Comparative Spectroscopic Studies of Iron(III) and Manganese(III) Salen Complexes Having a Weakly Coordinating Triflate Axial Ligand

Abstract

Abstract We thoroughly compared spectroscopic and magnetic properties of mononuclear iron(III) and manganese(III) complexes with symmetric and nonsymmetrical salen ligands, in order to investigate the relation between spectroscopic properties and electronic structures. Magnetic susceptibility and dual-mode electron paramagnetic resonance data show the assignment of [FeIII(salen)(OTf)] and [MnIII(salen)(OTf)] as high-spin S = 5/2 and S = 2 electronic configurations, respectively, irrespective of the electron-donating properties and symmetry of the salen ligand. Further insights into electronic structures of central metal are obtained from 2H NMR spectra of selectively deuterated complexes, in which [FeIII(salen)(OTf)] and [MnIII(salen)(OTf)] exhibit well-resolved paramagnetic NMR signals of quite different shift patterns, due to the presence or absence of the unpaired electron in the dx2 - y2 orbital expected for S = 5/2 iron(III) or S = 2 manganese(III) centers.