Magnetic properties in high-spin mononuclear manganese(III) inverted N-confused porphyrin complexes: Antiferromagnetic interaction of Mn(2-NCH2CHCH2NCTPP)Br versus ferromagnetic interaction of Mn(2-NCH2-p-C6H4-CO2CH3NCTPP)Br

The crystal structures of diamagnetic (2-aza-2-(4′-methyl methylbenzoate)-5,10,15,20-tetraphenyl-21-carbaporphyrinato-N,N′,N″) nickel(II) [Ni(2-NCH2-p-C6H4-CO2CH3NCTPP); 5], paramagnetic bromo(2-aza-2-(4′-methyl methylbenzoate)-5,10,15,20-tetraphenyl-21-carbaporphyrinato-N,N′,N″) manganese(III) [Mn(2-NCH2-p-C6H4-CO2CH3NCTPP)Br; 7], and paramagnetic bromo(2-aza-2-allyl-5,10,15,20-tetraphenyl-21-carbaporphyrinato-N,N′,N″) manganese(III) [Mn(2-NCH2-CHCH2NCTPP)Br; 6] were determined. The coordination sphere around Ni(II) in 5 is described as four-coordinate square-planar, whereas for Mn(III) in 6 and 7, it is a five-coordinate square pyramid (SPY-5) in which the unidentate Br− ligand occupies the axial site. The geff value of 10.7 (or 11.1) measured from the parallel polarization of the X-band EPR spectra at 4 K is consistent with a high spin mononuclear manganese(III) centre (S = 2) in 6 (or 7). The magnitude of the axial (D) zero-field splitting (ZFS) for the mononuclear Mn(III) centre in 6 (or 7) was determined approximately as −3.3 cm−1 (or −0.92 cm−1) by paramagnetic susceptibility measurements. Owing to the weak C(39A)–H(39B)⋯BrBA [or C(45A)–H(45B)···BrC] intermolecular hydrogen bonds, the mononuclear Mn(III) neutral molecules of 6 (or 7) are arranged in a dimeric network. A weak Mn(III)···Mn(III) antiferromagnetic interaction (JAF = −0.02 cm−1) operates via a MnAA (dz2) ‖ BrAA (pz) ‖ H(39D) (s) ‖ C(39B) ‖ N(4B) ‖ C(16B) ‖ C(17B) ‖ MnBA superexchange pathway in complex 6. Moreover, a weak Mn(III)⋯Mn(III) ferromagnetic interaction (JF = 0.58 cm−1) operates via a MnC (dz2) ‖ BrC (pz) ⊥⊥ H(45B) (s) ‖ C(45A) ‖ N(4A) ‖ C(18A) ‖ C(17A) ‖ MnA superexchange pathway in 7.

This work reports X-ray crystal structures of two new inverted N-confused porphyrin complexes, paramagnetic Mn(2-NCH2-CHCH2NCTPP)Br (6) and paramagnetic Mn(2-NCH2-p-C6H4-CO2CH3NCTPP)Br (7). The ESR and magnetic susceptibility study of 6 and 7 has yielded actual structural information and magnetic superexchange coupling in terms of the parameters of the D and J for 6 and 7.Figure optionsDownload as PowerPoint slide