trans-[Cr(tmc)X2] complexes (tmc=1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecane, XF, Cl, Br, H2O, OH, NO3) have been prepared and spectroscopically characterized. The redox potentials of the tmc complexes and of the analogous cyclam complexes (cyclam=1,4,8,11-tetraazacyclotetradecane) were determined by cyclic voltammetry. The potentials of the tmc complexes are 1.1±0.1 V more positive. Their long wavelength absorption is red-shifted by 50 to 100 nm with respect to that of the analogous cyclam complexes. The shift was consistent with a linear dependence of the polarographic half-wave potentials on the transition energies of the first spin allowed ligand field bands, observed on a series of chromium(III) amine complexes. The reaction entropies for the reduction of trans-[Cr(cyclam)(H2O)2]3+, trans-[Cr(cyclam)(OH)2]+, and trans-[Cr(tmc)(OH)2]+, ΔS=88±2, 200±40 and 53±8 J mol-1 K-1, respectively, were obtained from the temperature dependence of the redox potential. It was shown that trans-[Cr(cyclam)(H2O)2]3+ catalyzes the electroreduction of nitrate.
|Number of pages||8|
|Journal||Inorganica Chimica Acta|
|State||Published - 1 Apr 1992|
ASJC Scopus subject areas
- Physical and Theoretical Chemistry
- Inorganic Chemistry
- Materials Chemistry