On the positronium spin conversion reactions caused by some macrocyclic CoII complexes

The rate constants, kCR, of ortho- into para-positronium (o-Ps→p-Ps) spin conversion reactions, CR, caused by the high-spin [CoIIsep]2+, [CoIIdinosar]2+ and [CoIIdiamsar]2+ macrocyclic complexes and also by high-spin [CoII sen]2+ tripod complex were measured at several temperatures. The delocalizations, β, of CoII unpaired electrons, promoted by the mentioned ligands, were determined by using the previously established correlations between kCR and the electron delocalization β of unpaired metal electrons. β is given by the ratio between the Racah inter-electronic repulsion parameters of complexes, B, and that of the free ions, B0. The β values are compared with those of the CoII complexes with en (1,2-ethanediamine), pn (1,2 propanediamine) and dien (2,2' diamino diethylamine) ligands. The kCR rate constants are also compared with those of the Ps oxidation reactions, OR, promoted by the corresponding CoIII complexes. It is concluded that, unlike OR's, the CR's do not occur by formation of hepta-coordinate adducts with Ps atoms