Proton ENDOR study of copper(II) bis(dithiocarbamate)

The proton hyperfine coupling tensors of the methylene protons in methyl-deuterated copper(II) bis(N,N-diethyldithiocarbamate) in a diamagnetic host crystal of the corresponding nickel complex have been measured by ENDOR spectroscopy. Two intermolecular and all four intramolecular proton coupling tensors could be determined. With the aid of spin densities, obtained from extended Hückel molecular orbital calculations, the anisotropic part of the tensors can be reproduced quantitatively, taking into account all two- and three-centre contributions. Comparison of the transition frequencies which are computed from the theoretical tensors with the experimental transitions enables the tracing of another five tensors which cannot be completely determined experimentally.     

EPR Studies on the intermolecular interactions of bis(di-ethanol-dithiocarbamato) copper(II)

The interaction of the title complex, [Cu(EtOH-dtc)₂], with I₂, Br₂ and different metal salts known as electron acceptors is studied in water-ethanol solution. Mixed-ligand complexes Cu(EtOH-dtc)⁺…X^? (X = Cl, Br, I, NO₃) are formed with X^? in the second coordination sphere of the metal ion. Cu(EtOH-dtc)₂ interacts with chloral-hydrate only in the presence of weak Lewis bases and Cu(EtOH-dtc)⁺…Cl^? mixed-ligand complex is formed. The interactions with metal chelates cause the formation of mixed-ligand chelate complexes. Cu(EtOH-dtc)₂ interacts with H₂O₂ and the appearance of mixed-ligand complexes as intermediate products is detected. The final product obtained is CuSO₄. In the presence of O₂ Cu(EtOH-dtc)₂ yielded spectra similar to the above intermediate products. The proposed mechanisms of all studied reactions are discussed on the ground of the recorded spectra.     

EPR study on the photoinduced electron transfer in the ternary complex (dithiocarbamato,dithiophosphato)copper(II)

The EPR study on equimolar solutions of Cu(dtc)₂ and Cu(dtp)₂ in aerated acetone, toluene and chloroalkane (CHCl₃ and CCl₄) solutions indicates that Cu(dtc)(dtp) is the only complex species present in solution. The analysis of the EPR spectra recorded after photo-irradiation in aerated acetone solutions enables the characterization of the intermediate paramagnetic species and provides a reasonable explanation.     

Effect of acidification on spectral parameters of solutions of mixed-ligand cyclometalated Pt(II) and Pd(II) complexes

The effect of acidification of water-ethanol solutions of cyclometalated Pt(II) and Pd(II) complexes with ethylenediamine and cyanide ligands is studied. It is found that, unlike the ethylenediamine complexes, the cyclometalated complexes with cyanide ligands are unstable and undergo irreversible decyclometalation.     

Spectral and luminescent properties of mixed-ligand complexes of palladium(II) and 7,8-benzoquinoline

Spectral and luminescent properties of mixed-ligand palladium(II) complexes—[PdBhq(μ-Cl)]₂, [PdBhqEn]ClO₄, and [PdBhqBpy]ClO₄, where Bhq stands for the 7,8-benzoquinoline ion—were studied. The absorption spectra of these complexes in the 25000–40000-cm^? range were found to have a number of spin-allowed transitions of the ₁(π-π*) type involving orbitals of the 7,8-benzoquinoline ligand. The luminescent characteristics of these compounds in a glass-forming matrix at 77 K are primarily determined by the participation of the ₃(π-π*) states of the 7,8-benzoquinoline ligand.     

Photo- and electroluminescence of mixed-ligand Eu(III) complexes

Spectral and luminescent properties of mixed-ligand Eu(III) complexes were studied in solutions and in polyvinylcarbazole (PVC) thin films. Trends in their variations were found depending on the complex structure and excitation mode. The electroluminescence was observed in ITO/PEDOT/Eu complex:PVC/CaMg/Al devices. Their current-voltage and voltage-brightness characteristics were investigated.     

ESR study of some asymmetric-triazine copper(II) complexes having high antiviral activity

Electron paramagnetic resonance (EPR) spectroscopy and molecular dynamics calculations have been used to compare the chemical environments of Cu(II) in three substituted asymmetric-triazine (as-triazine) complexes with a closely related complex that was reported previously to have Superoxide dismutase (SOD) and antiviral activities. The structure most strongly associated with the biological activity appears to be planar with two 6-membered chelate rings having 2N2O coordination around the copper atom.     

Peculiarities of crystal structures and magnetic properties of Cu(II) and Ni(II) mixed-ligand complexes on the 1,3-dithiole-2-thione-4,5-dithiolate basis

Mixed-ligand Cu(II) and Ni(II) complexes, [Cu(dmit)(bpy)]₂ (I), [Ni(dmit)(phen)₂] (II) and [Ni(dmit)(phen)₂]·CH₂Cl₂ (III) (dmit=1.3-dithiole-2-thione-4.5-dithiolate, phen=1.10-phenantroline, bpy=2.2′-bipyridine) have been prepared by ligand exchange between phen or bpy and (Bu₄N)₂[M(dmit)₂] (M=Ni, Cu) and characterized by elemental analysis, IR spectroscopy, single-crystal X-ray analysis and by investigation of magnetic and resonance properties. In complex I, the monomeric units form dimers in a head-to-tail arrangement by weak coordination bonds between copper and dithiolate sulfur atoms and π–π interactions between dmit and bpy from neighboring monomers. Dimers in I are further extended into chains by weak Cu–S(thione) contacts. In crystal packing of complex II and III, there exists a weak π–π interaction between two parallel phen molecules of the adjacent complexes. As a consequence, the magnetic and resonance characteristics of copper complex may be described in approximation of exchange-coupled pairs of Cu²⁺ ions with ion spin S=1/2. The nickel complexes are described by isotropic exchange model for single-site spin S=1.     

Local structure is critical for superoxide dismutase activity in copper complexes: Relationship between EPR parameters, structure and activity in some sterically hindered copper(II) bis(hydrazono-triazine) complexes

Electron paramagnetic resonance (EPR) spectrometry and molecular mechanics force field calculations have been performed on some sterically hindered copper(II) complexes with hydrazonotriazine ligands, in order to gain further insight into the relationship between their bonding, structures and biological activity. As was the case with Cu(II) bis(hydrazono-triazine) complexes studied previously, the most stable configuration for all of the complexes involves coordination of two nitrogen and two oxygen atoms (2N2O) in a distorted tetragonal arrangement. With the present complexes, however, the superoxide radical scavenging activities were very low, a result which may be explained by their inability to form a (nearly) square planar structure, which facilitates the copper redox cycling during superoxide dismutation.     

Methylene bromide chemistry and photochemistry on rutile TiO2(110)

The chemistry and photochemistry of methylene bromide (CD₂Br₂) on the rutile TiO₂(110) surface was probed using temperature programmed desorption (TPD). CD₂Br₂ desorbed in three desorption states at 145, 160 and 250 K tentatively assigned to desorption from the multilayer, from an η¹-CD₂Br₂ species and a bridging η²-CD₂Br₂ species, respectively. The latter two TPD states presumably involve binding of CD₂Br₂ molecules to the surface through Br coordination at five-coordinate Ti⁴⁺ surface sites. The 160 and 250 K TPD states saturated at coverages of 1.0 and 0.33 ML, respectively, where 1 ML is equivalent to the surface Ti⁴⁺ site density (5.2 × 10¹⁴ cm^? 2). No thermal decomposition of CD₂Br₂ was observed on either the clean surface or with preadsorbed O₂. UV irradiation of CD₂Br₂ on TiO₂(110) resulted in predominately photodesorption, with trace amounts of photodecomposition evidenced in TPD. The rate of CD₂Br₂ photodesorption from TiO₂(110) occurred with a low cross section (~ 2 × 10^? 21 cm²) similar to that expected from direct optical excitation of CD₂Br₂. This observation suggests that charge carriers generated in TiO₂(110) were no more effective in activating adsorbed CD₂Br₂ molecules than would be expected through direct molecular excitation. These findings suggest that photocatalytic destruction of halocarbons such as CD₂Br₂ on TiO₂ may preferentially occur though indirect processes (such as OH radical attack) as opposed to direct electron transfer processes involving charge carriers generated in TiO₂ by bandgap excitation.     

Charge transfer-transitions and X-ray photoelectron spectroscopy of copper(II) complexes

Satellite structure in the X-ray photoelectron (Cu 2p) spectra of some squareplanar cupric complexes has been compared to electron paramagnetic resonance and electronic spectra results on the electronic structure of these complexes. It is shown that these satellites can be assigned to various ligand → metal 3d or ligand → ligand* transitions within the monopole selection rules of the sudden approximation.     

On the symmetry of the xyz vibration in the photochemistry of Pt(II) D4h complexes

A symmetry concept is proposed that links the presence of vibronic structure in UV-visible spectra in d-systems, with the identification of a single photochemical reaction pathway. It is shown that the vibronic structure on some bands of the Pt(II) D_4h complexes is due to the non- degenerate, ungerade b_1u (xyz) vibration that points on an intramolecular twisting process for the photochemical cis-trans isomerization. The reaction coordinate is unambiguously defined in a coordinate system where x and y bisect the metal-ligand ML₂ angle.     

K-absorption spectral investigations on some dimeric copper(II) carboxylate complexes

The X-ray K-absorption edge position and the extended fine structure of copper in some copper(II) carboxylate complexes involving metal-metal exchange interaction have been investigated using a 40 cm bentcrystal spectrograph. It has been found that the edge position in these complexes shifts towards the higher energy side as the pK_a value of the corresponding acids increases. Sharp and narrow main peaks have been observed in all these complexes except the monomeric complex, copper(II) trichloroacetate. Estimates of metal-ligand average bond distances have also been made.     

ESCA study of Ni(II) dithiocarbazato complexes

N 1s, S 2p and Ni 2p_3/2 binding energies for the Ni(II) dithiocarbazates and N 1s and S 2p binding energies for the methyl esters of dithiocarbazic acids were measured. It was found that the band width of N 1s narrows on going from the esters to the complexes, thus suggesting a closer similarity between the two nitrogen atoms as a consequence of coordination. S 2p binding energies were found to be similar in the above complexes independent of the chromophore present in them. A possible explanation is suggested for this unusual result.     

Study of Cu K-edge in some copper (II) square planar complexes

The copper K-absorption edge in the complexes Cu(ammonia)₂ C₂O₄, Cu(methylamine)₂ C₂O₄, Cu(ethylamine)₂ C₂O₄ and Cu(aniline)₂ C₂O₄ has been investigated using the Cauchois-type bent crystal X-ray spectrograph. Three peaks, A, B and C, observed in the edges have been explained on the basis of molecular orbital theory.     

XAFS investigations of copper(II) complexes with tetradentate Schiff base ligands

X‐ray absorption fine structure spectra have been investigated at the K‐edge of copper in copper(II) salen/salophen complexes: [Cu(salen)] (1), [Cu(salen)CuCl₂].H₂O (2), [Cu(salophen)] (3) and [Cu(salophen) CuCl₂].H₂O (4), where salen^2? = N,N′‐ethylenebis (salicylidenaminato); salophen^2? = o‐phenylenediaminebis(salicylidenaminato). Complexes 1 and 3 are supposed to have one type of copper centers (called (Cu1)) and complexes 2 and 4 two types of copper centers (called (Cu1) and (Cu2)) having different coordination environments and geometries. A theoretical model has been generated using the available crystallographic data of complex 1 and it has been used for analysis of the extended X‐ray absorption fine structure (EXAFS) data of the four complexes to obtain the structural parameters for (Cu1) center. For this center, the obtained Cu–Cu distance (3.2 Å) verifies the binuclear nature of all the complexes. For determining the coordination geometry around (Cu2) center in 2 and 4, a theoretical model has been generated using the crystal structure of a Cu(II) complex, [Cu(C₁₆H₁₂N₂O₂Cl₂)]. This theoretical model has been fitted to the EXAFS data of 2 and 4 to obtain the structural parameters for (Cu2) center. The present analysis shows that (Cu1) center has square pyramidal geometry involving 2N and 3O donor atoms, whereas (Cu2) center has distorted tetrahedral geometry with 2O and 2Cl donor atoms. The values of the chemical shifts and presence of typical Cu(II) X‐ray absorption near‐edge spectroscopy features suggest that copper is in the +2 oxidation state in all these complexes. The intensity of ls → 3d pre‐edge feature has been used to investigate the geometry and binuclear nature of the complexes. Copyright © 2012 John Wiley & Sons, Ltd.     

X-ray photoelectron investigation of charge distribution in copper(II) phthalocyanine complexes

The charged states of atoms in unsubstituted copper(II) phthalocyanine (CuPcH₁₆) and hexade-cafluorinated copper(II) phthalocyanine (CuPcF₁₆) complexes and in thin films of them deposited on silicon substrates by vacuum thermal evaporation are investigated by X-ray photoelectron spectroscopy (XPS). The C(1s), N(1s), Cu(2p) core level energies and the charged states of atoms in the studied complexes are calculated using the DFT method. The performed experimental study and theoretical calculations show that the introduction of electron acceptor substituents into benzene rings mostly affects the atoms of benzene rings and insignificantly affects the charge state of nitrogen atoms in the pyrrole ring.