Ion exchange properties of β-eucryptite (LiAlSiO4): EPR investigation on copper-doped single crystals

Investigation of the ion exchange properties of β-eucryptite (LiAlSiO₄) single crystals indicates that it is impossible to substitute Li⁺ by other bigger univalent cations such as Na⁺, K⁺, or Ag⁺. On the contrary, Li⁺ exchange by bivalent cations, Cu²⁺ or Mn²⁺, is very easy. For a general orientation of the crystal with respect to the magnetic field, the EPR spectrum of Cu²⁺ ions in β-eucryptite consists of 12 sharp lines partially superimposed on a broad line. The sharp lines are attributed to isolated copper ions in the conducting channels. Cu²⁺ lies in sixfold coordinated Li″ sites, but not in the fourfold coordinated Li″ sites. The corresponding spin Hamiltonian parameters at T = 140 K are found to be: g_x = 2.362, g_y = 2.340, g_z = 1.990; ∥A_x∥ = 85 × 10^?4cm^?1, ∥A_y∥ = 71 × 10^?4cm^?1, ∥A_z∥ = 203 × 10^?4 cm^?1. The broad line is attributed to clusters of Cu²⁺ located in neighboring Li″ sites.     

The structure of the dithionite ion

The Raman spectra of aqueous and solid sodium dithionite have been recorded. Differences in the location, intensity, and number of observed bands are attributed to conformational changes in the dithionite ion. The structure of the aqueous ion is non-planar with a C_2h symmetry with an SS bond distance estimated to be 0.220–0.226 nm, as opposed to the dithionite structure in the Na₂S₂O₄·2H₂O salt which is known to have C_2ν structure with a bond distance of 0.2389 nm. The Raman spectra of aqueous dithionite are assigned to A_g (SO) = 997 cm^?1; B_g (SO) at 912 cm^?1, B_g SO₂ twist at 324 cm^?1. The remaining bands are a strong A_g, the SO₂ wag, the SO₂ scissor, and the SS stretch at 584, 461, and 232 cm^?1, respectively, but due to coupling all three motions are expected to exhibit substantial SS character. The variation of the spectra of the solid and aqueous sodium dithionite indicate strong environmental effect on the structure of the anion.     

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.     

Electronic absorption spectrum of copper formate tetrahydrate

Single crystals of copper formate tetrahydrate were grown at room temperature. Spectra in the near infrared at room temperature and in the visible at room and liquid air temperatures were recorded on a Unicam SP-700 spectrophotometer and Hilger medium quartz spectrograph respectively. The observed absorption bands have been attributed to an ion of Cu²⁺ in tetragonal symmetry with ²B_1g as the ground state. Taking into consideration the spin—orbit coupling associated with the tetragonal field, a successful interpretation of all the observed bands has been made. The band observed in the near infrared at 11000 cm^?1 has been indentified with a vibrational overtone mode of CO₂. The crystal parameters derived are Dq = ?1380 cm^?1, Ds = ?1950 cm^?1, Dt = ?205 cm^?1 and λ = ?830 cm^?1.     

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.     

Pulsed optical-optical double resonnance spectroscopy of A 1Σ+g state of 7Li2

Optical-optical double resonance using two nitrogen-laser pumped dye lasers has been used to make the first study of an excited ¹σ⁺_g state of ⁷Li₂. Preliminary molecular constants in cm^?1 are Te = 29972, Y₁₀ = 227, Y₂₀ = ?1.92, Y₀₁ = 0390, Y₀₂ = ?4.3 × 10_?6and Y₁₁ = ?1.4 × 10^?3,with r_e = 0. 351 nm.     

Beiträge zum thermischen Verhalten und zur Kristallchemie von wasserfreien Phosphaten. XV. Darstellung,Kristallstruktur und Eigenschaften von Kupfer(II)-ultraphosphat CuP4O11 (≙ Cu2P8O22)

Synthesis, Crystal Structure, and Properties of Copper(II) Ultraphosphate CuP₄O₁₁ CuP₄O₁₁ was synthesised from Cu₂P₄O₁₂ and P₄O₁₀ (500°C, sealed silica ampoules) using iodine and a few mg of CuP₂ or phosphorus as mineraliser. Chemical transport reactions in a temperature gradient 600 → 500°C led to the formation of well developed, colourless, transparent crystals with edge-lengths up to 5 mm (deposition rate m ≈? 2 mg/h). The crystal structure of copper(II) ultraphosphate (C1 ; Z = 8; a = 13.084(3) Å, b = 13.024(2) Å, c = 10.533(2) Å, α = 89.28(2)°, β = 118.42(2)°, γ = 90.30(2)°) has been determined and refined from X-ray data obtained from a pseudo-merohedrally twinned crystal (twin element two-fold rotation axis // b; volume ratio: 17/3; 3063 independent reflections with 2θ ? 53.4°; 291 variables; conventional residual (based on F) R1 = 0.038, wR2 = 0.101 (based on F²), GooF = 1.10). The crystal structure of CuP₄O₁₁ is built from four crystallographically independent ten-membered polyphosphate rings of very similar conformation. These rings are linked to form two-dimensional nets parallel (?2 0 1) planes. There is a close topological relationship between these nets and those formed in polyphosphides CdP₄ and CuP₂. Copper on two crystallographic sites (Cu₂P₈O₂₂) is coordinated by oxygen thus forming elongated [CuO₆] octahedra (d_eq(Cu? O) ≈? 1.96 Å; d_ax(Cu? O) ≈? 2.34 Å). The crystal g-tensor of CuP₄O₁₁ has been determined from powder samples to g₁ = 2.09, g₂ = 2.24, g₃ = 2.36. These values are in good agreement with molecular g-values from calculations within the framework of the angular overlap model on the two independent CuO₆ octahedra (Cu²⁺(1): g_x = 2.09, g_y = 2.10, g_z = 2.52; Cu²⁺(2): g_x = 2.08, g_y = 2.11, g_z = 2.52) assuming exchange coupling. The observed broad absorption band (7000 cm^?1 to 13000 cm^?1) from powder reflectance measurements (4000–28000 cm^?1) and the bulk magnetic susceptibility of μ_exp = 1.99 μ_B is also reproduced nicely by this calculations.     

Fluorescence spectroscopy of laser vaporized species

The plasma produced by a Nd-Yag laser above a metal surface is measured by time resolved optical spectroscopy. The emission of atoms, ions and diatomics is observed for silver, copper and molybdenum. (Cu₂, ωe=263.3 cm^?1 X-state, 189.8 cm^?1 A-state). From these small species clusters are formed with a size distribution between 10 and 80 Å diameter measured by electron microscopy.     

RESONANCE RAMAN SPECTRUM OF THE EXCITED 21Ag STATE OF ß-CAROTENE

Abstract— Resonance Raman (RR) bands assignable to the 2¹A_g excited state of ß-carotene are recorded using picosecond time-resolved resonance Raman (PTR³) spectroscopy. The RR spectrum contains bands in both the C-C (1204 cm^?1, 1243 cm^?1, and 1282 cm^?1) and C=C (1777 cm^?1) stretching regions. The time-dependent intensities of these RR features, measured with ? 30 ps. resolution, are found (i) to closely correlate with picosecond transient absorption (PTA) data recorded at 575 nm on the same sample and (ii) inversely correlate with the time-dependent intensities of RR bands assigned to the 1¹A_g ground state. Both of these observations support the assignment of these four RR features to the 2¹A_g excited state. These results remove uncertainties associated with earlier experiments in which excited-state RR scattering from (3-carotene was not observed in spite of predicted trends emanating from studies of shorter polyene compounds. The observed C=C band position also agrees with a recent report of this feature.     

Two-photon absorption spectrum of (2,2)-paracyclophane

The two-photon absorption spectrum of crystalline (2,2)-paracyclophane was measured in the regions of 31200–33800 cm^?1, 34700–36500 cm^?1, and 40800–48600 cm^?1 by monitoring the fluorescence intensity using a tunable dye laser as a two-photon excitation source. Two absorption bands in the region 34700–36500 cm^?1 were assigned to the two even-parity allowed ¹B_1g ← ¹A_1g and ¹B_2g ← ¹A_1g transitions.     

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.     

THE EPR SPECTRA OF TETRADENTATE SCHIFF BASE COMPLEXES OF COPPER (II) I. N,N'-Bis-(acetylacetone) ethylenediimine and N,N'-Bis-(1,1,1-trifluoroacetylacetone) ethylenediimine

Abstract

The EPR spectrum of N, N'-bis-(acetylacetone)ethylenediimino Cu(II), [Cu-en(acac)₂], and N, N'-bis-(1,1,1-trifluoroacetylacetone)ethylenediimino-Cu(II), [Cu-en(tfacac)₂], have been studied in doped single crystals of the corresponding Ni(II) chelate. The parameters in the usual doublet spin-Hamiltonian are found to be: Cu[en(acac)₂], g_z =2.183 ± 0.003, g_x =2.047 ± 0.004, g_y =2.048 ± 0.004, A_z =204.8 × 10^?4cm^?1, A_x =31.5 × 10^?4cm^?1, A_y =27.1 × 10^?4 cm^?1, A_zN= 12.8 × 10^?4 cm^?1 and A_xN =A_yN =14.3 × 10^?4 cm^?1: Cu[en(tfacac)₂], g_z =2.192 ± 0.002, g_x =2.048 ± 0.004, g_y =2.046 ± 0.004, A_z =200.8 × 10^?4 cm^?1, A_x =31.1 × 10^?4 cm^?1, A_y =28.3 × 10^?4 cm^?1, A_zN =12.8 × 10^?4 cm^?1 and A_xN =A_yN =14.6 × 10^?4 cm^?1. These parameters are related to coefficients in the molecular orbitals of the complex. It is found that the α-bonding is quite covalent and there is significant in-plane σ-bonding. From the nitrogen hyperfine structure it is determined that the hybridization on the nitrogen is sp².     

The stereochemistry of Tutton's salts X2[M(H2O)6](YO4)2

Neutron structure determinations have been made of Tutton's salts, X₂[M(H₂O)₆] (YO₄)₂, where Y = Se, X = K⁺, M = Cu²⁺; Y = S, X = K⁺, M = Ni²⁺, Cu²⁺, Zn²⁺; X = Rb⁺, Cs⁺, M = Cu²⁺. This work has shown that there are extensive hydrogen networks with almost linear hydrogen bonds from [M(H₂O)₆]²⁺ to (YO₄)^2?. The (H … O) distance increases in the Cu²⁺ series for X = K⁺ to Cs⁺ but there is no difference for the potassium copper salts when Y = Se or S. Three different distorted [M(H₂O)₆]²⁺ octahedra were found in the series (orthorhombic, tetragonal with two long and four short, or four long and two short bonds). The interatomic distances from X⁺ to the neighboring O in a distorted XO₈⁺ dodecahedron increases with increased cation size, implying that the X⁺ polyhedron is maintaining its shape.     

Crystal structure and infrared spectroscopy of MCl<Subscript>2</Subscript>·2CONH<Subscript>3</Subscript> (M = Cu,Mn)

Crystals of MCl₂·2CONH₃ (M = Cu²⁺, Mn²⁺) are synthesized from low-temperature water-formamide solutions and studied by crystal optical, single crystal X-ray diffraction, and infrared spectroscopy methods. The crystal structures of CuCl₂·2CONH₃ and MnCl₂·2CONH₃ are solved by direct methods and refined in the P1triclinic space group, R1= 0.043 and 0.038 for 501 and 686 reflections with F ₀ÃΣ(F₀) respectively. Unit cell parameters for Cu and Mn salts are: a = 3.705(1) Å and 3.685(1) Å, b = 7.049(2) Å and 7.136(2) Å, c = 7.375(2) Å and 7.779(2) Å, 6h =113.57(3)² and 117.17(2)², β = 96.17(3)² and 95.35(2)², γ = 94.85(3)² and 92.23(2)² respectively, Z= 1. In the studied crystal structures, MCl₄O₂ octahedra share Cl-Cl edges and form chains along the [100] direction. This direction corresponds to a morphological elongation of the obtained crystals and orientation of the maximum refractive index. The FT infrared spectra obtained in a range from 4000 cm^?1 to 300 cm^?1 are very close to the spectrum of liquid formamide, but exhibit better resolution of absorption bands.     

Studies on the <Emphasis Type="Italic">g</Emphasis>-factors of the copper(II)–oxygen compounds

The g factors for Cu²⁺ in meta-zeunerite (Cu(UO₂)₂(AsO₄)₂·3H₂O), kroehnkite (Na₂Cu(SO₄)₂·2H₂O), copper benzoate (Cu(PhCO₂)₂·3H₂O) and diaboleite (Pb₂Cu(OH)₄Cl₂) of the tetragonal phase are uniformly treated by high order perturbation formulas for 3d ⁹ ions in tetragonally elongated octahedra. The calculation results are in good agreement with the observed values and systematically analyzed in view of the local structures around Cu²⁺. The g anisotropies Δg (= g _‖?g _⊥) are largely ascribed to the local tetragonal elongations of the Cu²⁺ sites, characterized by the relative elongation ratios (R _‖?R _⊥)/R? ≈ 19%, 21%, 27% and 30% for metazeunertie, kroehnkite, copper benzoate and diaboletie, respectively. The anomalous valley (minimum) of relative g anisotropy for copper benzoate is attributed to the modification of the Cu²⁺ electronic states due to the phenyl ring. The ligand orbital contributions are found to be significant due to covalency, and should be taken into account. The present study would be helpful to the unified investigations of structures and properties of the copper oxygen compounds.     

123 Phases of composition CaBa2Cu2WO8 with substitutions of sodium and potassium for calcium and barium

Tetragonal (123) phases of compositions Ca_0.7Na_0.3Ba₂Cu₂WO₈, CaBa_1.7Na_0.3Cu₂WO₈, and CaBa_1.7K_0.3Cu₂WO₈, where tungsten occurs in Cu(1) positions and Cu³⁺ is in Cu(2) positions, were prepared from CaWO₄, BaCuO₂, and sodium and potassium nitrates at 1073 K in an oxygen flow. These phases constitute at least 90% of the samples; their unit call parameters are as follows: a = b = 0.4177(3) nm, c = 1.2561(8) nm; a = b = 0.4182(3) nm, c = 1.2564(8) nm; and a = b = 0.4194(3) nm, c = 1.2603(8) nm, respectively. Their X-ray diffraction patterns feature peaks that indicate a superstructure with all three unit cell parameters being doubled. The samples have weak conductive properties (room-temperature electrical conductivity ranges between 10^?6 and 10^?7 Ohm^?1 cm^?1). Conductivity versus temperature curves are indicative of the semiconductor character of the samples. Superconducting transitions do not occur up to 65 K.     

Fluorescence spectrum of the benzene radical cation in solid argon

Argon/benzene samples were condensed at 12 K with continuous argon resonance radiation. Laser excitation at 421 nm produced a weak emission with structure at 19770, 19140 and 18290 cm^?1, assigned to the ²A_2u → ²E_1g emission of C₆H₆⁺. Observation of 630 and 1480 cm^?1 intervals for the vibrations v₁₈ (e_2g) and v₆ (e_2g), respectively, supports this assignment.     

IR- and Raman-active normal vibrations of rare earth oxyfluorides,REOF; RE=Y,La, and Gd

The vibrational levels of selected rhombohedral rare earth oxyfluorides, REOF; RE = La, Gd, and Y, were deduced from the room temperature IR absorption and the Raman scattering spectra between 180 and 1000 cm⁻¹ and between 10 and 700 cm⁻¹, respectively. All four IR-active (2A_2u + 2E_u) and six Raman-active (3A_1g, + 3E_g) normal modes predicted by the group-theoretical analysis for the D_3d factor group were observed. The vibrations were assigned with the aid of their intensity and frequency in good agreement with the cubic fluorite-like structure of stoichiometric REOF.     

Copper(II) trinuclear complex with trimesic acid salicylidene hydrazone: Synthesis,structure, and magnetic properties

A trinuclear copper(II) complex of trimesic acid salicylidene hydrazone (H₆L) having the composition [Cu₃L · 4Py] · CH₃OH was synthesized and characterized. By X-ray crystallography, the crystals are triclinic: a = 11.7940(4) Å, b = 13.7241(5) Å, c = 15.8993(6) Å, α = 107.4120(10)°, β = 94.2900(10)°, γ = 105.5650(10)°, space group \(P\bar 1\), Z = 2. The number of symmetrically unique reflections having I > 2σ(I) is 7636, R = 0.0465, and R _w = 0.1198. The newly prepared complex contains, in its unit cell, two [Cu₃L · 4Py] molecules which are linked to form a dimer on account of phenoxo bridges (the Cu-O bond length is 2.555 the Cu…Cu distance is 3.348 Separations between them are 9.414, 9.371, and 9.667 of temperature is satisfactorily fitted in terms of a triangular cluster model (?2J = 2.2 cm^?1) with extra intermolecular interactions (zJ′ = 0.4 cm^?1). EPR spectra of solutions at 360–380 K feature a poorly resolved HFS, whose modeling gives a satisfactory result with allowance for the interaction of unpaired electrons with three equivalent copper nuclei (g = 2.098; a _Cu = 25.8 × 10^?4 cm^?1).     

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.