The crystal structures of acetato-N-tosylimido-meso-tetraphenylporphyrinatothallium(III), T1(N-NTs -tpp)(OAc) (1), and acetato-N-tosylimido-meso-tetraphenylporphyrinatogallium(III), Ga(N-NTs-tpp)(OAc) (2), were determined. The coordination sphere around the T1(3+) ion is a distorted square-based pyramid in which the apical site is occupied by a chelating bidentate OAc- group, whereas for the Ga3+ ion, it is a distorted trigonal bipyramid with O(3), N(3), and N(5) lying in the equatorial plane. The porphyrin ring in the two complexes is distorted to a large extent. For the T1(3+) complex, the pyrrole ring bonded to the NTs ligand lies in a plane with a dihedral angle of 50.8 degrees with respect to the 3N plane, which contains the three pyrrole nitrogens bonded to T1(3+), but for the Ga3+ complex, this angle is found to be only 24.5 degrees. In the former complex, T1(3+) and N(5) are located on the same side at 1.18 and 1.29 Angstrom from its 3N plane, but in the latter one, Ga3+ and N(5) are located on different sides at -0.15 and 1.31 Angstrom from its 3N plane. The free energy of activation at the coalescence temperature T-c for the intermolecular acetate exchange process in 1 in CD2Cl2 solvent is found to be Delta G(171)(+/-) = 36.0 kJ/mol through H-1 NMR temperature-dependent measurements. In the slow-exchange region, the methyl and carbonyl (CO) carbons of the OAc- group in 1 are separately located at delta 18.5 [(3)J(T1-C-13) = 220 Hz] and 176.3 [(2)J(T1-C-13) = 205 Hz] at -110 degrees C.