Thermal and EPR spectroscopic studies of novel coordination compound trans-bis(acesulfamato)tetraaquazinc(II) with Mn(II) impurity

The thermogravimetric analysis (TGA) and electron paramagnetic resonance (EPR) studies of powder and single crystals of bis(acesulfamato)tetraaquazinc(II), Zn(acs)(2)(H(2)O)(4), a novel coordination compound, are carried out. Previously synthesized bis(acesulfamato) tetraaquamanganese(II), Mn(acs)(2)(H(2)O)(4), is included into the host in trace amount as a paramagnetic probe for EPR analysis. Single crystal EPR spectra at room temperature are resolved and discussed. Low temperature EPR spectra down to 90K do not show remarkable change. At higher temperatures, however, the TGA and EPR spectra show changes around 335 K and 395 K; the causes and the mechanisms of changes are discussed.     

Vibronic effects in Cu(II)-doped Ba2Zn(HCO2)6 x 4 H2O

The temperature-dependent electron paramagnetic resonance (EPR) spectrum of approximately 1% Cu(II) ions doped into Ba 2Zn(HCO2)6 x 4 H2O was analyzed at the Q-band frequencies over the temperature range 100-350 K to obtain structural information about the local environment. It can be concluded that the host crystal imparts a large orthorhombic strain which mainly corresponds to a tetragonal compression imposed onto the Cu(II)O6 species. This results in a copper center which adopts an orthorhombically distorted elongated geometry with the elongated axis perpendicular to the direction of the tetragonal compression due to the host crystal. There are two possible axes of elongation, and these represent two conformers separated by approximately 320 cm(-1). The thermal population of the higher energy level averages the g values, giving the observed temperature-dependent EPR spectra. The averaging process is between vibronic levels that are localized at two different minima of a single ground-state potential energy surface. These vibronic levels correspond to vibrational levels having different electronic properties. The determination of the host lattice strain parameters from the Cu(II) EPR spectra means that the guest ion is used as a probe of the environment of the Zn(II) site. The structural data derived from the lattice strain parameters are correlated with those from the Ba 2Zn(HCO2)6 x 4 H2O crystal structure.     

Identification of static JT in copper(II) doped hexaimidazole M(II) lattices: M=Co and Ni: an EPR study

Single crystal EPR studies on Cu(II) doped paramagnetic host lattices, hexaimidazole M(II) dichloride tetrahydrate (M=Co and Ni), isomorphous with M=Zn, have been carried out from room temperature to 77K to understand the nature of Jahn-Teller (JT) distortion in these paramagnetic host systems. The paramagnetic impurity, doped in the present two paramagnetic host lattices, shows anisotropic EPR spectra with superhyperfine from ligands, even at room temperature. An interesting observation noticed in the EPR spectra at room temperature is that there are more resonances corresponding to the second site in the paramagnetic hosts than in the diamagnetic host at 4.2K. This difference in behavior between the diamagnetic and paramagnetic host lattices indicates a change in the depth of the JT valleys. The spin Hamiltonian parameters are evaluated for Cu(II) ion in both the host lattices and the relaxation times have been calculated for the ion in cobalt host lattice only.     

Synthesis, characterisation and electrochemical behaviour of Cu(II), Co(II), Ni(II) and Zn(II) complexes derived from acetylacetone and p -anisidine and their antimicrobial activity

Neutral tetradentate N₂O₂ type complexes of Cu(II), Ni(II), Co(II) and Zn(II) have been synthesised using the Schiff base formed by the condensation of acetylacetone andp-anisidine. Microanalysis, molar conductance, magnetic susceptibility, IR, UV-Vis,¹ H NMR, CV and EPR studies have been carried out to determine the structure of the complexes. From the data, it is found that all the complexes possess square-planar geometry. The EPR spectrum of the copper complex in DMSO at 300 K and 77 K was recorded and its salient features are reported. All the title complexes were screened for antimicrobial activity by the well diffusion technique using DMSO as solvent. The minimum inhibitory concentration (MIC) values were calculated at 37°C for a period of 24 h. It has been found that all the complexes are antimicrobially active and show higher activity than the free ligand.     

EPR spectra of Cu(2+) doped [Zn(sac)2(dmen)] and [Zn(sac)2(paen)] single crystals

Cu(2+) doped single crystals of [Zn(sac)2(dmen)] (sac: saccharinate, dmen: N,N'-dimethylethylendiamine) and [Zn(sac)2(paen)], (paen: N,N'-bis(3-propylamine)ethylendiamine) complexes have been investigated by electron paramagnetic resonance (EPR) technique. Detailed investigations of the EPR spectra indicate that Cu(2+) ion substitute with Zn(2+) ion and forms tetrahedral complex in [Zn(sac)2(dmen)] and octahedral complex in [Zn(sac)2(paen)] hosts. Principal values of the g and hyperfine tensors are determined and the ground state wave functions of Cu(2+) ions are obtained using EPR parameters.     

EPR study of the atom transfer radical polymerization (ATRP) of (meth)acrylates

Electron paramagnetic resonance (EPR) spectroscopy was applied to atom transfer radical polymerization (ATRP) of methyl methacrylate (MMA) and methyl acrylate (MA) in order to investigate the mechanism of the controlled/“living” radical polymerization system. Although initially only copper(I) species was added to the system as a catalyst, EPR signals of copper(II) species were observed during the polymerization of MMA initiated by ethyl 2-bromoisobutyrate and p-methylbenzenesulfonyl chloride, and polymerization of MA initiated by methyl 2-bromopropionate. As the polymerization proceeded, the concentration of copper(II) increased gradually until a steady state was reached. The EPR results indicate that 5–6% of copper(I) species converted to copper(II) species in polymerization of MMA and about 3% in polymerization of MA at 90°C.     

An EPR study of Cu doped diaquabis(nicotinamide)bis(o-sulfobenzimidato-N)-cadmium(II) single crystals

The electron paramagnetic resonance spectra of Cu²⁺ doped diaquabis(nicotinamide)bis(o-sulfobenzimidato-N)-cadmium(II) (hereafter, CdNAS) single crystals which were taken at room temperature are discussed. It was found from the analysis of the EPR data that the Cu²⁺ ions substitute for magnetically inequivalent Cd²⁺ ions. Two magnetically inequivalent Cu²⁺sites were observed. The principal values of the g and the hyperfine tensors were determined. The ground state wave functions of the unpaired electron of Cu²⁺ ions in two sites were constructed and type of the distortion was determined.     

The nature of Cu(II) species in ATRP: New insights via EPR

Identification of the paramagnetic species present in the Cu(I)Br‐catalyzed atom transfer radical polymerization (ATRP) of a model monomer (isobornyl acrylate) has been carried out by electron paramagnetic resonance (EPR) in the continuous wave mode at 90 K. Up to five different species—four copper‐based species and one organic radical—were detected with this technique. The EPR parameters of the copper‐based species are found to differ strongly, and originate from diverse isolated Cu(II) complexes, as well as dipolarly interacting and even exchange‐coupled Cu(II) species. The work highlights the complexity of the copper‐based EPR signal observed in copper‐mediated ATRP reactions. Analysis of the time evolution of the individual EPR contributions reveals the disadvantages of quantitative kinetics studies based on the summed EPR intensity of all copper‐based species, as is commonly used in literature for this type of reactions. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 1493–1501, 2010     

Copper(III) and vanadium(IV)-oxo corrolazines

As part of our efforts to develop the transition metal chemistry of corrolazines, which are ring-contracted porphyrinoid species most closely related to corroles, the vanadium and copper complexes (TBP)(8)Cz(H)V(IV)O (1) and (TBP)(8)CzCu(III) (2) of the ligand octakis(para-tert-butylphenyl)corrolazine [(TBP)(8)Cz] have been synthesized. The coordination behavior, preferred oxidation states, and general redox properties of metallocorrolazines are of particular interest. The corrolazine ligand in 1 was shown to contain a labile proton by acid/base titration and IR spectroscopy, serving as a -2 ligand rather than as the usual -3 donor. The oxidation state of the vanadium center in 1 was shown to be +4, in agreement with the overall neutral charge for this complex. The EPR spectrum of 1 reveals a rich signal consistent with a V(IV)(O) (d(1), S = 1/2) porphyrinoid species (g(xx) = 1.989, g(yy) = 1.972, g(zz) = 1.962). The electrochemical analysis of 1 shows behavior closer to that of a porphyrazine than a corrolazine, with a positively shifted, irreversible reduction at -0.65 V (vs Ag/AgCl). Resonance Raman and IR data for 1 confirm the presence of a triply bonded terminal oxo ligand with nu(V(16)O) = 975 cm(-1) and nu(V(18)O) = 939 cm(-1). The copper complex 2 exhibits a diamagnetic (1)H NMR spectrum, indicative of a bona fide square planar copper(III) (d(8), low-spin) complex. Previously reported copper corroles have been characterized as copper(III) complexes which exhibit a paramagnetic NMR spectrum at higher temperatures, indicative of a thermally accessible triplet excited state ([(corrole(*+))Cu(II)]). The NMR spectrum for 2 shows no paramagnetic behavior in the range 300-400 K, indicating that compound 2 does not have a thermally accessible triplet excited state. These data show that the corrolazine system is better able to stabilize the high oxidation state copper center than the corresponding corroles. Electrochemical studies of 2 reveal two reversible processes at +0.93 and -0.05 V, and bulk reduction of 2 with NaBH(4) generates the copper(II) species [(TBP)(8)CzCu(II)](-) (2a), which exhibits an EPR signal typical of a copper(II) porphyrinoid species.     

Charge-transfer photochemistry of bis(diethyl-diselenocarbamato)copper(II)

The photochemical reactions of bis(diethyl-diselenocarbamato)copper(II), Cu(Et2dsc)2, complex have been studied in toluene, CH2Cl2, CHCl3 and chloroalkane/EtOH mixed solvents. Charge-transfer irradiation induces intramolecular oxidation of the ligand and reduction of copper(II) to copper(I) as evidenced by EPR and UV-Vis spectra of the complex as well as quantum yield results. When photolysis is carried out in CHCl3 or CH2Cl2 or in the solvent mixture CHCl3/EtOH resp. CH2Cl2/EtOH of lower than 1:1 EtOH content, the primary photoproduct CuI(Et2dsc) is further oxidised in a dark reaction with the chloroalkane producing the corresponding paramagnetic mixed-ligand CuII(Et2dsc)Cl complex in equilibrium with its chloride-bridged and EPR silent, dimeric form Cu2(Et2dsc)2Cl2. At low concentration of EtOH the equilibrium is shifted to the dimeric form whereas at higher than 1:1 EtOH content in the mixed solvent CHCl3/EtOH it is shifted to CuII(Et2dsc)Cl. A reaction mechanism is proposed and the role of ethanol is discussed.     

Determination of the solution structures of melamine-based bis- and tris-macrocyclic ligand copper(II) complexes

A combination of molecular mechanics (MM), electron paramagnetic resonance spectroscopy (EPR), and spectra simulation (MM-EPR) has been used to determine the solution structures of di- and trinuclear copper(II) complexes of melamine-based oligomacrocyclic ligands. The spin Hamiltonian parameters of the mononuclear, melamine-appended macrocyclic ligand copper(II) complex have been determined by EPR spectroscopy and were also studied with DFT methods. These spin Hamiltonian parameters, together with the structural parameters obtained from models optimized with MM, have been used for the simulation of the EPR spectra of the di- and trinuclear complexes. For the dinuclear complex, the syn isomer is preferred over the anti, for which an X-ray structure exists; for the trinuclear complex, the syn,syn isomer is preferred over the syn,anti form. Additional support for these assignments comes from DFT calculations, and this demonstrates that the MM-DFT-EPR method is a reliable approach for the determination of solution structures and for the analysis of spin Hamiltonian parameters of dipolar, coupled transition metal complexes (g and A tensors and J values).     

Solution combustion derived nanocrystalline Zn(2)SiO(4):Mn phosphors: a spectroscopic view

Manganese doped nanocrystalline willemite powder phosphors Zn(2-x)Mn(x)SiO(4) (0.1(6)A(1) ground state. The mechanism involved in the generation of a green emission has been explained in detail. The effect of Mn content on luminescence has also been studied.     

Crystal structure and EPR studies of doped Cu2+ ion in [Zn(sac)2(en)2] single crystal

The tran-bis(ethylenediamine)bis(saccharinato)Zinc(II), [Zn(sac)₂(en)₂] (ZSED), (en: ethylenediamine and sac: saccharinate) complex has been synthesized and its crystal structure has been determined by X-ray diffraction analysis. The compound crystallizes in space group P2₁/c. The Zn(II) ion is hexa-coordinated by four nitrogens of two bidentate en ligands composing the basal plane and two nitrogen atoms from the monodentate two sac ligands (N-bonded) occuping the axial sites, adopting an elongated octahedral sphere. Both en and sac ligands occupy the trans positions of the coordination octahedron. The Zn(II) ion in title compound sits on a inversion centre and is octahedrally coordinated two bidentate en (ethylenediamine) and two sac (saccharinate) (N-bonded) ligands. The magnetic environments of Cu²⁺ doped [Zn(sac)₂(en)₂] complex have been identified by electron paramagnetic resonance (EPR) technique. Cu²⁺ doped ZSED single crystals have been studied at room temperature in three mutually perpendicular planes. The calculated results of the Cu²⁺ doped ZSED indicate that Cu²⁺ ion contains two magnetically inequivalent Cu²⁺ sites in distinct orientations occupying substitutional positions in the host lattice and show very high angular dependence.     

Structure of bis[ethyl (trifluoroacetyl)acetato]copper(II) and its adduct with 4-(dimethylamino)pyridine: EPR and X-ray study

Bis[ethyl (trifluoroacetyl)acetato]copper(II), [Cu(etfac)₂], has been prepared and studied by X-ray crystallography and EPR spectroscopy. The complex is centrosymmetrical and crystallizes in the P2₁/c space group with two formula units per unit cell. After dissolving of the complex in solid matrix or in suitable solvents some changes are detected in the EPR spectra and are discussed. The EPR spectra of the complex magnetically diluted in the corresponding Pd(II) complex reveal the presence of only one paramagnetic species further denoted as B. However, EPR spectra measured in solution indicate the presence of two different paramagnetic species: (i) non-distorted parent species B, and (ii) rhombic-distorted species A, which prevail in solutions. The A:B species ratio is a function of the solvent and temperature. The [Cu(etfac)₂] adduct with 4-(dimethylamino)pyridine has also been studied and found to crystallize in the C2/c space group. The adduct EPR spectrum monitored in solution shows the presence of only one paramagnetic species.     

EPR of VO2+ in double format, Ba2Zn(HCOO)6(H2O)4 single crystals

VO(2+) doped single crystal of Ba(2)Zn(HCOO)(6)(H2O)(4) (BZFA) were investigated using electron paramagnetic resonance (EPR) technique at ambient temperature. Detailed investigation of EPR spectra indicated that the VO(2+) substitutes the Zn(2+) in the structure. The sites with different orientations were observed for VO(2+) in Ba(2)Zn(HCOO)(6)(H2O)(4).single crystal, but the only intense site among these sites was evaluated to obtain spin-Hamiltonian parameters, which are the principal axis values of the g and the hyperfine tensors. The covalent bonding parameter for VO(2+) and Fermi contact term were calculated using the spin-Hamiltonian parameters.     

EPR study of Cu(2+)-doped tetraaqua-di(nicotinamide)Co(II) saccharinate single crystals

The electron paramagnetic resonance spectra of Cu(2+) impurities in [Co(nicotinamide)(2)(H(2)O)(4)](saccharinate)(2) single crystals have been studied at ambient temperature in three mutually perpendicular planes. The angular variation of the spectra shows that the Cu(2+) ion substitutes the Co(2+) site in the lattice. The EPR spectra of Cu(2+) ions are characteristic of tetragonally elongated octahedral site. The spin-Hamiltonien parameters were obtained from the single crystal EPR analysis. The ground-state wave function of Cu(2+) ion in the lattice has been constructed.     

Structures of o-hydroxy Schiff-base copper(II) complexes derived from p-benzylamines

Nine copper(II) complexes of o-hydroxy Schiff bases derived from benzylamine, p-methoxybenzylamine, p-nitrobenzylamine, salicylaldehyde, 2-hydroxy-1-naphthalenecarboxaldehyde, and 3-hydroxy-2-naphthalenecarboxaldehyde were synthesized and characterized by chemical analysis, mass spectrometry, UV-Vis, infrared and electron paramagnetic resonance (EPR) spectroscopy, and seven X-ray crystal structures. The X-ray diffraction studies of these compounds showed that the geometry around the copper is square planar in six of the seven complexes. EPR studies of all the complexes in DMF solution at 77 K suggest that their geometries in solution are square planar as well.     

Tridentate facial ligation of tris(pyridine-2-aldoximato)nickel(II) and tris(imidazole-2-aldoximato)nickel(II) To generate NiIIFeIIINiII, MnIIINiII, NiIINiII, and ZnIINiII and the electrooxidized MnIVNiII, NiIINiIII, and ZnIINiIII species: a magnetostructural, electrochemical, and EPR spectroscopic study

Eight hetero- and homometal complexes 1-6, containing the metal centers Ni(II)Fe(III)Ni(II) (1), Mn(III)Ni(II) (2), Ni(II)Ni(II) (3a-c and 4), Zn(II)Ni(II) (5), and Zn(II)Zn(II) (6), are described. The tridentate ligation property of the metal complexes tris(pyridine-2-aldoximato)nickel(II) and tris(1-methylimidazole-2-aldoximato)nickel(II) with three facially disposed pendent oxime O atoms has been utilized to generate the said complexes. Complex 1 contains metal centers in a linear arrangement, as is revealed by X-ray diffraction. Complexes were characterized by various physical methods including cyclic voltammetry (CV), variable-temperature (2-290 K) magnetic susceptibility, electron paramagnetic resonance (EPR) measurements, and X-ray diffraction methods. Binuclear complexes 2-6 are isostructural in the sense that they all contain a metal ion in a distorted octahedral environment MN(3)O(3) and a second six-coordinated Ni(II) ion in a trigonally distorted octahedral NiN(6) geometry. Complexes 1-4 display antiferromagnetic exchange coupling of the neighboring metal centers. The order of the strength of exchange coupling in the isostructural Ni(II)2 complexes, 3a-c, and 4, demonstrates the effects of the remote substituents on the spin coupling. The electrochemical measurements CV and square wave voltammograms (SQW) reveal two reversible metal-centered oxidations, which have been assigned to the Ni center ligated to the oxime N atoms, unless a Mn ion is present. Complex 2, Mn(III)Ni(II), exhibits a reduction of Mn(III) to Mn(II) and two subsequent oxidations of Mn(III) and Ni(II) to the corresponding higher states. These assignments of the redox processes have been complemented by the X-band EPR measurements. That the electrooxidized species [3a]+, [3b]+, [3c]+, and [4]+ contain the localized mixed-valent NiIINiIII system resulting from the spin coupling, a spin quartet ground state, S(t) = 3/2, has been confirmed by the X-band EPR measurements.     

Synthesis, crystal structure, EPR spectra of Cu2+ doped [Zn(methylisonicotinate)2(H2O)4]·(sac)2 single crystal

The tetraaquabis(methylisonicotinate)zinc(II) disaccharinate [hereafter, [Zn(mein)2(H2O)4]·(sac)2], complex has been synthesized and characterized by spectroscopic IR, EPR and X-ray diffraction technique. The octahedral Zn(II) ion, which rides on a crystallographic centre of symmetry, is coordinated by two monodentate mein ligands through the ring nitrogen and four aqua ligands to form discrete [Zn(mein)2(H2O)4] unit, which captures two saccharinate ions in up and down positions, each through intermolecular hydrogen bonds. The magnetic environments of Cu2+ doped [Zn(mein)2(H2O)4]·(sac)2 complex have been identified by electron paramagnetic resonance (EPR) technique. EPR spectra of Cu2+ doped [Zn(mein)2(H2O)4]·(sac)2 single crystals have been studied between 113 and 300 K in three mutually perpendicular planes. The calculated results of the Cu2+ doped [Zn(mein)2(H2O)4]·(sac)2 indicate that Cu2+ ion contains two different complexes and each complexes are located in different chemical environments and each environment contains two magnetically inequivalent Cu2+ sites in distinct orientations occupying substitutional positions in the lattice. The vibrational spectra of this compound were discussed in relation to other compounds containing methyl isonicotinate and saccharinate complexes. The assignments of the observed bands were discussed.     

Electron paramagnetic resonance studies of Cu2+ ion in tetraaqua-di(nicotinamide)Ni(II)-saccharinates single crystals

X-band (approximately 9.8 GHz) electron paramagnetic resonance (EPR) measurement at ambient temperature in three mutually perpendicular planes have been carried out on a single crystal of Cu2+ doped mixed ligand complex of Ni(II) with saccharin and nicotinamide [Ni(Nic)2(H2O)4](sac)2. The angular dependent spectra showed that the Cu2+ ion enters Ni2+ sites in the lattice and distorted local environment of Ni2+ site. The principal g and A values, covalency parameter (alpha'2), mixing coefficients (alpha and beta) and Fermi contact term (K) have been evaluated from the EPR analysis. The ground-state wave function of the Cu2+ ion has been constructed using the alpha'2, alpha and beta values. The nature of the distortion present in the lattice is obtained from the values of the mixing coefficients.