Electron spin resonance spectra of frozen solutions of the copper( 11) chelates of cyclopentanetetracarboxylic acid formed by the interaction of copper(i1) chloride or perchlorate in various non-aqueous solvents indicate the formation of dimeric species in which exchange coupling or dipole-dipole coupling occurs. The formation of the dimeric species is dependent on the nature of the solvent and composition of the reaction mixture. In dimethylformamide the e.s.r. spectrum indicates the formation of dipole-dipole coupled copper(l1) pairs when the copper(ii) chloride to ligand ratio is 1 :I, whereas when this ratio is 1 :2 lowand high-field signals are observed such that a mixture of dimeric species exists. When copper( 11) perchlorate is used, the e.s.r. spectra point to the formation of dimericspecies in which exchange coupling occurs, though the magnetic parameters associated with the signal have different values from those observed for the exchange coupled species when copper(l1) chloride is used. Exchange coupling in dimeric species has been observed in the copper(l1) chelates of m-and p-hydroxybenzoic acids, and in the copper(l1) complexes of adenine formed in both aqueous and non-aqueous solutions. To evaluate the magnetic parameters associated with the signals due to species in which exchange coupling occurs, a general spin Hamiltonian to include the effects of exchange and dipole-dipole contributions has been used. Solution of the spin Hamiltonian has made possible the computation of the lineshape due to exchange coupled copper(i1) pairs. Thus sets of magnetic parameters have been collected for exchange coupled and dipole-dipole coupled copper(i1) pairs and the values obtained from the dipole-dipole coupled pairs used to suggest the possible structure of the dimeric species.
Articles you may be interested inElectronic processes during ion-beam sputtering of metals studied by resonance laser ionization mass spectrometry AIP Conf.Electron spin resonance measurements have been made on a number of copper (II) and vanadyl porphyrins. The spectra recorded at a sample temperature of 77°K have low field components attributed to I:!.M = 2 transitions which provided evidence for the existence of dimer species in solution. In one case, namely copper hematoporphyrin(IX) dimethylester, a resonance centered at 950 G is thought to be due to a I:!.M = 3 transition arising from a trimer species. The theory of the ESR spectra of dipolar coupled S =! transition metal ions with particular reference to systems involving copper (II) and vanadyl ions is outlined. The treatment has been developed to the point which makes a computer simulation of the I:!.M = 1 and I:!.M = 2 transitions possible in the systems studied. An important product of this is the evaluation of the distance between the metal ions in the dimeric species. The variation of this distance in the metalloporphyrins studied is related to subtle changes in structure brought about by the various substituents in the macrocylic system as well as to the nature of the transition metal ion.
Measurements are presented of the variation of stress and strain in metals as they are subjected to shock impulses of up to 200 kb and released. Results have been obtained for a magnesium alloy and for two grades of aluminium of very different yield strengths. The release characteristics of these metals are shown to be broadly consistent with a simple elasto-plastic model for metal behaviour. Elasto-plastic Hugoniots are fitted to published shock data for the metals used; a revised calibration is given for the manganin stress transducer employed, and a new method of construction is illustrated. Stress relaxation is observed in magnesium and is associated with the easy slip on the basal plane in hexagonal close-packed materials.
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