Positronium Spin-Conversion Reactions Promoted by 3d Complexes in Highand Low-Spin States

Continuing in our work on the correlations between the rate constants, k _CR, of the ortho into para-positronium conversion reactions, CR, promoted by complexes of various 3d ions and the metal electron delocalization caused by the ligands, the relationship between the parameters of the correlation lines pertinent to highand low-spin complexes of Cr^II, Mn^II, and Co^II ions was ascertained. Moreover, it was experimentally verified, for the first time, that the statistical probability of the CR promoted by paramagnetic compounds with S = 1/2 is three times larger than that of the CR caused by compounds with S > 1/2.     

Electron Delocalization in 3d Complexes Caused by Dimethylurea Checked by Positron Annihilation

The rate constants, k _CR, of ortho- into para-positronium conversion reactions promoted by paramagnetic 3d complexes are linearly correlated with the electron delocalization, , of unpaired metal electrons caused by ligands, being the ratio between the inter-electronic repulsion parameters in complexes and in the free gaseous ions. By applying a procedure previously described the values of Mn^II, Co^II, Ni^II complexes with dimethylurea were deduced from the mentioned correlations and compared with those of complexes with urea obtained both by the method of Ps reactions here applied and that based on UV-Vis absorption spectroscopy.     

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

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, B₀. 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.     

Electron delocalization of metal electrons in Fe complexes by positronium spin conversion reactions

The rate constants, k_CR, of conversion reactions, CR, of ortho- into para-positronium atoms promoted by 3d paramagnetic complexes of V^II, Cr^II, Cr^III, Mn^II, Co^II and Ni^II ions are linearly correlated with the electron delocalization β caused by the ligands. β's may be evaluated by means of the empirical equation β=1−th, where t and h are constants characteristic of the ion and ligands, respectively. The determination of the unknown t(Fe^II) value is here described. It was derived by means of the rate constants of the CR caused by some Fe^II complexes. It was found that t(Fe^II)=0.14±0.01. A relationship between t and the oxidation number of the metal ions is suggested.     

Positronium interactions with Cu(II) Ions in water

Summary Positronium reactions with Cu(II) ions in aqueous solution were investigated by measuring the concentration dependence of lifetime spectra and of 1D-ACAR curves for the following Cu (II) complexes: [Cu(H₂O)₆[²⁺, [Cu(NH₃)₄ (H₂O)₂]²⁺ and [Cu(EDTA)(H₂O)]²⁻. The combined analysis of lifetime and ACAR data shows that Cu(II) ions:a) reduce the formation of positronium (inhibition effect),b) promote both ortho ⇌ para conversion and redox reactions. It was also found that inhibition and reaction rate constants are affected by the ligand type.     

Electron Delocalization Caused in 3d Complexes by Azide and Chloride Ligands Checked by Positronium Spin-Exchange Reactions

The rate constants k _CR of orthointo para-positronium conversion reactions promoted by 3d complexes are linearly correlated with the electron delocalization of unpaired metal electrons caused by ligands, as measured by the ratio between the interelectronic repulsion parameters in complexes and in the free gaseous ions (1 > 0). The values may be evaluated by means of the following empirical equation: = 1 t _M h _L, where t _M and h _L are characteristic constants of 3d ions and ligands, respectively. By measuring k _CR and applying the correlations mentioned above, h _L constants may be derived providing that t _M is known. The method was used to measure the h _L value of N^– ₃, not yet known, and to check that of Cl^– ligand.