Axial Vertex Research Articles

Chemical Bonding Topology of Metal-Centered Polygonal Wheels: Two-Dimensional Analogues of Metallaboranes Related to Benzene and Cyclopentadienide.

The anion [Au@Ru5(CO)15(μ-CO)4]- has a pentagonal wheel structure that can be derived from a hypothetical pentagonal ruthenium carbonyl cluster Ru5(CO)20 by insertion of a gold atom in the center, thereby splitting the original Ru5 pentagon in Ru5(CO)20 into five AuRu2 triangles. The six electrons used to form 3c-2e bonds in three of the five AuRu2 triangles suggest a relationship to the aromatic sextet of the likewise pentagonal cyclopentadienide anion. Furthermore, the pentagonal wheel framework of [Au@Ru5(CO)15(μ-CO)4]- can be derived from a pentagonal bipyramid, such as that found in the deltahedral borane anion B7H72-, by bringing the two C5 axial vertices together at the center of the equatorial pentagon. Similarly, the hexagonal wheel complexes Ni@P6R6 and Pd@Pd6(μ-N═CtBu2)6 with six triangular faces can be derived from a hexagonal bipyramid, such as that found in the dirhenaborane (η5-Me5C5)2Re2B6H4Cl2, by bringing the two C6 axial vertices together at the center of the equatorial hexagon. A reasonable chemical bonding model for the hexagonal wheel complexes has three-fold symmetry with 3c-2e bonds in three of these six triangular faces analogous to the C═C double bonds in a Kekulé structure of benzene.

Explicit calculation of the two-loop corrections to the chiral magnetic effect with the NJL model

Chiral Magnetic Effect(CME) is usually believed not receiving higher order corrections due to the non-renormalization of AVV triangle diagram in the framework of quantum field theory. However, the CME-relevant triangle, which is obtained by expanding the current-current correlation requires zero momentum on the axial vertex, is not equivalent to the general AVV triangle when taking the zero-momentum limit owing to the infrared problem on the axial vertex. Therefore, it is still significant to check if there exists perturbative higher order corrections to the current-current correlation. In this paper, we explicitly calculate the two-loop corrections of CME within NJL model with Chern-Simons term which ensures a consistent $\mu_5$. The result shows the two-loop corrections to the CME conductivity are zero, which confirms the non-renomalization of CME conductivity.

Deviations from the Most Spherical Deltahedra in Rhenatricarbaboranes Having 2n + 2 Wadean Skeletal Electrons.

Density functional theory studies on the rhenatricarbaboranes C3Bn-4Hn-1Re(CO)3 (n = 7-12) show that the lowest energy polyhedra for n-vertex metallaboranes having 2n + 2 skeletal electrons and sufficiently dissimilar vertex atoms can deviate from the most spherical closo deltahedra predicted by application of the Wade-Mingos rules. Furthermore, the lowest energy structures of these rhenatricarbaboranes are found to avoid C-C edges and have carbon atoms located at degree 4 rather than degree 5 vertices. The lowest energy structures for the 7-vertex C3B3H6Re(CO)3 system all have a central C3B3Re closo deltahedron, namely the pentagonal bipyramid with the rhenium atom at a degree 5 axial vertex and all three carbon atoms at degree 4 equatorial vertices. However, the lowest energy structure for the 8-vertex C3B4H7Re(CO)3 is not the most spherical closo 8-vertex deltahedron, namely the bisdisphenoid, but instead a central C3B4Re hexagonal bipyramid with mutually nonadjacent degree 4 vertices for the carbon atoms. Similarly, the lowest energy 10-vertex C3B6H9Re(CO)3 structures are derived from isocloso deltahedra having three degree 4 vertices for all three carbon atoms rather than from the most spherical 10-vertex closo deltahedron, namely the bicapped square antiprism with only two degree 4 vertices. However, for the 9-vertex C3B5H8Re(CO)3 system, the most spherical closo deltahedron, namely the tricapped trigonal prism, has three mutually nonadjacent degree 4 vertices, which is ideal for the three carbon atoms and thus is the preferred deltahedron. The preferred deltahedron for the 11-vertex C3B7H10Re(CO)3 remains the most spherical closo deltahedron despite having only two degree 4 vertices for the carbon atoms. Furthermore, the six lowest energy 12-vertex C3B8H11Re(CO)3 structures are all based on the regular icosahedron generally favored in polyhedral borane chemistry despite its complete lack of degree 4 vertices for the carbon atoms.

Cobalt(II) complexes with pentadentate Schiff bases 2,6-diacetylpyridine hydrazones: Syntheses and structures

Seven new cobalt(II) complexes based on the Schiff bases, 2,6-diacetylpyridine bis(isonicotinoylhydrazone) (H2L1) and 2,6-diacetylpyridine bis(nicotinoylhydrazone) (H2L2), are synthesized and studied by X-ray diffraction analysis: [Co(H2L1)(NCS)2] · 2.25H2O (I), [Co(H2L2)(NCS)2] · CH3OH (II), [Co(H2L2)(NCS)(H2O)]NCS (III), [Co(H4L1)(NCS)2](NO3)2 · 2H2O (IV), [Co(H4L1)(NCS)2][Co(NCS)4] · 0.75H2O (V), [Co(H4L2)(NCS)2][Co(NCS)4] · 1.75H2O (VI), and [Co(H2L2)(NCS)(CH3OH)]2[Co(NCS)4] · 2CH3OH (VII) (CIF files CCDC 941186 (I), 1457906 (Ia), 1457905 (II), 941187 (III), 1457907 (IV), 1457908 (V), 1457909 (VI), and 941188 (VII)). The organic ligands in the complexes act as pentadentate neutral H2L or doubly protonated (H4L)2+ coordinated through the same set of donor atoms N3O2. In all compounds I–VII, the coordination polyhedron of the Co2+ ion in a complex with the Schiff bases has a shape of a pentagonal bipyramid. The hydrazones are arranged in the equatorial plane of the bipyramid. Its axial vertices are occupied by the nitrogen atoms of the NCS‾ anions in compounds I, II, and IV–VI and by the nitrogen atoms of NCS‾ and oxygen of the water molecule in compound III or methanol in compound VII. The NO 3 - anions or [Co(NCS)4]2‾ complex anions obtained by the reactions are involved along with the NCS‾ anions in the formation of compounds IV–VII.

Structure Characteristic Evaluation of Triclinic and Orthorhombic LiVOPO4 of Cathode Materials in Lithium Ion Batteries

LiVOPO4 has the stable structure result from stable PO4 unit, high potential of 4.0 V compare with LiFePO4 (3.5 V), and it has a theoretical capacity of 166 mAh g-1, which is slightly lower than LiFePO4 (170 mAh g-1). In addition to this, it appears the high theoretical energy density (664 Wh/kg) as against the 578 Wh/kg for LiFePO4. Based on the spatial arrangement of VO6 octahedral and PO4 tetrahedral units, which host the lithium ions in the interstitial sites of the framework, LiVOPO4 exists different crystallographic phases such as α-, β-. γ-. δ-. ε-, ω- LiVOPO4. Triclinic α-LiVOPO4 and orthorhombic β-LiVOPO4among them has magnificent electrochemical performance. VO6 octahedral was consisted of four oxygen atoms in the equatorial and two oxygen atoms at the axial vertices of the octahedron. The oxygen at the axial has different bond length. In this study, we compared the physical properties of triclinic α-LiVOPO4 and orthorhombic β-LiVOPO4., This materials were synthesized by the sol-gel method. The starting materials used vanadium oxide, lithium carbonate, ammonium dihydrogen phosphate. The used precursors measured the DSC (Differential Scanning Calorimeter) to confirm the phase transition temperature. And structure analysis of synthesized LiVOPO4 and impurities formation were confirmed through the XRD measurement. Also, SEM (Scanning Electron Microscopy) and EDS (Energy dispersive X-ray spectroscopy) measured to confirm the particle size of synthesized LiVOPO4 and distribution of atoms. And local structure such as bond length, oxidation state, and parameter of unit cell was confirmed by rietveld refinement and XAFS (X-ray Absorption Fine Structure). The Electrochemical Li ion intercalation performances such as EIS (Electrochemical Impedance spectroscopy), CV (Cyclic Voltammetry), CD (charge-discharge), rate capability also evaluated as the cathodes.

Synthesis and crystal structure of the coordination compound of cadmium diiodide monohydrate with quinoxaline

The coordination compound [CdI2(Quinox)2(H2O)] has been synthesized by the reaction between CdI2 and quinoxaline (Quinox, C8H6N2) in a water–ethanol (1: 5) solution, and its crystal structure has been determined. Crystals are orthorhombic, space group Pnma, a = 13.069(1) A, b = 15.218(1) A, c = 9.423(1) A, V = 1874.0(3) A3, ρcalcd = 2.284 g/cm3, Z = 4. The cadmium atom is located in the plane m and has a distorted trigonal bipyramidal coordination; two crystallographically nonequivalent iodine atoms and the O(H2O) atom are in the equatorial plane, and the two nitrogen atoms of two symmetric Quinox ligands are in the axial vertices (Cd(1)–N(1), 2.490(3) × 2 A; Cd(1)–I(1), 2.7533(6) A; Cd(1)–I(2), 2.7280(7) A). The angles at the cadmium atom are 157.1 (2)° between the axial nitrogen atoms and 107.9(1)°–130.8(1)° between the equatorial atoms (maximum value corresponds to the ICdI angle). The complexes are linked into supramolecular strips via O–H…N hydrogen bonds.

Coordination molecular compounds of cadmium(II) iodide with dimethylpyridines

The reactions of CdI2 with dimethylpyridines (Me2Py is C7H9N) afford complexes CdI2(2,3-Me2Py)2] (I), [CdI2(2,6-Me2Py) (II), and CdI2(3,5-Me2Py)2 (III). The structures of compounds I and II are determined. The crystals of complex I are orthorhombic, space group Pbca, a = 7.930(1) A, b = 15.537(1) A, c = 29.943(1) A, V = 3689.1(5) A3, ρcalcd = 2.090 g/cm3, Z = 8. The crystals of complex II are monoclinic, space group C2/c, a = 14.784(1), b = 11.991(1), c = 17.711(1) A, β = 90.39(1)°, V = 1081.1(2) A3, ρcalcd = 2.908 g/cm3, Z = 4. The structure of compound I is built of discrete neutral complexes [CdI2(2,3-Me2Py)2]. The Cd polyhedron is a distorted tetrahedron (Cd-I 2.289–2.295, Cd-N 2.708–2.734 A, angles N(I)CdN(I) 103.1°-114.8°). Polymer chains [CdI2(2,6-Me2Py)]∞ extended along the direction [100] are observed due to the bridging iodine atoms in structure II. The Cd polyhedron is a trigonal bipyramid containing iodine atoms at the axial vertices (Cd-Iaks 3.040 A) and two iodine atoms and the nitrogen atom of the Me2Py ligand in the equatorial plane Me2Py (Cd-Ieq 2.840 A, Cd-N 2.309 A). The compounds in the solid state are photoluminescent.

Ward–Green–Takahashi identities and the axial-vector vertex

The colour-singlet axial-vector vertex plays a pivotal role in understanding dynamical chiral symmetry breaking and numerous hadronic weak interactions, yet scant model-independent information is available. We therefore use longitudinal and transverse Ward–Green–Takahashi (WGT) identities, together with kinematic constraints, in order to ameliorate this situation and expose novel features of the axial vertex: amongst them, Ward-like identities for elements in the transverse piece of the vertex, which complement and shed new light on identities determined previously for components in its longitudinal part. Such algebraic results are verified via solutions of the Bethe–Salpeter equation for the axial vertex obtained using two materially different kernels for the relevant Dyson–Schwinger equations. The solutions also provide insights that suggest a practical Ansatz for the axial-vector vertex.

Shape adjustment of cable mesh reflector antennas considering modeling uncertainties

Cable mesh antennas are the most important implement to construct large space antennas nowadays. Reflector surface of cable mesh antennas has to be carefully adjusted to achieve required accuracy, which is an effective way to compensate manufacturing and assembly errors or other imperfections. In this paper shape adjustment of cable mesh antennas is addressed. The required displacement of the reflector surface is determined with respect to a modified paraboloid whose axial vertex offset is also considered as a variable. Then the adjustment problem is solved by minimizing the RMS error with respect to the desired paraboloid using minimal norm least squares method. To deal with the modeling uncertainties, the adjustment is achieved by solving a simple worst-case optimization problem instead of directly using the least squares method. A numerical example demonstrates the worst-case method is of good convergence and accuracy, and is robust to perturbations.

CdS formation upon decomposition of Cd(n-BuOCS2)2 in EtOH and DMF and the crystal structure of Cd(Ph3P)(n-BuOCS2)2 · Ph3P

The thermal decomposition of the chelate Cd(n-BuOCS2)2 (I) in EtOH and DMF, either in the absence or in the presence of Ph3P, yields finely disperse CdS particles. Mixed-ligand complex Cd(Ph3P)(n-BuOCS2)2 (II) has been synthesized. Cd(Ph3P)(n-BuOCS2)2 · Ph3P (III) single crystals have been grown. By X-ray crystallography, the crystal structure of III is built of [Cd(Ph3P)(n-BuOCS2)2] mononuclear complex molecules and uncoordinated Ph3P molecules, which reside inside channels formed by complex II molecules. The coordination polyhedron around a Cd atom is a tetragonal pyramid where the base is formed by the four S atoms of the two bidentate chelating ligands n-BuOCS2− and the P atom of the Ph3P ligand is at the axial vertex. In the structure of III, there are supramolecular assemblies of two complex II molecules.

Synthesis, structure, and blue photoluminescence of the coordination chain polymer [Cd2(L)Cl4] n (L = 2-(3,5-dimethylpyrazol-1-yl)-4-methylquinoline)

The complex of CdCl2 with 2-(3,5-dimethylpyrazol-1-yl)-4-methylquinoline (L), Cd2(L)Cl4 (I), is synthesized. According to the X-ray diffraction data, the structure of coordination polymer I is formed by chains in which two crystallographically independent Cd atoms linked by the bridging Cl atoms have different coordination numbers (5 and 6) and different environments. Five Cl atoms form the coordination polyhedron of the Cd(2) atom: a square pyramid (Cd-Cl 2.554(3)–2.689(3) A) completed to a bipyramid by the CI atom at a substantially longer distance of 2.865(4) A. Two Cl atoms and the N atom of quinoline fragment L are arranged in the equatorial plane of the coordination polyhedron of the Cd(1) atom, which is a distorted trigonal bipyramid. The axial vertices are occupied by the N atom of the pyrazole cycle of L and the Cl atom. Five-membered metallocycles CdCN3 are formed upon the coordination of bidentate chelating ligands L. The planes of L of two adjacent chains are parallel (the distances between them are ∼3.5 A), which suggests the π-π interaction between the planes. The luminescence excitation spectrum of compound I has a broad band with λmax = 350 nm. The spectrum of bright blue photoluminescence of compound I (300 K, λexc = 340 nm) contains an intense band with λmax = 420 nm.

Ion-selective properties of 1,8-bis [2-(dihydroxyphosphinyl)phenoxy]-3,6-dioxaoctane (H4L3), synthesis and vibrational spectra of copper and zinc complexes with H4L3, and crystal and molecular structure of [Cu(H4L3)(H2O)3][(H2L3)(H2O)

The ion-selective properties of 1,8-bis[2-(dihydroxyphosphinyl)phenoxy]-3,6-dioxaoctane (H4L3) have been studied and its potentiometric selectivity coefficients have been determined. New complexes [Cu(H4L3)(H2O)3][(H2L3)(H2O)] (I) and Zn(H4L3)(H2L3) · 3H2O, and Cu(H2L3) · 2(H2O) have been synthesized and characterized. The crystal and molecular structure of I has been determined by X-ray crystallography and vibrational spectroscopy. The crystals are monoclinic, a = 10.279(5) A, b = 26.532(13) A, c = 8.399(4) A, β = 99.270(8)°, V = 2260.8(7) A3, Z = 2, space group Cm, R = 0.0347 for 4325 reflections with I > 2σ(I). Ionic compound I is composed of the [Cu(H4L3)(H2O)3]2+ complex cations and [(H2L3)(H2O)]2− anions. In the cation, the Cu2+ cation located in the m plane is bound to a tetragonal pyramidal (TP) array. The equatorial plane of the TP is formed by two phosphoryl oxygen atoms of the podand (Cu(1)-O, 1.921(2) A) and two O atoms of two water molecules (av. Cu(1)-O, 1.981(3) A). The third water molecule is at the axial vertex of the TP at a considerably larger distance (Cu(1)-O, 2.139(3) A). The anion is of the host-guest type. The host is the deprotonated podand (H2L3)2−, and the guest is the water molecule. The latter is bound to the terminal hydroxyl groups of two phosphoryl groups of the podand by two acceptor hydrogen bonds and to two central ether oxygen atoms of the (H2L3)2− anion by one donor bifurcated hydrogen bond. The cations and anions in the structure are linked by hydrogen bonds to form chains parallel to the c axis.

Structures of nitrato-(2-hydroxybenzaldehydo) (2,2′-bipyridyl)copper and nitrato-(2-hydroxy-5-nitrobenzaldehydo)(2,2′-bipyridyl)copper

Nitrato-(2-hydroxy-5-nitrobenzaldehydo)(2,2′-bipyridyl)copper (I) and nitrato-(2-hydroxybenzaldehydo)(2,2′-bipyridyl)copper (II) were synthesized and characterized by X-ray diffraction. The coordination polyhedron of the central copper atom in complex I can be described as a distorted tetragonal pyramid whose base is formed by the phenol and carbonyl oxygen atoms of the monodeprotonated 2-hydroxy-5nitrobenzaldehyde molecule and the nitrogen atoms of the 2,2′-bipyridyl ligand and whose apex is occupied by the oxygen atom of the nitrato group. In the crystal structure, complexes I are linked by the acido ligands and the NO2 groups of the aldehyde molecule into infinite chains. In complex II, the central copper atom is coordinated by 2-hydroxybenzaldehyde, 2,2′-bipyridyl, and the nitrato group, resulting in the formation of centrosymmetric dimers. The coordination polyhedron of the central copper atom can be described as a bipyramid (4 + 1 + 1) with the same base as in complex I. The axial vertices of the bipyramid are occupied by the oxygen atom of the nitrato group and the bridging phenol oxygen atom of the adjacent complex related to the initial complex by a center of symmetry. In the crystal structure, complexes II are hydrogen bonded into infinite chains.

The structures and stabilities of small diarsenic-doped silicon clusters

The structures and stabilities of As2-doped Sin (n=1–7) clusters have been investigated at the B3LYP level of theory, incorporating the 6-311+G∗ basis set. An isosceles triangle is predicted to be the lowest-energy structure of the As2Si cluster, whereas the global minimum of As2Si2 possesses an As–As-butterfly structure. The ground state structures for As2Si3, As2Si4 and As2Si5 are all bipyramids: trigonal, tetragonal and pentagonal, respectively, which could have important applications as building blocks to synthesize silicon nanowires. The most stable isomer of As2Si6 possesses a tricapped trigonal bipyramid structure. The lowest energy structure of As2Si7 can be viewed as a substitutional structure of the tricapped trigonal prism Si9 isomer. In the majority of the lowest energy isomers, the two As atoms tend to be separated from each other, in order to maximize the number of Si–As bonds, and therefore locate at the axial vertex or face-capping atomic positions, especially for As2Si4–As2Si7. According to results of the incremental binding energies, the HOMO–LUMO gaps and the vertical ionization potentials, the As2Si3 and As2Si6 clusters are relatively stable compared to their neighbors. Natural bond orbital analyses suggest that delocalized electrons and multi-centered bonds play an important role in stabilizing the low-energy As2Sin structures.

10.1007/s11173-008-1008-x

The crystal structures of (5-bromosalicylidenethiosemicarbazido)aquacopper(II) sulfato(5-bromosalicylidenethiosemicarbazido)aquacuprate(II) tetrahydrate (I), (5-nitrosalicylidenethiosemicarbazido)dimethylsulfoxide(methanol)copper(II) sulfate (II), and catena(μ-thiocyanato)(5-nitrosalicylidenethiosemicarbazido)copper(II) (III) were determined. In structure I, the independent part of the unit cell contains four water molecules of crystallization and the cation-anion complex [Cu(H2O)(L)][Cu(H2O)(L)(SO4)] containing two nonequivalent copper complexes (A and B). In these, the metal atom coordinates monodeprotonated 5-bromosalicylaldehyde thiosemicarbazone (HL) and water molecules, and in anion B also a sulfate ion. In complex ions A and B, sulfur, azomethine nitrogen, and phenolic oxygen of the salicylidene thiosemicarbazone fragment, and also water molecule form a distorted planar square around the metal atom. The axial vertex of the pyramid in anion B is occupied by the oxygen atom of the monodentate sulfate anion. In structure II, the independent part of the unit cell contains the (5-nitrosalicylidenethiosemicarbazido)dimethylsulfoxide(methanol)copper(II) complex cation and the sulfate anion. The coordination polyhedron of the central atom is a slightly distorted tetragonal pyramid whose base is formed by sulfur, azomethine nitrogen, phenolic oxygen of thiosemicarbazone, and dimethyl sulfoxide oxygen. The axial position is occupied by the methanol oxygen atom. In structure III, the copper atom coordinates 5-nitrosalicylaldehyde thiosemicarbazone and the thiocyanate ion, which combines complexes into infinite polymer chains along the [010] direction. The copper coordination polyhedron in III is a slightly distorted tetragonal pyramid whose base is formed by sulfur, azomethine nitrogen, phenolic oxygen of thiosemicarbazone, and nitrogen of thiocyanate ion, the axial vertex is occupied by sulfur of thiocyanate ion of the neighboring complex.

10.1007/s11173-008-3010-8

A novel complex adduct, diaqua(trinitrato)iron(III) 18-crown-6, [Fe(NO3)3(H2O)2] · 18-crown-6, was synthesized and its crystal structure was studied by X-ray diffraction: space group C2/c, a = 10.073, b = 18.069, c = 25.326 Å, β = 91.51°, Z = 8. The structure was solved by the direct method and refined by the full-matrix least-squares method in the anisotropic approximation to R = 0.076 for 4090 independent reflections (CAD-4 automated diffractometer, λMoKα). The structure contains isolated complex molecule [Fe(NO3)3(H2O)2] and two halves of independent molecules 18-crown-6, one of which is statistically disordered about axis 2, while another one is located around the inversion center and is somewhat disordered with respect to the latter. In the complex molecule, the coordination polyhedron of the Fe3+ cation is a distorted pentagonal bipyramid with five O atoms of three NO 3 − ligands in a base and two O atoms of two water molecules in the axial vertices. The alternating complex molecules and the disordered 18-crown-6 molecules are joined by hydrogen bonds into “thick” infinite chains along the z axis.

Synthesis and crystal structures of binuclear complexes of cobalt(II) and cadmium(II) diisobutyldithiophosphinates with hexamethylenetetramine

Heteroligand complexes [Co2(HMTA)(iso-Bu2PS2)4] (I) (μeff = 4.67 μB) and [Cd2(HMTA)(iso-Bu2PS2)4] (II) have been synthesized. Single crystals of compounds I and II have been obtained. The crystals are monoclinic: a = 32.622(2) A, b = 9.4891(6) A, c = 21.7570(13) A, β = 125.774(1)o, V = 5464.3(6) A,3, Z = 4, ρcalcd = 1.331 g/cm3 for I; a = 34.6092(7) A, b = 9.5595(2) A, c = 22.3473(5) A, β = 127.144(1)o, V = 5893.5(2) A, Z = 4, ρcalcd = 1.355 g/cm3 for II; space group for both complexes C2/c. Structures I and II are based on discrete binuclear molecules. The coordination polyhedra of the Co and Cd atoms are distorted tetragonal pyramids NS4, with the bases formed by four S atoms of two bidentate chelating ligand iso-Bu2PS2− and the axial vertices occupied by N atoms of bidentate bridging HMTA ligand. The character of interaction of the molecules in structures I and II is considered.

Oxonitrates VO(NO3)3 and MoO2(NO3)2 and nitronium and nitrosonium nitratometallates as nitrating agents

Dissolution of vanadium in anhydrous HNO3 followed by exposure of the solution in a dessicator over P2O5 gave liquid vanadyl trinitrate (I). The X-ray diffraction analysis of I was carried out for a single crystal grown on cooling the liquid in a sealed capillary. The structure is composed of VO(NO)3 molecules in which the V atom has an unusually high C.N. 7; it coordinates the terminal O atom and three bidentate nitrate groups to form a distorted pentagonal bipyramid as the coordination polyhedron with the terminal O atom occupying one axial vertex. Using the GAMESS program package, ab initio calculation of the structure of VO (NO3)3 in the liquid phase was carried out. It was shown that in all three physical states, vanadyl trinitrate retains its molecular structure almost invariable. Toluene and naphthalene nitration using I and (NO2)[Fe(NO3)4], NO[Cu(NO3)3], (NO)3/4(NO2)1/4[Zr(NO3)5], and MoO2(NO3)2 proceeds at high rates at low temperatures to give an unusually high para-nitrotoluene percentage in the products as compared with the ortho-isomer. The activity of the studied compounds in the nitration of naphthalene decreases in the series VO(NO3)3 > (NO)3/4(NO2)1/4[Zr(NO3)5] > MoO2(NO3)2.

(Dibenzo-18-crown-6)potassium tetrachloroferrate(III): Synthesis and crystal structure

A new complex [K(Db18C6)]+[FeCl4]− (I) is synthesized and its structure is studied by X-ray diffraction analysis. The crystals are triclinic: space group P $$ \bar 1 $$ , a = 17.998, b = 18.670, c = 19.590 A, α = 106.61°, β = 104.55°, γ = 113.87°, Z = 8. The structure is solved by a direct method and refined by the full-matrix least-squares method in the anisotropic approximation to R = 0.057 by 13 670 independent reflections (CAD-4 automated diffractometer, λMoK α). All the four independent complex cations [K(Db18C6)]+ are host-guest, and in each complex cation the K+ cation is localized in the cavity of the Db18C6 crown ligand. The coordination polyhedron of K+ (coordination number nine) is a distorted hexagonal bipyramid with the base of all six O atoms of the Db18C6 ligand, the axial vertex at the Cl atom of the [FeCl4]− anion, and another bifurcated axial vertex at two Cl atoms of another [FeCL4]− anion. All the four independent [FeCL4]− anions are orientationally disordered and have somewhat distorted tetrahedral structure. In crystal I, the alternating complex cations [K(Db18C6)]+ and [FeCL4]− anions form infinite polymer chains by the K-Cl bonds.

Axial-vector coupling and chiral anomaly in the spectral quark model

We studied the Adler-Bardeen-Bell-Jackiw anomaly in the context of a finite chiral quark model known as the spectral quark model. Within this model, we obtain the general nonlocal form of the axial vertex compatible with a nonvanishing axial coupling, in the chiral limit. The triangle anomaly is computed and we show that the obtained dependence of the axial vertex with the spectral mass is necessary to ensure both finiteness and the correct violation of the chiral Ward-Takahashi identity.