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- Author or Editor: A. Fantola Lazzarini x
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Abstract
In order to ascertain possible relationships between the rate constants, KSE, of positronium, Ps, spin exchange /SE/ reactions promoted by 3d aqua ions and the electron configuration of the ion, the KSE's of Mn
aq
2+
and Co
aq
2+
aqua ions were measured together with that of [Cr(NH3)6]3+. The KSE's values obtained are discussed together with those of the Cr
aq
3+
, Fe
aq
2+
, Ni
aq
2+
and [Ni(NH3)6]2+ ions previously measured. It was found that Cr
aq
3+
and Mn
aq
2+
KSE's are 
1 M–1ns–1, while those of Fe
aq
2+
, Co
aq
2+
and Ni
aq
2+
ions are 2.5 M–1ns–1. Thus the KSE values of 3d aqua ions do not depend solely on the number of their unpaired electrons as it was found for the 4f aqua ions. The trend observed parallels that of the electron delocalization from the metal atom; the delocalization occurs only with Fe
aq
2+
, Co
aq
2+
and Ni
aq
2+
ions, but not with the Cr
aq
3+
and Mn
aq
2+
aqua ions. The trend of the KSE's of aqua, ammine and perhaps of chloro complexes parallels that of ligand capabilities to cause d-electron cloud expansion, and thus d-electron delocalization from metal atoms.
