ELECTRON-TRANSFER KINETICS AND THERMODYNAMIC CHARACTERIZATION OF COPPER(II I) COMPLEXES WITH ACYCLIC TETRATHIAETHERS IN AQUEOUS-SOLUTION/

The kinetics of a series of Cu(II/I)-acyclic tetrathiaether complexes reacting with several oxidizing and reducing reagents have been examin ed in aqueous solution at 25 degrees C. This investigation has include d a re-examination of Cu-II/I(Me-2-2,3,2-S-4) (Me-2-2,3,2-S-4 = 2,5,9, 12-tetrathiatridecane L12a), containing the ethylene-trimethylene-ethy lene: bridging sequence, plus three newly synthesized ligands containi ng an alternate bridging sequence of trimethylene-ethylene-trimethylen e: 2,6,9,13-tetrathiatetradecane (Me-2-3,2,3-S-4 L12b) and two cyclohe xanediyl-substituted derivatives, viz., cis-1,2-bis[(3-methylthiopropy l)thio]cyclohex (cis-cyhx-Me-2-3,2,3-S-4 = L14) and trans-1,2-bis[(3-m ethylthiopropyl)thio]cyclohexane (trans-cyhx-Me-2-3,2,3-S-4 = L15). Th e corresponding phenylene derivative, 1,2-bis[(3-(methylthio)propyl)th io]benzene (bz-Me-2-3,2,3-S-4 = L13), was also synthesized but did not form a measurable copper complex. The conditional stability constants for (CuL)-L-II (K-CuIIL') and (CuL)-L-I (K-CuIL') and the (CuL)-L-II/ I format redox potentials (Ef) vs NHE at 25 degrees C (generally at mu = 0.10 (NaClO4)) are as follows: for L12b, 15 M-1, 1.0 x 10(13) M-1, 0.83 V; for L14, 2.8 x 10(2) M-1, (9.9(5) x 10(13) M-1, 0.75 V; for L1 5, 8.8 x 10(2) M-1, 6.(3) x 10(13) M-1, 0.77 V. Application of the Mar cus relationship to the experimentally determined cross-reaction rate constants yielded self-exchange rate constants for all four (CuL)-L-II /I acyclic systems which were relatively constant for both oxidation a nd reduction under a wide range of conditions. This contrasts sharply with previous results obtained for corresponding macrocyclic ligand sy stems.