The new compound benzoato meso-tetra(4-methoxyphenylporphyrinato)thallium(III), Tl(tmpp)(C 6 H 5 CO 2 ), has been synthesized and its molecular structure determined by X-ray analysis. The coordination sphere of the Tl 3+ ion is an approximate square-based pyramid in which the apical site is occupied by an asymmetric-bidentate C 6 H 5 CO 2 − group. The average Tl-N bond distance is 2.24(1)A˚and the Tl atom is displaced 0.811A˚from porphyrin plane. The Tl(1)-O(5) and Tl(1)-O(6) distances are 2.57(2) and 2.27(2)A˚, respectively. Variable temperature 13 C NMR measurements show that the benzoato group of Tl(tmpp)(C 6 H 5 CO 2 ) in CD 2 Cl 2 solvent undergoes intramolecular exchange. In the slow exchange region, the carbonyl and C 1″ carbons of the benzoato group are separately located at 167.8 ppm [with 2 J (Tl- 13 C) coupling constant 212 Hz] and 128.3 ppm [with 3 J (Tl- 13 C) coupling constant 282 Hz] for T1 (tmpp)(C 6 H 5 CO 2 ) in CD 2 Cl 2 at −90°C. In the fast exchange region, the C * OO and C 1″ carbons of the C 6 H 5 CO 2 − ligand in CD 2 Cl 2 at 21°C are singlets at 168.4 and 130.3 ppm, respectively. The comparison of the ring current effect (Δδ) for the benzoate ligand of Tl(tmpp)(C 6 H 5 CO 2 ) and benzoato meso-tetra(4-methoxyphenylporphyrinto)tin(IV), Sn(tmpp)(C 6 H 5 CO 2 ) 2 , is also reported.