Exothermic sintering of aluminium with a high content of copper: A.P. Savickii, G.N. Romanov (Russian Academy of Sciences, Tomsk, Russia), Science of Sintering, Vol 25, No 1/2, 1993, 9–14

Abstract

The reaction of Cp(dppe)FeI with the ligands 2,2′- and 4,4′-dithiobispyridine (S2(Py)2) give the mononuclear or binuclear complexes of the type [Cp(dppe)Fe-S2(Py)2]PF6, [Cp(dppe)FeSPy]PF6 or [{Cp(dppe)Fe}2-μ-SPy](PF6)2 depending on the reaction condition. Reaction of Cp(dppe)FeI with dithiobispyridines in presence of TlPF6 as halide abstractor and using CH2Cl2 as a solvent gives the complexes [Cp(dppe)Fe-4,4′-S2(Py)2)2]PF6 (1) and [CpFe(dppe)-2,2′-S2(Py)2]PF6 (2) whereas the same reaction using CH3OH as a solvent and NH4PF6 as the halide abstractor leads to the formation of the FeIII–thiolate complex [Cp(dppe)Fe-2,2′-SPy]PF6 (3) and the mixed-valence complex [Cp(dppe)FeIII-μSPy-FeII(dppe)Cp](PF6)2 (4). Magnetic and ESR measurements are in agreement with one unpaired electron delocalized between them. Mössbauer data indicate clearly the presence of two different iron sites, each one of the N-bonded and S-bonded iron atoms, with intermediate oxidation state FeIIFeIII. An electron transfer intervalence absorption was observed for this complex at 780 nm (in CH2Cl2). By applying the Hush theory the intervalence parameters were obtained; α=0.028, Hab=361 cm−1 which indicate Class II Robin–Day. Estimation of the rate electron transfer affords a value kth=6.5×106 s−1. Solvent effect on the intervalence transition follow the Hush prediction for high dielectric constants solvents which permit the evaluation of the outer and inner-sphere reorganizational parameters, which were analyzed and discussed. The electronic interaction parameters compare well with those found for electron transfer in metalloproteins.