Preparation, spectral behaviour and oxidation of some new zinc(II) salicylaldimines containing sterically hindered phenol.

A series of new bis[N-(2,6-di-tert-butyl-1-hyxyphenyl)salicylideneminato]zinc(II) complexes bearing one or two HO- and CH3O-substituents on the salicylaldehyde moiety were prepared, and their spectroscopic properties (IR, electronic, 1H NMR) as well as the ESR spectra of the one-electron oxidation products were examined. The 1H NMR examination of Zn(Lx)2 indicates that, contrary to expectations, the proton resonances of the complexes are shifted to the high-field side compared with those of the free ligands. Oxidation of these compounds with PbO2 results in the formation of mono- and biradical types Zn(II)-stabilized phenoxyls in which there are both anisotropic and alternating line-width trends. Some spectral patterns are typical for weak interacting (J < A) or the case of J approximately A biradicals, in which ESR signal appeared as superimposition of two non-interacting monoradical centers with S = 1/2. ESR studies on biradicals type of Zn(L*x)2 at 300 and 77 K did not show any evidence of strong exchange coupling in these systems. All radical species were characterized by the ESR parameters.     

Synthesis, spectroscopy, and electrochemistry of copper(II) complexes with N,N'-bis(3,5-di-t-butylsalicylideneimine)polymethylenediamine ligands

Bulky salen CuL(x) derived from aliphatic polymethylene diamines, H(2)N-(CH(2))(x)-NH(2), where n = 2-6, and 3,5-di-t-butylsalicylaldehyde (H(2)L(x)) and some corresponding tetrahydrosalan complexes (CuL(x)') have been synthesized and characterized by their IR, UV-vis absorption and EPR spectra, by magnetic moments and by cyclic voltammetry in acetonitrile (for H(2)L(x)) and DMF (for CuL(x)). Complexes CuL(x) and CuL(x)' are magnetically normal (mu(exp) = 1.83-1.91 mu(B)). EPR spectra CuL(x) characterized by the axial g and A(Cu) tensors with g parallel > g perpendicular and without (14)N-shf resolution in CHCl(3)/toluene at 300 and 150K. The CV studies on acetonitrile solutions of H(2)L(x) revealed a well-defined quasi-reversible redox wave at E(1/2) = 0.95-1.15 V versus Ag/AgCl but CV of the CuL(x) complexes in DMF exhibit weak pronounced irreversible oxidation waves at E(pa)(1) = 0.51 - 098 V and E(pa)(2) = 1.16 - 1.33 V attributable to metal centered Cu(II/III) and ligand centered CuL(x)/CuL(x)*+ couples, respectively. A poorly defined wave was observed for the quasi-reversible reduction Cu(II)/Cu(I) at potentials less than -1.0 V.     

Non linear transport properties of an insulating YBCO nano-bridge

We have investigated the transport properties of an insulating sub-micrometric YBa₂Cu₃O_{7- δ} bridge, patterned on a thin film. As expected for a variable-range-hopping insulator, transport is found to be non linear. The reduced dimension allows for the observation of individual fluctuators generating random telegraph noise, whose dynamics could be explored as a function of the temperature and transport current. Some recordings clearly exhibit three levels fluctuating resistance, with comparable level separation and correlated dynamics, which likely result from the existence of two states or correlated clustered charge traps.     

Spectroscopic and electrochemical characterization of di-tert-butylated sterically hindered Schiff bases and their phenoxyl radicals

A series of sterically hindered N-arylsalicylaldimines (SAs) previously prepared from substituted salicylaldehydes (X-Sal, where X = H, Cl, Br, NO2, OH, OCH3) and 2,6-di-t-butyl-1-hydroxyaniline (LxH) and 2,5-di-t-butylaniline (Lx'H) were characterized by 1H and 13C NMR, UV-Vis and electrochemical methods. The electronic spectra (ES) (X = OH, OCH3) in alcoholic solvents (MeOH, EtOH, PrOH, iso-PrOH) unlike other solvents exhibit a new absorption band in the region 630-675 nm (epsilon = 19-242 M(-1) cm(-1)), which are not characteristic for other SA known in literature. The ESR studies of primary phenoxyl radicals generated from LxH by their oxidation with PbO2 reveal that some of them with the time are converted to more stable secondary Coppinger's radical. The cyclic voltammograms of LxH and Lx'H except NO2-substituted ones in CH3CN are similar and along with two or three irreversible anodic waves at the potentials ranging from 0.0 to +1.9 V versus Ag/AgCl, also display one or two irreversible reduction waves at potentials -0.6 to +0.5 V. A series of a new SA prepared from 3,5-di-t-butylsalicylaldehyde and mono-substituted anilines (X = H, o-, p-F, Cl, Br, OCH3, p-t-butyl, 5,6-benzo) were characterized by analytical, spectroscopic (IR, UV-Vis, 1H and 13C NMR), and electrochemical techniques. The ES spectra of o-, p-Cl, p-Br, o-CH3 and 5,6-benzo-substituted SA did not exhibit expected absorptions at 400-500 nm in alcoholic solutions.     

Electromagnetic annihilation of a lepton-antilepton pair into a hyperon pair with an account of polarizations and form factors

The annihilation of a lepton-antilepton pair into a pair of or -hyperons is examined. Expressions are found for the differential cross section in the CM system with an account of the strange-particle form factors, and with separate accounts of the random polarization of the initial and final particles.In conclusion, the author thanks Doctor of Physicomathematical Sciences B. K. Kerimov for suggesting the topic and for valuable advice.     

Synthesis, spectroscopy and redox behaviors of 4,6-di-t-Bu-, 4-Me-6-t-Bu- and 4-t-Bu-2-nitrosophenolato copper(II) complexes; Characterization of radical species generated by PPh3

The synthesis, spectroscopy (IR, UV-Vis, ESR), magnetic and thermal behaviors, as well electrochemistry and reactivity towards PPh3 of alkyl-substituted bis(2-nitrosophenolato)copper(II) complexes, CuLx2, where Lx = 4,6-di-t-Bu-2-nitrosophenolato (L1), 4-CH3-6-t-Bu-2-nitrosophenolato (L2), 4-t-Bu-2-nitrosophenolato (L3) mono-anion ligands, are presented. The solid-state and solution ESR spectra showed an axially symmetric g-tensors with gII > g 2.03 indicating that the unpaired electron is located in the dx2 - y2orbital. When CuLx2 complexes were treated with an excess of PPh3 in air or under vacuum in toluene (or other solutions) at 300K, as confirmed by UV-Vis and ESR examination, without formation of PPh3 adduct of the complexes, the immediately generation of semiquinone type radical species and reduction of Cu(II) to Cu(I) were observed. In the case of CuL(1)(2) the further conversion of the generated primary radical species to secondary bis(PPh3)2(phenoxazinolato)Cu(I) semiquinone type radical was detected. The cyclic voltammetry (CV) of CuLx2 exhibited two successive quasi-reversible ligand centered reductions and two irreversible metal and ligand centered oxidation processes. Electrochemical behaviors were interpreted in terms of the existence two-valence tautomeric nitroso and oximato isomers of CuLx2 in solution.