14N ENDOR study of Cu(II)-doped triglycine sulfate crystals (TGS)

¹⁴N ENDOR investigations of the bis(glycinato)-Cu(II) complex substituted into single crystals of ferroelectric triglycine sulfate (TGS) reveal the full tensors of the magnetic dipole as well as the electric quadrupole couplings. The two nitrogen nuclei of the copper complex are magnetically non-equivalent and consequently the point symmetry of the Cu(gly)₂ complex in the ferroelectric TGS is C₁. The nuclear quadrupole couplings are analysed using the Townes-Dailey approach and sp³ hybridization to obtain the electronic population at the nitrogen. The results are compared with the findings from the treatment of the magnetic nitrogen hyperfine coupling.     

The structure of the paramagnetic impurities in triglycine sulfate single crystals

ENDOR investigations of the bis(glycinato)-Cu(II) (NH₂CH₂COO)₂Cu and bis(glycinato)-oxo-V(IV) (NH₂CH₂COO)₂VO complexes in the ferroelectric triglycine sulfate (TGS) single crystals are reported. Magnetic hyperfine constants of the ligand nuclei are given. The ENDOR investigati confirm the conclusion derived from EPR studies that the copper and vanadyl ions occupy interstitial lattice sites forming bis(glycinato) complexes wit triclinic symmetry C₁. Molecular theoretical calculations of the EPR and ENDOR parameters of different paramagnetic impurities in TGS were performe using the self-consistent charge and configuration (SCCC) version of the extended Hückel theory (EHT). By using perturbation theory the parameters of the spin hamiltonian were determined.     

63Cu and 31P endor study of Tetra-n-Butylammonium-(Maleonitriledithiolato) (Monoethyldithiophosphato) cuprate(II)/Nickelate(II) (n-Bu4N)[Cu/Ni(mnt)(H(et)dtp)]

The ⁶³Cu quadrupole, the ⁶³Cu hyperfine and ³¹P hyperfine coupling tensors of the mixed-ligand chelate (n-Bu₄N)[⁶³Cu(mnt)(H(et)dtp)] doped into the corresponding nickel complex have been measured by ENDOR spectroscopy. Conclusion are drawn concerning the symmetry of the Cu complex. The ⁶³Cu quadrupole tensors and the ³¹P hyperfine tensors can be understood assuming a “transannular Cu 3d_itx2 -_ity2-P 3s overlap”.     

Endor spectra of Cu(sal)2:Ni(sal)2

Proton, nitrogen and ⁶³Cu ENDOR spectra of the bis(salicylaldoximato)Cu(II) complex substituted in bis(salicylaldoximato)Ni(II) single crystals are reported. Magnetic hyperfine coupling constants of ligand proton and nitrogen nuclei derived by first order analysis are given and discussed. Dipolar parts of some proton hyperfine interactions are shown to correlate with the Cu—proton distance.     

Ab initio MO LCAO UHF calculations of magnetic hyperfine interactions in σ radicals. Isotropic and anisotropic couplings of NO2 and CO2−

The magnetic hyperfine coupling constants in NO₂ and CO₂^? have been computed by an initio methods. Spin annihilation is found to be essential in order to obtain useful results for the dipolar couplings, but has much less influence on the isotropic couplings. The electric quadrupole coupling constants have also been evaluated, and are in good agreement with available experimental data.     

17O Hyperfine structure in single crystal ESR spectra of Cu(II) picolinate: Zn(II) picolinate-4H2O

ESR spectra of ¹⁷O modifications of Cu(II)picolinate substituted in Zn(II)picolinate-4H₂O single crystals are reported. Values of ¹⁷O hyperfine coupling tensors, orientation angles and approximate relative spin densities at the O and N nuclei are given.     

ESR-Untersuchungen zu Struktur- und Bindungsverhältnissen von tri- und bicyclischen Cobalt(II)- und Kupfer(II)-Chelaten mehrzähniger Schiffscher Basen des Typs M(O N N O) und M(S N)2 sowie zur Sauerstoffadduktbildung der Cobalt(II) Chelate

Structural and Bonding Properties of Quadridentate and Bidentate Cobalt(II) and Copper(II) Schiff Base Complexes and Oxygenation Behavior of the Co^II Complexes. An ESR Study ESR investigations on the low-spin cobalt(II) chelates bis(benzoylacetaldehyde)-ethylendiimine-cobalt(II), bis(benzoylacetaldehyde)-1,2-cyclohexandiimine-cobalt(II) and bis(p-chlor-β-mercaptozimtaldanilato)-cobalt(II) as well as the corresponding copper(II) chelates are reported. The large anisotropy of the g tensor of the Co^II chelates caused by strong spin-orbit interactions, and the position of the maximum g tensor component g_x in the molecules obtained by comparison with the ESR spectra of the Cu^II complexes predicts a MO for the unpaired electron which consists mainly of the Co d_yz obital. In solution (CHCl₃/pyridine) the Co^II chelates react immediately with molecular oxygen forming [CoL_n(O₂)(py)] species characterized by ESR spectra with strongly reduced g tensor anisotropy and small ⁵⁹Co hyperfine coupling constants. The unpaired electron appears to be mainly localized in the O₂-part of hte molecules. The CoN₂S₂ coordination sphere shows a lower affinity to oxygen than the CoN₂O₂ type complexes. In the CuN₂O₂ complexes the unpaired electron is found to be in a MO containing the Cu d_xy orbital. Due to remarkable covalency¹⁴ N and H hyperfine interactions are observed in the ESR spectra. Analyzing the hyperfine coupling constants the extent of unpaired spin density on the N donor atoms and the N-2s/2p hybridization degree is estimated.     

Deuteron magnetic resonance study of single crystals of NaDSeO3

A deuteron magnetic resonance study of a single crystal of NaDSeO₃ at room temperature is reported. The observed electric field gradient tensors correspond to two nonequivalent hydrogen bonds. The quadrupole coupling constants ($\text{eQq}\text{h}$) and asymmetry parameters (η) are found to be 172.8 and 0.07 kHz for D(1), and 152.5 and 0.08 kHz for D(2). D(2) are ordered, but D(1) are found to be dynamically disordered. The DMR results are consistent with recent X-ray reinvestigation. No phase transitions have been encountered in the temperature range 336 to 77 K.     

Structure and magnetism of an exchange coupled system: An NMR approach

A binuclear copper(II) complex [Cu₂L(OH)](C1O₄)₂·2H₂O has been synthesized and characterized by X-ray crystallography and¹H-NMR studies. The crystal structure shows that the bridging angles between Cu(l)-O(l)-Cu(2) and Cu(l)-O(2)-Cu(2) are 98.9(2)° and 102.2(2)° respectively. The Cu(l)-Cu(2) distance is 3.0097(12)?. This indicates that the interaction between the two copper atoms is antiferromagnetic in nature. The geometry around Cu(l) is distorted square-pyramid with one water molecule occupying the axial fifth position, whereas, the geometry around Cu(2) is distorted square-planar with weak interactions of one of the perchlorate anion. There are eight molecules present in the unit cell. There is an interdimer interaction between the dimers. The temperature-dependent¹H-NMR chemical shift studies have been performed on six different protons of this complex which reveals that the exchange coupling constant (− 2J) is same for all protons (208 ± 1 cm⁻¹). However, the hyperfine coupling constant (A′) was found to be different in magnitude as well as in sign. We also report solvent dependent NMR properties.     

1,2,3-propanetriol radicals formed during oxidative stress

The presented results attempt to approximate the proper structure of the radical formed as a result of the oxidation of 1,2,3-propanetriol. To fulfil the aim unstable radical originated in 1,2,3-propanetriol was trapped by PBN. Resulted spin adduct was measured using EPR spectroscopy and the isotropic hyperfine coupling constants a_iso(¹⁴N) and a_iso(¹H) were obtained by simulation of the EPR spectrum. The next step consisted of conducting a comparative analysis of EPR parameters, based on the calculations conducted at the DFT and MP2 methods level in open-shell formalism including solvent effects. For comparison, calculations were also carried out at the level of combined methods (UB3LYP/QCISD and UMP2/QCISD) in terms of the ONIOM formalism. Comparison of the experimental EPR data of the isotropic hyperfine coupling constants a_iso(¹⁴N) and a_iso(¹H) with the calculated parameters indicate that oxidation of 1,2,3-propanetriol leads to a carbon centred radical where unpaired electron is situated on the second (middle) carbon of 1,2,3-propanetriol. What is important, this conclusion could be made regardless of the chosen calculation method. However, it could be stated that for calculation of the isotropic hyperfine coupling constants a_iso(¹⁴N) and a_iso(¹H) of PBN/gly• adducts, UMP2 polarisable conductor calculation model with two ethanol molecules is explicitly defined.     

1H-,2H-,13C- and 14N-endor studies of coppinger's radicals in liquid solutions and in liquid crystals

Proton and non-proton ENDOR studies are reported on isotopically labelled Coppinger's radical (galvinoxyl) and on N-Coppinger's radical in isotropic solutions and in liquid-crystalline mesophases. The hyperfine coupling constant shifts have been measured over the temperature range of the nematic mesophase and an analysis of the shifts in terms of anisotropic hyperfine tensors and ordering parameters is given. A short phenomenological discussion of the ¹³C and¹⁴N ENDOR response is presented. Several methods for the sign determination of hyperfine coupling constants are discussed. Finally, a survey of the ENDOR spectroscopy on galvinoxyl type biradicals is given.     

Deuterium nuclear quadrupole hyperfine coupling in benzene-d1 observed by pulsed microwave fourier transform spectroscopy

The deuterium nuclear quadrupole hyperfine splitting of the 0(0,0)-1(0,1) pure rotational transition of benzene-d₁ has been observed with the help of a pulsed microwave Fourier transform spectrometer. Microwave pulses with a power of up to 56 W have been applied to the sample under low pressure and temperature. From the observed splitting the coupling constant χ_oa = 223(12) kHz has been determined. The quadrupole coupling tensor has been calculated by the ab initio method. The experimental result compares well the calculated values using different basis sets.     

Estimates of magnetic resonance parameters in semi-empirical quantum chemistry

The possibility to reliably estimate the magnetic resonance parameters (MRP) can significantly increase the information content of experimentally recorded spectra. Here we consider in detail semi-empirical estimates of the ESR spectra parameters: isotropic hyperfine coupling constants, anisotropic hyperfine coupling tensors and g-tensors. The results show that the semi-empirical procedures give estimates of MRP comparable in quality with those of complicated ab initio and DFT schemes. It was underlined that a special attention should be given to geometric parameters of free radicals. The automatic procedure to determine molecular geometries of free radicals on the ground of their spectral characteristics was discussed.     

Hydrogen bond studies : 79. Correlation curves for properties of hydrogen bonded water molecules based on ab initio calculations

Correlation curves have been derived from previous ab initio MO-LCAO-SCF calculations made on water molecules in hydrates. The OH-stretching frequency shifts have been correlated with: (a) ratios of the intensity of v?v_OH for bonded water to that for free water, (b) shifts in the OH-distances and (c) quadrupole coupling constants for deuterium in D₂O. Shifts in quadrupole coupling constants are also correlated with shifts in OH-distances. Comparisons have been made with experimental data and the agreement is found to be satisfactory.     

Manipulating the Oxidation State of CuxO Catalysts to Optimize the Selectivity of Gaseous Products in Electrochemical CO2 Reduction

Copper-based (Cu-based) catalysts can efficiently convert carbon dioxide to multicarbon products by electrochemical reduction. In this paper, the electrocatalyst with the coexistence of three valence states of Cu(0)-Cu(I)-Cu(II) was successfully prepared by adjusting the experimental conditions. The catalyst was derived from Cu/Cu₂O prepared on carbon cloth and exhibited excellent CO₂ reduction performance. For carbon-gaseous products, the Faradaic efficiencies for the Cu-2 catalyst consisting of Cu(0)-Cu(I)-Cu(II) were 35.45±3.40 % at −1.66 V vs. RHE, of which 23.85±1.18 % for C₂H₄. And the synergistic effect of Cu(0)-Cu(I)-Cu(II) significantly improved the selectivity of the catalyst to C₂H₄. This paper provided an efficient method to rationally tune the valence state of Cu-based catalysts to improve CO₂ reduction performance.     

Evaluation of MNDO approximation in quantum-chemical calculations of anisotropic hyperfine coupling tensors in free radicals

The MNDO approximation was tested for applicability in quantum-chemical calculations of anisotropic hyperfine coupling tensors using the same set of 17 free radicals as that used previously in evaluating a new procedure for quantum-chemical estimates of constants of isotropic hyperfine coupling with protons in the framework of the same approach. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2242–2247, December, 1999.     

NH2 radicals trapped in NH3 single crystals and various polycrystalline ammonia matrices

?H₂ radical trapped in various ammonia matrices has been investigated by ESR spectroscopy. From the study of the coupling tensors of the ?H₂ radical in a single crystal of NH₃, and taking into account the motions of this radical, it is shown that for all these matrices the spectra can be interpreted on the basis of coupling tensors which give for all cases the same isotropic coupling constants: a_N = 11.3 G, a_H = 24.6 G. Nitrogen and hydrogen coupling tensors for the motionless ?H₂ radical are also discussed     

Use of molecular dynamics simulations with ab initio SCF calculations for the determination of the deuterium quadrupole coupling constant in liquid water and bond lengths in ice

The deuterium quadrupole coupling constant and asymmetry parameter in heavy water were determined using ab initio SCF calculations. Snapshots from a molecular dynamics simulation were used to give liquid water cluster configurations and the influence of simulation parameters on the quadrupole coupling constant was investigated. The electronic potential model and the number of molecules in the molecular dynamics simulation and the pressure of the system were found to have only a small influence on the quadrupole coupling constant. The average value of the quadrupole coupling constant at room temperature, corrected for the known deficiency of the ab initio calculation in the gas phase, yields a quadrupole coupling constant of 253 kHz, in perfect agreement with the most recent experiments. The oxygen—deuterium bond lengths in ice Ih, ice II, and ice IX were determined using experimental quadrupole coupling constants and a model equation. An averaged bond length of 98.9 pm was obtained for the Ih form, which is approximately 2 pm shorter than that determined by neutron diffraction studies, whereas the bond lengths for the four deuterium sites in ice II and the three sites in ice IX are in fair agreement with experiment. © John Wiley & Sons, Inc.     

How CO2 Interacts with Carboxylic Acids: A Rotational Study of Formic Acid–CO2

The rotational spectra of the 1:1 formic acid–carbon dioxide molecular complex and of its monodeuterated isotopologues are analysed in the 6.5–18.5 and 59.6–74.4 GHz frequency ranges using a pulsed jet Fourier transform microwave spectrometer and a free‐jet absorption millimetre wave spectrometer, respectively. Precise values of the rotational and quartic centrifugal distortion constants are obtained from the measured frequencies, and quadrupole coupling constants are determined from the deuterium hyperfine splittings. Structural parameters are estimated from the moments of inertia and their differences among isotopologues: the complex has a planar structure with the two subunits held together by a HC(O)OH???O=C ? O (2.075 Å) and a HC(OH)O???CO₂ (2.877 Å) interactions. The ab initio intermolecular binding energy, obtained at the counterpoise corrected MP2/aug‐cc‐pVTZ level of calculation, is D_e=17 kJ mol^?1.     

Rotational isomerism as studied by nuclear quadrupole coupling.: Theoretical and experimental 14NX tensors for hydrazine,methylhydrazine, and 1,2-dimethylhydrazine

The nuclear quadrupole coupling constants of the ¹⁴N nuclei for hydrazine, the inner and outer conformers of methylhydrazine, and the inner-outer and the outer-outer conformers of 1,2-dimethylhydrazine are calculated by an ab initio SCF method, and also by a CI calculation for hydrazine. The results are compared with available experimental values. Characteristic dependence of the X tensors on the conformational structure is demonstrated. An application of theoretical hyperfine structures to a spectral analysis is discussed.