Electrolyte effects on the intervalence transition within discrete binuclear cyano-bridged complexes. An estimation of activation free energy from static, optical and electrochemical data

A study of the metal-to-metal charge-transfer (MMCT) transition within the binuclear cyano-bridged complexes cis-[L13CoIII(μ-NC)FeII(CN)5]− (L13 = 12-methyl-1,4,7,10-tetraazacyclotridecan-12-amine), trans-[L14CoIII(μ-NC)FeII(CN)5]− (L14 = 6-methyl-1,4,8,11-tetraazacyclotetradecan-6-amine) and trans-[L15CoIII(μ-NC)FeII(CN)5]− (L15 = 10-methyl-1,4,8,12-tetraazacyclopentadecan-10-amine) has been carried out in electrolyte solutions at varying concentrations. Using these data, as well as the reaction free energies obtained from electrochemical measurements, the reorganisation and activation free energies for the forward and reverse thermal electron-transfer processes have been estimated. The changes of these parameters with the electrolyte concentration, as well as those of the energy of the maximum MMCT band and the reaction free energy, are mainly due to ion-pairing effects.

Graphical abstractStructure and UV-spectrum of the trans-[L14CoIII(μ-CN)FeII(CN)5]− complex. The picture shows experimental (symbols) and simulated (solid lines) data of the characteristic bands for the chromophores CoIII and FeII. The metal to metal charge transfer (MMCT) band is also shown (dashed line). The connection between optical and thermal electron transfer processes allow the estimation of the activation free energy.Figure optionsDownload full-size imageDownload as PowerPoint slide