High-Spin Chloro Mononuclear MnIII Complexes: A Multifrequency High-Field EPR Study

Abstract

The isolation, structural characterization, and electronic properties of two six-coordinated chloromanganese (III) complexes, [Mn(terpy)(Cl)₃] (1) and [Mn(Phterpy)(Cl)₃] (2), are reported (terpy=2,2′:6′2′′-terpyridine, Phterpy=4′-phenyl-2,2′:6′,2′′-terpyridine). These complexes complement a series of mononuclear azide and fluoride Mn(III) complexes synthesized with neutral N-tridentate ligands, [Mn(L)(X)₃] (X=F⁻or N₃⁻and L=terpy or bpea [N,N-bis(2-pyridylmethyl)-ethylamine)], previously described. Similar to these previous complexes, 1 and 2 exhibit a Jahn–Teller distortion of the octahedron, characteristic of a high-spin Mn(III) complex (S=2). The analysis of the crystallographic data shows that, in both cases, the manganese ion lies in the center of a distorted octahedron characterized by an elongation along the tetragonal axis. Their electronic properties were investigated by multifrequency EPR (190–475 GHz) performed in the solid state at different temperatures (5–15 K). This study confirms our previous results and further shows that: i) the sign of D is correlated with the nature of the tetragonal distortion; ii) the magnitude of D is not sensitive to the nature of the anions in our series of rhombic complexes, contrary to the porphyrinic systems; iii) the |E/D| values (0.124 for 1 and 0.085 for 2) are smaller compared to those found for the [Mn(L)(X)₃] complexes (in the range of 0.146 to 0.234); and iv) the E term increases when the ligand-field strength of the equatorial ligands decreases.