Redox chemistry of bis(terpyridine)manganese(II) complexes – A molecular view

Abstract

Oxidation of bis (terpyridine)manganese(II) complexes with a constrained octahedral geometry, leads to a high spin manganese(III) compression Jahn-Teller distortion geometry, while reduction results in a high spin manganese(II) complex which is antiferromagnetically coupled to one localized π-radical anion ligand. The provided linear relationships between experimental redox potentials and density functional theory calculated energies can be used to predict the redox potentials of related bis (terpyridine)manganese(II) complexes. • [Mn II (tpy) 2 ] 2+ has a constrained octahedral geometry. • [Mn III (tpy) 2 ] 3+ has a compression Jahn-Teller geometry. • [Mn IV (tpy) 2 ] 4+ has a constrained octahedral geometry. • Reduction of [Mn II (tpy) 2 ] 2+ gives the high spin [Mn II (tpy)(tpy) • ] 1+ complex. • Linear relationships between experimental redox potentials and DFT calculated energy. A density functional theory study of the oxidation and reduction of a series of bis (terpyridine)manganese(II) complexes showed that oxidation results in a high spin manganese(III) compression Jahn-Teller distortion geometry, while reduction results in a high spin manganese(II) complex which is antiferromagnetically coupled to one localized π-radical anion ligand. Experimental reports on the redox chemistry of [Mn II (tpy) 2 ] 2+ complexes, reported two oxidation and three reduction processes. The DFT results of this study, on the electronic structure of the molecules involved in the redox processes, assign the oxidation processes metal based, with the formation of [Mn III (tpy) 2 ] 3+ and [Mn IV (tpy) 2 ] 4+ respectively. Contrary to oxidation that is metal based, DFT results show that the reduction processes are ligand based, with the formation of [Mn II (tpy)(tpy) • ] 1+ and [Mn II (tpy • ) 2 ] 0 respectively, where (tpy • ) 1− is a π-radical anion that couples antiferromagnetically to the high spin Mn II ion. Correlations between experimental redox potentials and density functional theory calculated energies were established, which can be used to predict redox potential as well as electrophilic and nucleophilic reactivity of further substituted bis (terpyridine)manganese(II) complexes.