Ground State Of Cu2 Research Articles

Variable temperature EPR studies of Cu2+ and VO2+ doped potassium dihydrogen citrate (C6H7KO7)

Electron paramagnetic resonance (EPR) studies of single crystals and powder samples of Cu2+ and VO2+ doped potassium dihydrogen citrate (PDHC) have been carried out at different temperatures. The temperature-dependant g and A values have been obtained for powder spectra of both Cu2+ and VO2+ ions in PDHC and the ground state of Cu2+ ion has been determined. The powder spectra recorded for Cu2+ ion in the temperature range 70–298K are discussed with Jahn–Teller distortion. It is concluded that the g and A values of Cu2+: PDHC show the static property at low temperatures. For all temperatures, the result g//<g⊥<ge of VO2+: PDHC indicates that the unpaired electron exists in the dxy orbital.

Role of copper content on EPR, susceptibility and optical studies in poly(vinylalcohol) (PVA) complexed poly(ethyleneglycol) (PEG) polymer films

Polymer films of poly(vinylalcohol) (PVA) complexed with poly(ethyleneglycol) (PEG) with different dopant concentrations of Cu2+ ions are prepared by solution casting technique. Improvement in the crystallinity of the samples is observed with the X-ray diffraction (XRD) and scanning electron microscopy (SEM) analysis. Thermal transition and thermal degradation of the films with respect to copper concentration were studied by Differential Scanning Calorimetry (DSC) and thermo gravimetric analysis (TGA). The change in glass transition temperature (Tg) as a function of copper concentrations (x=1–5mol%) has been attributed to branching and steric effects in PVA+PEG complexes. In TGA curves low thermal degradation in the samples has been observed with high copper content. The EPR spectra of all the polymer samples exhibit resonance signals characteristic of Cu2+ ions. The spin-Hamiltonian parameter, indicate that the ground state of Cu2+ ions is dx2-y2 and the site symmetry around Cu2+ ions is tetragonally distorted octahedral site. The spin concentration (N) participating in the resonance is measured as a function of temperature and it obeys Boltzmans law. The paramagnetic susceptibility (χ) is calculated from the EPR data at various temperatures and the Curie constant (C) is evaluated. The optical absorption spectrum exhibits a broad band at 784nm which is assigned to the 2B1g→2B2g transition.

Coordination behavior of tetraaza [N4] ligand towards Co(II), Ni(II), Cu(II), Cu(I) and Pd(II) complexes: Synthesis, spectroscopic characterization and anticancer activity

Novel eight Co(II), Ni(II), Cu(II), Cu(I) and Pd(II) complexes with [N4] ligand (L) i.e. 2-amino-N-{2-[(2-aminobenzoyl)amino]ethyl}benzamide have been synthesized and structurally characterized by elemental analysis, spectral, thermal (TG/DTG), magnetic, and molar conductivity measurements. On the basis of IR, mass, electronic and EPR spectral studies an octahedral geometry has been proposed for Co(II), Ni(II) complexes and Cu(II) chloride complex, square-pyramidal for Cu(I) bromide complex. For Cu(II) nitrate complex (6), Pd(II) complex (8) square planar geometry was proposed. The EPR data of Cu(II) complexes in powdered form indicate dx2−y2 ground state of Cu(II) ion. The antitumor activity of the synthesized ligand and some selected metal complexes has been studied. The palladium(II) complex (8) was found to display cytotoxicity (IC50=25.6 and 41μM) against human breast cancer cell line MCF-7 and human hepatocarcinoma HEPG2 cell line.

Electron Paramagnetic Resonance Studies of Cu&amp;lt;sup&amp;gt;2+&amp;lt;/sup&amp;gt; and VO&amp;lt;sup&amp;gt;2+&amp;lt;/sup&amp;gt; Spin Probes in RO-Li&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt;O-Na&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt;O-K&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt;O-B&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt;O&amp;lt;sub&amp;gt;3&amp;lt;/sub&amp;gt; (R = Zn, Mg, Sr and Ba) Glass Systems

Mixed alkali and alkaline earth oxide glasses of RO-Li2O-Na2O-K2O-B2O3(R = Zn, Mg, Sr and Ba) system were studied by electron paramagnetic resonance (EPR) and optical absorption spectroscopy. Cu2+ and VO2+ ions were used as the spin probes. The glasses containing 1 mole% of Cu2+ and 2mole% of VO2+ were prepared by the melt quenching method. X-ray diffraction studies of the samples did not reveal crystalline phases. EPR measurements were made at X-band frequencies with 100 kHz field modulation, at 310 K. Optical spectra were recorded in the wavelength range 300 nm - 800 nm. From the EPR spectra the spin-Hamiltonian parameters were evaluated. The spin-Hamiltonian parameter values in the case of Cu2+ indicated that the ground state of Cu2+ was orbital (2B1g) and the site symmetry around Cu2+ is tetragonally distorted octahedral. The variation of gll and All with the alkaline earth oxide (RO) composition was found to be non-linear which may be due to the change in the ligand field strength at the site of Cu2+ ions. From the spin-Hamiltonian parameters of VO2+, it was observed that the vanadyl ions exist as VO2+ ions in octahedral coordination with tetragonal compression and have C4V symmetry with ground state dxy. Tetragonality (△gll/△g) of V4+ ion sites exhibited non-linear variation with RO content, which indicated change in the ligand field at the site of V4+. A broad optical absorption band was observed in the glass containing Cu2+ ions corresponding to the 2B1g → 2B2g transition. From the EPR and optical data the bond parameters were evaluated. In the case of VO2+ ions, the covalency rates were estimated.

ESR, optical absorption, IR and Raman studies of xTeO2 + (70 − x)B2O3 + 5TiO2 + 24R2O:1CuO (x = 10, 35 and 60 mol%; R = Li, Na and K) quaternary glass system

xTeO2+(70−x)B2O3+5TiO2+24R2O:1CuO (x=10, 35 and 60; R=Li, Na and K) glass system were studied by spectroscopic techniques such as ESR, optical absorption, Raman and IR. From ESR spectra, the spin Hamiltonian parameter values indicate that the ground state of Cu2+ is dx2−y2 and the site symmetry around the Cu2+ ion is tetragonally distorted octahedral coordination. Bonding parameters calculated from optical absorption and ESR data are found to change with alkali oxide and TeO2 content. Bonding parameters indicate a slight covalency for the in-plane σ bonding as compared to in-plane and out-of-plane π bonds. Both Raman and IR results show that glass network consists of TeO3, TeO4, BO3, BO4 and RiO4 group as basic structural groups. BO3–BO4− ring structure interconnected by TeO3− and TeO4− groups, where the BO4− groups are neighbors of the TeO3− groups. BO3→BO4 transition is also observed, which correlates with the transition of TeO4→TeO3 via TeO3+1.

Spiral ground state in the quasi-two-dimensional spin-12system Cu2GeO4

We apply density functional theory band structure calculations, the coupled cluster method, and exact diagonalization to investigate the microscopic magnetic model of the spin-$\frac{1}{2}$ compound Cu${}_{2}$GeO${}_{4}$. The model is quasi-two-dimensional, with uniform spin chains along one direction and frustrated spin chains along the other direction. The coupling along the uniform chains is antiferromagnetic, $J\ensuremath{\simeq}130$ K. The couplings along the frustrated chains are ${J}_{1}\ensuremath{\simeq}\ensuremath{-}60$ K and ${J}_{2}\ensuremath{\simeq}80$ K between nearest neighbors and next-nearest neighbors, respectively. The ground state of the quantum model is a spiral, with a reduced sublattice magnetization of 0.62 ${\ensuremath{\mu}}_{B}$ and a pitch angle of ${84}^{\ifmmode^\circ\else\textdegree\fi{}}$, both renormalized by quantum effects. The proposed spiral ground state of Cu${}_{2}$GeO${}_{4}$ opens a way to magnetoelectric effects in this compound.

Structural studies and anticancer activity of a novel (N 6O 4) macrocyclic ligand and its Cu(II) complexes

A novel (N 6O 4) macrocyclic ligand ( L) and its Cu(II) complexes have been prepared and characterized by elemental analysis, spectral, thermal (TG/DTG), magnetic, and conductivity measurements. Quantum chemical calculations have also been carried out at B3LYP/6-31+G(d,p) to study the structure of the ligand and one of its complexes. The results show a novel macrocyclic ligand with potential amide oxygen atom, amide and amine nitrogen atoms available for coordination. Distorted square pyramidal ([Cu(L)Cl]Cl·2.5H 2O ( 1), [Cu(L)NO 3]NO 3 ·3.5H 2O ( 2), and [Cu(L)Br]Br ·3H 2O ( 4) and octahedral ([Cu(L)(OAc) 2] ·5H 2O ( 3)) geometries were proposed. The EPR data of 1, 2, and 4 indicate d 1 x 2 − y 2 ground state of Cu(II) ion with a considerable exchange interaction. The measured cytotoxicity for L and its complexes ( 1, 2) against three tumor cell lines showed that coordination improves the antitumor activity of the ligand; IC 50 for breast cancer cells are ≈8.5, 3, and 4 μg/mL for L and complexes ( 1) and ( 2), respectively.

Optical absorption and EPR studies on (70 − x)Bi 2O 3– xLi 2O–30(ZnO–B 2O 3) (0 ⩽ x ⩽ 20) glasses

Glasses with composition (70 − x)Bi 2O 3– xLi 2O–30(ZnO–B 2O 3) where (0 ⩽ x ⩽ 20) have been prepared using melt quench technique. DSC studies showed that the glass transition temperature increases with Bi 2O 3 content. Optical absorption spectra of the pure glasses reveled that the cut off wave length increased and optical band gap energy decreased with increase in Bi 2O 3 content. Electron paramagnetic resonance (EPR) and optical absorption studies of zinc-bismuth based glasses were made by introducing Cu 2+ as a spin probe. It is observed that the spin-Hamiltonian parameters calculated from the EPR spectra are influenced by the glass composition. The Cu 2+ ions are in well-defined axial sites but subjected to small distortion leading to the broadening of the spectra. The spin-Hamiltonian parameter values indicate that the ground state of Cu 2+ is d x 2 - y 2 and the site symmetry around Cu 2+ ions is tetragonally distorted octahedral. The optical absorption spectra exhibited a broad band corresponding to the d– d transition bands of Cu 2+ ion. By correlating EPR and optical absorption data, the bond parameters are evaluated and correlated with the optical basicity of the glasses obtained from various techniques.

Mixed alkali effect in Cu2+ doped boroarsenate glasses—EPR and optical absorption studies

The local structure around Cu 2+ ion has been examined by means of electron paramagnetic resonance and optical absorption measurements in x K 2 O–(40− x )Na 2 O–50B 2 O 3 –10As 2 O 3 (0⩽ x ⩽40) glasses. The site symmetry around Cu 2+ ions is found to be tetragonally distorted octahedral and the ground state of Cu 2+ is d x 2 - y 2 . The spin-Hamiltonian parameter g || goes through a minima whereas A ∥ goes through a maxima around R K =0.5, showing the mixed alkali effect. The glass exhibited broad absorption band centred 12,239 cm −1 corresponding to the transition 2 B 1g → 2 B 2g . By correlating the EPR and optical absorption data, the molecular orbital coefficients α 2 and β 1 2 are evaluated for the present glass system. The IR studies show that the glass system contains BO 3 and BO 4 units in the disordered manner.

Room-temperature ferromagnetism in Cu+ implanted ZnO nanowires

We experimentally showed ferromagnetism at above 300 K for ZnO nanowires prepared by reactive vapour deposition and subsequently implanted with 2 at% of Cu. The magnetic moments of the samples annealed in oxygen and in argon at 600 °C for 120 min are about 0.42 µB and 0.33 µB per Cu atom, respectively. No ferromagnetism-related secondary phase existed according to the results of x-ray diffraction, x-ray photoelectron spectroscopy and transmission electron microscopy including HRTEM and EELS mapping. It can be concluded that the d9 configuration in the ground state of Cu2+ plays an important role in ferromagnetism. This controllable and shallow doped ion implantation technique may find potential applications in spintronic, especially nano-spintronic, devices.

Elimination of HBr from CH 3Br by Cu + and Au +: A DFT study

The elimination of HBr from CH 3Br by ground state of Cu + and Au + has been investigated by using DFT methods. A mechanism of one-step HBr elimination leading to CuCH 2 + was identified. For the formation of AuCH 2 +, besides the one-step mechanism, another two-step HBr elimination pathway through a C–Br bond insertion intermediate was also found, and this pathway is energetically more favorable than the one-step mechanism. The calculated reaction energy barriers show that the formation of AuCH 2 + is energetically much more favorable than the formation of CuCH 2 +. The experimental observations are well explained.

Electron paramagnetic resonance and optical absorption spectral studies on tetrahedrite and tennantite minerals

The behaviour of transition metal ions in tetrahedrite and in tennantite has been studied by electron paramagnetic resonance and optical absorption spectroscopy in the UV–Vis and NIR regions. The ground state of Cu(II) ion in both the minerals is confirmed as 2B1g. In both the minerals, two sets of three characteristic bands observed in the optical absorption spectra are assigned to the transitions, 2B1g→2A1g, 2B1g →2B2 and 2B1g→2Eof Cu(II) ion in tetragonal field. The presence of bands in optical absorption spectrum is an evidence for iron impurity in the tetrahedrite and Mn(II) in tennantite mineral. The copper content in tetrahedrite and tennantite is about 40 wt%. The NIR spectra are due to water present in the samples.

Two novel grid networks based on Keggin-type polyoxometalate clusters assembled through weak Cu⋯O interactions

Two novel grid networks based on Keggin-type polyoxoanion, formulated [Cu(2,2′-bipy)2](HPMo12O40)·H2O (1) and [Cu(2,2′-bipy)2](HPW12O40)·H2O (2) have been synthesized hydrothermally and characterized by elemental analyses, IR, EPR and X-ray single crystal diffraction. 1 is a 2D grid network built by the interconnection of bisupporting polyoxoanion clusters assembled through weak Cu⋯O interactions. The EPR spectrum of 1 indicates that its unpaired electrons are placed in dx2−y2 orbital of the ground state of Cu(II). Compound 2 is isostructural with compound 1.

Optical absorption and EPR studies on beaverite mineral

The behaviour of transition metal ions in beaverite mineral has been studied by spectroscopic techniques such as electron paramagnetic resonance and absorption spectroscopy in the UV–vis and NIR regions. The ground state of Cu(II) ion in beaverite is confirmed as 2B 1g since g ∥ > g ⊥ (2.42 > 2.097). A resonance noticed at g = 2.017 is ascribed to Fe(III) impurity. Two sets of three characteristic bands observed in the optical absorption spectra are assigned to the same transitions, 2B 1g → 2A 1g, 2B 1g → 2B 2 and 2B 1g → 2E g of Cu(II) ion in tetragonal field. The presence of Fe(III) bands is supportive evidence for iron impurity in the mineral. Mid infrared spectrum is due to overtones and combination tones of water and hydroxyl groups.

High-field ESR study of one-dimensional [formula omitted] Heisenberg antiferromagnet with next-nearest exchange interaction

High-field ESR measurements of Cu[2-(2-aminomethyl)pyridine]Br 2 (Cu(ampy)Br 2) powder sample, which is a model substance of the S = 1 2 one-dimensional Heisenberg antiferromagnet (1DHAF) with a frustration, have been performed in the frequency region from 40 to 480 GHz using the pulsed magnetic field up to 16 T. The obtained g-values are g / / = 2.06 and g ⊥=2.06, which suggest that the orbital ground state of Cu 2+ in Cu(ampy)Br 2 is the x 2– y 2 orbital state. Distinct frequency dependent g-shift is observed below 4.2 K from the temperature dependence measurements. The possibility of the phase transition below 4.2 K is discussed from the frequency dependence results at 1.7 and 4.2 K.

Optical absorption and EPR studies on enargite

The behaviour of transition metal ions in enargite has been studied by electron paramagnetic resonance and absorption spectroscopy in the UV–VIS and near-IR regions. The ground state of Cu(II) ions in enargite is confirmed as 2B1g since g11>g⊥ (2.54>2.11). Three characteristic bands observed in the optical absorption spectra at 8275, 13105 and 18420 cm−1 are assigned to the transitions, 2B1g→2A1g, 2B1g→2B2 and 2B1g→2Eg, respectively, of Cu(II) ion in the tetragonal field. The presence of Fe(II) bands is an evidence for iron impurities in the mineral.

The origin of low‐dimensional magnetism in Cu(en )2Pt(CN)4

AbstractMagneto‐structural correlations in Cu(en )2Pt(CN)4 (en = C2H8N2) have been investigated by experimental studies of the magnetic properties and hydrogen bond geometry. The analysis of electron paramagnetic resonance spectra confirmed the d z2 electronic ground state of Cu(II) ion expected from room temperature X‐ray measurements. Magnetization and susceptibility data indicate the presence of weak exchange coupling J /k B = –0.4 K. Consequently, a spin diffusive regime in the spin relaxation can be expected at 4 K, and the angular dependence of the linewidth can be qualitatively explained by considering two‐dimensional magnetic behaviour. (© 2006 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Optically detected magnetic resonance of Cu, Fe and Mn defects inLiNbO3

The optical absorptions of Cu2+, Fe3+ and Mn2+ in LiNbO3 are investigated using optically detected magnetic resonance (ODMR). Themethod is based on the changes of the magnetic circular dichroism (MCD)bands of the ions, caused by the magnetic resonances of the paramagneticground states of these ions. All transitions reached from the ground state ofCu2+ lie between 1180 and 860 nm. Three bands are observed, resulting from combined spin–orbitand trigonal field splitting of the first excited crystal field states. All features resulting fromFe3+ have to be ascribed to the forbidden transitions from the6A tothe 4G cubic precursor states. Their weak and narrow optical transitionsare superimposed on the wide and strong intervalence absorption ofFe2+. This ion leads to a diamagnetic contribution to the MCD, resultingfrom the Zeeman admixture of the first excited spin state ofFe2+ to its diamagnetic ground state. The MCD ofMn2+ is caused by an intervalence transition to the conduction band. ODMR allows us to detectthese bands, lying near 400 nm, which in plain optical absorption are coveredby strong precursor absorptions before the onset of the fundamental transition.

Optical absorption and electron spin resonance studies of Cu2+ in Li2O-Na2O-B2O3-As2O3 glasses

The local structure around Cu2+ ion has been examined by means of electron spin resonance and optical absorption measurements in xLi2O-(40-x)Na2O-50B2O3-10As2O3 glasses. The site symmetry around Cu2+ ions is tetragonally distorted octahedral. The ground state of Cu2+ isd x 2−y 2.The glass exhibited broad absorption band near infrared region and small absorption band around 548 nm, which was assigned to the 2B1g →2Eg transition.

Towards accurate all-electron quantum Monte Carlo calculations of transition-metal systems: Spectroscopy of the copper atom

In this work we present all-electron fixed-node diffusion Monte Carlo (FN-DMC) calculations of the low-lying electronic states of the copper atom and its cation. The states considered are those which are the most relevant for the organometallic chemistry of copper-containing systems, namely, the (2)S, (2)D, and (2)P electronic states of Cu and the (1)S ground state of Cu(+). We systematically compare our FN-DMC results to CCSD(T) calculations using very large atomic-natural-orbital-type all-electron basis sets. The FN-DMC results presented in this work provide, to the best of our knowledge, the most accurate nonrelativistic all-electron correlation energies for the lowest-lying states of copper and its cation. To compare our results to experimental data we include the relativistic contributions for all states through numerical Dirac-Fock calculations, which for copper (Z=29) provide almost the entire relativistic effects. It is found that the fixed-node errors using Hartree-Fock nodes for the lowest transition energies of copper and the first ionization potential of the atom cancel out within statistical fluctuations. The overall accuracy achieved with quantum Monte Carlo for the nonrelativistic correlation energy (statistical fluctuations of about 1600 cm(-1) and near cancelation of fixed-node errors) is good enough to reproduce the experimental spectrum when relativistic effects are included. These results illustrate that, despite the presence of the large statistical fluctuations associated with core electrons, accurate all-electron FN-DMC calculations for transition metals are nowadays feasible using extensive but accessible computer resources.