Calculation of the rotational magnetic moments of the ammonia and water molecules

We calculate the rotational magnetic moments and the corresponding g-factors for water and ammonia. Our results are g_xx = 0.397, g_yy = 0.769 and _zz = 0.345 for water and g_xx = g_yy = 0.69 and g_zz = 0.51 for ammonia. The experimental values are g_xx = 0.585, g_yy = 0.742 and g_zz = 0.666 for water and g_xx = g_yy = 0.56 and g_zz = 0.484 for ammonia.     

EPR probing of bonding and spin localization of the doublet-quartet states in a spin-frustrated equilateral triangular lattice: Cu3(O2C16H23)6·1.2 C6H12

We present high-frequency (34 and 95 GHz) EPR spectroscopic measurements of the magnetic parameters of both the ground state (spin-doublet) and the excited state (spin-quartet) of the model frustrated-spin triangular lattice of Cu₃(O₂C₁₆H₂₃)₆·1.2 C₆H₁₂, containing the Cu₃⁶⁺ core. From 295 down to about 100 K, the EPR spectra from single crystals consist of a well-resolved triplet, but with the central component being overlapped by a single peak. At 4 K, the triplet is replaced by a singlet. The triplet is shown to arise from the quartet state, located at 324 K above the ground state. Its magnetic parameters are: D = –535 G, E = 0, g_// = 2.209, g_⊥ = 2.057 with the parallel direction being the three-fold axis of the Cu₃⁶⁺ core. The singlet is assigned to the S = 1/2 ground state, with g_xx = 2.005, g_yy = 2.050, and g_zz = 2.282. Its hyperfine structure was that from a single Cu nucleus, with A_zz = 157 G, and A_xx = A_yy < 60 G, demonstrating that in the doublet state the unpaired electron is localized on only one of the three Cu²⁺ ions. We ascribe this localization to an antiferromagnetic exchange interaction between Cu₃⁶⁺ cores, with zJ′ = –0.15 K. These results serve as a basis for detailed theoretical calculations of spin dynamics and electronic bonding in a frustrated triangular magnetic lattice. To cite this article: B. Cage et al., C. R. Chimie 6 (2003) 000–000.     

Electron paramagnetic resonance and optical studies of Cu2+ doped bis(thiourea)cadmium chloride single crystal

Electron paramagnetic resonance (EPR) and optical studies have been carried out on Cu²⁺ doped bis(thiourea)cadmium chloride single crystal, which belongs to a potential semi-organic non-linear material, at room temperature. The spin Hamiltonian parameters were determined as g_xx = 2.04331, g_yy = 2.04373, g_zz = 2.05750 and A_xx = 91G, A_yy = 115G, A_zz = 136G. These parameters suggest that the spectroscopic splitting parameter g and hyperfine splitting parameter A exhibit rhombic symmetry. The optical study reveals that the non-linear optical property of the host lattice has been enhanced due to Cu²⁺ doping.     

Chromium ion incorporation in the crystal structure of BGO

Comprehensive investigations have been performed by EPR and optical spectroscopy for Bi₃GeO₄ crystals doped with chromium ions. It is demonstrated that the known optical absorption spectrum for chromium ions, specifically, the triplet in the region 600–900 nm has an analog in the EPR spectra — the center with electron spin S = 1. The spectrum is described by the spin-Hamiltonian with the parameters D = 550 G, E = 10 G, g _xx = g _yy = 1.915, g _zz = 1.932. The EPR spectrum is dictated by Cr⁴⁺ incorporation at the germanium sites. Luminescence observed in the region 1.2–1.7 μm is also caused by transitions of Cr⁴⁺ with tetrahedral surroundings to germanium sites. Original Russian Text Copyright ? 2005 N. V. Chernei, V. A. Nadolinnyi, N. V. Ivannikova, V. A. Gusev, I. N. Kupriyanov, V. N. Shlegel, and Ya. V. Vasiliev __________ Translated from Zhurnal Strukturnoi Khimii, Vol. 46, No. 3, pp. 444–450, May–June, 2005.     

Structural elucidation of transition metal complex by single crystal EPR study

Single crystal EPR studies of Mn(II) doped hexaaquazincdiaquabis(malonato) zincate [Zn(H₂O)₆][Zn(mal)₂(H₂O)₂] have been carried out at room temperature using X-band spectrometer to identify the location of the dopant. Single crystal rotations along the three orthogonal axes show more than 30 line pattern EPR spectra indicating the presence of two types of dopant ions in the host lattice, with intensity ratio of 6:1. However, the latter could not be followed due to its low intensity during crystal rotations. The spin-Hamiltonian parameters, estimated from the three mutually orthogonal crystal rotations are: g_xx = 1.972, g_yy = 2.000, g_zz = 2.023, A_xx = 8.95, A_yy = 9.48, A_zz = 9.93 mT, D_xx = −34.49, D_yy = −3.26, D_zz = 37.74 mT and E = 15.6 mT. The direction cosines of one of the principal values of g match with that of Zn-O bond in the host lattice, suggesting that the Mn(II) ion entered the lattice substitutionally. The large value of E is indicative of low symmetry of the substitutional site, in accordance with the crystal structure of the isomorphous [Zn(H₂O)₆][Cu(mal)₂(H₂O)₂]. Covalency of Mn-O bond, estimated from Matamura’s plot, is 9%. Various admixture coefficients, bonding and optical parameters have also been calculated.     

The two-photon excitation spectrum of a carbazole single crystal at 4.2 K

The low-energy system in the polarized two-photon excitation spectrum of carbazole at 4.2 K has been measured by detecting fluorescence pulses from deliberately added anthracene. Herzberg—Teller activity was detected for Some A₁ vibrations. The two-photon operators contribute to the two-photon cross section in the order yy ≈ zz ? xx.     

Paramagnetic resonance of interstitial mo5+ in a tio2 lattice

Paramagnetic absorption of Mo⁵⁺ has been studied in a polycrystalline TiO₂ rutile lattice, The g tensor (g_x = 1.897, g_y = 1.920, g_z = 1.857) and the hyperfine tensor (A_x = 32.7, (A_y = 51.2, (A_z = 58.5 (in 10^?4 cm^?1)) are in agreement with those expected for an nd¹ ion in an interstitial position.     

C Anisotropic chemical shift in a single crystal of benzophenone

The ¹³C resonance of the carbonyl carbon in a single crystal of benzophenone was studied by Fourier transform NMR at room temperature. Rotation patterns about the three cyrstallographic axes yielded the orientations of the major axis systems of the chemical shift tensor σ relative to the crystallographic axes for the four molecules in the unit cell. The principal elements of σ were found to be: σ_xx = −79 ± 4, σ_yy = −36 ± 4, and σ_zz = +94 ± 4 ppm , relative to CS₂. The Z axis of the nearly axially symmetric σ tensor was found to be perpendicular to the plane spanned by the carbonyl carbon and the carbon and oxygen atoms directly bound to it.     

EPR of copper ions in Pb<Subscript>2</Subscript>MoO<Subscript>5</Subscript> crystals

The article presents the results of EPR studies of Pb₂MoO₅ crystals containing a copper impurity. Based on the analysis of angular dependences of the EPR spectra, it is found that copper ions incorporate into the structure of the Pb₂MoO₅ crystal in the Cu²⁺ state and occupy the molybdenum site with the formation of a linear extended Cu(II)–V(O)–Pb(IV) defect along the а axis of the crystal. An oxygen vacancy appears in the structure of the defect to compensate the charge and the lead ion acquires the Pb⁴⁺ charge state. According to the structure of this center, one magnetically non-equivalent position with the direction of main values of А and g of A(Cu)_zz and g_zz tensors parallel to the а axis is observed in the EPR spectra. Moreover, the EPR spectra exhibit an addition hyperfine structure from one lead atom on which the unpaired electron density is 0.061%. The obtained data on the structure of the defect formed when the copper impurity incorporates into the Pb₂MoO₅ crystal provided the assumption that the observed light scattering when the light beam is directed perpendicular to the а axis may be due to the cooperative effect of the presence of di- and tetravalent ions substituting for molybdenum in the linear configuration of Pb–O–Mo bonds.     

Thermotropic ionic liquid crystals of pyridinium octylphosphate A N.M.R. and X-ray study

Abstract

A thermotropic ionic lamellar phase from non-stoichiometric pyridinium octyl-phosphates has been investigated by multinuclear N.M.R. and X-ray diffraction. At room temperature and above, this phase is formed for pyridine to octylphosphoric acid molar ratios from 0.2 to 0.8.²H and ¹³C relaxation experiments show that the pyridinium ion undergoes a very anisotropic motion with D_zz > D_xx ? D_yy, z and x being the perpendicular direction to the ring and the c ₂ symmetry axis, respectively. The order parameters given by the ²H quadrupolar splittings and the ¹³C chemical shift anisotropy (CSA) are S_zz = 0.13, S_yy = -0.08 and S_xx = -0.05, showing that the pyridinium ring is preferentially oriented parallel to the lamellar plane. The ³¹P CSA and the C1-P dipolar splitting yield S_zz = 0.33 and S_xx ? S_yy for the octylphosphate anion. The order parameters of alkyl C-H bonds have been obtained from the J resolved two-dimensional ¹³C N.M.R. spectra of oriented samples. Two limiting conformational models have been considered to calculate the S _CH. One of them is reasonably consistent with the structure derived from X-ray experiments and has been used to calculate the dipolar ³¹P relaxation. Taking into account the CSA contribution, the relaxation measurements performed at 36, 121 and 202 MHz show that the octylphosphate anion undergoes a quasi-axial reorientation about the long molecular axis x with D∥/D⊥ = 4 and D⊥ ? 10⁷ rad/s at 300 K.     

EPR study of the nature of the impurity centers responsible for the scintillation properties of the Li<Subscript>2</Subscript>Zn<Subscript>2</Subscript>(MoO<Subscript>4</Subscript>)<Subscript>3</Subscript> crystal

The binary molybdate Li₂Zn₂(MoO₄)₃ of a new crystal type was characterized by EPR, optical spectroscopy, and X-ray diffraction methods. The crystals have the Pnma symmetry group and the lattice parameters a = 5.1139(5) Å, b = 10.4926(13) Å, c = 17.6445(22) Å; Z = 4. The crystals possess scintillation properties; emission is caused by the presence of impurity levels in the forbidden band. The EPR studies of the nature of the impurity centers responsible for the scintillation characteristics of the crystal showed that the centers were Cu²⁺ ions substituted for zinc ions in the oxygen octahedra. The directions of the main values of the g and tensors (g _zz , A _zz ) correspond to the direction of O-Cu-O of the oxygen octahedron distorted along the Z axis. The EPR spectra of the copper ions are described by the spin Hamiltonian with the parameters g _‖ = 2.38, g _⊥ = 2.06; A _‖ = 116 G, A _⊥ = 0 G.     

Synthesis and properties of (VO)<Subscript>0.09</Subscript>V<Subscript>0.18</Subscript>Mo<Subscript>0.82</Subscript>O<Subscript>3</Subscript> · 0.54H<Subscript>2</Subscript>O microrods

The (VO)_0.09V_0.18Mo_0.82O₃ · 0.54H₂O microrods of hexagonal symmetry system with the unit cell parameters a = 10.586 Å and c = 3.698 Å were obtained for the first time under hydrothermal conditions (T = 160°C, τ = 30?50 h). Particles were 1–2 μm in diameter and up to 45 μm in length. The compound is thermally stable up to 469°C. The core-electron Mo3d, V2p, and O1s and valence-band X-ray photoelectron spectra and IR spectra of the samples were studied. The molybdenum atoms in the complex oxide have the oxidation state Mo⁶⁺. The vanadium atoms introduced into the h-MoO₃ lattice in molybdenum positions have the oxidation state V⁵⁺. Approximately one-third of vanadium atoms as vanadyl ions (VO)²⁺ are located in the channels of h-MoO₃ lattice, thus stabilizing the latter.     

Détermination des Axes Propres et des Valeurs Principales du Tenseur ḡ dans deux Radicaux Libres Nitroxydes par Étude de Monocristaux

The low temperature phase structure of the nitroxide radical 2,2,6,6-tetramethyl piperidin-1-oxyl (Tanane) is isomorphic of 2,2,6,6-tetramethyl-4-piperidinol-1-oxyl (Tanol). An ESR study of single crystals yielded the principal values and position of principal axes of the ? tensor in these two radicals. The major significant differences observed in Tanol are a moderate decrease in the g_xx, g_yy and g_zz values, and a deviation of the principal axes situated in the molecular mirror plane from the N? O bond and π-orbital, respectively (8° ± 2°). The intermolecular hydrogen bond is probably responsible for this fact.     

Electronic absorption spectrum of Fe3+ doped in ammonium chloride single crystal

The electronic absorption spectrum of the Fe²⁺ ion doped in ammonium chloride has been studied at room and liquid air temperatures. The observed bands have been assigned transitions from the ground ⁶A_1g(S) state to the excited ⁴A_1g(⁴E_g), ⁴T_1g(G) and ⁴T_2g(G) states. The cubic field approximation with D_q = 675 cm^?1, B = 645 cm^?1 and C = 4.4 B is found to give a good fit to the observed band positions.It is further concluded that the site symmetry of the Fe³⁺ ion in the crystal is lowered from O_h to C_4v symmetry at liquid air temperature.     

Synthesis, structure, and 13C and 31P CP/MAS NMR of the tetraphenylantimony(V) di-iso-propyl phosphorodithioate complex [Sb(C6H5)4{S2P(O-iso-C3H7)2}] and its solvated form [Sb(C6H5)4{S2P(O-iso-C3H7)2}] · 1/2C6H6: An example of the monodentate coordination of dithio ligands

The crystalline tetraphenylantimony(V) O,O′-di-iso-propyl phosphorodithioate complex [Sb(C₆H₅)₄{S₂P(O-i-C₃H₇)₂}](I) and its solvated form [Sb(C₆H₅)₄{S₂P(O-i-C₃H₇)₂}] · 1/2C₆H₆(II) were synthesized. Solid compounds I and II were studied by MAS NMR (¹³C, ³¹P). The ³¹P NMR chemical shift anisotropy ³¹P δ_aniso = (δ _zz ? δ_iso) and asymmetry parameter η = (δ _yy ? δ _xx )/(δ _zz ? δ_iso) were calculated using χ ² plots constructed on the basis of the ³¹P MAS NMR data. The O,O′-di-iso-propyl phosphorodithioate ligands in both complexes are characterized by predominantly the axially symmetric ³¹P chemical shift tensor (for the case δ _zz < δ _xx ≈ δ _yy ) with close values of anisotropy parameters (δ_aniso and η), which reflects their identical S-monodentate structural function. X-ray crystallography showed that II has a trigonal-bipyramidal molecular structure with the uncommon monodentate coordination of the Dtph ligands through an S atom in an axial position of the trigonal bipyramid and the benzene molecule in the outer sphere.     

Polymeric thallium(I) O,O′-diisopropyl dithiophosphate [Tl{S2P(O-iso-C3H7)2}]n: Synthesis, structure, and 13C and 31P CP/MAS NMR spectra

The crystalline polymeric thallium(I) O,O′-diisopropyl dithiophosphate [Tl{S₂P(O-iso-C₃H₇)₂}] _n (I) was obtained and examined by solid-state ¹³C and ³¹P CP/MAS NMR spectroscopy. Diagrams of the χ² statistic were constructed from the complete ³¹P MAS NMR spectra and used to calculate the ³¹P chemical shift anisotropy (δ_aniso = (δ _zz − δ_iso)) and the asymmetry parameter (η = (δ _yy − δ _xx )/(δ _zz − δ_iso)). The ³¹P chemical shift tensor has a nearly axial symmetry (η = 0.22, δ _zz < δ _yy ≈ δ _xx ). The MAS NMR spectral patterns correspond to the negative sign of δ_aniso (δ _zz < δ _yy < δ _xx ), which indicates bridging or chelating-bridging coordination of the dithiophosphate ligands (Dtph). X-ray diffraction analysis revealed a polymeric structure of compound I. The polymer chain consists of alternating mononuclear [Tl{S₂P(O-iso-C₃H₇)₂}] molecules with opposite spatial orientations. The Dtph ligands are coordinated in a mixed, chelating-μ₃-bridging fashion. The shape of the ³¹P NMR signal was interpreted in terms of the ³¹P-^203,205Tl coupling pattern proposed from crystallographic data.     

Characterization and Physical Properties of PbO-As2O3 Glasses Containing Molybdenum Ions

PbO-As₂O₃ glasses containing different concentrations of MoO₃ ranging from 0 to 1 mol% (in steps of 0.2) were prepared. The samples were characterized by X-ray diffraction, differential thermal analysis and scanning electron microscopy. A number of studies, viz., optical absorption, magnetic susceptibilities, ESR spectra, IR spectra, elastic properties (Young's modulus E, shear modulus G and microhardness H) and dielectric properties (constant ε, loss tan δ, a.c. conductivity σ_ac over a range of frequency and temperature and breakdown strength), have been carried out on these glasses. Optical absorption, ESR and magnetic susceptibility measurements suggest that when MoO₃ concentration is greater than 0.4 mol% in the glass matrix, molybdenum ions exist in Mo⁵⁺ state with Mo(V)O⁻₃ complexes that act as modifiers in addition to Mo⁶⁺ state with MoO₄ and MoO₆ structural groups. The studies on elastic and dielectric properties indicate that the mechanical and insulating strengths of the glass are considerably high when the content of MoO₃ is about 0.4 mol% in the glass matrix.     

Synthesis, structure, and 13C and 31P CP/MAS NMR of crystalline modifications of the polynuclear thallium(I) O,O′-dicyclohexyl phosphorodithioate complex [Tl{S2P(O-cyclo-C6H11)2}]n

Two crystalline modifications (Ia and Ib) of the polynuclear thallium (I) O,O′-dicyclohexyl phosphorodithioate complex [Tl{S₂P(O-cyclo-C₆H₁₁)₂}] _n have been synthesized and characterized by CP/MAS NMR (¹³C, ³¹P). From full ³¹P CP/MAS NMR spectra, the χ² plots were constructed to calculate the ³¹P chemical shift anisotropy ³¹P − δ_aniso = (δ_zz − δ_iso) and asymmetry parameters η = (δ _yy − δ _xx )/(δ _zz − δ_iso). The data obtained for the O,O′-dicyclohexyl phosphorodithioate (Dtph) groups (in both modifications) are evidence that the ³¹P chemical shift tensors are intermediate between rhombic and axially symmetric. However, whereas the rhombic component dominates for Ia, the tensor for Ib is close to axially symmetric (for δ _zz < δ _yy ≈ δ _xx ). The same pattern of the MAS spectra corresponding to negative δ_aniso (δ _zz < δ _yy < δ _xx ) points to a bridging or terminal/bridging coordination mode of the Dtph groups. X-ray crystallography shows that complex Ib has a polynuclear structure (of the chain polymer type). The chains are composed of alternating structurally nonequivalent noncentrosymmetric binuclear molecules [Tl₂{S₂P(O-cyclo-C₆H₁₁)₂}₂]. All Dtph ligands have the terminal/μ₃-bridging coordination mode.     

ESR of Mo5+ in YVO4: A substitutional off-center ion

The electron spin resonance of MoO^3?₄ in YVO₄ was studied at 4.2K. The Mo⁵⁺ has a d_xy ground state and is shown to move off the V⁵⁺ substitutional site of D_2d symmetry to one of four crystallographically equivalent off-center sites of C₂ symmetry, located in the 〈110〉 direction. The Mo⁵⁺ spectrum is compared to Cr⁵⁺ in YVO₄ and YPO₄ and V⁴⁺ in ZrSiO₄ and other zircon-like crystals which show dynamic effects that we interpret as tunneling or thermally activated hopping between off-center sites.     

Electron Paramagnetic Resonance Study on Supported Molybdenum Catalysts. Part 1: Interaction of Molybdenum Oxide with Silica and Signal Anlsotropy

The effects of reduction, evacuation and adsorbate adsorption on Mo/SiO₂ catalysts prepared by impregnation were studied by means of the electron paramagnetic resonance (EPR) technique. Pentavalent molybdenum species in the overlayer (Mo₀⁵⁺, g? = 1.941, g| = 1.895) and at the interface (Mo_i⁵⁺, g? = 1.952, g| = 1.866) between MoO₃ and SiO₂ were distinguished in the EPR spectra; they were observed from samples reduced at T < 573 K and T > 573 K respectively. The difference in their nature reflected the extent of their interaction with the support. Mo₀⁵⁺ existed in the MoO3 overlayer of the catalyst and interacted only weakly with the support. Mo_i⁵⁺ from the Mo ions connected directly to SiO₂ was affected strongly by the support. The anisotropic factor of the measured Mo_i⁵⁺ signals increased with the extent of support interaction. Superoxide ions (O₂, g₁ = 2.016, g₂ = 2.011, g₃ = 2.006) were found upon oxygen adsorption on samples evacuated at temperatures above 573 K. The observed O₂ may exist at the interface between MoO₃ and the support.