Inversion Center Research Articles

Syntheses and crystal structures of the ethanol, acetonitrile and diethyl ether Werner clathrates bis-(iso-thio-cyanato-κN)tetra-kis-(3-methyl-pyridine-κN)nickel(II).

The reaction of nickel(II)thio-cyanate with 3-methyl-pyridine (3-picoline; C6H7N) in different solvents leads to the formation of crystals of bis-(iso-thio-cyanato-κN)tetra-kis-(3-methyl-pyridine-κN)nickel(II) as the ethanol disolvate, [Ni(NCS)2(C6H7N)4]·2C2H5OH (1), the acetonitrile disolvate, [Ni(NCS)2(C6H7N)4]·2CH3CN (2), and the diethyl ether monosolvate, [Ni(NCS)2(C6H7N)4]·C4H10O (3). The crystal structures of these compounds consist of NiII cations coordinated by two N-bonded thio-cyanate anions and four 3-methyl-pyridine ligands to generate NiN6 octa-hedra with the thio-cyanate groups in a trans orientation. In compounds 1 and 2 these complexes are located on centers of inversion, whereas in compound 3, they occupy general positions. In the crystal structures, the complexes are packed in such a way that cavities are formed in which the solvent mol-ecules are located. Compounds 1 and 2 are isotypic, which is not the case for compound 3. In compounds 1 and 2 the solvate mol-ecules are disordered, whereas they are fully ordered in compound 3. Disorder is also observed for one of the 3-methyl-pyridine ligands in compound 2. Powder X-ray diffraction and IR measurements show that at room temperature all compounds decompose almost immediately into the same phase, as a result of the loss of the solvent mol-ecules.

The local symmetry of trivalent europium ion activated Li4Ca2B8O16 red-emitting phosphors with high color purity and excellent thermal stability

Exploring for red-emitting phosphor materials with supper property plays a key role in the development of white light-emitting diodes (WLEDs). Simultaneously, the crystal structure has a crucial effect on its luminescence properties. In this work, we synthesized a type of new red-emitting Li4Ca2B8O16: Eu3+ phosphor via the solid-state reaction. The phase purity, crystal structure, surface morphology, decay behavior, thermal stability, the correspondence between local symmetry and luminescence properties were investigated in detail. Under the optimal 393 nm excitation, Li4Ca2B8O16: 0.33Eu3+ shows a strong red emission located at 612 nm ascribed to the 5D0→7F2 transition of Eu3+. The calculated Judd-Ofelt parameters (Ω2 and Ω4) have clarified that Eu3+ has lower symmetry without an inversion center, resulting in the high value of R/O (the emission intensity ratio of 5D0→7F2 to 5D0→7F1) of 7.95 at x = 0.33 mol. The Li4Ca2B8O16: 0.33Eu3+ phosphor exhibits a high color purity of 94.99% with the chromaticity coordinates of (0.6547, 0.3449), perfect internal quantum efficiency (99.75%) and excellent thermal stability at high temperature (90.91% at 150 °C). The results indicate that this new Li4Ca2B8O16: Eu3+ phosphor can be used as the potential red component for pc-WLEDs.

Synthesis, Crystal Structure and Hydrogen Bond Properties of {[HNC5H4B(OH)(OCH3)- 4]2PdCl2} New Compound

Bu çalışmada, yeni bileşik {[HNC5H4B(OH)(OCH3)-4]2PdCl2} sentezlendi ve kristal yapısı belirlendi. Bileşik, monoklinik kristal sisteminde P21/n uzay grubunda a=3.8749 (8) Å, b=10.177 (2) Å, c=20.403 (4) Å, α= γ = 90°, β =91.78° ve Z=2 birim hücre parametrelerinde kristallendi. Bileşikteki Pd iyonu inversiyon merkezinde ve dörtlü bir koordinasyona sahiptir. N–Pd–N* ve Cl–Pd–Cl* açıları 180° olduğu için, Pd iyonu kare düzlem geometriye sahiptir. Bileşikteki CH···O, CH···Cl ve π···π etkileşimleri, bc düzleminde ve a ekseni boyunca 3 boyutlu bir yapı oluşturmaktadır.

Crystal structures of two new divalent transition-metal salts of carb-oxy-benzene-sulfonate anions.

Hexa-aqua-nickel(II) bis-(3-carb-oxy-4-hy-droxy-benzene-sulfonate) dihydrate, [Ni(H2O)6][C6H3(CO2H)(OH)SO3]2·2H2O, (I), crystallizes in the triclinic space group P with the nickel(II) aqua complexes on centers of inversion. The carboxyl-ate group is protonated and neither it nor the sulfonate group is involved in direct coordination to the metal ions. The structure consists of alternating layers of inorganic cations and organic anions linked by O-H⋯O hydrogen bonds that also include non-coordinated water mol-ecules of crystallization. The first-row divalent transition-metal salts of this anion are reported as both dihydrates and tetra-hydrates, with two distinct structures for the dihydrates that are both layered but differ in the hydrogen-bonding pattern. Compound (I) represents the second known example of one of these structures. Hexa-aqua-cobalt(II) bis-(3-carb-oxy-benzene-sulfonate) dihydrate, [Co(H2O)6][C6H4(CO2H)SO3]2·2H2O, (II), also crystallizes in triclinic P with the cobalt(II) aqua complexes on centers of inversion. The structure is also built of alternating layers of complex cations and organic anions without direct coordination to the metal by the protonated carboxyl-ate or unprotonated sulfonate groups. A robust O-H⋯O hydrogen-bonding network involving primarily the coordin-ated and non-coordinated water mol-ecules and sulfonate groups directs the packing. This is the first reported example of a divalent transition-metal salt of the 3-carb-oxy-benzene-sulfonate anion.

Optimal algorithms for inverse obnoxious center location problems under the weighted Chebyshev and Hamming cost norms on networks

This article deals with the inverse obnoxious center location problem on general networks in which the edge lengths are modified at the minimum overall cost with respect to given modification bounds such that a predetermined facility point becomes an obnoxious center location under the modified edge lengths on the perturbed network. Exact combinatorial algorithms with linear time complexities are developed for obtaining the optimal solutions of the problem under the weighted Chebyshev, bottleneck-type Hamming and sum-type Hamming cost norms.

Tetra-carbonyldi-μ-chlorido-di-chlorido-bis-(η5-cyclo-penta-dien-yl)diirondigallium(2 Fe-Ga).

The title compound, [Fe2Ga2(C5H5)2Cl4(CO)4], has an iron-gallium bond distance of 2.3028 (3) Å. The gallium atoms are connected by two bridging chlorine atoms, each gallium also has one terminal chlorine. The mol-ecule has an inversion center located between the gallium atoms. The cyclo-penta-dienyl ligand is disordered over two sites with an occupancy of 0.57 (2) for the major occupied site.

Chirality in the Solid State: Chiral Crystal Structures in Chiral and Achiral Space Groups.

Chirality depends on particular symmetries. For crystal structures it describes the absence of mirror planes and inversion centers, and in addition to translations, only rotations are allowed as symmetry elements. However, chiral space groups have additional restrictions on the allowed screw rotations as a symmetry element, because they always appear in enantiomorphous pairs. This study classifies and distinguishes the chiral structures and space groups. Chirality is quantified using Hausdorff distances and continuous chirality measures and selected crystal structures are reported. Chirality is discussed for bulk solids and their surfaces. Moreover, the band structure, and thus, the density of states, is found to be affected by the same crystal parameters as chirality. However, it is independent of handedness. The Berry curvature, as a topological measure of the electronic structure, depends on the handedness but is not proof of chirality because it responds to the inversion of a structure. For molecules, optical circular dichroism is one of the most important measures for chirality. Thus, it is proposed in this study that the circular dichroism in the angular distribution of photoelectrons in high symmetry configurations can be used to distinguish the handedness of chiral solids and their surfaces.

Ferroelectricity in Charge-Ordering Crystals with Centrosymmetric Lattices

The switchability between the two ferroelectric (FE) states of an FE material makes FEs widely used in memories and other electronic devices. However, for conventional FEs, its FE switching only occurs between the two FE states whose spatial inversion symmetry is broken. The search for FE materials is therefore subject to certain limitations. We propose a new type of FEs whose FE states still contain spatial inversion centers. The change in polarization of this new type of FEs originates from electronic transfer between two centrosymmetric FE states under an external electric field. Taking BaBiO3 as an example, we show that charge-ordering systems can be a typical representative of this new type of FEs. Moreover, unlike traditional ferroelectrics, the change in polarization in this new type of FEs is quantum in nature with the direction dependent on the specific FE transition path. Our work therefore not only extends the concept of FEs but may also open up a new way to find multiferroics.

Crystal structure of an indium-salicyl-hydroximate complex cation: [In4(H2shi)8(H2O)6](NO3)4·8.57H2O.

The synthesis and crystal structure for the title compound, hexa-aqua-hexa-kis(μ-2-hy-droxy-benzene-carbo-hydrox-a-mato)bis-(2-hy-droxy-benzene-carbo-hydrox-a-m-ato)tetra-indium(III) tetra-nitrate 8.57-hydrate + unknown solvent, [In4(H2shi)8(H2O)6](NO3)4·8.57H2O·solvent, where H2shi- is salicylhydrox-imate (C7H5NO3), are reported. The complex cation of the structure, [In4(H2shi)8(H2O)6]4+, is a dimer with a step-like topology and possesses an inversion center that relates each [In2(H2shi)4(H2O)3]2+ side of the complex cation. Each InIII ion is seven-coordinate with a penta-gonal-bipyramidal geometry, and the salicyl-hydroximate ligands have a 1- charge as only the oxime oxygen of the ligand is deprotonated. Four inter-stitial nitrate anions maintain the charge balance of the compound. One of the nitrate anions (and its symmetry equivalent) is disordered over two different orientations with an occupancy ratio of 0.557 (7) to 0.443 (7). The inter-stitial solvent water mol-ecules show substantial disorder. Approximately 8.57 water mol-ecules per formula unit were refined as disordered and partially occupied, while a suitable model could not be devised for the other extensively disordered solvent mol-ecules (water and possibly methanol as this was the synthesis solvent). Thus, these latter solvent mol-ecules were instead treated with the SQUEEZE routine [Spek (2015). Acta Cryst. C71, 9-18.] as implemented in the program PLATON, and the procedure corrected for 151 electrons within solvent-accessible voids of 367 Å3.

Poly[bis-(μ2-N,N-di-methyl-formamide-κ2 O:O)bis-(μ4-thio-phene-2,5-di-carboxyl-ato-κ4 O:O':O'':O''')dicobalt(II)

The asymmetric unit of the title three-dimensional metal-organic hybrid compound, [Co2(C6H2O4S)2(C3H7NO)2] n , comprises two cobalt(II) cations, one residing on a twofold axis and the other on a centre of inversion, one thio-phene-2,5-di-carboxyl-ate (tdc2-) ligand and one coordinating di-methyl-formamide (DMF) solvent mol-ecule. Both of the cobalt(II) cations exhibit an octa-hedral coordination environment from the four carboxyl O atoms of the tdc2- anions in a μ 4-κ 1:κ 1:κ 1:κ 1 fashion and two O atoms from DMF. A pair of carboxyl O atoms and one DMF molecule connect the adjacent cobalt(II) cations into an infinite chain, leading to a rod-spacer framework with rhombus-window channels, yet no residual solvent-accessible voids are present because the coordinating DMF molecules are oriented into the potential channels.

Crystal structure of 4,4'-(diazenediyl)dipyridinium nitrate perchlorate.

The title compound, C10H10N4 2+·NO3 -·ClO4 -, was obtained unexpectedly by the reaction of Co(ClO4)2·6H2O and cytidine-5'-monophosphate with 4,4'-azo-pyridine in an aqueous solution of nitric acid. The mol-ecular structure comprises two planar 4,4'-diazenediyldipyridinium dications lying on inversion centres and perchlorate and nitrate anions in general positions. In the crystal, N-H⋯O hydrogen bonds between dications and anions lead to the formation of [232] chains.

Synthesis and characterization of 1,4-di(1H-imidazol-1-yl) butane dihydrate and 1,4-di(1H-2-methylimidazol-1-yl) butane tetrahydrate: A study of the methyl group effect on spectroscopic data, thermal properties, and the crystal structures

Two bis(imidazole) derivatives, 1,4-di(1H-imidazol-1-yl) butane dihydrate (DImB·2H2O) and 1,4-di(1H-2-methylimidazol-1-yl) butane tetrahydrate (DMImB·4H2O were synthesized. The crystallization was performed from an aqueous ethanol by slow evaporation technique. X-ray crystallography was used to confirm the molecular structures of both crystals. The results from crystal structure analysis displayed that DImB·2H2O was crystallized in the orthorhombic crystal system and Pbca space group with a = 14.7805(4) Å, b = 5.22600(10) Å, and c = 15.6110(4) Å. The molecule lies in the center of inversion, making the asymmetric unit consist of half of the parent molecule with one unit of the water molecule, whereas DMImB·4H2O displayed the triclinic crystal system and R-3 space group with a = 21.526(3) Å, b = 21.526(3) Å, and c = 9.3333(12) Å. The molecule lies on a center of inversion, making the asymmetric molecules consist of half of the parent molecule with two units of the water molecules. The effect of replacing hydrogen atoms at C2 of two imidazole rings with the methyl groups on spectroscopic properties was investigated using FTIR, MS, 1H, and 13C NMR. The infrared spectrum demonstrated the presence of water molecules in DMImB·4H2O, which showed a more intense O‒H group peak than DImB·2H2O. The effect of methyl groups was studied on the chemical shifts, multiplicity, and coupling constants of hydrogen atoms, and carbon chemical shifts of imidazole rings. Mass spectra of both compounds showed [M+Na]+ and [2M+Na]+ in positive ion mode (ESI+). In addition, the thermal phase transitions and thermal stability of the bis(imidazole) derivatives were studied using the DSC and TGA/DTG. The crystalline structures of DImB and DMImB recorded and the methyl effect was investigated on the size of molecules, arrangement of molecules in the crystal lattice, lattice planes, solvent void, length, angle, and torsion.

Square skyrmion crystal in centrosymmetric systems with locally inversion-asymmetric layers

We investigate an instability toward a square-lattice formation of magnetic skyrmions in centrosymmetric layered systems. By focusing on a bilayer square-lattice structure with the inversion center at the interlayer bond instead of the atomic site, we numerically examine the stability of the square skyrmion crystal (SkX) based on an effective spin model with the momentum-resolved interaction in the ground state through the simulated annealing. As a result, we find that a layer-dependent staggered Dzyaloshinskii–Moriya (DM) interaction built in the lattice structure becomes the origin of the square SkX in an external magnetic field irrespective of the sign of the interlayer exchange interaction. The obtained square SkX is constituted of the SkXs with different helicities in each layer due to the staggered DM interaction. Furthermore, we show that the interplay between the staggered DM interaction and the interlayer exchange interaction gives rise to a double-Q state with a uniform component of the scalar chirality in the low-field region. The present results provide another way of stabilizing the square SkX in centrosymmetric magnets, which will be useful to explore further exotic topological spin textures.

Bis{[amino-(iminium-yl)meth-yl]urea} tetra-kis-{2-[(di-methyl-amino)(iminium-yl)meth-yl]guanidine} di-μ6-oxido-tetra-μ3-oxido-tetra-deca-μ2-oxido-octa-oxidodeca-vanadium(V) tetra-hydrate.

The title compound, (C4H12N5)4(C2H7N4O)2[V10O28]·4H2O, is a by-product obtained by reacting ammonium metavanadate(V), metformin hydro-chloride and acetic acid in the presence of sodium hypochlorite, at pH = 5. The crystal structure comprises a deca-vanadate(V) anion (V10O28)6- lying on an inversion centre in space group P , while cations and solvent water mol-ecules are placed in general positions, surrounding the anion, and forming numerous N-H⋯O and O-H⋯O hydrogen bonds. Metforminium (C4H12N5)+ and guanylurea (C2H7N4O)+ cations display the expected shape. Inter-estingly, in physiology the latter cation is known to be the main metabolite of the former one. The reported structure thus supports the role of sodium hypochlorite as an oxidizing reagent being able to degrade metformin hydro-chloride to form guanylurea.

The contribution of intermolecular spin interactions to the London dispersion forces between chiral molecules.

Dispersion interactions are one of the components of van der Waals (vdW) forces that play a key role in the understanding of intermolecular interactions in many physical, chemical, and biological processes. The theory of dispersion forces was developed by London in the early years of quantum mechanics. However, it was only in the 1960s that it was recognized that for molecules lacking an inversion center, such as chiral and helical molecules, there are chirality-sensitive corrections to the dispersion forces proportional to the rotatory power known from the theory of circular dichroism and with the same distance scaling law R-6 as the London energy. The discovery of the chirality-induced spin selectivity effect in recent years has led to an additional twist in the study of chiral molecular systems, showing a close relation between spin and molecular geometry. Motivated by it, we propose in this investigation to describe the mutual induction of charge and spin-density fluctuations in a pair A-B of chiral molecules by a simple physical model. The model assumes that the same fluctuating electric fields responsible for vdW forces can induce a magnetic response via a Rashba-like term so that a spin-orbit field acting on molecule B is generated by the electric field arising from charge density fluctuations in molecule A (and vice versa). Within a second-order perturbative approach, these contributions manifest as an effective intermolecular exchange interaction. Although expected to be weaker than the standard London forces, these interactions display the same R-6 distance scaling.

New insight into two penta-coordinated multinuclear copper(II) single-armed salamo-based complexes

With the reactions of a single-armed salamo-based ligand H3L and two kinds of copper(II) salts (Cu(OAc)2·H2O or CuCl2·2H2O) in mixed organic solvents, respectively, two penta-coordinated Cu(II) complexes [Cu2(L)(µ-OAc)]·MeOH (1) and [Cu4(L)2Cl2]·EtOH·CH2Cl2 (2) have been successfully constructed. The precise structures of the two Cu(II) complexes obtained by solvent evaporation method are measured by single crystal X-ray diffraction analyses. The di-nuclear complex 1 crystallizes in triclinic space group P-1, where the main structure is compose of two Cu(II) atoms, one completely deprotonated ligand (L)3− unit, one bridged μ-OAc− counter-anion and one crystallized methanol molecule. The tetra-nuclear complex 2 with an inversion center crystallizes in the same space group as 1 and contains four Cu(II) atoms, two fully deprotonated salamo-based ligand (L)3− units, two bridged Cl− counter-anions, one crystallized dichloromethane and one ethanol molecules. Compared to preceding complexes based on other single-armed salamo-based ligands, the structure of complex 2 reported in this work is unique and has never been found in previous literatures. All of Cu(II) atoms in complexes 1 and 2 are penta-coordinated with the geometries of distorted tetragonal pyramid, and the τ5 value of all Cu(II) atoms have been calculated and all results are less than 0.5. Hirshfeld surfaces analyses of complexes 1 and 2 have been established to explain the interactions of crystal structures, and the corresponding two-dimensional (2D) fingerprint plots have been carried out to quantify the intermolecular interactions. In addition, fluorescence properties of complexes 1 and 2 have been investigated.

Symmetry progression and possible polar metallicity in NiPS3 under pressure

van der Waals solids are ideal platforms for the discovery of new states of matter and emergent properties under external stimuli. Under pressure, complex chalcogenides like MPS3 (M = Mn, Ni, Co, V) host sliding and structural transitions, insulator-to-metal transitions, the possibility of an orbitally-selective Mott state, piezochromism, and superconductivity. In this work, we bring together diamond anvil cell techniques, infrared and Raman scattering spectroscopies, and X-ray diffraction with a detailed symmetry analysis and first-principles calculations to uncover a series of high-pressure phases in NiPS3. Remarkably, we find five different states of matter between ambient conditions and 39 GPa—quite different than in the other MPS3 materials. Even more strikingly, infrared spectroscopy and X-ray diffraction combined with a symmetry analysis reveal both metallicity and loss of the inversion center above ~23 GPa suggesting that NiPS3 may be a polar metal with a P3m1 space group under these conditions and P1 symmetry under maximum compression. In addition to identifying a candidate polar metal ripe for further inquiry, we suggest that pressure may tune other complex chalcogenides into this elusive state.

Lithium-boron-aluminum glasses and glass-ceramics doped with Eu3+: A potential optical thermometer for operation over a wide range of temperatures with uniform sensitivity

• Eu-doped Li 2 O - B 2 O 3 −Al 2 O 3 glasses and glass ceramic were synthesized. • The calculated Judd-Ofelt intensity parameters of these media were ~ 10 −20 cm −1 . • The glass ceramic showed greater emission intensity than the precursor glass. • They are efficient probes for optical thermometry using peak-valley ratio method. • Nearly constant relative sensitivity was obtained over a wide temperature range. In this work, lithium-boron-aluminum (LBA) glasses doped with Eu 3+ were produced by the traditional melting method. These precursor glasses (PG) were heat treated at 400 and 450 °C for 6 h to produce glass-ceramics (GC). The X-ray diffraction measurements showed the formation of a crystalline phase. In the LBA GCs, crystal growth is nucleated at the surface and an increase in the emission intensity of the heat-treated glasses compared with the PG was observed. Spectral analysis of the luminescence indicated that Eu 3+ occupies low-symmetry site (asymmetry ratio ≈ 4) and without an inversion center. The emission spectra were analyzed using Judd-Ofelt theory and the intensity parameters Ω 2 , Ω 4 and Ω 6 were calculated. The values of these parameters were not significantly affected by the heat treatment process. The application of these materials as optical temperature sensors using the valley-peak intensity ratio (VPIR) was investigated using the multi-peak spectral profile of the 5 D 0 → 7 F J luminescence bands of Eu 3+ . We estimated the relative sensitivity, the figure-of-merit of the thermometer, to be as high as 0.40 ± 0.02% K −1 . Interestingly, some VPIR that were explored presented a constant value for the relative sensitivity across the temperature interval used in our experiment (between 312 and 393 K), which is advantageous for sensor operation over a broad temperature range.

Synthesis, crystal structure and Hirshfeld surface analysis of hexa-aqua-nickel(II) bis-(4-hy-droxy-benzoate) dihydrate.

The title compound, [Ni(H2O)6](PHB)2·2H2O (1) (PHB = 4-hy-droxy-benzoate, C7H5O3), was obtained by the reaction of NiCl2, 4-hy-droxy-benzoic acid (PHBA) and mono-ethano-lamine in aqueous ethanol solution. The NiII ion is coordinated by six water mol-ecules and is located on an inversion center. The outer coordination sphere in the asymmetric unit comprises one PHB anion and one water mol-ecule, i.e. the compound is a salt and a hydrate consisting of three components. In the crystal, the components are packed into an inter-molecular network stabilized by O-H⋯O hydrogen bonds. A comprehensive Hirshfeld surface analysis was carried out to investigate the inter-molecular inter-actions in detail.

Synthesis and crystal structure of di-aqua-(1,4,8,11-tetra-aza-cyclo-tetra-deca-ne)zinc(II) bis-(hydrogen 4-phospho-natobiphenyl-4'-carboxyl-ato)(1,4,8,11-tetra-aza-cyclo-tetra-deca-ne)zinc(II).

In the asymmetric unit of the title compound, trans-di-aqua-(1,4,8,11-tetra-aza-cyclo-tetra-decane-κ4 N 1,N 4,N 8,N 11)zinc(II) trans-bis-(hydrogen 4-phospho-natobiphenyl-4'-carboxyl-ato-κO)(1,4,8,11-tetra-aza-cyclo-tetra-decane-κ4 N 1,N 4,N 8,N 11)zinc(II), [Zn(C10H24N4)(H2O)2][Zn(C13H9O5P)2(C10H24N4)], both Zn atoms lie on crystallographic inversion centres and the atoms of the macrocycle in the cation are disordered over two sets of sites. In both macrocyclic units, the metal ions possess a tetra-gonally elongated ZnN4O2 octa-hedral environment formed by the four secondary N atoms of the macrocyclic ligand in the equatorial plane and the two trans O atoms of the water mol-ecules or anions in the axial positions, with the macrocyclic ligands adopting the most energetically favourable trans-III conformation. The average Zn-N bond lengths in both macrocyclic units do not differ significantly [2.112 (12) Å for the anion and 2.101 (3) Å for the cation] and are shorter than the average axial Zn-O bond lengths [2.189 (4) Å for phospho-nate and 2.295 (4) Å for aqua ligands]. In the crystal, the complex cations and anions are connected via hydrogen-bonding inter-actions between the N-H groups of the macrocycles, the O-H groups of coordinated water mol-ecules and the P-O-H groups of the acids as proton donors, and the O atoms of the phospho-nate and carboxyl-ate groups as acceptors, resulting in the formation of layers lying parallel to the (110) plane.