions, such as the N‒H···N or N‒H···O hydrogen bonds in the crystal structure. The stability of the molecule from hyper-conjugative interactions and charge delocalization has been analyzed using natural bond (NBO) analyses.

Structural and magnetocaloric properties in the aeschynite type GdCrWO6 and ErCrWO6 oxides

The crystal structure, microstructure, magnetic phase transitions and magnetocaloric effect (MCE) in KNaSnF6-type GdCrWO6 and ErCrWO6 oxides have been investigated. Both GdCrWO6 and ErCrWO6 oxides are confirmed to crystalize in a polar aeschynite type structure with the space group of Pna21 (No.33, oP36). The grain size remains relatively average according to the SEM graph. Under low magnetic field of 0.1 T, the ErCrWO6 oxide undergoes two successive magnetic transitions around 22 and 7 K, whereas only a weak magnetic transition around 6 K can be noticed. The paramagnetic Curie temperatures θp are fitted to be −17.0 and −16.6 K for GdCrWO6 and ErCrWO6 oxides, respectively, suggesting that the antiferromagnetic (AFM) interaction is dominant at ground state. With the magnetic field change (ΔH) of 0–7 T, the peak value of magnetic entropy change (-ΔSM), refrigeration capacity (RC), relative cooling power (RCP) and 5 K lift temperature-averaged ΔSM (TEC) are figured to be 9.13 J/kg-K, 152 J/kg, 190 J/kg and 9.07 J/kg-K for GdCrWO6 as well as to be 5.3 J/kg-K, 128 J/kg, 161 J/kg and 5.09 J/kg-K for ErCrWO6, respectively. The MCE parameters for GdCrWO6 and ErCrWO6 oxides are comparable with recently reported RE-based MCE oxides, indicating present GdCrWO6 and ErCrWO6 oxides also considerable for cryogenic magnetic refrigeration (MR).

Structural Transformation and Second-Harmonic-Generation Activity in Rare-Earth and d0 Transition-Metal Oxysulfides RE3NbS3O4 (RE = Ce, Sm, Gd, Dy).

Investigations of inorganic compounds with mixed anions have drawn much attention. Here, three oxysulfides, Sm3NbS3O4 (1), Gd3NbS3O4 (2), and Dy3NbS3O4 (3), are obtained by solid-state reactions. 1 and 2 crystallize in the polar space group Pna21, while 3 crystallizes in the centric space group Pnma. The anionic frameworks of 1 and 2 are built by isolated distorted [NbS2O4]7- octahedra, while [NbS3O4]9- is used for 3. 1 and 2 exhibit phase-matchable second-harmonic-generation (SHG) effects of about 0.3 and 0.4 × AGS at 2.1 μm. The [NbS2O4]7- octahedron was first used as a SHG-active motif for nonlinear-optical (NLO) materials. A systematic analysis of the transformation between these crystal structures, NLO performances, and magnetic behaviors, as well as first-principles theoretical studies, is presented. This work enriches the study on relatively rarely explored NLO-active metal oxysulfides.

Optical, electrical, HOMO-LUMO and first-order hyperpolarizability studies on 2-amino-5-bromopyridinium 4-hydroxybenzoate-an organic single crystal for opto-electronic applications

Organic single crystals of 2-Amino-5-bromopyridinium 4-hydroxybenzoate were grown by slow evaporation technique at room temperature. Single crystal XRD confirms that the crystal belongs to orthorhombic system with noncentrosymmetric space group Pna21. Functional groups presents in the synthesized compound were confirmed by FTIR analysis. UV-Vis studies shows that crystal has a lower cutoff wave length at 388 nm with an optical band gap of 2.9 eV. Dielectric studies were carried out to study the charge transport mechanism in the crystal. Photoconductivity measurements were performed. Powder SHG efficiency of the compound was found to be three times the value of KDP.

Hydrothermal Synthesis and Solid-State Laser Refrigeration of Ytterbium-Doped Potassium-Lutetium-Fluoride (KLF) Microcrystals

Hydrothermal methods are used for the first time to synthesize distinct crystallographic stoichiometries within the potassium-lutetium-fluoride phase diagram for applications in solid-state laser refrigeration. Four crystalline phases were synthesized hydrothermally and doped with 10% Yb(III) ions, namely, orthorhombic K2LuF5 (space group Pnma), trigonal KLuF4 (space group P3121), orthorhombic KLu2F7 (space group Pna21), and cubic KLu3F10 (space group Fm3̅m), with each phase exhibiting unique microcrystalline morphologies. Among the four phases, the most significant cooling was observed for the KLuF4 phase, which showed an overall refrigeration of 8.6 ± 2.1 K below room temperature. Laser refrigeration for KLuF4 was measured by observing both the eigenfrequencies of optomechanical cantilevers in vacuum and also the Brownian dynamics of optically trapped microcrystals in water. Cooling was also observed for the first time for the K2LuF5 phase in vacuum based on measurements of the mean luminescence wavelength of Yb(III) ions. Cooling was not observed with the other two phases.

Evolution from sinusoidal to collinear A-type antiferromagnetic spin-ordered magnetic phase transition in Tb1−x Pr x MnO3 solid solution

The present study reports on the structural and magnetic phase transitions in Pr-doped polycrystalline Tb0.6Pr0.4MnO3, using high-resolution neutron powder diffraction (NPD) collected at SINQ spallation source, to emphasize the suppression of the sinusoidal magnetic structure of pure TbMnO3 and the evolution to a collinear A-type antiferromagnetic ordering. The phase purity, Jahn–Teller distortion, and one-electron bandwidth for eg orbital of Mn3+ cation have been calculated for polycrystalline Tb0.6Pr0.4MnO3, in comparison to the parent materials TbMnO3 and PrMnO3, through the Rietveld refinement study from x-ray diffraction data at room temperature, which reveals the GdFeO3 type orthorhombic structure of Tb0.6Pr0.4MnO3 having Pnma space group symmetry. The temperature-dependent zero field-cooled and field-cooled dc magnetization study at low temperature down to 5 K reveals a variation in the magnetic phase transition due to the effect of Pr3+ substitution at the Tb3+ site, which gives the signature of the antiferromagnetic nature of the sample, with a weak ferromagnetic component at low temperature-induced by an external magnetic field. The field-dependent magnetization study at low temperatures gives the weak coercivity having the order of 2 kOe, which is expected due to the canted-spin arrangement or ferromagnetic nature of Terbium ordering. The NPD data for Tb0.6Pr0.4MnO3 confirms that the nuclear structure of the synthesized sample maintains its orthorhombic symmetry down to 1.5 K. Also, the magnetic structures have been solved at 50 K, 25 K, and 1.5 K through the NPD study, which shows an A-type antiferromagnetic spin arrangement having the magnetic space group Pn′ma′.

Evidence for Local Structural Distortion and Mixed States of Fe in <i>β</i>-NaFeO<sub>2</sub>: A Bond Valence Sum Analysis

We have analyzed the crystal structure, interatomic distances and bond valence sums in β-phase of sodium ferrite based on neutron diffraction measurement at room temperature. The Rietveld analysis performed using Pna21 space group obtains smaller lattice constants compared to the previous reports. This discrepancy is attributed to the sodium deficiency. We notice that the Na-O bonds are shortened, while Fe-O bonds are elongated. The calculated bond valence sum around the sodium and the iron ions are 1.08 and 2.64, respectively. This indicates the presence of Fe2+-Fe3+ mixed valence state.

Structural, vibrational, optical properties and theoretical studies of new noncentrosymmetric material: Bis(2-Amino-5-(methylthio)-1,3,4-thiadiazol-3-ium) pentachloroantimonate

A new non-centrosymmetric Sb(III) halide complex with formula (C3H6N3S2)2SbCl5 (complex 1) has been synthesized by reaction between antimony trioxide (Sb2O3) and 2-Amino-5-(methylthio)-1,3,4-thiadiazole (AMT,) in an aqueous solution of hydrochloric acid. Single crystal X-ray diffraction analysis shows that this compound crystallizes in orthorhombic system with the non-centrosymmetric space group Pna21. Its crystal structure consists of isolated (C3H6N3S2)+ cations and square pyramidal shape [SbCl5]2− anions. The anions are disposed to form a polymeric chain in which each subunit is connected to the others through a Cl bridge. The organic cations are connected to these chains via H-bonding N-H…Cl and C-H…Cl. The intermolecular interactions which ensure the cohesion between different entities were analyzed by DFT calculations and Hirshfeld surface analysis. Ab-initio DFT calculations were also used to investigate geometric and electronic properties of complex 1 and AMT. Absorption, photoluminescence and infrared spectroscopy have been carried out. DFT calculations with different functionals have been used to gain a better insight into its vibrational and optical properties and a good agreement was found between experiments and calculations. The thermal stability of compound was studied by thermal analysis.

Chiral crystallization of a zinc(II) complex.

The compound, {6,6'-dimeth-oxy-2,2'-[(4-azaheptane-1,7-di-yl)bis-(nitrilo-meth-an-yl-idyne)]diphenolato}zinc(II) methanol monosolvate, [Zn(C22H27N3O4)]·CH3OH, at 298 K crystallizes in the ortho-rhom-bic space group Pna21. The Zn atom is coordinated by a penta-dentate Schiff base ligand in a distorted trigonal-bipyramidal N3O2 geometry. The equatorial plane is formed by the two phenolic O and one amine N atom. The axial positions are occupied by two amine N atoms. The distorted bipyramidal geometry is also supported by the trigonality index (τ), which is found to be 0.85 for the mol-ecule. In the crystal, methanol solvent mol-ecule is connected to the complex mol-ecule by an O-H⋯O hydrogen bond and the complex mol-ecules are connected by weak supra-molecular inter-actions, so achiral mol-ecules generate a chiral crystal. The Hirshfeld surface analysis suggests that H⋯H contacts account for the largest percentage of all inter-actions.

Novel low-εr MGa2O4 (M = Ca, Sr) microwave dielectric ceramics for 5 G antenna applications at the Sub-6 GHz band

Two novel low-εr gallates MGa2O4 (M = Ca, Sr) have been synthesized via a standard solid-state reaction method. According to the X-ray diffraction results, CaGa2O4 crystallizes in space group Pna21 with an orthorhombic symmetry, while SrGa2O4 belongs to the monoclinic P21/c system. Both ceramics show ever-improving microstructures with the increasing sintering temperature. The optimal microwave dielectric properties (εr = 9.2, Qf = 66,000 GHz, τf =–85 ppm/°C for SrGa2O4 and εr = 10.6, Qf = 15,400 GHz, τf =–58 ppm/°C for CaGa2O4) are obtained when sintered at 1275 °C. A patch antenna is fabricated using SrGa2O4 ceramics as the substrate, which realizes a return loss of –19.94 dB and total efficiency of –1.38 dB (72.8 % in power ratio) at 4.84 GHz. The exceptional performances indicate that SrGa2O4 ceramics are promising candidates for antenna applications at the Sub-6 GHz band.