Salicylate exchange in meso-tetraphenylporphyrinato salicylato thallium (III), Tl (tpp) (2-OH-C 6H 4CO 2) and 13C NMR investigation of its homolog thiocyanato (meso-tetra-p-tolyl-porphyrinato)thallium (III), Tl (tptp) (SCN)

Abstract

This work determines the crystal structure of meso-tetraphenylporphyrinato salicylato thallium (III), Tl (tpp) (2-OH-C 6H 4CO 2) (or Tl (tpp) (SA)). The coordination sphere of the Tl 3 ion is an approximately square-based pyramid in which a chelating bidentate 2-OH-C 6H 4CO − 2 group occupies the apical site. The average Tl (1)–N bond distance is 2.221 Å and the Tl atom is displaced 0.76 Å from the porphyrin plane. The Tl (1)–O(1) and Tl (1)–O(2) distance are 2.36 (1) and 2.47 (1) Å, respectively. Variable temperature 13 C NMR measurements reveal that the salicylato group of Tl (tpp) (SA) in CD 2Cl 2 solvent undergoes a ligand exchange. In the slow exchange region, the carbonyl and C 1″ carbons of the salicylato group are separately located at 169.6 ppm [with a 2 J (Tl– 13 C) coupling constant of 157 Hz] and 111.5 ppm [with a 3 J (Tl– 13 C) coupling constant of 180 Hz] for Tl (tpp) (SA) in CD 2Cl 2 at −90°C. In the fast exchange region, the C∗O and C 1″ carbons of the 2-OH-C 6H 4CO − 2 ligand in CD 2Cl 2 at 24°C are singlets at 169.8 and 112.5 ppm, respectively. The 13 C resonance of the axial isocyanato ligand in the compound thiocyanato ( meso-tetra- p-tolyl-porphyrinato)thallium (III), Tl (tptp) (SCN), was observed at 110.7 ppm (24°C) with 2 J (Tl– 13 C) coupling constant 253 Hz. This finding suggests that thiocyanato group is, as thiocyanate type, axially coordinated to the Tl atom in Tl (tptp) (SCN). In addition, there is no SCN − exchange in the same compound.