Inversion Axis Research Articles

Spin-to-orbital momentum conversion via electro-optic Pockels effect in crystals

In the present work we have demonstrated a possibility for real-time operation by orbital an-gular momentum (OAM) of optical beams via Pockels effect in solid crystalline materials. Basing on the analysis of optical Fresnel ellipsoid perturbed by conically shaped electric field, we have shown that the point groups of crystals convenient for the conversion of spin angular momentum (SAM) to OAM should contain a three-fold symmetry axis or a six-fold inversion axis. The results of our experimental studies and theoretical simulations of the SAM-to-OAM conversion efficiency carried out for LiNbO3 crystals agree well with each other.

A tetragonal form of dysprosium orthomolybdate at room temperature

In the present tetragonal modification of dysprosium orthomolybdate, Dy(2)(MoO(4))(3), the Dy, one Mo and one O atom are located on a mirror plane with Wyckoff symbol 4e, while another Mo atom is located on a fourfold inverse axis, Wyckoff symbol 2a. A single crystal was selected from a polycrystalline mixture of the Dy(2)O(3)-ZrO(2)-MoO(3) system and was stable at room temperature for at least three months. The structure refinement does not indicate the presence of Zr on the Dy sites (to within 1% accuracy). Thus, the stabilization of the tetragonal form is due to disordered positions for a second O atom and split positions for a third O atom that also maintain the DyO(7) coordination, which is not expected for short Dy-O distances [2.243 (6)-2.393 (5) Å].

RbSn2(PO4)3, a NASICON-type phosphate

The title compound, rubidium ditin(IV) tris­(phosphate), RbSn2(PO4)3, belongs to the NASICON-type family of phosphates and crystallizes in the space group R . The structure is composed of PO4 tetra­hedra (1 symmetry) and two slightly distorted SnO6 octa­hedra, both with 3. symmetry, which are inter­linked through corner-sharing O atoms to form a 3 ∞[Sn2(PO4)3]− framework. The Rb+ cations are located on threefold inversion axes in the voids of this framework and exhibit a coordination number of 12. The crystal studied was twinned by merohedry with a component ratio of 0.503:0.497.

Tris(η5-cyclopentadienyl)hafnium(III)

In the crystal structure of the title compound, [Hf(C5H5)3], three cyclo­penta­dienyl ligands surround the HfIII atom in a trigonal–planar geometry. The mol­ecule lies on a sixfold inversion axis.

Gastric inversion or malposition in 38% of supine anesthetized sated rats

Gastric positional abnormalities developed in three of eight adult female rats which, after fasting overnight, fed on chow pellets until sated. This was judged to have occurred when they paused five minutes. They were then anesthetized with pentobarbital and placed supine. Laparotomy revealed that two (25%) had gastric inversion. Their bulging stomachs had flipped so that most of the greater curvature lay beneath the liver. The spleen, normally covered by the distended stomach, was fully exposed. The axis of inversion was from the LES to the duodenal bulb. One rat's organ (13%) was malpositioned. Its food mass lay along the distal greater curvature within the mid- and distal corpus and antrum, causing the stomach to be primarily horizontal. Comparing these three rats with the five whose stomachs had retained their typical orientations revealed no significant differences by unpaired t-tests, P < 0.05, for either initial body weights (mean ± s.d.) (200 ± 7g vs 191 ± 11g, P = 0.4), or food intake (4.95 ± 0.62g vs 4.63 ± 1.48g, P= 0.8). The gross positional abnormalities likely occurred while administering intraperitoneal anesthesia. For this the rat was held with its head downwards to avoid puncturing the gut, shifting the food mass. However, on being placed supine the distended stomachs of five reverted to their normal positions. Personal support.

Versatile Chemistry of Butadienesulfinate Salts with (Cp*RuCl)4: Tetrameric, Allylsulfene, and Ion-Pair Ruthenium Compounds

Reactions of the tetranuclear (Cp*RuCl)4 (1) with the corresponding butadienesulfinate salts Li[SO2CH═CR′CH═CHR] [R = R′ = H, (2a); R = H, R′ = Me, (2b); R = R′ = Me, (2c)] in THF result in the formation of tetrameric [Cp*Ru(1,2,5-η-SO2CH═CR′CH═CHR)LiCl]4 [R = R′ = H, (3); R = H, R′ = Me, (4); R = R′ = Me, (5)] complexes. Compound 5 has been isolated in two pseudo-polymorphic crystal forms as 5 in space group P421c and as 5·3THF, where there are three molecules of solvated THF per tetramer, in space group I4. Both tetramers occupied a crystallographic 4-fold-roto inversion axis. In both structures the tetramer symmetry is S4, and these distorted cubane-like kernel structures are similar to the one found in compound 1. If potassium butadienesulfinates are used in the reaction with 1 instead of lithium salts 2a−c, mononuclear allylsulfene ruthenium compounds [Cp*Ru(1−5-η-SO2CH═CR′CH═CHR)] [R = R′ = H, (6); R = H, R′ = Me, (7)] are isolated. The analogous compound 8 [R = R′ = Me] was prepared directly from...

Mechanisms for visuomotor adaptation to left–right reversed vision

Behavioral studies suggest that the adaptation of planar arm movements to rotated visual feedback is achieved by the interplay of a gradual process which slowly rotates participants’ responses by up to +/−90°, and a discrete process which changes the responses by means of axis inversion. The processes for adaptation to left–right reversed visual feedback are far less well understood. To clarify this issue, 12 healthy participants performed pointing movements to targets presented in eight different directions, before and during exposure to left–right reversed visual feedback. We quantified the direction of each response 150 ms after movement onset and analyzed the time-course of those directions throughout the adaptation phase, separately for different targets. For targets along the axis of inversion, we only found an increase of response variability, for targets perpendicular to that axis, we observed a discrete 180° change of response direction, and for diagonal targets, we found a discrete 180° change followed by a gradual “backward” shift of 90°. The present findings confirm that sensorimotor adaptation is based on discrete and gradual processes, that both types of processes can occur concurrently, and suggests that those processes can contribute to adaptation in a target-specific fashion.

Sr 10[(PO 4) 5.5(BO 4) 0.5](BO 2): Growth and crystal structure of a strontium phosphate orthoborate metaborate closely related to the apatite-type crystal structure

Single crystals of the strontium phosphate orthoborate metaborate, Sr 10[(PO 4) 5.5(BO 4) 0.5](BO 2), were grown from the melt and investigated by X-ray diffraction (space group P 3 ¯ , No. 147; a=9.7973(8) Å, c=7.3056(8) Å, V=607.29(10) Å 3, Z=1). The crystal structure is closely related to apatite and contains linear metaborate groups, [BO 2] − (point group D ∞h , B–O=1.284(11) Å) taking positions within the channels running along the three-fold inversion axis. Strontium sites are found to be fully occupied while [PO 4] 3− tetrahedra are partially replaced by [BO 4] 5− groups.

Tetrakis(pyridine-2-carboxylato-κ2N,O)palladium(IV) dihydrate

The asymmetric unit of the title compound, [Pd(C6H4NO2)4]·2H2O, consists of a quarter of a neutral PdIV complex and half of a solvent water mol­ecule. In the complex, the PdIV ion is located on a fourfold inversion axis and eight-coordinated in a distorted dodeca­hedral environment by four N and four O atoms from four symmetry-related pyridine-2-carboxyl­ate (pic) anionic ligands. In the crystal, the water mol­ecule is involved in O—H⋯O hydrogen bonding, and weak inter­molecular C—H⋯O hydrogen bonds occur. There are also inter­molecular π–π inter­actions between adjacent pyridine rings, with a centroid–centroid distance of 3.715 (3) Å.

Characterisation of a resolution enhancing image inversion interferometer

Image inversion interferometers have the potential to significantly enhance the lateral resolution and light efficiency of scanning fluorescence microscopes. Self-interference of a point source's coherent point spread function with its inverted copy leads to a reduction in the integrated signal for off-axis sources compared to sources on the inversion axis. This can be used to enhance the resolution in a confocal laser scanning microscope. We present a simple image inversion interferometer relying solely on reflections off planar surfaces. Measurements of the detection point spread function for several types of light sources confirm the predicted performance and suggest its usability for scanning confocal fluorescence microscopy.

A neutral cubane with a ZnII4O4core: tetrabenzoatotetrakis(μ3-hydroxydi-2-pyridylmethanolato)tetrazinc(II)–acetone–methanol (1/2/1)

In the title compound, [Zn4(C11H9N2O2)4(C7H5O2)4]·2(CH3)2CO·CH3OH, the tetra­nuclear mol­ecule lies on a fourfold inversion axis. ZnII ions and μ3-O atoms in the cubane core occupy alternating vertices, forming two inter­penetrating tetra­hedra. Each ZnII ion is further coordinated by two N atoms from two different (py)2C(OH)O ligands (py is pyrid­yl) and one O atom from a monodentate benzoate ligand, forming a distorted octa­hedral environment. The (py)2C(OH)O ligand acts in an η1:η3:η1:μ3 manner, forming two five-membered ZnNCCO chelating rings with two different ZnII atoms sharing a common C—O bond, and an alkoxide-type bond to a third ZnII ion. There are four symmetry-related intra­molecular O—H⋯O hydrogen bonds between the two types of ligands. In the asymmetric unit, there is a half-occupancy acetone solvent mol­ecule and a half-occupancy methanol solvent molecule that lies on a twofold rotation axis.

Structural and Photoluminescence Studies of a Europium(III) Tetrakis(β-diketonate) Complex with Tetrabutylammonium, Imidazolium, Pyridinium and Silica-Supported Imidazolium Counterions

Tetrakis(naphthoyltrifluoroacetonato)lanthanate(III) complexes (Ln = Eu, Gd) containing the cations tetrabutylammonium, [NBu(4)](+); 1-butyl-3-methylimidazolium, [C(4)mim](+); and 1-butyl-3-methylpyridinium, [C(4)mpyr](+), have been prepared and structurally characterized by single-crystal X-ray diffraction. The {EuO(8)} coordination sphere in [NBu(4)][Eu(NTA)(4)] is best described as a distorted dodecahedron, where the metal ion is located at the 4-fold inversion axis with only one crystallographically independent NTA residue. In [C(4)mim][Eu(NTA)(4)] and [C(4)mpyr][Gd(NTA)(4)], the central Ln(3+) ions are coordinated by eight oxygen atoms from four distinct beta-diketonate ligands, in an overall distorted square-antiprismatic geometry. Besides electrostatic interactions, the crystal packing in all three structures is stabilized by offset pi-pi interactions involving the naphthyl rings of neighboring complexes (and, for [C(4)mim][Eu(NTA)(4)] and [C(4)mpyr][Gd(NTA)(4)], neighboring naphthyl/imidazolium and naphthyl/pyridinium rings) and C-H...pi contacts. The photoluminescence properties of the three Eu(III) complexes were studied at room temperature and -259 degrees C by measuring emission and excitation spectra, (5)D(0) emission decay curves, and absolute emission quantum yields. Under ligand excitation (lambda(ex) = 290-395 nm), the quantum yields (room temperature) were in the range 0.72-0.77 for the 1-butyl-3-methylimidazolium salt. An immobilized analogue of this complex was prepared by supporting [Eu(NTA)(4)](-) on an ordered mesoporous silica derivatized with 1-propyl-3-methylimidazolium groups. The disappearance of the intra-4f(6) lines in the excitation spectrum of the supported material indicated an increase in the ligand's sensitization process of the Eu(3+) ions, relative to direct intra-4f(6) excitation. The emission quantum yield measured for the supported material (0.32-0.40, for excitations between 265 and 360 nm) is the highest so far reported for lanthanide-containing ordered mesoporous silicas.

Poly[[tris[μ-2,2′-(butane-1,4-diyldithio)bis(1,3,4-thiadiazole)-κ2N4:N4′]copper(II)] bis(perchlorate)

In the title compound, {[Cu(C8H10N4S4)3](ClO4)2}n, the CuII atom is located on a threefold inversion axis coordinated by six N atoms of symmetry-equivalent 2,2′-(butane-1,4-diyl­dithio)bis­(1,3,4-thia­diazole) ligands in a slightly distorted octa­hedral geometry. Adjacent CuII atoms are linked by the bridging bidentate thia­diazole ligands, which are situated about inversion centers. This leads to the formation of a three-dimensional network structure.

Broadband Conductivities and Fluidities of Fragile Ionic Liquids

Conductivity and fluidity spectra of two room temperature ionic liquids, BMIm-BF4 and HMIm-BF4, taken at different temperatures, are presented and compared with each other. BMIm-BF4 and HMIm-BF4 are short for 1-butyl-3-methyl-imidazolium tetrafluoroborate and 1-hexyl-3-methyl-imidazolium tetrafluoroborate, respectively. In their temperature and frequency dependences, flow of charge and shear flow are found to display close similarities. The distinguishing features of the ion dynamics in fragile ionic liquids as compared to ionic solids are seen to arise from the absence of a network that provides pre-formed vacant sites for the ions to move in. In ionic liquids, the dispersive behaviour of the frequency-dependent conductivity is thus characterized by a temperature-independent end frequency. This key feature, along with Arrhenius activated elementary displacements, is shown to yield the well-known non-Arrhenius temperature dependence of the DC conductivity. In Arrhenius-type plots, DC conductivity and fluidity can be superimposed over the entire temperature range above the glass transition. As a consequence, ionic conduction and shear flow can be traced back to elementary displacements with identical activation energy. On the inverse temperature axis, a small positive shift, Δ=(1/T⊗−1/T), is required for the superposition. Remarkably, fluidities taken at temperature T correspond to conductivities taken at the slightly lower temperature T⊗ not only at DC, but in the entire frequency range studied. Indeed, according to the data as well as to our modelling, the entire conductivity and fluidity spectra superimpose when considered at T⊗ and T, respectively, with identical values of their end angular frequency. The still unknown time correlation function for shear flow is hence expected to have significant features in common with the current density autocorrelation function.

Hexaamminecobalt(III) hexacyanidomanganate(III)

The asymmetric unit of the title compound, [Co(NH3)6][Mn(CN)6], contains one Co and one Mn atom, both lying on threefold inversion axes, and one NH3 and one CN group. The octa­hedral environments around CoII and MnII are generated by symmetry and show very slight deviations from ideal geometry. A three-dimensional network is created by N—H⋯N hydrogen bonds.

Hexakis(dimethyl sulfoxide-κO)chromium(III) trichloride

In the title compound, [Cr(C2H6OS)6]Cl3, each CrIII ion is located on a three-fold inversion axis and is coordinated by six dimethyl­sulfoxide ligands [Cr—O = 1.970 (2)–1.972 (2) Å; O—Cr—O = 88.19 (9) and 91.81 (9)°] in a slightly distorted octa­hedral geometry. The Cl− anions take part in the formation of weak C—H⋯Cl hydrogen bonds, which contribute to the crystal packing stabilization.

On the Coupling of Guided Waves Propagation in Piezoelectric Crystals Subject to Initial Fields

This paper deals with the study of the coupling conditions for propagation of planar guided waves in a piezoelectric semi-infinite plane (called sagittal plane) subject to initial electro-mechanical fields. The piezoelectric material behaves linearly and without attenuation and the waveguide propagates in a normal mode. We suppose that the material is subject to initial electro-mechanical fields. If the sagittal plane is normal to a direct, resp. inverse dyad axis, we derive that the fundamental equations' system decomposes for particular choices of the initial electric field. In this way we obtain mechanical and piezoelectric waves generalizing the classical guided waves from the case without initial fields. Furthermore, we obtain a similar decomposition of mechanical and electrical boundary conditions, which enable us to characterize the obtained guided waves.

(±)-N-[4-Acetyl-5-methyl-5-(4-methylcyclohex-3-enyl)-4,5-dihydro-1,3,4-thiadiazol-2-yl]acetamide

The new title thiadiazole compound, C14H21N3O2S, was semi-synthesized starting from 1-(4-methyl­cyclo­hex-3-en­yl)ethanone, a natural product isolated from Cedrus atlantica essential oil. The stereochemistry has been confirmed by single-crystal X-ray diffraction. The thia­diazo­line ring is roughly planar, although it may be regarded as having a half-chair conformation. The cyclo­hexenyl ring has a half-chair conformation. The most inter­esting feature is the formation of a pseudo-ring formed by four mol­ecules associated through N—H⋯O hydrogen bonds around a fourfold inversion axis, forming an R 4 4(28) motif.

Catena-Poly[[tetrakis(hexamethylphosphoramide-κO)bis(nitrato- κ2O,O′)ytterbium(III)] [silver(I)-di-μ-sulfido-tungstate(VI)(Ag—W)-di-μ-sulfido

The self-assembly of tetra­thio­tungstate(VI), silver sulfide and ytterbium(III) nitrate in hexa­methyl­phospho­ramide (hmp) resulted in a one-dimensional anionic W/S/Ag polymer, {[Yb(NO3)2(C6H18N3OP)4][WAgS4]}n. The central Yb coordination polyhedron in the cationic complex [Yb(hmp)4(NO3)2]+ is a distorted square anti­prism. The [YbO8] assembly has an approximate fourfold inversion axis along the bis­ector of one of the chelating nitrate groups. The polymeric anion {[WS4Ag]−}n presents a distorted linear configuration, with W—Ag—W and Ag—W—Ag angles of 160.81 (7) and 153.41 (7)°, deviating significantly from the ideal 180°. The anionic chains in the title compound are similar to those in {N(C6H5CH2)(C2H5)3[MoS4Ag]}n: they both have a similar wave-like appearance but have different orientations. The former propagate along the c axis, while the latter have two orientations: one parallel to the a axis and the other parallel to the b axis.

Dipyridine[5,10,15,20-tetrakis(4-carboxyphenyl)porphyrinato]cobalt(II) pyridine tetrasolvate monohydrate

In the title compound, [Co(C48H28N4O8)(C5H5N)2]·4C5H5N·H2O, the Co atom lies on a fourfold inversion axis, with the N atom and one C atom of the axial pyridine ligand on a twofold axis. Four pyridine solvent mol­ecules hydrogen bond to the carboxyl­ate groups of the porphyrin. The structure generates a hydro­phobic void that incorporates a disordered solvent water mol­ecule whose O atom lies on another fourfold inversion axis.