Magnetic properties in high-spin mononuclear manganese(III) inverted N-confused porphyrin complexes: Antiferromagnetic interaction of Mn(2-NCH2CH@CH2NCTPP)Br versus ferromagnetic interaction of Mn(2-NCH2-p-C6H4-CO2CH3NCTPP)Br

Abstract

The crystal structures of diamagnetic (2-aza-2-(40-methyl methylbenzoate)-5,10,15,20-tetraphenyl-21- carbaporphyrinato-N,N0 ,N00) nickel(II) [Ni(2-NCH2-p-C6H4-CO2CH3NCTPP); 5], paramagnetic bromo (2-aza-2-(40-methyl methylbenzoate)-5,10,15,20-tetraphenyl-21-carbaporphyrinato-N,N0 ,N00) 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,N0 ,N00) manganese(III) [Mn(2-NCH2-CH@CH2NCTPP)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 ðd2 zÞ k BrAA (pz) k H(39D) (s) k C(39B) k N(4B) k C(16B) k C(17B) k MnBA superexchange pathway in complex 6. Moreover, a weak Mn(III) Mn(III) ferromagnetic interaction (JF = 0.58 cm 1) operates via a MnC ðd2 zÞ k BrC (pz) ? H(45B) (s) k C(45A) k N(4A) k C(18A) k C(17A) k MnA superexchange pathway in 7.