Studies have been conducted on the electron-transfer kinetics of the Cu(II/I) complexes formed with two dialcoholic derivatives of the macrocyclic tetrathiaether [14]aneS4, syn- and anti-3,6,10,13-tetrathiacyclotetradecane-1,8-diol. For Cu(II/I)(syn-[14]aneS4-diol), the self-exchange rate constant has been determined directly from NMR line broadening : k11(ex) = 2.9 X 10(3) M-1 S-1 (25-degrees-C), DELTAH(double dagger) = 33 +/- 5 kJ mol-1, DELTAS(double dagger) = -68 +/- 20 J K-1 mol-1. For both Cu(II/I)L systems, extensive cross-reaction electron-transfer kinetics have also been measured using four different reductants and four different oxidants, spanning a wide range of reaction potentials. The patterns in the k11 values obtained by application of the Marcus square root relationship are consistent with the previously proposed dual-pathway square scheme mechanism in which both pathways have been accessed. Under appropriate conditions, limiting first-order kinetics, independent of the counter reagent concentration, have also been observed for the oxidation of both Cu(I)L species, indicating the onset of conformationally-controlled "gated" behavior. The evaluated self-exchange rate constants representative of each pathway (i.e., k11(A) and k11(B) in units of M-1 s-1) and the evaluated rate constant for the Cu(I)L conformational change (k(RP) in units of s-1) are as follows at 25-degrees-C and mu = 0.1 M : for the syn complex, log k11(A) = 3.6 +/- 0.2, log k11(B) = -0.4 +/-0.3, and log k(RP) = 2.20 +/- 0.02; for the anti complex, log k11(A) = 4.3 +/- 0.2, log k11(B) = -2.0 +/- 0.4, and log k(RP) = 1.70 +/- 0.03. The 10(6)-fold difference in the k11 values obtained for the two pathways in the latter system represents the widest range of conditions for gated behavior yet observed, suggesting that the Cu(II)L metastable intermediate (Q) is particularly unstable relative to the Cu(I)L metastable intermediate (P). Crystallographic structural data are also reported for each of the Cu(II)L species. [Cu(II)(syn-[14]aneS4-diol)(ONO2)]NO3 crystallizes in the monoclinic space group P2(1)/a with a = 9.238(1) angstrom, b = 13.248(2) angstrom, c = 15.321(2) angstrom, beta = 104.21(1)degrees, V = 1817.5(4) angstrom3, Z = 4; [Cu(II)(anti-[14]aneS4-diol)](ClO4)2 crystallizes in the monclinic space group P2(1)/c with a = 5.8472(9) angstrom, b = 17.764(3) angstrom, c = 9.601(1) angstrom, beta = 102.43(1)degrees, V = 973.8(2) angstrom3, Z = 2.