Silver(II) complexes of tetraazamacrocycles: Studies on e.p.r. and electron transfer kinetics with thiosulfate ion

Mahammad Ali, Alexander I. Shames, Sumana Gangopadhyay, Basudeb Saha, Dan Meyerstein

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15 Scopus citations

Abstract

The e.p.r. studies of Ag II complexes of three tetraazamacrocycles, 1,4,8,11-tetraazacyclotetradecane (cyclam) (I), 5,5,7,12,12,14-hexamethyl-1,4,8,11-tetraazacyclo-teradecane-4,11-diene (Me 6CD) (II) and 5,5,7,12,12,14-hexamethyl-1,4,8,11-tetraazacyclo- teradecane (Me 6Cy) (III) and the electron transfer between [Ag II(cyclam)] 2+ and thiosulfate ion are described. The e.p.r. studies reveal that the spectra are almost the same as those reported earlier, particularly, for polycrystalline material and are typical of a d 9 planar Ag II complexes. Previous e.p.r. studies on these square planar polycrystalline complexes showed no ligand hyperfine splitting. Reinvestigation of the e.p.r. spectra of these complexes in both the solid state and in solution at room (T ∼ 297 K) and at low (T = 120 K) temperature reveals resolved hyperfine structures in solution for [Ag(Me 6CD)] 2+ and [Ag(Me 6Cy)] 2+ complexes, Surprisingly, such a structure was not observed in solutions of [Ag(cyclam)] 2+. Computer simulations of the hyperfine structure observed in solutions are in good agreement with structural formulae proposed. The oxidation of thiosulfate ion by [Ag(cyclam)] 2+ follows the rate law: -d/dt[Ag II(cyclam) 2+] = (k 1Q 1[H+] + k 2Q 2K a2)/([H+] + K a2)[Ag II(cyclam) 2+][S 2O 3 2-] and an inner-sphere mechanism is proposed, based on the spectral and kinetic evidence.

Original languageEnglish
Pages (from-to)463-470
Number of pages8
JournalTransition Metal Chemistry
Volume29
Issue number5
DOIs
StatePublished - 1 Aug 2004

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