Exchange interactions in a trigonal chromium (III) dimer. Optical spectroscopy of tris-(μ-hydroxo)-bis-[(1,4,7-trimethyl-1, 4,7-triazacyclononane) chromium(III)] triperchlorate

High-resolution absorption, luminescence, Zeeman and MCD experiments were performed on single crystals of the title compound. The singlet-triplet and triplet-quintet exchange splittings in the ground state are 138 and 267 cm^?1, respectively. The corresponding exchange parameters are 2J= ?128 cm^?1 and j = 1.6 cm^?1. The zero-field splitting in the ground level is ?2.25 cm^?1. The lowest-energy emitting state is a ³E state, split into four spinor components with a total spread of 8 cm^?1.     

Energy levels and intensities of the absorption spectrum of the U3+ ion in anhydrous formic acid

The absorption spectrum of the U³⁺ ion in anhydrous formic acid was recorded in the range 4100–23,000 cm^?1. The electrostatic, spin-orbit and configuration interaction parameters obtained from a least-squares fit to eight observed levels are: E¹ = 2882.7 cm^?1, E² = 13.8 cm^?1, E³ = 285.4 cm^?1, ξ_5f = 1654 cm^?1, α = 19.8 cm^?1, β = ?380.3 cm^?1 and γ = 1000.0 cm^?1. Intensity calculations gave good agreement with the oscillator strengths of observed bands only if some of the experimental band areas were combined.     

Die rotationsisomerie des bicyclopropyls.: II. Die gauche/trans-isomerisierungsenthalpie und-entropie von bicyclopropyl aus ir-intensitäts-messungen. Ein experimenteller test

The determination of the enthalpy ΔH and entropy ΔS of the isomerization bicyclopropy l(trans)? bicyclopropyl(gauche) in the liquid phase by the IR intensity method is described. It is assumed that the ratio of the integral absorption coefficients of the two reference bands at 1351 cm^?1 (gauche) and 1291 cm^?1 (trans), which both belong to the same type of vibration, is temperature independent. The two values ΔH = ?160 ± 40 cal Mol^?1 and ΔS = ?0.4 ± 0.5 cal (Mol · Grad)^?1 respectively. ΔS_U = ?1.8 ± 0.5 cal (Mol · Grad)^?1 thus determined agree well with the corresponding results obtained from NMR and electron diffraction measurements. However, from the pair of reference bands at 695 cm^?1 (gauche) and 1291 cm^?1 (trans), which do not belong to the same type of vibration, strongly differing values for ΔH and ΔSresult under the same assumption as above, which apparently is not applicable in this case.It is shown through these data that the “Fateley-Test” does not provide a suitable tool to decide whether the absorption coefficients of the reference bands are temperature independent or not. The reason for this insignificance is the relatively poor accuracy and reproducibility of measured IR band intensities obtainable up to now.The relative density of bicyclopropyl between ?60°C and + 50°C was determined.     

Thermal decomposition kinetics of bisthiourea cadmuim(II) tetrathiocyanato diammine chromate(III)

Cadmium thiourea reinickate undergoes two-stage thermal decomposition on heating. The DTG peak temperatures are 291 and 469°C and the corresponding DTA temperatures are 255 and 490°C. The kinetic parameters for the first stage decomposition are E* ≈ 120kJ mole^?1; Z ≈ 1.2 × 10⁸ cm³ mole^?1 sec^?1 and ΔS* ≈ ?95 J mole^?1 K^?1. For the second stage, E* ≈ 133 kJ mole^?1; Z ≈ 6.1 × 10⁵ cm^?1 mole^?1 sec^?1 and ΔS* ≈ ?142 J mole^?1 K^?1.     

Direct electrochemistry and electrochemical biosensing of glucose oxidase based on CdSe@CdS quantum dots and MWNT-modified electrode

The direct electron transfer of glucose oxidase (GOx) was achieved based on the immobilization of CdSe@CdS quantum dots on glassy carbon electrode by multi-wall carbon nanotubes (MWNTs)-chitosan (Chit) film. The immobilized GOx displayed a pair of well-defined and reversible redox peaks with a formal potential (E ^θ’) of ?0.459 V (versus Ag/AgCl) in 0.1 M pH 7.0 phosphate buffer solution. The apparent heterogeneous electron transfer rate constants (k _s) of GOx confined in MWNTs-Chit/CdSe@CdS membrane were evaluated as 1.56 s^?1 according to Laviron's equation. The surface concentration (Γ*) of the electroactive GOx in the MWNTs-Chit film was estimated to be (6.52?±?0.01)?×?10^?11?mol?cm^?2. Meanwhile, the catalytic ability of GOx toward the oxidation of glucose was studied. Its apparent Michaelis–Menten constant for glucose was 0.46?±?0.01 mM, showing a good affinity. The linear range for glucose determination was from 1.6?×?10^?4 to 5.6?×?10^?3?M with a relatively high sensitivity of 31.13?±?0.02 μA?mM^?1?cm^?2 and a detection limit of 2.5?×?10^?5?M (S/N=3).     

EPR studies of a molybdenyl complex in single crystals of NH4Cl

Electron paramagnetic resonance of [MoOCl₅]^2? has been studied in single crystals of NH₄Cl. At room temperature the interaction of the unpaired electron with both the even and odd isotopes of molybdenum has been observed. The existence of metal-halogen π bonding is established by the observation of the ligand superhyperfine interaction at liquid nitrogen temperatures. Various possible models corresponding to the different spatial configurations of the molybdenyl complex in the lattice are considered to explain the experimentally observed features. The spectra are analysed using the usual spin-hamiltonian corresponding to tetragonal symmetry. The spin-hamiltonian parameters obtained are: g_∥ = 1.964, g_? = 1.945, A_∥ = 75.53 × 10^?4 cm^?1, A_⊥ = 38.42 × 10^?4 cm^?1.     

Effect of styrene–acrylonitrile content on 0.5?M NaI/0.05?M I2 liquid electrolyte encapsulation for dye-sensitized solar cells

The effect of a gel polymer electrolyte (GPE) as the redox electrolyte used in dye-sensitized solar cells was studied. A GPE solution consisting of 0.5?M sodium iodide, 0.05?M iodine, and ethylene carbonate/propylene carbonate (1:1 w/w) binary solvents was mixed with increasing amounts of styrene–acrylonitrile (SAN). Bulk conductivity measurements show a decreasing trend from 4.54 to 0.83×10^?3?S?cm^?1 with increasing SAN content. The GPE exhibits Newtonian-like behavior and its viscosity increases from 0.041 to 1.093?Pa?s with increasing SAN content. A balance between conductivity (1.3?×?10^?3?S?cm^?1) and viscosity (1.4?Pa?s) is observed at 19?wt.% SAN. Fourier transform infrared spectroscopy detects elevated ring torsion at 706?cm^?1 upon the addition of SAN into the liquid electrolyte. This indicates that SAN does not bond with the liquid electrolyte. Finally, the potential stability window of 19?wt.% SAN, which ranges from ?1.68 to 1.38?V, proves its applicability in solar cells.     

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.     

Time-resolved ESR study of the lowest excited triplet states of para-quinones in glassy matrices at 77 k

The lowest excited nπ* triplet of 9.10-anthraquinone, 1.4-naphthoquinone and 1,4-benzoquinone were studied in glassy matrices at 77 K using a time-resolved ESR method. The D value of the triplet state of 9,10-anthraquinone varied from ?0.351 cm^?1 in a polar solvent to ?0.318 cm^?1 in a non-polar solvent. Both 1,4-naphthoquinone and 1,4-benzoquinone in polar solvents showed triplet state spectra with a D value of ?0.330 cm^?1. A computer simulation revealed the existence of widely distributed zero-field splitting parameters in the glassy condition. These data are compared with an analysis of CIDEP results of para-quinones.     

Infrarot-Untersuchungen an substituierten Flavanonen und den isomeren 2′-Hydroxychalkonen

IR data of eight substituted flavanones and their isomeric hydroxychalkones have been recorded in order to assign the various absorption bands and to study the effect of substituents on C=C out-of-plane deformation (400–700 cm^?1), C?H out-of-plane deformation (700–1000 cm^?1), C?H in-plane deformation (1000–1300 cm^?1), C?O stretch (≈1200 cm^?1), OCH₃ (1200–1300 cm^?1), O?H deformation (1300–1400 cm^?1), CH₃ deformation (1300–1500 cm^?1), benzene ring vibration (1400–1600 cm^?1) and C=O stretch (≈1650 cm^?1). The δ_C?H (ring A) in 2′,4′-dihydroxy-3-nitrochalkone appears at 826 cm^?1 (s), while in the isomeric flavanone it shows up as three bands, viz., 807 (w), 833 (m) and 881 cm^?1 (w). This difference principally arises due to the presence of the electron withdrawing nitro substituent. The C=O stretching vibration in flavanones appears at a higher frequency than in the corresponding hydroxychalkones. This is perhaps due to the lack of conjugation in the former class of compounds. Chloro substituents (ring B) in different positions exert differing effects on ν_C?O. These differences can be rationalized in terms of a field-effect exerted by the chlorine atom.     

Composition-controlled metal-insulator transitions and minimum metallic conductivity in the oxide systems LaNi1−xMxO3 (M = Cr,Mn, Fe,or Co)

The composition-controlled metal-insulator transition in the perovskite systems LaNi_1?xM_xO₃ (M = Cr, Mn, Fe, and Co) has been investigated by transport measurements over the temperature range 12–300 K. These systems, which have critical electron densities (n_c) in the range (1–2) × 10²⁰ electrons cm^?3, exhibit sharp metal-insulator transitions at the base temperature. The corresponding minimum metallic conductivity (σ_min), separating the localized and itinerant electronic regimes, is of the order of 10² ohm^?1 cm^?1. Particular attention is paid to the idea of σ_min scaling with n_c, and our present results are compared with earlier studies of the metal-insulator transition in low (e.g., Ge:Sb) and high (e.g., metal-ammonia, supercritical Hg) electron-density systems. A link is established between the transport and magnetic properties of the title systems at the metal-insulator transition.     

Halometallates of 1-methyl-4,4-dimercapto-piperidinium. Evidence of strong hydrogen bonds with participating thiol groups

Chlorometallates of transition and B subgroup elements are readily prepared and precipitated by reaction of the corresponding metallic salts with 1-methyl-4,4-dimercaptopiperidinium chloride. These chlorometallates investigated were [ZnCl₄]^2?, [CdCl₃]^?, [CoCl₄]^2?, [CuCl₅]^3? and [FeCl₄]^2?. Strong SH … Cl interactions, but not NH … Cl, have been evidenced by IR spectroscopy in the zinc, cadmium and cobalt complexes. The SH and NH absorptions are observed at ? 2480 cm^?1 and 3060 cm^?1, respectively. Partial deuteration of the [ZnCl₄]^2? complex with d₁-methanol, shifted these IR signals to 1800 and 2260 cm^?1, clearly evidencing a X-hydrogen type of bond. The SH … Cl interaction is smaller in the [FeCl₄]^2? complex, and practically nonexistent in the [CuCl₅^3? complex.     

Vibrational spectra and torsional analyses of cis-2,3-dimethyloxirane and trans-2,3-dimethyloxirane

The Raman spectra of cis-2,3-dimethyloxirane and trans-2,3-dimethyloxirane in the vapor, liquid, and polycrystalline solid phases are reported for the region between 25 and 3100 cm^?1. The IR spectra of these two compounds between 80 and 4000 cm^?1 in the vapor and polycrystalline solid phases are also reported. In the IR and Raman spectra of gaseous trans-2,3-dimethyloxirane a total of eight torsional transitions have been observed. In the Raman spectrum of the cis compound in the vapor phase, four torsional transitions have been observed. From these experimental data, periodic barriers to the methyl torsional motions have been calculated to be 905 ± 7 cm^?1 (2.5 kcal mol^?1) for the trans molecule and 617 ±5 cm^?1 (1.76 kcal mol^?1) for the cis molecule. Additionally, complete vibrational assignments based on band contours, depolarization values, and group frequencies are proposed for both molecules and gas-phase thermodynamic functions have been calculated. These results are compared to the corresponding quantities for some similar molecules.     

Low-temperature heat capacity of L- and DL-phenylglycines

Heat capacity of crystalline L- and DL-phenylglycines was measured in the temperature range from 6 to 305?K. For L-phenylglycine, no anomalies in the C _p (T) dependence were observed. For DL-phenylglycine, however, an anomaly in the temperature range 50?C75?K with a maximum at about 60?K was registered. The enthalpy and the entropy changes corresponding to this anomaly were estimated as 20?J?mol^?1 and 0.33?J?K^?1 mol^?1, respectively. In the temperature range 205?C225?K, an unusually large dispersion of the experimental points and a small change in the slope of the C _p (T) curve were noticed. Thermodynamic functions for L- and DL-phenylglycines in the temperature range 0?C305?K were calculated. At 298.15?K, the values of heat capacity, entropy, and enthalpy are equal to 179.1, 195.3?J?K^?1 mol^?1, and 28590?J?mol^?1 for L-phenylglycine and 177.7, 196.3?J?K^?1 mol^?1 and 28570?J?mol^?1 for DL-phenylglycine. For both L- and DL-phenylglycine, the C _p (T) at very low temperatures does not follow the Debye law C ?C T ³ . The heat capacity C _p (T) is slightly higher for L-phenylglycine, than for the racemic DL-crystal, with the exception of the phase transition region. The difference is smaller than was observed previously for the L-/DL-cysteines, and considerably smaller, than that for L-/DL- serines.     

Resonance enhanced three-photon absorption of molecular iodine

D ← X resonance enhanced three-photon excitation spectrum of iodine was observed by a cw intracavity absorption technique. Vibrational quantum numbers of D ← X transitions are given for every major spectral feature. The corresponding one-photon enhancement from the B state is evident from the one-photon vibrational assignment. The spectroscopic constants for the D state are v₀₀ = 40 998 cm^?1 ω′₀ = 113 cm^?1 and ω′₀χ′₀ = 0.045 cm^?.     

Adsorption of cinnamaldehyde at the mercury-water interface

The adsorption of cinnamaldehyde from aqueous 1 M KCl has been determined by means of differential capacity, zero charge potential and maximum surface tension measurements. A Frumkin isotherm is obeyed with α = 2.4, corresponding to repulsive interaction, and Γ_s= 3.5 × 10^?10 mol cm^?2, which is independent of potential in the range ?350/?750 mV. The standard free energy of adsorption is a quadratic function of potential with maximum adsorption occurring at the potential of zero charge. The interaction of the molecular dipole with the electric field and the partial charge transfer between the electrode and the adsorbate are considered.     

Potassium-conducting solid electrolytes in the K3 − 2x Cd x PO4 system

New potassium-conducting solid electrolytes of the K_{3 ? 2x} Cd _x PO₄ system are synthesized and studied. A wide range of solid solutions reaching x ≈ 0.35 with the structure of high-temperature modification of potassium orthophosphate forms in the system. An addition of cadmium ions leads to an abrupt increase in the K₃PO₄ conductivity due to the formation of potassium vacancies. The highest conductivity is approximately 10^?2 S cm^?1 at 300°C and above 10^?1 S cm^?1 at 700°C.     

Potential energy curves for ground and excited states of NaLi from ab initio calculations with effective core polarization potentials

Sixteen low-lying electronic states of NaLi are investigated by SCF/valence Cl calculations including core polarization effects by means of an effective potential. Spectroscopic constants are obtained with estimated uncertainties of ΔR_e ? 0.01 Å, Δω_e ? 0.6 cm^?1 and ΔD_e ? 80 cm^?1. From a comparison of experimental and theoretical G(υ) values, we suggest a ground-state dissociation energy of 7093 ± 5 cm^?1. Using our rovibrational energies and recently measured excitation lines, we are able to improve the T_e values and dissociation energies of five excited states to an accuracv of ±8 cm^?1.     

Interpretation of the light scattering spectrum of paramagnetic FeF2

The Raman spectrum of a single crystal of FeF₂ is reported and the transitions in the range of 900–1500 cm^?1 are assigned to the spin-orbit levels of the Fe²⁺ ion in a field of D_2h symmetry. The value of the tetragonal and rhombic distortion parameters calculated from the spectra are ?1162 cm^?1 and 110 cm^?1, respectively and the spin-orbit coupling parameter λ = ?91.3 cm^?1. The computed energy level diagram is in agreement with the EPR spectrum of this compound.     

Raman and Photoluminescence Spectroscopic Detection of Surface‐Bound Li+O2− Defect Sites in Li‐Doped ZnO Nanocrystals Derived from Molecular Precursors

We present a detailed study of Raman spectroscopy and photoluminescence measurements on Li‐doped ZnO nanocrystals with varying lithium concentrations. The samples were prepared starting from molecular precursors at low temperature. The Raman spectra revealed several sharp lines in the range of 100–200 cm^?1, which are attributed to acoustical phonons. In the high‐energy range two peaks were observed at 735 cm^?1 and 1090 cm^?1. Excitation‐dependent Raman spectroscopy of the 1090 cm^?1 mode revealed resonance enhancement at excitation energies around 2.2 eV. This energy coincides with an emission band in the photoluminescence spectra. The emission is attributed to the deep lithium acceptor and intrinsic point defects such as oxygen vacancies. Based on the combined Raman and PL results, we introduce a model of surface‐bound LiO₂ defect sites, that is, the presence of Li⁺O₂^? superoxide. Accordingly, the observed Raman peaks at 735 cm^?1 and 1090 cm^?1 are assigned to Li? O and O? O vibrations of LiO₂.