The values of the electron self-exchange rate constants, k(11(ex)), for the copper(II/I) complexes formed with the cyclic tetrathiaethers [13]aneS(4) and [15]aneS(4) have been determined using H-1-NMR line-broadening measurements in D2O at several different temperatures to yield the following results for 25 degrees C, corrected to mu = 0.1 M (NO3-) : for Cu-II/I([13]aneS(4)), k(11(ex)) = 3.2 x 10(5) M(-1) s(-1), Delta H-double dagger = 10 +/- 1 kJ mol(-1), Delta S-double dagger = -106 +/- 7 J K-1 mol(-1); for Cu-II/I([15]aneS(4)), k(11(ex)) = 1.2 x 10(4) M(-1) s(-1), Delta H-double dagger = 21 +/- 1 kJ mol(-1), Delta S-double dagger = -97 +/- 7 J K-1 mol(-1). The cross-reaction rate constants have also been determined in aqueous solution by means of stopped-flow methods for these complexes reacting with a series of selected oxidants and reductants : Co-II(Me(4)[14]tetraeneN(4))(H2O)(2), Ru-II(NH3)(4)bpy, Ru-III(NH3)(5)py, RU(II)(NH3)(6), COIII(Me(4)[14]tetraeneN(4))(H2O)(2), Ru-III(NH3)(4)bpy, Ni-III([14]aneN(4))(H2O)2, Ru-III(NH3)(2)(bpy)(2), and Fe-III(4,7-Me(2)phen)(3). The self-exchange rate constants calculated by applying the Marcus relationship to the rate constants for reactions involving Cu(II)L reduction (k(11(Red))) are within experimental error of each other and agree with the k(11(ex)) values determined by NMR. However, as in earlier studies, the self-exchange rate constant values calculated from Cu(I)L oxidation reactions (k(11(Ox))) are generally smaller, except for very slow cross reactions. This pattern of behavior is in agreement with our previously proposed dual-pathway square scheme in which conformational change and the electron-transfer step occur in a sequential, rather than a concerted, manner. For the Cu-II/I([13]aneS(4)) system; a lower limit of k(RP) greater than or equal to 200 s(-1) is estimated for the rate constant representing the conformational change from the ground state Cu(I) species to the metastable intermediate which precedes the electron transfer step via the preferred pathway. For the Cu-II/I([15]aneS(4)) system, a rough limit of k(RP) less than or equal to 5 s(-1) is suggested by the data. Moreover, for this latter system, the secondary pathway was found to be more competitive than is the case for either the Cu-II/I([13]aneS(4)) system or the previously studied Cu-II/I([l4]aneS(4)) system, so that gated behavior is anticipated to occur only within a very narrow set of conditions.