TETRADENTATE MACROCYCLIC COMPLEXES OF PLATINUM - X-RAY CRYSTAL-STRUCTURES AND REDOX BEHAVIOR OF COMPLEXES CONTAINING NITROGEN OR SULFUR DONOR ATOMS

Several complexes of platinum containing aliphatic tetradentate (N or S donors) macrocyclic (12-16-membered rings) ligands have been prepared and characterized. The most thoroughly examined of these complexes were those containing 14-membered macrocyclic ligands. In this series of complexes, the half-wave potential of the Pt(MCL)2+/Pt(MCL)Cl2(2+) couple (in 1 M NaCl) increased in a regular manner as secondary amine donors were successively replaced by thioether donors (MCL = a macrocyclic ligand). This pattern of behavior was correlated with changes of interligand repulsions (between axial Cl- and the equatorially coordinated macrocycle) that accompany the change of ligand conformation from the axially unrestricted endo conformation of coordinated 1,4,7,11-tetraazacyclotetradecane ([14]aneN4) to the somewhat restricted exo conformation adopted by 1,4,7,11-tetrathiacyclotetradecane ([14]aneS4). Related shifts in potentials were found in methyl-substituted tetraazacyclotetradecane complexes. [Pt([14]aneN4)Cl2]Cl2.HCl.H2O, PtN4C10H23Cl5O, crystallizes in the monoclinic space group P2(1)/n with Z = 1 and a = 7.5059 (9) angstrom, b = 18.812 (5) angstrom, c = 7.669 (2) angstrom, and beta = 99.09 (2)-degrees. The structure refined to R = 0.050 and R(w) = 0.062 for 1592 reflections. [Pt(ms-(5,12)-Me6[14]aneN4)](ClO4)2.2H2O, PtN4C16H40Cl2O10 (ms-(5,12)-Me6[14]aneN4 = meso-5,7,7,12,14,14-hexamethyl-1,4,8,11-tetraazacyclotetradecane), crystallizes in the monoclinic space group P2(1)/c with Z = 2 and a = 10.0331 (9) angstrom, b = 16.198 (3) angstrom, c = 8.660 (1) angstrom, and beta = 107.48 (1)-degrees. The structure refined to R = 0.035 and R(w) = 0.024 for 1526 reflections. [Pt([14]aneS4)](ClO4)2, PtS4C10H20Cl2O8, crystallizes in the monoclinic space group P2(1)/n with Z = 4 and a = 12.098 (1) angstrom, c = 12.557 (2) angstrom, and beta = 98.69 (1)-degrees. The structure refined to R = 0.043 and R(w) = 0.042 for 2703 reflections.