Influence of the Type of Macrocycle on the Stabilisation of the High Oxidation State of the Manganese Ion and Electrode Processes

Dinuclear di-<i>µ</i>-oxo complexes of Mn³⁺ and Mn⁴⁺ ions, and mononuclear complexes of Mn³⁺ ions with tetraazamacrocycles ([12]aneN₄, [14]aneN₄, [15]aneN₄) and <i>C</i>-substituted derivative (Me₆[14]aneN₄) as well as mononuclear complexes of Mn²⁺ ions with <i>N</i>-substituted derivatives ((<i>N</i>-Me)₂[14]aneN₄, (<i>N</i>-Me)₄[14]aneN₄, (<i>N</i>-Me)Me₂py [14]aneN₄) and with oxo₂[14]aneN₄ were studied. Based on spectroscopic (UV VIS and IR) and conductometric studies, the types of synthesised complexes (<i>cis</i> or <i>trans</i> isomers of mononuclear Mn³⁺ complexes, oxygen bridges and class II according to Robin and Day classification for dinuclear complexes) were determined. On the basis of voltammetric and spectroelectrochemical studies, <i>trans-cis</i> isomerisation at the level of Mn²⁺ ion complexes and <i>cis-trans</i> isomerisation at the level of Mn³⁺ ion complexes were demonstrated for complexes of ligands with free C positions. The <i>N</i>-substituted derivatives oxidise according to the EC mechanism, in which the follow-up reaction is a disproportionation reaction. The thermodynamic stabilisation of Mn³⁺ ions was determined by comparing the formal potentials (<i>E_f</i>⁰), the disproportionation constants (<i>k</i>₁) and the formation constants (<i>β^III</i>). The study showed the possibility of oxidation of mononuclear, pseudo-octahedral Mn³⁺ ion complexes to dinuclear complexes and the greatest stabilisation of Mn³⁺ ions, both in monomers and dimers of ligands with free <i>N</i> positions.