The new ligands 1,9-bis(3,5-dimethyl-1-pyrazolyl)-2,5,8-trithianonane (L1) and 1,9-bis(benzimidazolyl)-2,5,8-trithianonane (L2) and their Cu(II) complexes as the BF4-, ClO4-, and CF3SO3- salts have been prepared. The X-ray structures of [Cu(L1)] [BF4]2 and [Cu(L3)][CF3SO3]2 (L3 = 1,9-bis(2-pyridyl)-2,5,8-trithianonane) have been determined. Crystal data for monoclinic [Cu(L1)] [BF4]2 : space group C2/c (No. 15); a = 20.84(1) angstrom, b = 18.74(4) angstrom, c = 14.980(9) angstrom; beta = 120.00(3)degrees; Z = 8; R = 0.041, R(w) = 0.073 for 2641 reflections. Crystal data for monoclinic [Cu(L3)] [CF3SO3]2 : space group P2(1)/c (No. 14); a = 12.217(5) angstrom, b = 14.636(4) angstrom, c = 15.102(3) angstrom; beta = 97.87(2)degrees; Z = 4; R = 0.077, R(w) = 0.061 for 1600 reflections. The electronic and ESR spectra and cyclic voltammetry of the new complexes have been determined and are discussed in terms of their structures in both solid and solution. Evidence is presented for subtle but significant steric influences on the kinetics and thermodynamics of Cu(II)/Cu(I) redox and upon the electronic structures of the Cu centers.