Département de chimie moléculaire

The electronic properties of the high spin mononuclear MnII complexes [Mn(tpa)(NCS)2] (1) (tpa = tris-2-picolylamine), [Mn(tBu3-terpy)2](PF6)2 (2) (tBu3-terpy = 4,4',4"-tri-tert-butyl-2,2':6',2"-terpyridine) and [Mn(terpy)2](I)2 (3) (terpy = 2,2':6',2"-terpyridine) with an N6 coordination sphere were detd. by multifrequency EPR spectroscopy. The x-ray structures of 1·MeCN and 2·C4H10O·0.5EtOH·0.5MeOH reveal that the MnII ion lies at the center of a distorted octahedron. Crystallog. data are given. The D-values of 1-3 all fall in the narrow range of 0.041 to 0.105 cm-1. The comparison of the results reported here and those found in the literature is consistent with the following observation: the D value is sensitive to the coordination no. (6 or 5) of the MnII ion as long as the coordination sphere involves only N and/or O based ligands. This magneto-structural correlation was analyzed in this work though DFT model calcns. The zero-field splitting (zfs) parameters of 1-3 were calcd. and are in reasonable agreement with the exptl. values. Hypothetical simplified models [Mn(NH3)x(OH2)y]2+ (x+y = 5 or 6 and [Mn(NH3)5X]+ (X = OH, Cl)) were constructed to study the origin of the zfs. This study reveals (i) that D is sensitive to the coordination no. (5 or 6) of the MnII ion, (ii) for the five coordinate systems the major contribution to D is the spin-orbit coupling part, (iii) for the six coordinate systems the major contribution to D is the spin-spin interaction and (iv) the deprotonation of a H2O ligand increases D, consistent with the relative ligand fields of OH- vs. H2O. [on SciFinder(R)]