Magnetic susceptibility and ground-state zero-field splitting in high-spin mononuclear manganese(III) of inverted N-methylated porphyrin complexes: Mn(2-NCH3NCTPP)Br

Abstract

The crystal structures of diamagnetic dichloro(2-aza-2-methyl-5,10,15,20-tetraphenyl-21-carbaporphyrinato-N,N',N '')-tin(IV) methanol solvate [Sn(2-NCH3NCTPP)Cl-2 center dot 2(0.2MeOH); 6 center dot 2(0.2MeOH)] and paramagnetic bromo(2-aza-2-methyl-5,10,15,20-tetraphenyl-21-carbaporphyrinato-N,N',N '')-manganese(III) [Mn(2-NCH3NCTPP)Br; 5] were determined. The coordination sphere around Sn4+ in 6 center dot 2(0.2MeOH) is described as six-coordinate octahedron (OC-6) in which the apical site is occupied by two transoid Cl- ligands, whereas for the Mn3+ ion in 5, it is a five-coordinate square pyramid (SPY-5) in which the unidentate Br- ligand occupies the axial site. The g value of 9.19 (or 10.4) measured from the parallel polarization (or perpendicular polarization) of X-band EPR spectra at 4 K is consistent with a high spin mononuclear manganese(III) (S = 2) in 5. The magnitude of axial (D) and rhombic (E) zero-field splitting (ZFS) for the mononuclear Mn(III) in 5 were determined approximately as -2.4 cm(-1) and -0.0013 cm(-1), respectively, by paramagnetic susceptibility measurements and conventional EPR spectroscopy. Owing to weak C(45)-H(45A)...Br(1) hydrogen bonds, the mononuclear Mn(III) neutral molecules of 5 are arranged in a one-dimensional network. A weak Mn(III)...Mn(III) ferromagnetic interaction (J = 0.56 cm(-1)) operates via a [Mn(1)-C(2)-C(1)-N(4)-C(45)-H(45A)...Br(1)-Mn(1)] superexchange pathway in complex 5.