On the positronium spin conversion reactions caused by some macrocyclic Co II complexes

Abstract

The rate constants, k CR, of ortho- into para-positronium ( o-Ps→ p-Ps) spin conversion reactions, CR, caused by the high-spin [Co IIsep] 2+, [Co IIdinosar] 2+ and [Co IIdiamsar] 2+ macrocyclic complexes and also by high-spin [Co II sen] 2+ tripod complex were measured at several temperatures. The delocalizations, β, of Co II unpaired electrons, promoted by the mentioned ligands, were determined by using the previously established correlations between k CR 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, B 0. The β values are compared with those of the Co II complexes with en (1,2-ethanediamine), pn (1,2 propanediamine) and dien (2,2′ diamino diethylamine) ligands. The k CR rate constants are also compared with those of the Ps oxidation reactions, OR, promoted by the corresponding Co III complexes. It is concluded that, unlike OR's, the CR's do not occur by formation of hepta-coordinate adducts with Ps atoms.