Synthesis, spectroscopic characterizations, cyclic voltammetry investigation and molecular structure of the high-spin manganese(III) trichloroacetato meso-tetraphenylporphyrin and meso-tetra-(para-bromophenyl)porphyrin complexes

Abstract

We present here the synthesis of two manganese(III) trichloroacetato porphyrins, namely (trichloroacetato)[5,10,15,20-tetraphenylporphyrinato]manganese(III) [MnIII(TPP)(TCA)] (1) and (trichloroacetato)[(5,10,15,20-tetra-(para-bromophenyl)porphyrinato]manganese(III) hemi-chloroform hemi-dichloromethane solvates [MnIII(TBrPP)(TCA)]·1/2CHCl3·1/2CH2Cl2 (2). These two new coordination compounds have been characterized by elemental analysis, UV–Vis, IR and 1H NMR spectroscopies, mass spectrometry, cyclic voltammetry and X-ray crystallography. The UV–Vis spectra of 1 and 2 exhibit hyper type electronic spectra with very red shifted Soret bands, while the proton NMR spectra of these two Mn(III)-trichloroacetato metalloporphyrins present the β-pyrrole protons of the TPP and TBrPP porphyrinates as very upfield shifted bands, indicating that the two Mn(III) derivatives are high-spin (S=2) with the ground state electronic configuration (dxy1)(dxz,yz2)(dz21). The redox potential values of 1 and 2 are very close to each other and to other penta-coordinated high-spin Mn(III) metalloporphyrins. The average equatorial distance between the Mn cation and the nitrogen atoms of the porphyrin macrocycle (Mn–Np) of 1 and 2 are very close and are in the normal range for high-spin Mn(III) metalloporphyrins. The displacement of the manganese atom from the porphyrin mean plane (PC) of the TBrPP derivative (2) is smaller than that of the TPP species (1) [0.147 (1) and 0.236 (1)Å for 2 and 1 respectively], which is also the case for the deformations of the porphyrin core, where the TPP species (1) exhibits much higher waving and saddle deformations than the TBrPP derivative (2). Notably, the molecular structures of 1 and 2 present face to face π–π dimer formation with PC⋯PC distances of 3.69 and 3.88Å, and Mn⋯Mn distances of 5.57 and 4.80Å, respectively.