Fevzi Köksal

Synthesis, spectroscopy and redox chemistry of bis(n-aryl-3,5-di-tert-butylsalicylaldiminato)copper(II) complexes

A series of new bis(N-aryl-3,5-di-tert-butylsalicylaldiminato)copper(II) complexes (I), prepared from 3,5-di-tert-butylsalicylaldehyde and mono-substituted anilines, X-C6H4NH2(X = H, o-F, Cl, Br, CH3, CH3O; p-F, Cl, Br, CH3, CH3O, t-Bu and 5,6-benzo), and their spectroscopic properties as well as electrochemistry and reactivity toward PPh3 are described. Comparison of g ‖ (2.223–2.249), A ‖ (150–170 G) tensors and the axial symmetry parameter, g ‖/A ‖, (140–155 cm) of I with those of model Cu(II) complexes reveals that the coordination site is distorted from square planar toward tetrahedral geometry. The di-tert-butyl groups on the salicylaldehyde moiety unlike those introduced on the aniline rings do not facilitate reactivity toward PPh3. Electrochemical studies of I in acetonitrile solutions reveal highly irreversible behavior, due to chemical or stereochemical changes subsequent to electron transfer. In the oxidation of some complexes with (NH4)2Ce(NO3)6 in acetonitrile at 300 K, along with decreasing ESR signals of Cu(II), the appearance of coordinated phenoxyl radical signals centered at g = 2.004 were detected. The CV studies on acetonitrile solutions of I revealed well-resolved quasi-reversible redox waves at  = 0.61–0.99 V and  = 1.09–1.23 V (vs. Ag/AgCl) attributable to ligand-centered oxidation processes to yield corresponding coordinated phenoxyl radical species such as Cu(II)(phenoxyl)(phenolate) and Cu(II)(phenoxyl)2.

Electron spin resonance age determination of a travertine sample from the southwestern part of Turkey

Abstract Travertine powdered samples collected from Denizli in the southwestern part of Turkey appear to be suitable for dating by ESR analysis due to presence of a g =2.0006 ESR signal. In general, ESR spectra of natural travertine show two absorption lines: g =2.0006 and g =2.0056. 60 Co gamma-ray irradiations enhance the g =2.0006 signal but not g =2.0056. The signal amplitude of the g =2.0056 line remains constant and shows no dose dependence after annealing at 150–180°C for periods from 15 min to 2 days. Line g =2.0056 disappears in turn after an annealing of 15 min at 400°C. Thermal annealing experiments at different temperatures for different annealing times show that the only travertine ESR signal stable enough for dating of ages over the past 10 Ma, is the one at g =2.0006. The present ESR dating result is 1.11±0.11 Ma. The g =2.0006 signal used for dating appears to correspond with the 280°C TL peak, but at elevated temperatures the mean life, accumulated dose and age of the latter is significantly less than that measured by post irradiation analysis using the ESR signal. This can be attributed to coming from other carbon-containing paramagnetic centers. In fact, gamma-ray absorbed dose rate dependence of the ESR signal has been studied, and no dependence was observed over a 12-fold change in dose rate.

Electron paramagnetic resonance of VO2+ in Cd(HCOO)22H2O and Pb(HCOO)2 single crystals

Abstract The EPR spectra of VO2+ in Cd(HCOO)22H2O and Pb(HCOO)2 single crystals and powders were studied at room temperature. The angular variations of the spectra indicated that the VO2+ enters Cd2+ and Pb2+ sites in their respective host crystals. Two magnetically inequivalent sites in Cd(HCOO)22H2O and Pb(HCOO)2 for VO2+ were observed. The principal values of the spin-Hamiltonian parameters g and A were determined from the single crystal and powder EPR spectra. Using the EPR parameters and diffuse reflectance data molecular orbital bonding coefficients and crystal field parameters of VO2+ have been evaluated and discussed.

Electron paramagnetic resonance of some γ-irradiated drugs

Abstract Some drugs, used mainly in treatment of some neurological diseases and hypertension were exposed to γ-irradiation, and the samples were investigated by electron paramagnetic resonance (EPR). The observed spectra were interpreted in terms of some type of alkyl and amine radical fragments. The spectra were computer simulated and the g values of the radicals and the hyperfine structure constants of the free electron with nearby protons were determined. The species were found to be stable at room temperature for more than a year. The samples were found to display no EPR signal without irradiation.

Synthesis, spectroscopic characterization and EPR studies on electron transfer reactions of bis[N-(2,5-di-tert-butylphenyl)salicylaldiminato]copper complexes with PPh3

New bidentate N-(2,5-di-tert-butylphenyl)salicylaldimines bearing X = H, HO, CH3O, Br, NO2, 3,5-di-Br, 3-NO2-5-Br and 5,6-benzo substituents on the salicylaldehyde moiety, LxH, and their mononuclear bis[N-(2,5-di-tert-butylphenyl)salicylaldiminato]copper(II) complexes, Cu(Lx)2, have been prepared and investigated by IR, UV-Visible, 1H NMR, ESR spectroscopy, magnetic measurements, as well as reactions of Cu(LX)2 with PPh3 were studied. It has been found that some complexes with X = HO and CH3O unlike their electron-withdrawing and unsubstituted analogues are readily reduced by PPh3 via intramolecular electron transfer from ligand to copper(II) to give Cu-stabilized radical intermediates. The spectra of the primary radicals interpreted in terms of couplings of unpaired electron with (63,65)Cu, 31P, 14N nuclei and aromatic protons.

Thermoluminescence and electron spin resonance properties of some travertines from Turkey

Abstract For the sake of dating certain calcite geological samples, the TL and ESR properties of travertines from Denizli (in the southwestern part of Turkey) were studied and the effects of pre-heating temperature and pre-heating time on the sensitivity of the samples to radiation evaluated. Heat treatment above 350°C increases the sensitivity of all radiation-induced TL peaks except the 330°C glow peak. Results of gamma-ray dose calibration in travertine (CaCO3 crystal of trigonal symmetry) indicate that the 180 and 280°C TL peak amplitudes increase exponentially with dose. We show that second-order kinetics characterizes the 180 and 280°C glow peaks reasonably well. The Mn2+ lines of the ESR spectra are used to investigate the thermal decomposition processes of travertine samples, showing very good agreement with those of thermogravimetry. Glow mechanisms of TL in travertine have also been studied using ESR analysis. The pre-heating and subsequent laboratory irradiation procedure is found to enhance the TL and ESR signals of CO33− and CO2− centres. An isochronal thermal anneal sequence experiment showed that 180 and 280°C peaks in travertines are correlated with CO33− and CO2− centres in the same way that the peak at 330°C is correlated with SO2− centres. A model for the recombination mechanism is suggested on the basis of the TL and ESR measurements.

Electron paramagnetic resonance of Cu2+ in Cd(NH4)2(SO4)2 · 6H2O

Abstract The electron paramagnetic resonance spectra of Cu2+ in Cd(NH4)2(SO4)2 · 6H2O powder and single crystals have been recorded at 300 K and 113 K. The angular variation of the spectra indicated the substitution of the host Cd2+ with Cu2+. Two magnetically inequivalent sites for Cu2+ have been observed. The spectra were fitted with a rhombic spin Hamiltonian and the Hamiltonian parameters were determined. The g and A tensors were found to be coaxial within the limits of experimental errors and the ground state wavefunction of the complex has been constructed.

A Product Operator Description of 2D-J Resolved NMR Spectroscopy for IS n Spin System (I=1/2, S=1)

Abstract Using the product operator technique, an analytical description of heteronuclear 2D-J resolved NMR spectroscopy for a weakly coupled IS n (I=I/2, S=1, n=1, 2, 3) spin system is presented. As a pulse sequence, the most commonly used one, the gated decouple sequence, is used. The obtained analytical results were found to be in good agreement with the experimental ones.

EPR of gamma irradiated Nα-acetyl L-glutamic acid and Nα-acetyl L-glutamine

Abstract Single crystals of Nα-acetyl L-glutamic acid and Nα-acetyl L-glutamine were γ-irradiated and the paramagnetic species formed were investigated at room temperature by electron spin resonance technique. The observed species in Nα-acetyl L-glutamic acid single crystal were attributed to the, HOOCCH 2 CH 2 C (NHCOCH 3 )COOH radical; and those in Nα-acetyl L-glutamine single crystal to the NH 2 COCH 2 CH 2 C( NHCOCH 3 ) COOH and NH 2 COCH 2 CH 2 CH ( NHCOCH 3 ) C O OH radicals. The g values and the hyperfine coupling constants of the unpaired electron with the environmental methylene, methine protons and 14 N nucleus were determined.

Synthesis, spectroscopic characterization and redox reactivity of some transition metal complexes with salicylaldimines bearing 2,6-di-phenylphenol.

New bidentate N-(2,6-di-phenyl-1-hydroxyphenyl) salicylaldimines bearing X=H and 3,5-di-t-butyl substituents on the salicylaldehyde ring, L(x)H, and their copper(II) complexes, M(Lx)2, (M=Cu(II), Co(II), Pd(II), Ni(II) and Zn(II)) have been synthesized and characterized by IR, UV/vis, 1H NMR, 13C NMR, ESR spectroscopy, magnetic susceptibility measurements, as well as their oxidation with PbO(2) and reduction (for Cu(Lx)2) with PPh(3) were investigated. ESR studies indicate that oxidation of M(Lx)2 produces ligand-centered M(II)-phenoxyl radical species. The Cu(Lx)2 complexes, unlike others M(Lx)2, are readily reduced by PPh3 via intramolecular electron transfer from ligand to copper(II) to give unstable radical intermediates which are converted to another stable secondary radical species. The analysis of ESR spectra of Cu(Lx)(2), Co(L1)(2) and generated phenoxyl radicals are presented.