The ESR spectra for a series of binuclear trigonal bipyramidal copper complexes show that the SOMO is largely composed of the t w o equivalent dZ2 orbitals on copper; the temperature independence of the ESR parameters shows that this is a relatively strong bond, and since the unpaired electron is antibonding, the a-bond must be even stronger; these results are contrasted with the more common situation that arises when the electron is shared between t w o d,2-y2 type orbitals.

Exposure of [N2H62+S042-] at 77 K to 6OCo y-rays gave SO4.radicals and a novel species with two equivalent nitrogen nuclei and six equivalent protons, thought t o be N2H6'+ formed by electron capture; these species readily gave NH3.+ radicals on annealing.

No abstract

In the pseudo-geminal(1a) and pseudo-ortho[2.2](2,5)pyrazinophane (2a) the methylene hydrogens oriented syn towards the aza function can be selectively replaced by deuterium, to give 1b and 2b. The corresponding radical anions were generated in 1,2-dimethoxyethane by reaction of the parent compounds with alkali metal mirror, and their EPR and ENDOR spectra were recorded. General triple resonance, providing the relative signs of the 1H coupling constants, and selective deuteriation of the syn methylene hydrogens led to full assignment in all cases. As anticipated, the magnitudes of the nitrogen and ring proton coupling constants are about one half the magnitudes of those of the corresponding 2,5-dimethylpyrazine radical anion 3˙–. For the two sets of methylene protons, considerably different coupling constants were found; 1a˙–: a(Hsyn)=+2.54, a(Hanti)=+0.24 G; 2a˙–: a(Hsyn)=+1.60, a(Hanti)=+0.30 G. The radical cations of 1a and 2a were prepared by exposure of the parent compounds, as dilute solutions in CFCl3, to 60Co γ-rays at 77 K. The results establish that these are π-radicals rather than σ-radicals despite the fact that the dimethylated monomers (pyrazine radical cations) are clearly σ-species. The results for the pseudo-ortho-derivative cation show that there are two sets of inequivalent CH2 protons

Pyrimidine and s-triazine radical cations have been prepared by exposing dilute solutions in freons to 60Co γ-rays at 77 K, and studied by EPR spectroscopy. Spectral interpretation is difficult because of the unknown angle (θ) subtended between the principle directions of the 14N hyperfine axes. Various deuteriated derivatives have been used, together with a range of computer-simulated spectra, which show how the spectra for a two-equivalent-nitrogen system change with θ. From these, the best spectra have been selected for comparison with experiment. The results are discussed in terms of two alternative interpretations offered previously. It is concluded that neither is correct, because of the neglect of weak outer features which are only clearly defined for the 2,4,6-trimethyl s-triazine derivative. The new results show that the SOMO is largely concentrated on two nitrogen ‘lone-pair ’in-plane orbitals with a nodal-surface passing through positions 2 and 5. The estimated p : s ratio on each nitrogen is ca. 4.8