COMPARISON OF THE INFLUENCE OF SATURATED NITROGEN AND SULFUR DONOR ATOMS ON THE PROPERTIES OF COPPER(II/I) MACROCYCLIC POLYAMINO POLYTHIAETHER LIGAND COMPLEXES - REDOX POTENTIALS AND PROTONATION AND STABILITY-CONSTANTS OF CUIL SPECIES AND NEW STRUCTURAL DATA

The relative influence of amine nitrogen and thiaether sulfur donor atoms upon the electrochemical behavior of the Cu(II/I) redox couple has been investigated by utilizing saturated macrocyclic polyamino polythiaether ligands of the 14-membered quadridentate and 15-membered quinquedentate series. The values of E(f) (vs NHE) determined at 25-degrees-C in aqueous solution containing 0.10 M perchlorate ion for the copper complexes formed with the specific ligands are as follows: [14]aneS4, 0.58 V; [14]aneNS3, 0.38 V; [14]aneN2S2, 0.04 V; [14]aneNSSN, -0.01 V; [14]aneN3S, less-than-or-equal-to -0.24 V (est); [14]aneN4, -0.66 V (est); [15]aneS5, 0.68 V; [15]aneNS4, 0.46 V; [15]aneN2S3, 0.10 V. From the dependence of E(f) on pH, it has also been possible to evaluate the mixed-mode protonation constants K(H1(Cu(I)L)m for some of the Cu(I)L complex species, for which the logarithmic values are as follows: [14]aneN2S2, 3.9; [15]aneNS4, 4.17; [15]aneN2S3, 5.90. The electrochemical potentials show a fairly linear relationship with the value of x in each of the donor sets NxS4-x and NxS5-x. Empirical calculations suggest that the magnitude of the macrocyclic effect increases with each substitution of a saturated nitrogen donor atom for a thiaether sulfur donor atom. Combining the potentials with earlier measurements on the stability constants of the Cu(II)L complexes (which were linearly related to the value of x) permits calculation of the stability constants of the Cu(I)L complexes which are found to be independent of the value of x for a specific ligand family with K(Cu(I)L' almost-equal-to 5 x 10(13) for the [14]aneNxS4-x series of complexes and K(Cu(I)L' almost-equal-to 4 x 10(15) for the [15]aneNxS5-x series. The only anomaly occurs for the case where x = 0 for which, in each series, the K(Cu(I)L' value is about 100-fold smaller. These results demonstrate that Cu(I) exhibits little preference between saturated N and S donor atoms, contrary to the popular belief that sulfur donors stabilize the +1 oxidation state. Thus, the dependence of the Cu(II/I) potential on the relative number of N and S donor atoms is almost entirely a function of the preference of Cu(II) for amine nitrogen relative to thiaether sulfur as a donor atom. A crystallographic structure of the Cu(I)([14]aneNS3) complex reveals that all four ligand donor atoms are coordinated to Cu(I) in a flattened tetrahedral geometry. Crystal data [Mo K-alpha radiation (lambda = 0.71073 angstrom)] at ambient temperature are as follows: CuS3NC10H21ClO4, triclinic crystal system, space group P1BAR, a = 8.468 (1) angstrom, b = 9.327 (2) angstrom, c = 12.311 (2) angstrom, alpha = 69.62 (2)-degrees, beta = 87.07 (1)-degree, gamma = 67.60 (1)-degree, V = 838.9 (3) angstrom3, Z = 2, R = 0.042, R(w) = 0.056.