Monodentate and bidentate trifluoroacetato ligands in bis(trifluoroacetato)-(N-methyl-meso-tetraphenylporphyrinato)thallium(III) -: a new dynamic 4:3 piano stool seven-coordinate geometry

The crystal structure of bis(trifluoroacetato)-(N-methyl-meso-tetraphenylporphyrinato) thallium(III), Tl(N-Me tpp)(CF3CO2)(2) (2), was established and the coordination sphere around the Tl3+ ion is described as 4:3 tetragonal base-trigonal base piano stool seven-coordinate geometry in which the two cis CF3CO2- groups occupy two apical sites. The plane of the three pyrrole nitrogen atoms [i.e. N(2). N(3) and N(4)] strongly bonded to Tl3+ is adopted as the reference plane 3N. The pyrrole N(1) ring bearing the methyl group [i.e. C(45)H-3] is the most deviated one from the 3N plane making a dihedral angle of 23.3degrees whereas smaller angles of 9.9. 2.7 and 4.7degrees occur with pyrroles N(2), N(3). and N(4), respectively. Because of the larger size of the thallium(III) ion, Tl is considerably out of the 3N plane: its displacement of 1.02 Angstrom is in the same direction as that of the two apical CF3CO2- ligands. The intermolecular trifluoroacetate exchange process for 2 in CD2Cl2 solvent is examined through F-19 and C-13 NMR temperature-dependent measurements, In the slow-exchange region, the CF3 and carbonyl (CO) carbons of the CF3CO2- groups in 2 are separately located at delta 114.3 ((1)J(C-F) = 290 Hz. (3)J(Tl-C) = 411 Hz] and 155.1 [(2)J(C-F) = 37 Hz, (2)J(Tl-C) = 204 Hz], respectively, at - 106 degreesC. In the same slow-exchange region. the fluorine atoms of 2, Tl(N-Me-tpp)(CF3CO2)(+) and the free CF3CO2- are located at delta - 73.76 [(4)J(Tl-F) = 44 Hz], - 73.30 [(4)J(Tl-F) = 22 Hz], and - 76.15 ppm at - 97 degreesC. respectively. (C) 2001 Elsevier Science Ltd. All rights reserved.