Possess Inversion Symmetry Research Articles

Growth and characterization of nitrophenol complexes with piperazine and pyridine derivatives

1-amino-4-methyl piperazine bis (4-nitrophenol) (1A4MP4N) and 2-amino-5-methyl pyridinium 4-nitrophenolate 4-nitrophenol (2A5MP4N) have been grown as single crystals using slow evaporation solution growth technique at room temperature. The grown crystals were characterized by single crystal X-ray diffraction and its lattice parameters were determined. 1A4MP4N and 2A5MP4N were crystallized in monoclinic crystal system with P21/n and Cc space group respectively. In 1A4MP4N, piperazine ring possesses inversion symmetry and has a chair conformation. Piperazine ring linked to 4-nitrophenol molecule through O3-H3D···N2 hydrogen bond forms C(5) chain motif. In 2A5MP4N, N1 atom in 2-amino-5-methyl pyridinium cation is connected with 4-Nitrophenolate anion through N1-H1···O11 hydrogen bond thus forms C(12) chain motif. Hirshfeld surface mapping analysis is carried out for both crystal structures. The fingerprint plot for H···H intermolecular contacts cover a major portion (41 %) of the Hirshfeld area of 1A4MP4N and O···H (35.7%) intermolecular contacts play a major role in 2A5MP4N. The Taucs plot reveals that band gaps of 1A4MP4N and 2A5MP4N are 2.66 eV and 5.18 eV respectively. From Z-scan technique the third order nonlinear optical susceptibility is found to be χ3 = 1.21322 × 10−9 esu and 1.75752 × 10−9 for both crystals.

A new tetra-kis-substituted pyrazine carb-oxy-lic acid, 3,3',3'',3'''-{[pyrazine-2,3,5,6-tetra-yltetra-kis(methyl-ene)]tetra-kis-(sulfanedi-yl)}tetra-propionic acid: crystal structures of two triclinic polymorphs and of two potassium-organic frameworks.

Two polymorphs of the title tetra-kis-substituted pyrazine carb-oxy-lic acid, 3,3',3'',3'''-{[pyrazine-2,3,5,6-tetra-yltetra-kis-(methyl-ene))tetra-kis-(sulfanedi-yl]}tetra-propionic acid, C20H28N2O8S4, (H4L1), have been obtained, H4L1_A and H4L1_B. Each structure crystallized with half a mol-ecule in the asymmetric unit of a triclinic P unit cell. The whole mol-ecules are generated by inversion symmetry, with the pyrazine rings being located about inversion centers. The crystals of H4L1_B were of poor quality, but the X-ray diffraction analysis does show the change in conformation of the -CH2-S-CH2-CH2- side chains compared to those in polymorph H4L1_A. In the crystal of H4L1_A, mol-ecules are linked by two pairs of O-H⋯O hydrogen bonds, enclosing R 2 2(8) ring motifs forming layers parallel to plane (100), which are linked by C-H⋯O hydrogen bonds to form a supra-molecular framework. In the crystal of H4L1_B, mol-ecules are also linked by two pairs of O-H⋯O hydrogen bonds enclosing R 2 2(8) ring motifs, however here, chains are formed propagating in the [001] direction and stacking up the a-axis. Reaction of H4L1 with Hg(NO3)2 in the presence of a potassium acetate buffer did not produce the expected binuclear complex, instead crystals of a potassium-organic framework were obtained, poly[(μ-3-{[(3,5,6-tris-{[(2-carb-oxy-eth-yl)sulfan-yl]meth-yl}pyrazin-2-yl)meth-yl]sulfan-yl}propano-ato)potassium], [K(C20H27N2O8S4)] n (KH3L1). The organic mono-anion possesses inversion symmetry with the pyrazine ring being located about an inversion center. A carb-oxy H atom is disordered by symmetry and the charge is compensated for by a potassium ion. A similar reaction with Zn(NO3)2 resulted in the formation of crystals of a dipotassium-organic framework, poly[(μ-3,3'-{[(3,6-bis-{[(2-carb-oxy-eth-yl)sulfan-yl]meth-yl}pyrazine-2,5-di-yl)bis(methyl-ene)]bis-(sulfanedi-yl)}dipropionato)dipotassium], [K2(C20H26N2O8S4)] n (K2H2L1). Here, the organic di-anion possesses inversion symmetry with the pyrazine ring being located about an inversion center. Two symmetry-related acid groups are deprotonated and the charges are compensated for by two potassium ions.

Ethylene Glycol Dihedral Angle Dynamics: Relating Molecular Conformation to the Raman Spectrum of the Liquid.

The central OCCO dihedral of the ethylene glycol (EG) molecule exists in both trans and gauche geometries in the liquid. The presence of the trans conformer had been inferred from the Raman spectra by interpreting the occurrence of bands in the Raman spectra that were absent in the infrared as evidence for inversion symmetry and hence the trans conformation. The validity of this interpretation is questionable as not all conformations of the EG molecule, where the OCCO dihedral is trans, possess inversion symmetry. We show here that the resolution of the apparent paradox is intimately related to the conformation and dynamics of not just the central OCCO but also the two terminal dihedrals of the EG molecule. Using ab initio molecular dynamics simulations, we show that changes in conformation associated with the three dihedral angles are not infrequent; a number of events are observed during the course of the simulations allowing for a straightforward estimate of the kinetic parameters. More importantly, these parameters allow us to address and resolve the problems in interpreting the Raman spectra and consequently relate molecular conformation to the Raman spectrum of the EG molecule in the liquid state.

Large Rashba unidirectional magnetoresistance in the Fe/Ge(111) interface states

The structure inversion asymmetry at surfaces and interfaces gives rise to the Rashba spin-orbit interaction (SOI), that breaks the spin degeneracy of surface or interface states. Hence, when an electric current runs through a surface or interface, this Rashba effect generates an effective magnetic field acting on the electron spin. This provides an additional tool to manipulate the spin state in materials such as Si and Ge possessing inversion symmetry in their bulk form. The existence of Rashba states could be demonstrated by photoemission spectroscopy at the interface between different metals and Ge(111) and by spin-charge conversion experiments at the Fe/Ge(111) interface even though it is made of two light elements. In this paper, we identify the fingerprint of the Rashba states at the Fe/Ge(111) interface by magnetotransport measurements in the form of a large unidirectional magnetoresistance of up to $0.1%$. From its temperature dependence, we find that the Rashba energy splitting is larger than in pure Ge(111) subsurface states.

Crystal structures of [(μ2-L1)di-bromidodicopper(II)] dibromide and poly[[(μ2-L1)diiodido-dicopper(I)]-di-μ-iodido-dicopper(I)], where L1 is 2,5,8,11,14,17-hexa-thia-[9.9](2,6,3,5)-pyrazino-phane.

The reaction of the hexa-thia-pyrazino-phane ligand, 2,5,8,11,14,17-hexa-thia-[9.9](2,6,3,5)-pyrazino-phane (L1), with copper(II) dibromide led to the formation of a binuclear complex, [μ2-2,5,8,11,14,17-hexa-thia-[9.9](2,6,3,5)-pyrazino-phane]bis-[bromi-docopper(II)] dibromide, [Cu2Br2(C16H24N2S6)]Br2, (I). The complex possesses inversion symmetry with the pyrazine ring being situated about a center of symmetry. The ligand coordinates to the copper(II) atom in a bis-tetra-dentate manner and the copper atom has a fivefold NS3Br coordination environment with a distorted shape. The reaction of ligand L1 with copper(I) iodide also gave a binuclear complex, which is bridged by a Cu2I2 unit to form a two-dimensional coordination polymer, poly[[μ2-2,5,8,11,14,17-hexa-thia-[9.9](2,6,3,5)-pyrazino-phane]tetra-μ-iodido-tetra-copper(I)], [Cu4I4(C16H24N2S6)] n , (II). The binuclear unit possesses inversion symmetry with the pyrazine ring being located about a center of symmetry. The Cu2I2 unit is also located about an inversion center. The two independent copper(I) atoms are both fourfold coordinate. That coordinating to the ligand L1 in a bis-tridentate manner has an NS2I coordination environment and an irregular shape, while the second copper(I) atom, where L1 coordinates in a bis-monodentate manner, has an SI3 coordination environment with an almost perfect tetra-hedral geometry. In the crystal of I, the cations and Br- anions are linked by a number of C-H⋯S and C-H⋯Br hydrogen bonds, forming a supra-molecular network. In the crystal of II, the two-dimensional coordination polymers lie parallel to the ab plane and there are no significant inter-layer contacts present.

(Invited) Mn4+ r-Line Emission Intensity: The Ways of Its Enhancement

Mn4+-based red phosphors are excellent materials to be used for making white LEDs with warm white light. They can be excited by the blue or ultraviolet light to produce red photoluminescence (PL), which is due to the parity and spin-forbidden 2Eg→4A2g transition. However, in many host materials, the intensity of the 2Eg→4A2g zero-phonon line (R-line) is very weak due to the presence of the inversion center of the crystallographic site occupied by the manganese ions. As a result, the red-shifted Stokes components dominate in the emission spectra of such hosts, but this leads to the decreased overlap of the PL spectra with human eye sensitivity curve and decreased intensity of the phosphor (lower lumen/Watt value). Therefore, finding the recipes of enhancement of the R-line intensity and production of brighter phosphors is an important scientific and technological task. In the present work we establish the key parameters responsible for the energy and the intensity of the Mn4+ R-line. Thorough consideration and analysis of the optical spectra for a large number of the Mn4+-based phosphors allowed to draw the following conclusions: The energetic position of the R-line is determined by the “Mn4+-ligand” bonding covalence. Most phosphors for the solid state lighting can be conditionally divided into fluorides and oxides (where the fluorine or oxygen ions are the Mn4+ nearest neighbors, respectively). In ionic fluorides, the Mn-F bonding covalence is weak, which shifts the R-line to higher energies, with the emission wavelength at about 620 nm. In covalent oxides, the stronger Mn-O bonding covalence lowers the energy of the 2Eg state, moving the emission to about 650 nm.In the host crystals, where the Mn4+ ions are located at the sites without inversion center, the R-line intensity is higher compared with the crystals possessing inversion symmetry at the Mn4+ Absence of the inversion center relaxes the parity section rule, which enhances the R-line intensity. As a result, the phosphor luminosity is increased considerably. The inversion center can be removed by cation co-doping, when different cations in the second coordination sphere around the Mn4+ ion remove the inversion center. As an example, a figure below shows the PL spectra of K2SiF6:Mn4+ and NaKSiF6:Mn4+. In the former case the ideal MnF6 octahedron with the inversion center does not allow for high R-line intensity. It the latter case structural disorder and mixed occupation at the K/Na site results in the presence of different cations in the second coordination sphere. As a result, the intensity of the R-line is increased by several times. Therefore, to get the phosphors with increased luminosity one has to focus on the host materials without inversion center at the dopant sites. If, however, the inversion symmetry exists, it should be broken by additional co-doping that would produce structural disorder around the dopant. Figure 1

Imaging of π-conjugated polymer/fullerene blends used in organic photovoltaics by nonlinear photoluminescence emission

A number of image microscopies have been applied to films of π-conjugated polymers and their fullerene blends used in photovoltaic applications; however, they seldom are able to map the polymer/fullerene grain interfaces and detect microscopic defects in the blend films. We have conducted multiphoton microscopy using a 65-fs mode-locked laser at 1.56 μm for spectroscopy and mapping of films of two prototype π-conjugated polymers, namely MEH-PPV and P3HT combined with their blends of PCBM fullerene molecules. The pristine polymer films have shown third harmonic generation and three-photon photoluminescence emission bands that are used for mapping the film topography with micrometer spatial resolution. Since the nonlinear photoluminescence band of the photogenerated charge transfer excitons (CTE) at the polymer/fullerene interfaces in films of polymer/fullerene blends is substantially redshifted compared to that of the excitons in pristine polymers, we could readily map the polymer/fullerene grain interfaces using the nonlinear CTE photoluminescence emission. From the multiphoton imaging of the polymer/fullerene films, we show that the polymer super-grains in MEH-PPV/PCBM are substantially larger than those in P3HT/PCBM, which may be detrimental to charge transport and, in turn, to photovoltaic applications, in agreement with smaller power conversion efficiencies obtained for solar cells based on the former blend. In addition, we also found second harmonic generation emission bands in the MEH-PPV/PCBM blend that result from micron-size embedded defects that do not possess inversion symmetry that forms during the film deposition process at ambient conditions. Multiphoton microscopy and spectroscopy are valuable additions to the tools of organic semiconductor films and devices for investigating the properties and growth of polymer/fullerene blends used for photovoltaic applications with micron spatial resolution.

The crystal structures of the ligand N-(quinolin-8-yl)pyrazine-2-carboxamide and of a tetra-nuclear copper(II) complex.

The title tridentate ligand, C14H10N4O, N-(quinolin-8-yl)pyrazine-2-carboxamide (HL1), crystallizes with three independent mol-ecules (A, B and C) in the asymmetric unit. All three mol-ecules are relatively planar (r.m.s. deviations are 0.068, 0.055 and 0.06 Å, respectively), with the NH H atom forming three-centered (bifurcated) intra-molecular N-H⋯N hydrogen bonds in each mol-ecule. There is also an intra-molecular C-H⋯O contact present in each mol-ecule, involving the benzene ring of the quinoline unit and the amide carboxamide O atom. In the crystal, the three mol-ecules stack in columns with the various mol-ecules being linked by offset π-π inter-actions [inter-centroid distances vary from 3.367 (5) to 3.589 (5) Å], forming layers parallel to the ab plane. The title complex, [Cu4(C42H44N8O16)]·2CH3OH, {hexa-μ-acetato-1:2κ2 O:O';2:3κ8 O:O';3:4κ2 O:O'-di-methanol-1κO,2κO-bis-[N-(quinolin-8-yl)pyrazine-2-carboxamide]-1κ3 N,N',N'';4κ3 N,N',N''-tetra-copper(II) methanol disolvate} (I), was obtained by the reaction of HL1 with Cu(CH3CO2)2. It consists of a tetra-nuclear complex with a central tetra-kis-(μ-acetato)-dicopper paddle-wheel moiety linked on either side via bridging acetato ions to a mononuclear copper(II)-(L1) complex; it crystallizes as a methanol disolvate. The complex possesses inversion symmetry, being located about a center of symmetry situated at the mid-point of the Cu⋯Cu bond of the paddle-wheel moiety. In the crystal, the complex mol-ecules are linked by O-H⋯O hydrogen bonds, forming chains along the [01] direction, which are linked by offset π-π inter-actions [inter-centroid distance = 3.7367 (11) Å] and C-H⋯O hydrogen bonds, leading to the formation of a supra-molecular framework.

Multiphoton Microscopy of π-Conjugated Copolymers and Copolymer/Fullerene Blends for Organic Photovoltaic Applications

Organic photovoltaic (OPV) cells based on π-conjugated copolymer/fullerene blends are devices with the highest power conversion efficiencies within the class of organic semiconductors. Although a number of image microscopies have been applied to films of π-conjugated copolymers and their fullerene blends, seldom have they been able to detect microscopic defects in the blend films. We have applied multiphoton microscopy (MPM) using a 65 fs laser at 1.56 μm for spectroscopy and mapping of films of various π-conjugated copolymers and their fullerene blends. All pristine copolymer films have shown third harmonic generation (THG) and two-photon or three-photon photoluminescence that could be used for mapping the films with micrometer spatial resolution. Since the fullerenes have much weaker THG efficiency than those of the copolymers, we could readily map the copolymer/fullerene blend films that showed interpenetrating micron-sized grains of the two constituents. In addition, we also found second harmonic generation from various micron-sized defects in the films that are formed during film deposition or light illumination at ambient conditions, which do not possess inversion symmetry. The MPM method is therefore beneficial for organic films and devices for investigating the properties and growth of copolymer/fullerene blends for OPV applications.

Models for potential dendritic nitric oxide donors: crystal structures of two 2-nitroanilino precursors and nitric oxide-release behavior of the nitrosated derivatives.

Two molecular precursors to dendrimeric materials that could serve as slow and sustained NO-releasing therapeutic agents have been synthesized and characterized. N1,N4-Bis(2-nitrophenyl)butane-1,4-diamine, C16H18N4O4, (I), crystallizes in a lattice with equal populations of two molecules of different conformations, both of which possess inversion symmetry through the central C-C bond. One molecule has exclusively anti conformations along the butyl chain, while the other has a gauche conformation of the substituents on the first C-C bond. N2,N2-Bis[2-(2-nitroanilino)ethyl]-N1-(2-nitrophenyl)ethane-1,2-diamine, C24H27N7O6, (II), crystallizes with one unique molecule in the asymmetric unit. Neighboring pairs of molecules are linked into dimers via N-H...O amine-nitro hydrogen bonds. The dimers are assembled into layers that stack in an A-B-A-B sequence such that the repeat distance in the stacking direction is over 46 Å. Molecular NO-release agents N1,N4-bis(2-nitrophenyl)-N1,N4-dinitrosobutane-1,4-diamine, C16H16N6O6, (III), and N1-(2-nitrophenyl)-N2,N2-bis{2-[(2-nitrophenyl)(nitroso)amino]ethyl}-N1-nitrosoethane-1,2-diamine, C24H24N10O9, (IV), were prepared via treatment of (I) and (II), respectively, with NaNO2 and acetic acid. The release of NO from solid-phase samples of (III) and (IV) suspended in phosphate buffer was monitored spectroscopically over a period of 21 days. Although (IV) released a greater amount of NO, as expected due to it having three NO moieties for every two in (III), the (IV):(III) ratio of the rate and extent of NO release was significantly less than 1.5:1, suggesting that some combination of electronic, chemical, and/or steric factors may be affecting the release process.

Crystal structure of bis-(1-ethyl-1H-imidazole-κN3)(5,10,15,20-tetra-phenyl-porphyrinato-κ4N)iron(II) tetra-hydro-furan monosolvate.

The title complex, [Fe(C44H28N4)(C5H8N2)2]·C4H8O, possesses inversion symmetry with the iron(II) atom located on a center of symmetry. The metal atom is coordinated in a symmetric octa-hedral geometry by four pyrrole N atoms of the porphyrin ligand in the equatorial plane and two N atoms of 1-ethyl-imidazole ligands in the axial sites; the complex crystallizes with a tetra-hydro-furan solvent mol-ecule. The average Fe-Np (Np is a porphyrin N atom) bond length is 1.995 (3) Å and the axial Fe-NIm (NIm is an imidazole N atom) bond length is 1.994 (2) Å. The two 1-ethyl-imidazole ligands are mutually parallel. The dihedral angle between the 1-ethyl-imidazole plane and the plane of the closest Fe-Np vector is 24.5°. In the crystal, the only significant inter-molecular inter-actions present are C-H⋯π inter-actions.

Phase evolution of lithium intercalation dynamics in 2H-MoS2.

Due to the easy intralayer gliding and weak interlayer van der Waals interaction in transition metal dichalcogenides (TMDs), ion (particularly Li+) intercalation has been used to modify and tune their atomic structures to obtain the desired optical, electronic and chemical properties for future optoelectronics and energy storage applications. A good understanding of the transformative structures during intercalation is critical. In this paper, we investigate the structural transformation dynamics of 2H-MoS2 using electrochemical Li+ intercalation for 2H-MoS2. The introduction of Li+ changes the local symmetry of the MoS2 in favor of the dT phase, clearly indicated by the appearance of Raman peaks of the dT phase. Further Li+ insertion causes the samples to become single-layer-like, characterized by the disappearance of the 32 cm-1 Raman peak. We also observe for the first time that the photoluminescence (PL) emission gradually redshifts with decreasing intensity, followed by eventual vanishing of the PL peak in the dT-MoS2 phase. By the nudged elastic band (NEB) calculations, we propose the 2H-1T-dT phase transition mechanism of MoS2 for Li+ intercalated samples. Our claims are supported by high resolution-transmission electron microscopy (HR-TEM). Our study deepens the understanding of the phase transition dynamics upon lithium intercalation, which is of great value to possible optoelectronic devices based on the phase engineering of TMDs. The new Li-stabilized dT-MoS2 phase does not possess inversion symmetry and may present a feasible way to achieve Weyl state tuning in a single material via phase engineering.

Competing Structural Instabilities in the Ruddlesden–Popper Derivatives HRTiO4 (R = Rare Earths): Oxygen Octahedral Rotations Inducing Noncentrosymmetricity and Layer Sliding Retaining Centrosymmetricity

We report the observation of noncentrosymmetricity in the family of HRTiO4 (R = Eu, Gd, Dy) layered oxides possessing a Ruddlesden–Popper derivative structure, by second harmonic generation and synchrotron X-ray diffraction with the support of density functional theory calculations. These oxides were previously thought to possess inversion symmetry. Here, inversion symmetry is lifted by rotations of the oxygen-coordinated octahedra, a mechanism that is not active in simple perovskites. We observe a competition between rotations of the oxygen octahedra and sliding of a combined unit of perovskite–rocksalt–perovskite blocks at the proton layers. For the smaller rare earth ions, R = Eu, Gd, and Dy, which favor the octahedral rotations, noncentrosymmetricity is present but the sliding is absent. For the larger rare earth ions, R = Nd and Sm, the octahedral rotations are absent, but the sliding at the proton layers is present to optimize the length and direction of hydrogen bonding in the crystal structure. Th...

Crystal structure of 2,5-bis-(4-methyl-pyridin-2-yl)pyrazine chloro-form disolvate.

The heterocyclic molecule in the title solvate, C16H14N4·2CHCl3, possesses inversion symmetry, with the inversion centre situated at the centre of the pyrazine ring. The outer pyridine rings are inclined to the central pyrazine ring by 4.89 (9)°. The compound crystallized as a chloro­form disolvate with the solvent mol­ecules linked to the title mol­ecule by C—H⋯N hydrogen bonds. In the crystal, mol­ecules are further linked by π–π inter­actions involving the pyrazine and pyridine rings of neighbouring mol­ecules [inter-centroid distance = 3.5629 (12) Å; symmetry code: x, y + 1, z + 1].

Bis[2,6-bis-(1H-pyrazol-1-yl)pyridine]-deca-kis-(μ2-3-nitro-benzoato)bis-(3-nitro-benzoato)tetra-dysprosium(III): a linear tetra-nuclear dysprosium compound based on mixed N- and O-donor ligands.

The title compound, [Dy4(C7H4NO4)12(C11H9N5)2] or Dy4(L1)12(L2)2, where HL1 = 3-nitro­benzoic acid and HL2 = 2,6-bis­(1H-pyrazol-1-y1)pyridine, is a linear tetra­nuclear complex possessing inversion symmetry. The two central inversion-related DyIII atoms are seven-coordinate, DyO7, with a monocapped triangular-prismatic geometry. The outer two DyIII atoms are eight-coordinate, DyO5N3, with a bicapped triangular-prismatic geometry. The outer adjacent DyIII atoms are bridged by three L1− carboxyl­ate groups, while the inner inversion-related DyIII atoms are bridged by four L1− carboxyl­ate groups. The L2 ligands are terminally coordinated to the outer DyIII atoms in a tridentate manner. In the crystal, mol­ecules are linked via C—H⋯O hydrogen bonds, forming a two-dimensional network parallel to (001). Two carboxyl­ate O atoms, and N and O atoms of three nitro groups, are disordered over two positions, with a refined occupancy ratio of 0.552 (6):0.448 (6).

1,4,10,13-Tetraoxa-7,16-diazoniacyclooctadecane bis(1H-pyrrole-2-carboxylate)

In the title salt, C12H28N2O4 2+·2C5H4NO2 −, the 1,4,10,13-tetra­oxa-7,16-di­aza­cyclo­octa­decane dication possesses inversion symmetry. In the crystal, the pyrrole-carboxyl­ate anions are linked via pairs of N—H⋯O hydrogen bonds, forming inversion dimers. These dimers are linked by the dications, via N—H⋯O hydrogen bonds, forming chains propagating along [110].

4-Nitrophenol–piperazine (2/1)

In the title adduct, C6H5NO3·0.5C4H10N2, the piperazine ring possesses inversion symmetry and has a chair conformation. Its mean plane makes a dihedral angle of 65.45 (7)° with the 4-nitro­phenol ring. In the crystal, the piperazine ring is linked to two 4-nitro­phenol mol­ecules via O—H⋯N hydrogen bonds. The mol­ecules are also linked via bifurcated N—H⋯(O,O) hydrogen bonds involving the NO2 O atoms, forming a two-dimensional network lying parallel to (102). The networks are linked via C—H⋯O hydrogen bonds, forming a three-dimensional structure.

Adiabatic transformation as a search tool for new topological insulators: Distorted ternary Li2AgSb-class semiconductors and related compounds

We demonstrate that first-principles based adiabatic continuation approach is a very powerful and efficient tool for constructing topological phase diagrams and locating non-trivial topological insulator materials. Using this technique, we predict that the ternary intermetallic series Li$_2M'X$ where $M'$=Cu, Ag, Au, or Cd, and $X$=Sb, Bi, or Sn, hosts a number of topological insulators with remarkable functional variants and tunability. We also predict that several III-V semimetallic compounds are topologically non-trivial. We construct a topological phase diagram in the parameter space of the atomic numbers of atoms in Li$_2M'X$ compounds, which places a large number of topological materials presented in this work as well as in earlier studies within a single unified topological framework. Our results demonstrate the efficacy of adiabatic continuation as a useful tool for exploring topologically nontrivial alloying systems and for identifying new topological insulators even when the underlying lattice does not possess inversion symmetry, and the approaches based on parity analysis are not viable.

NMR-crystallographic study of two-dimensionally self-assembled cyclohexane-based low-molecular-mass organic compounds

Using a combined approach based on scanning electron microscopy, powder X-ray diffraction as well as 1D and 2D multinuclear solid-state NMR spectroscopy, we were able to determine the morphology and the crystal structures for a set of three supramolecular compounds with different hydrogen bonding motifs, namely N,N′-(cyclohexane-trans-1,4-diyl)bis(2,2-dimethylpropanamide) 1, 1,1′-(cyclohexane-trans-1,4-diyl)bis(3-tert-butylurea) 2 and N1,N4-bis(tert-butylcarbamoyl)cyclohexane-trans-1,4-dicarboxamide 3. Based on a complete signal assignment of the 1D solid-state MAS NMR spectra (1H, 13C, 15N) employing 2D HETCOR experiments and a quantitative evaluation of the corresponding resonances, the content of the asymmetric unit was determined to one half of a molecule. Probing the molecular configuration with 1H–1H double-quantum experiments revealed an intramolecular hydrogen bond for compound 3 while 1 and 2 form exclusively intermolecular H-bonds. Ab initio structure solutions applying real space methods with an included close-contact penalty were carried out for all compounds. The following Rietveld refinements led to excellent wRp-values between 2.5% and 4.1%. Compounds 1 and 2 crystallise isostructurally in the monoclinic space group P21/c exhibiting a pseudo-biaxial hydrogen bond motif. 3 crystallises in the triclinic space group P with intermolecular head-to-tail hydrogen bonds connecting the molecules to one-dimensional ribbons. Nevertheless, all compounds grow in a sheet-like morphology with lateral dimensions of several hundred micrometres indicating a fast growth in two dimensions along two of the crystal axes. Since all three molecules possess inversion symmetry cancelling the molecular dipole moment the growth mechanism itself has to be dominantly driven by the formation of hydrogen bond networks.

Tris[4-(dimethyl-amino)-pyridinium][(bis-μ-dichlorido)-deca-aqua-dichlorido-dineodymium(III)] penta-chloride dihydrate.

The title compound, (C7H11N2)3[Nd2Cl4(H2O)10]Cl5·2H2O, consists of three 4-(dimethyl­amino)­pyridinium cations, one of which is disordered about an inversion center, one [Nd2Cl4(H2O)10]2+ dication possessing inversion symmetry, five chloride anions, one of which is disordered over two inversion centers, and two lattice water mol­ecules. The 4-(dimethyl­amino)­pyridinium cations are protonated at the pyridine N atoms and form N—H⋯Cl hydrogen bonds with Cl− counter-ions. The dimethyl­amino groups (C/N/C) lie close to the plane of the pyridinium rings, making dihedral angles of 1.6 (6)° and 6.5 (3)°. In the crystal, the [Nd2Cl4(H2O)10]2+ dications are linked via O—H⋯O and O—H⋯Cl hydrogen bonds, forming sheets lying parallel to the bc plane. These sheets are linked via O—H⋯Cl hydrogen bonds, forming a three-dimensional network. The 4-(dimethyl­amino)­pyridinium cations are located in the cavities and linked to the framework by C—H⋯Cl interactions.