3186 13000, Office of Basic Energy Sciences, Division of Chemical Sciences, and the National Institutes of Health, Biotechnology Resource Program, ~ i ~ i ~ i ~ ~ of Research R ~ ~ ~ ~ ~ ~ ~ ~ . we thank D ~ ~ . M. K, id^^^^^ and s. p. cramer for their assistance with early experiments. Registry No. S, 7704-34-9;K2S04, 7778-80-5;tetramethylene sulfone, J. Am. Chem. SOC. zyxwvu 1989, Ill, 3186-3194 126-33-0; diphenyl sulfone, 127-63-9; dibenzothiophene sulfone, 1016- 05-3; tetramethylene sulfoxide, 1600-44-8;2-methylthiophene,554-14-3; benzothiophene, 95- 15-8; dibenzothiophene, 132-65-0; methionine, 63- 68-3; thianthrene, 92-85-3; dioctyl sulfide, 2690-08-6; tetramethyl- thiophene, 14503-5 1-6; benzyl phenyl sulfide, 83 1-91-4; 2-naphthalene- thiol, 91-60-1; cysteine, 52-90-4; diphenyl disulfide, 882-33-7; thio- hemianthraquinone, 68629-85-6. Equilibrium Dynamics in the Thallium( 111)-Chloride System in Acidic Aqueous Solution Istvan Banyai' and Julius Glaser* Contribution from The Royal Institute of Technology (KTH), Department zyx of Inorganic Chemistry, S-100 44 Stockholm, Sweden. Received August 9, 1988 Abstract: Kinetics of ligand exchange in the thallium(II1)-chloride system in aqueous three molar perchloric acid solution was studied by measuring 2osTl NMR line widths at 25 OC. The rate constants for the reactions TICIm3-"' zyxwvutsr + *TlCI,'-" & *TICIm3-"' + TlCI,'-" are kol = 4.5 X lo4 (7.8 X lo3 at 0 "C), k12 = 5.2 X lo4 (1.5 X lo4), kz3 = 2.7 X IO7 (3.3 X lo6), k3, < 3 X lo7 M-'s-'; for the reaction TI3+ + TIC12+ zyxwvu 2 2T1CI2+ kO2 = 6.4 x 105 M-1 s-1 (1.7 X lo5), and for the anation reactions k'.c,.i) TICI,'" + C1- T1C1,+12-" k',,, < 1 X lo8, k'12 = 3.3 X lo8 (2.4 X lo8), k'23 = 1.3 X lo9, and k'34 = 4.7 X lo8 M-l s-'. The first type of exchange dominates at low chloride to thallium ratios (CItot/TItot) = R zyxwvuts 5 2, the second type is only observed when the species TI3+ and TlCl2+ are present, whereas the third one dominates at all higher R values. The activation parameters for the reaction represented by kol are AH* = 49 (12) kJ mol-l and AS* = +12 (k0.3) J mol-' K-I. A mechanism for this reaction is suggested to be a dissociatively activated interchange process. The activation parameters for the reaction represented by k'34 are AH* = 6.6 kJ mol-' and AS* = -107 J mol-l K-I. An associatively activated interchange mechanism for this reaction is proposed. The stability constant for the complex T1C152- was estimated to be K5 = [TIC152-]/{[TlC14-] [Cl-]} = 0.5 M-'. The complexes formed in the thallium(III)-chloride system are among the strongest metal-ion-chloride complexes, and their equilibria have been extensively studied.2-8 There is information on their structures both in solid and in ~ o l u t i o n . ~ - ~ ~ However, there are only a few results on the kinetics of the complex for- mation and ligand exchange reactions of the thallium(II1) ion."+" (I) Permanent address: Department of Physical Chemistry, Lajos Kossuth (2) Lee, A. G. The Chemistry of Thallium; Elsevier: Amsterdam, 1971; (3) Ahrland, S.; Grenthe, I.; Johansson, zyxwvutsr L.; Noren, B. Acta Chem. Scand. (4) Ahrland, S.; Johansson, L. Acta Chem. Scand. 1964, zyxwvutsrqp 18, 2125. (5) Woods, M. J. M.; Gallagher, P. K.; Hugus, Z. Z.; King, E. L. Znorg. (6) Kul'ba, F. Y.; Mironov, V. E.; Mavrin, I. F. Zh. Fiz. Khim. 1965, 39, (7) Glaser, J.; Biedermann, G. Acta Chem. Scand. 1986, A40, 331. (8) Glaser, J.; Henriksson, U. zyxwvutsrqponm J. Am. Chem. SOC. 1981, 103, 6642. (9) Davies, E. D.; Long, D. A. J. Chem. SOC. A 1968, 2050. (10) Biedermann, G.; Spiro, T. G. Chem. Scr. 1971, I, 155. (1 I) (a) Spiro, T. G. Inorg. Chem. 1965, 4, 731. (b) Zbid. 1967, 6, 569. (12) Glaser, J.; Johansson, G. Acta Chem. Scand. 1982, A36, 125. (13) Glaser, J. Acta Chem. Scand. 1982, A36, 451. (14) Kawai, Y.; Takahashi, T.; Hayashi, K.; Imamura, T.; Nakayama, H.; (15) Funada, R.; Imamura, T.; Fujimoto, M. Bull. Chem. SOC. Jpn. 1979, (16) Lincoln, S. F.; Sandercock, A. C.; Stranks, D. R. Aust. J. Chem. (17) Henriksson, U.; Glaser, J. Acta Chem. Scand. 1985, A39, 355. University, H-4010 Debrecen, Hungary. pp 44-91, and references therein. 1963, 17, 1567. Chem. 1964, 3, 1313. 2595. Fujimoto, M. Bull. Chem. SOC. Jpn. 1972, 45, 1417. 52, 1535. 1975, 28, 1901. The reason is probably that these reactions are rather fast not only on the traditional kinetic time scale but also on the NMR time scale of common N M R nuclei, e.g., 'H or 35Cl.16 Although there is a lot of data for the ligand and solvent exchange for the octahedral three-valent metal ions,I8 an inves- tigation of dynamics in the thallium(III)-chloride system seems to be interesting. Structural studies showed that the geometry of thallium-halide complexes is different depending on the number of coordinated ligand^.'^-'^ In aqueous solution the aquated thaHium(II1) ion, the pentaaqua monochloro, and tetraaqua di- chloro complexes are probably octahedral, the trichloro complex is tetrahedral or trigonal bipyramidal or both in equilibrium, but the fourth complex is clearly tetrahedral. These changes in the structure should influence the ligand exchange kinetics. In the case of AI3+, Ga3+, and In3+ the mechanism of solvent exchange shows a trend to turn from a dissociatively into asso- ciatively activated process when the ionic radius increases.19 Although the mechanism of solvent exchange is sometimes dif- ferent from the mechanism of ligand exchange, in many cases similar trends have been observed. Kawai et al. studied the complex formation between Ga3+, In3+,and TI3+ and semi-xylenol orange14 and later between TI3+ and 4-(2-pyridylazo)resorcinol,15 by stopped-flow technique and found that the second-order rate (18) Wilkins, R. G. The Study of Kinetics and Mechanism of Reactions (19) van Eldik, R. Inorganic High Pressure Chemistry Kinetics and in Transition Metal Complexes; Allyn and Bacon: Boston, 1974. Mechanisms; Elsevier: Amsterdam, 1986. 0002-7863/89/ 151 1-3186$01.50/0 , I , 0 1989 American Chemical Society