EPR and electronic spectral studies of bis(dihalcogenocarbamato)copper(II)-solvent interactions

The interaction of bis(diethyldithiocarbamato)copper(II), Cu(Et2dtc)2, and bis(diethyldiselenocarbamato)copper(II), Cu(Et2dsc)2, complexes with solvents is studied by EPR and electronic spectroscopy. The solvents used are CCl4, CHCl3, CH2Cl2, C6H5 x CH3, DMFA and DMSO. It is found that Cu(Et2dsc)2 is destroyed in a first order reaction in CCl4 with an activation energy of 5.2 kcal/mol. The other complex, Cu(Et2dtc)2, is only destroyed in DMSO. The observed effects and reaction pathways are discussed in terms of solute-solvent donor-acceptor interactions taking into account the differences in the electronic structures of both complexes.     

Effect of solute-co-ordinating solvent interactions and temperature on the EPR and electronic spectra of bis(dithiophosphato)copper(II)

The self-redox reaction proceeding between two molecules of the complex bis(disubstituted-dithiophosphato)copper(II), CuII(R2-dtp)2, is studied by EPR and UV-VIS spectroscopy in DMFA, DMSO and pyridine. The effect of temperature and disulphide concentration in the solutions is also evaluated. The EPR spectra show that the g-values of CuII(R2-dtp)2 increase when it is dissolved in co-ordinating solvents, whereas the copper hyperfine splitting decreases compared to the corresponding values in non-co-ordinating solvents. Under the same conditions, a hypsochromic shift is observed in the maximal absorption at 420 nm of the electronic spectra which corresponds to the ligand-to-metal charge-transfer (LMCT) transition of the complex. The results are explained with the formation of axial or equatorial adducts between CuII(R2-dtp)2 and the co-ordinating solvents used. On the other hand, the molar absorptivity of the LMCT band and the intensity of the EPR spectrum increase strongly with the nature of the used co-ordinating solvent, the time after dissolution and the quantity of added disulphide. Both also depend on the size and shape of remote ligand substituents and they increase in the order Me < Et < i-Pr. Beer's law is not obeyed immediately after dissolution of copper bis-dithiophosphate complexes. However, after standing for 24 h in the dark, DMFA solutions exhibit linear absorption/concentration dependence with approximately 70% higher molar absorptivity. An additional increase of the LMCT band and EPR intensity is found after heating the solution up to 50 degrees C for a short time, as well as after addition of the corresponding disulphide of dithiophosphate [(RO)2P(S)S-S(S)P(RO)2] to the CuII(R2-dtp)2 solution. As a result, the molar absorptivity value at the maximum of the LMCT band of Cu[(i-PrO)2-dtp]2 increases from 7.9 x 10(3) m(-1) dm3 cm(-1) immediately after dissolution to 2.9 x 10(4) m(-1) dm3 cm(-1). In DMSO and pyridine, the intensity of both the EPR signal and LMCT band of CuII(R2-dtp)2 continuously decrease after the preparation of the solutions. A small increase is only observed immediately after the addition of the corresponding disulphide of dithiophosphate. While DMFA forms stable adducts with Cu[(i-PrO)2-dtp]2, adduct formation with DMSO and pyridine destroys the initial complex.     

Solvent Effect on the Ligand Exchange between Bis(diethyldithiocarbamato)copper(II) and Bis(diethyldiselenocarbamato)copper(II)

EPR and spectrophotometric study on the products of ligand‐exchange taking place on mixing bis(diethyldiselenocarbamato)copper(II), [Cu(Et₂dsc)₂], and bis(diethyldithiocarbamato)copper(II), [Cu(Et₂dtc)₂], solutions is reported. EPR spectra monitored at room temperature for one month period reveal a stable equilibrium among the parents (chromophores CuS₄ and CuSe₄) and the obtained mixed‐chelate [Cu(Et₂dtc)(Et₂dsc)] complex (chromophore CuS₂Se₂) in heptane, hexane, benzene, toluene, acetone, DMFA, DMSO and dichloromethane. In CCl₄ and CHCl₃ two new additional EPR spectra appear attributed to the mixed‐chelate complexes with the chromophores CuSSe₃ and CuS₃Se which are not observed with electronic spectroscopy. The intensities of all five EPR spectra decrease with the time. It is assumed that the new mixed‐chelates observed in CCl₄ and CHCl₃ are obtained in a reaction of [Cu(Et₂dtc)(Et₂dsc)] or [Cu(Et₂dtc)₂] with the ester of diselenocarbamic acid which is formed in a parallel reaction of [Cu(dsc)₂]with CCl₄ or CHCl₃.     

EPR study on the ligand-exchange reaction between bis(diethyldiselenocarbamato)copper(II) and bis(octyldithiocarbonato)copper(II)

EPR study on the ligand-exchange reaction between bis(diethyldiselenocarbamato)copper(II), Cu(Et2dsc)2, and bis(octyldithiocarbonato)copper(II), Cu(octxant)2, in CH2Cl2, CHCl3, CCl4, C6H6 and C6H5.CH3 is reported for the first time. Mixing of equimolar amounts of the parents (chromophores CuSe4 and CuS4, respectively) in C6H6, C6H5.CH3 and CH2Cl2 makes EPR signals of both parents superimposed by the spectrum of a mixed-chelate Cu(xant)(dsc) complex (chromophore CuS2Se2). A new additional EPR spectrum appears in CHCl3 or CCl4 due to a five-coordinate mixed-ligand complex with the chromophore Cu(S3Se)S as follows by comparing the g-values of parents and mixed-ligand complexes. The appearance of this complex could be explained having in mind donor-acceptor properties of complexes, solvents and the resultant reaction of Cu(octxant)2 with the ester of diselenocarbamic acid yielded in Cu(Et2dsc)2 destruction by CCl4 or CHCl3.     

Synthesis, electronic and ESR spectral studies on copper(II) nitrate complexes with some acylhydrazines and hydrazones

This paper describes the preparation of [Cu(bh)(2)(H(2)O)(2)](NO(3))(2)], [Cu(ibh)(2)(NO(3))(2)], [Cu(ibh)(2)(H(2)O)(2)](NO(3))(2) and [Cu(iinh)(2)(NO(3))(2)] (bh=benzoyl hydrazine (C(6)H(5)CONHNH(2)); ibh=isonicotinoyl hydrazine (NC(5)H(4)CONHNH(2)); ibh=isopropanone benzoyl hydrazone (C(6)H(5)CONHN=C(CH(3))(2); iinh=isopropanone isonicotinoyl hydrazone (NC(5)H(4)CONHN=C(CH(3))(2)). These copper(II) complexes are characterized by elemental analyses, molar conductances, dehydration studies, ESR, IR and electronic spectral studies. The electronic and ESR spectra indicate that each complex exhibits a six-coordinate tetragonally distorted octahedral geometry in the solid state and in DMSO solution. The ESR spectra of most of the complexes are typically isotropic type at room temperature (300K) in solid state as well as in DMSO solution. However, all the complexes exhibit invariably axial signals at 77K in DMSO solution. The trend g(||)>g( perpendicular)>g(e,) observed in all the complexes suggests the presence of an unpaired electron in the [Formula: see text] orbital of the Cu(II). The bh and inh ligands bond to Cu(II) through the >CO and NH(2) groups whereas, ibh and iinh bond through >CO and >CN groups. The IR spectra of bh and ibh complexes also show HOH stretching and bending modes of coordinated water.     

Thermodynamics of ligand exchange reactions between bis(dithiocarbamato)copper(II) and copper(II) salts. An EPR study

EPR spectroscopy was chosen to investigate the ligand exchange reactions between copper(II) bis(dithiocarbamate), Cu(dtc)2, and copper(II) salts which proceeds with the formation of mixed-ligand complexes of the type Cu(dtc)X, where X = Cl, NO3, ClO4. Large concentrations of 1:1 mixed-ligand complexes of this type are obtained as indicated by the EPR spectra of acetone, CHCl3/EtOH, CHCl3/i-PrOH, CCl4/EtOH and CCl4/i-PrOH, solutions of Cu(dtc)2 and the appropriate copper(II) salt CuCl2, Cu(NO3)2 or Cu(ClO4)2. Double integration of Cu(dtc)2 EPR signals obtained at temperatures between 240 and 310 K affords the calculation of the equilibrium constant (K) of the reaction: Cu(dtc)2 + CuX2 <==> 2 Cu(dtc)X in all solvents as a function of T. From the values of K the stability constant beta of the mixed-ligand complexes has been derived. The error associated with the calculated stability constant is +/- 10%. Thermodynamic parameters (deltaH0, deltaG0 and deltaS0) are determined from the temperature dependence of K as measured by EPR spectroscopy.     

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.     

Vanadocene(IV) dicyanide complexes: the evidence super-hyperfine coupling for compounds with 13CN ligands

An EPR study of the vanadocene complexes (C(5)H(5))2V(CN)2 and (CH(3)C(5)H(4))2V(CN)2 was carried out. Such compounds show strong super-hyperfine coupling (|a(iso)(13C)| approximately 1.27 mT) when 13C labeled cyanide is used for their preparation. Super-hyperfine splitting was observed in the isotropic spectra of solution samples as well as in the anisotropic spectra of frozen solutions. Such studies were supplemented with structural characterization of the parent compounds. Molecular structure of the complex (CH(3)C(5)H(4))2V(CN)2 was determined by single-crystal X-ray diffraction analysis. Both compounds were characterized by infrared and Raman spectroscopy.     

Aggregation properties of bis(salicylaldiminato)zinc(II) Schiff-base complexes and their Lewis acidic character

The synthesis, characterization, (1)H NMR, optical absorption and fluorescent properties of a series of amphiphilic Schiff-base bis(salicylaldiminato)zinc(II) complexes are reported. Detailed (1)H NMR, DOSY NMR, optical absorption and fluorescence spectroscopy studies indicate the existence of aggregate species in solutions of non-coordinating solvents. The degree of aggregation is related to the nature of the bridging diamine. Chloroform solutions of complexes where the bridging diamine contains a naphthalene or the pyridine nucleus are always characterized by the presence of defined dimer aggregates, whereas oligomeric aggregates are likely formed by complexes where the bridging diamine contains a benzene ring. In coordinating solvents or in the presence of coordinating species, a complete deaggregation of the complexes occurs, because of the axial coordination to the Zn(II) ion, accompanied by considerable changes in the (1)H NMR and optical absorption spectra. The effect of the alkyl chains length seems to play a minor role in the aggregation properties, as noticed by (1)H NMR data, optical absorption and fluorescence spectra, which remain almost unaltered on changing the chain length.     

Synthesis,characterization and comparative DNA interaction studies of new copper(II) and nickel(II) complexes containing mesalamine drug using molecular modeling and multispectroscopic methods

Complexes of copper(II) and nickel(II) containing the drug mesalamine (5-ASA) have been synthesized and characterized by FT-IR, mass and UV–vis spectra, elemental analysis, and theoretical methods. The binding interactions between mesalamine and its Cu(II) and Ni(II) complexes with calf thymus DNA (ct-DNA) were investigated using absorption, fluorescence emission and circular dichroism (CD) spectroscopies, and viscosity measurements. Absorption spectra of 5-ASA, Cu(II) and Ni(II) complexes showed hypochromism. The calculated binding constants (K_b) obtained from UV–vis absorption studies were 1.27 × 10³, 1.6 × 10³, and 1.2 × 10⁴ M^?1 for 5-ASA, Cu(II) and Ni(II) complexes, respectively. The compounds induced detectable changes in the CD spectra of ct-DNA (B → A structural transition, B → C structural transition and stabilization of the right-handed B form, for mesalamine, Cu(II) and Ni(II) complexes, respectively). The competitive binding experiments with Hoechst 33258 indicated that 5-ASA and copper complex could interact as groove binders. Furthermore, Ni complex had no effect on the fluorescence intensity and peak position of MB-DNA system. Finally, the results obtained from experimental and molecular modeling showed that complexes bind to DNA via minor-groove binding.     

Spectrochemical Properties of Noncubical Transition Metal Complexes in Solution. XII. Angular Overlap Studies of Salicylideneethylenediamine Cu(II) Complex in Various Solvents

As a part of our general interest in the UV-Vis spectroscopy of multidentate mixed-donor ligands, the (salicylideneethylenediamine)Cu(II) complex has been prepared and characterized by elemental analyses, solubility in common solvents, molar conductivities, and ultraviolet (UV), and visible (Vis) spectroscopy. The combined results of spectrophotometric measurements and EPR spectra, as well as known the X-ray structure for solids, were used to determine the structure of the investigated complex in solutions. The spectra of [Cu(salen)] (H₂salen = salicylideneethylenediamine), were measured in various solvents at room temperature, resolved by Gaussian analysis, and angular overlap model (AOM) treated in C _2v symmetry. Because of overparametrization problems, the bis(salicylaldehyde)Cu(II) complex has been characterized and AOM treated. The results of this have been used for AOM studies of [Cu(salen)]. The effect of the solvents upon the - and -bonding ligand abilities is discussed.     

EPR Spectra of Copper(II) Complexes with N,N-Dialkyl Amino Acids. The Influence of Water dissolved in Organic Solvents on the Copper(II) Coordination Sphere

EPR spectra of four bis(N,N-dialkyl-L-α-aminoacidato) copper(II) complexes were studied with the aim to determine the effect of the water molecules dissolved in organic solvents on the electronic states of copper(II). It was shown that water dissolved in methylene chloride or dioxan influence the copper(II) electronic states. If the amino acid side chains are long enough to form the aliphatic intramolecular van der Waals contacts, the water molecules will induce the change in the conformation of the whole complex.     

Ligandenaustauschreaktionen am Bis(1,3-diselenol-2-selon-4,5-diselenolato)-kupferat(II) ([Cu(dsis)2]2−) mit Kupfer(II)-Vier- und Fünfringchelaten geminaler und vicinaler ungesättigter Dichalkogenoliganden. Eine EPR-Untersuchung

Ligand Exchange on Bis(1,3-diselenole-2-selone-4,5-diselenolato)cuprate(II) ([Cu(dsis)₂]^2?) with Cu^II Four and Five Ring Bis-chelates Containing Unsaturated Vicinal and Geminal Dichalcogeno Ligands. An EPR Study Ligand exchange reactions (“chelate metathesis”) of bis(1,3-diselenole-2-selone-4,5-diselenolato)cuprate(II), ([Cu(dsis)₂]^2?, with other Cu^II four- or five-ring chelates of unsaturated dichalcogeno ligands are reported. The small solubility of salts of the title complex in common solvents like acetone or chloroform requires pyridine. Mixed-ligand complexes could be detected for all combinations of two starting complexes studied by means of their g_o and a_o^Cu (EPR) parameters. Due to the coordinating properties of pyridine and electronic reasons commonly used linear dependences of the g value from the composition of the first coordination sphere (“additivity rules”) are not applicable.     

Bioactivity of some divalent M(II) complexes of penicillin based Schiff base ligand: Synthesis,spectroscopic characterization,and thermal study

A series of four novel metal complexes of Co(II), Ni(II), Cu(II) and Zn(II) were synthesized from Schiff base derived from amoxicillin (AMX) and picolinaldehyde (PC2). The ligand and metal complexes were fully characterized by physical and spectral techniques such as elemental microanalysis, conductivity, FT-IR, ¹H & ¹³C NMR, UV–vis, mass spectra, EPR, magnetic moment measurement, TGA/DTA, PXRD and antibacterial activity study. The spectroscopic study revealed 1:2 metal ligand ratio and coordination sites in the ligand for metal ions were evaluated by analysis of the spectral results. The surface morphology of the complexes was evaluated by SEM analysis. Molar conductivity implies non-electrolytic nature of the complexes. UV–vis. spectral study nicely supports octahedral geometry for Co(II) and Zn(II) complexes and tetrahedral geometry for Cu(II) complex. The kinetic parameters were extracted from Coats-Redfern equation. The PXRD study revealed nano-crystalline nature of Co(II), Ni(II) & Cu(II) complexes and amorphous nature of Zn(II) complex. The proposed geometry of the complexes was optimized by MM2 calculation supported in Cs-ChemOffice Ultra-11 program. The ligand and metal complexes were screened for antibacterial potency against four human pathogenic clinical strains of bacteria and the data revealed their promising antibacterial activity.     

Synthesis, spectroscopic studies and crystal structure of the Schiff base ligand L derived from condensation of 2-thiophenecarboxaldehyde and 3,3'-diaminobenzidine and its complexes with Co(II), Ni(II), Cu(II), Cd(II) and Hg(II): Comparative DNA binding studies of L and its Co(II), Ni(II) and Cu(II) complexes

The Schiff base ligand, N,N'-bis-(2-thiophenecarboxaldimine)-3,3'-diaminobenzidine (L) obtained from condensation of 2-thiophenecarboxaldehyde and 3,3'-diaminobenzidine, was used to synthesize the complexes of type, [M2L2]Cl4 [M=Co(II), Ni(II), Cu(II), Cd(II) and Hg(II)]. The newly synthesized ligand (L) was characterized on the basis of the results of elemental analysis, FT-IR, 1H NMR, 13C NMR, mass spectroscopic studies and single crystal X-ray crystallography. The characteristic resonance signals in 1H NMR and 13C NMR spectra indicated the presence of azomethine group as a result of condensation reaction. The stoichiometry, bonding and stereochemistries of complexes were ascertained on the basis of results of elemental analysis, magnetic susceptibility measurements, molar conductance and spectroscopic studies viz., FT-IR, 1H and 13C NMR, UV-vis and EPR. EPR, UV-vis and magnetic moment data revealed an octahedral geometry for complexes with distortion in Cu(II) complex and conductivity data show 1:2 electrolytic nature of complexes. Absoption and fluorescence spectroscopic studies supported that Schiff base ligand L and its Co(II), Ni(II) and Cu(II) complexes exhibited significant binding to calf thymus DNA. The complexes exhibited higher affinity to calf thymus DNA than the free Schiff base ligand L.     

Synthesis,characterization, and antioxidant activities of three Cu(II) complexes with Schiff-base ligands

Cu(II) complexes of three bis(pyrrol-2-yl-methyleneamine) ligands were synthesized and characterized by elemental analyses, mass spectra, and IR spectra. X-ray diffraction analysis shows that [CuL³]₂ is a dinuclear complex with an extremely distorted square-planar geometry. Furthermore, the antioxidant activities of the compounds have been investigated. The electrochemical properties of the Cu(II) complexes have also been studied by cyclic voltammetry. The Cu(II) complexes show similar superoxide dismutase (SOD) activity compared with that of the native Cu, Zn-SOD.     

钆(Ⅲ)混合阴离子配合物的电子顺磁共振谱

稀土离子Gd^3 和Eu^2 体系在室温下可得到清晰的电子顺磁共振（EPR）图谱。由谱图可获取顺磁离子的自旋态、配位结构、晶体场强和电子能级等重要信息。Gd(Ⅲ）作为顺磁性的结构探针,在研究蛋白质结构和金属离子间的相互作用方面已得到应用。但至今对Gd(Ⅲ）配合物EPR波谱研究报导不多,仅限于三元配合物和玻璃质固体掺杂Gd(Ⅲ）的波谱研究,且Gd(Ⅲ）波谱均具“U”谱特征(g-6.0,2.8和2.0）。本文研究了三种新的Gd(Ⅲ）四元配合物在不同条件下的EPR谱,得到一些新 的结果,并利用自旋Hamilton理论解释了不同类型的图谱特征。     

Spectroscopic evaluation of Co(II), Ni(II) and Cu(II) complexes derived from thiosemicarbazone and semicarbazone

Co(II), Ni(II) and Cu(II) complexes were synthesized with thiosemicarbazone (L(1)) and semicarbazone (L(2)) derived from 2-acetyl furan. These complexes were characterized by elemental analysis, molar conductance, magnetic moment, mass, IR, electronic and EPR spectral studies. The molar conductance measurement of the complexes in DMSO corresponds to non-electrolytic nature. All the complexes are of high-spin type. On the basis of different spectral studies six coordinated geometry may be assigned for all the complexes except Co(L)(2)(SO(4)) and Cu(L)(2)(SO(4)) [where L=L(1) and L(2)] which are of five coordinated square pyramidal geometry.     

Structure of copper(II)-histidine based complexes in frozen aqueous solutions as determined from high-field pulsed electron nuclear double resonance

W-band (95 GHz) pulsed EPR and electron-nuclear double resonance (ENDOR) spectroscopic techniques were used to determine the hyperfine couplings of different protons of Cu(II)-histidine complexes in frozen solutions. The results were then used to obtain the coordination mode of the tridentate histidine molecule and to serve as a reference for Cu(II)-histidine complexation in other, more complex systems. Cu(II) complexes with L-histidine and DL-histidine-alpha-d,beta-d2 were prepared in H2O and in D2O, and orientation-selective W-band 1H and 2H pulsed ENDOR spectra of these complexes were recorded at 4.5 K. These measurements lead to the unambiguous assignment of the signals of the H alpha, H beta, imidazole H epsilon, and the exchangeable amino, Ham, protons. The 14N superhyperfine splitting observed in the X-band EPR spectrum and the presence of only one type of H alpha and H beta protons in the W-band ENDOR spectra show that the complex is a symmetric bis complex. Its g parallel is along the molecular symmetry axis, perpendicular to the equatorial plane that consists of four coordinated nitrogens in histamine-like coordinations (NNNN). Simulations of orientation-selective ENDOR spectra provided the principal components of the protons' hyperfine interaction and the orientation of their principal axes with respect to g parallel. From the anisotropic part of the hyperfine interaction of H alpha and H beta and applying the point-dipole approximation, a structural model was derived. An unexpectedly large isotropic hyperfine coupling, 10.9 MHz, was found for H alpha. In contrast, H alpha of the Cu(II)-1-methyl-histidine complex where only the amino nitrogen is coordinated, showed a much smaller coupling. Thus, the hyperfine coupling of H alpha can serve as a signature for a histamine coordination where both the amino and imino nitrogens of the same molecule bind to the Cu(II), forming a six-membered chelating ring. Unlike H alpha the hyperfine coupling of H epsilon is not as sensitive to the presence of a coordinated amino nitrogen of the same histidine molecule.     

Molecular magnetic properties of two-copper(II) containing complexes [Cu(II) (1-phenylamidino-O-n-butylurea) en (H2O)]2(2+) and [Cu(II) sulphato-mono (1-phenylamidino-O-methylurea)]2. An EPR study

Electron paramagnetic resonance (EPR) investigations were conducted on [Cu(II) (1-phenylamidino-O-n-butylurea) en (H2O)]2(2+) (1) and [Cu(II) sulphato-mono (1-phenylamidino-O-methylurea)]2 (2) respectively, in the temperature range 300-77K. Fine structure characteristics of S = 1 system, was observed in both complexes with zero field splitting of 0.0525 and 0.0225 cm(-1), respectively, suggesting the formation of dimeric complexes. The presence of the half-field signal (DeltaMs= +/-2), in the complex 1, further confirmed the formation of dimer. The temperature dependence of EPR signal intensity has given evidence for the ferromagnetic (FM) coupling between the two Cu2+ ions. The isotropic exchange interaction constants J, were evaluated from this and were found out to be approximately 57 and approximately 27 cm(-1), respectively, for the complexes 1 and 2. The photoacoustic spectra of these complexes had shown a band around 26,400 cm(-1) characteristic of metal-metal bonding giving an independent support for the existence of dimeric Cu2+ species. The high magnetic moment values at room temperature for complex 1 (2.68 microB) and complex 2 (2.00 microB), obtained from the magnetic susceptibility measurements, support the formation of ferromagnetically coupled Cu2+ dimers.