The nephelauxetic effect and ortho- to para-positronium conversion reactions promoted by Cr(III) complexes

Lazzarini, A.L. Fantola; Lazzarini, E.

doi:10.1007/bf00672015

Cited by 7 publications

(3 citation statements)

References 15 publications

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“…A similar conclusion also emerges by comparing the expected and experimental k CR of Cr III complexes formed with mixed arrays of ligands containing NCS -, CNand even Clligands; later on it will be shown that this behaviour is also presented by the complexes of other metal ions formed with the same ligands (Fantola- Lazzarini and Lazzarini, 1992a).…”

Section: •2•5 a Systematic Investigation Of Se Reactions Caused By 3d Metal Complexes 4•2•5a Cr III Complexessupporting

confidence: 63%

“…In this event, the ␥ = k CR c value progressively decreases during the measurements of PAL spectra because the k CR of aquated complexes are less than those of the original complexes. The problem was resolved by plotting ␥ vs the time t elapsed from the moment of salt dissolution and by extrapolating the experimental ␥ values at t / ks t = 0; details may be found in Fantola Lazzarini and Lazzarini (1992a). The ␥ are plotted vs t given by:…”

Section: •2•4 a Working Hypothesismentioning

confidence: 99%

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REACTIVITY OF 3d METAL COMPLEXES TOWARDS POSITRONIUM ATOMS

Lazzarini

1999

prog. rct. kin. mech.

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The rate constants of oxidation and spin exchange reactions of positronium, Ps, atoms promoted at various temperatures by numerous 3d complexes are reviewed. The experimental methods used in the field are also described. It is shown that the rate constants of Ps oxidation, kOx, and Ps conversion reactions, kCR, may easily be interpreted on the basis of ligand field theory. In particular, values of kCR were found to be linearly correlated with delocalization of unpaired electrons of the metal ions caused by the ligands, as is described by the ratio β between the inter-electronic repulsion parameters in complexes and in the free gaseous ions. The empirical equation used to estimate β seems to work better than previously believed. This should also be considered an achievement of the experiments reviewed. The main conclusion is that, not only may Ps reactions with 3d complexes be easily interpreted by means of ligand field theory, but that the measurements of k for Ps reactions may, reciprocally, constitute a new method for investigating 3d complexes. Evidence was also found that the same conclusions should also be true for reactions of muonium, Mu.

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Section: •2•5 a Systematic Investigation Of Se Reactions Caused By 3d Metal Complexes 4•2•5a Cr III Complexessupporting

confidence: 63%

Section: •2•4 a Working Hypothesismentioning

confidence: 99%

REACTIVITY OF 3d METAL COMPLEXES TOWARDS POSITRONIUM ATOMS

Lazzarini

1999

prog. rct. kin. mech.

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“…6 not only confnnns the conjecture by Mc Gervey and De Benedetti and the result by Bisi et al, concerning the capability of Cu~q to promote ortho-para conversion reactions, but also demonstrates that this type of reaction is promoted by all Cu(II) complexes studied in the present work; probably, this is true for other Cu(II) compounds; b) on the other hand, the decreasing stage of the curves of fig. 6 demonstrates the predominant effect of inhibition and oxidation at high concentrations; c) the conflicting conclusions of previous works find their explanation in the different ranges of concentration explored, falling either in the dominant conversion regime (low concentration) or in the region where inhibition and oxidation are prevailing; d) quantitative differences between the reaction constants of the three complexes show that the ligands have a marked effect on the reaction mechanisms; it is interesting to point out that the values reported in table IV show that ksE increases according to the capability of ligands to cause the expansion of 3d electron clouds (nephelauxetic effect) [22,23].…”

Section: -Experimental Resultsmentioning

confidence: 95%