Electronic structures and reduction potentials of Cu(II) complexes of [N,N′-alkyl-bis(ethyl-2-amino-1-cyclopentenecarbothioate)] (alkyl=ethyl, propyl, and butyl)

Copper(II) complexes of NN'-alkyl-bis(ethyl-2-amino-1-cyclopentenecarbod-ithioate) [alkyl=ethyl (L2), propyl (L3), and butyl(L4)] ligands have been synthesized and characterized. Analytical data for all three complexes show 1:1 copper-ligand stoichiometry. Well-resolved EPR spectra were recorded in toluene, benzene, and methylene chloride solutions at room temperature and in glassy toluene or toluene-methylene chloride mixtures in the range 20-150 K. The superhyperfine pattern unambiguously demonstrates coordination of two nitrogen atoms to copper; and the spin-Hamiltonian parameters [CuL2, g(parallel to) = 2.115, A(parallel to) = 187x 10(-4) cm(-1); CuL3, g(parallel to) = 2.128, A(parallel to) = 165 x 10(-4) cm(-1); CuL4, g(parallel to) = 2.138, A(parallel to) = 147 x 10(-4) cm(-1)] are as expected for a CuN2S2 coordination core. Quasi-reversible electrochemical behavior was observed in methylene chloride: the Cu(II)/Cu(I) reduction potentials increase from -1.17 V (Edegrees vs Ag/AgNO3) for CuL2 to -0.74 V for CuL4, indicating greater stabilization of Cu(I) in CuL4. Taken together, these data demonstrate that lengthening the N,N'-alkyl chain distorts the planar CuN2S2 core (CuL2) toward a flattened tetrahedral geometry (CuL4).