Copper(II)thiolate coraplexes of the CuN 4S type were synthesized: (1,1-difluoro-4,5,11,12-tetramethyl- 1-bora-3,6,10,13-tetraaza-2,14-dioxocyclotetradeca- 3,5,10,12-tetraenato)(SR)copper(II) (R (C 6H 5) 3C, 4-ClC 6H 4, and 2-C 10H 7), (1,1-difluoro-4,5, 12,13-tetramethyl-1-bora-3,6,11,14-tetraaza-2,15-dioxocyclopentadeca- 3,5,11,13-tetraenato)(triphenylmethanethiolato)copper(II), and (2-oximino-10-oximiato- 3,9-dimethyl-4,8-diazaundeca-3,8-diene)(triphenylmethanethiolato)copper(II). These complexes exhibit an absorption band assignable to the thiolate sulfur-to-copper charge transfer (c.t.) transition in the 340–420 nm region in methanol; the band maximum is shifted to low frequencies with increasing of not only the electron-donating ability of the thiolate ligand but also the electron-accepting ability of the CuN 4 moiety. The cyclic voltarametry of the complexes in dichloromethane shows a quasi- reversible redox couple at E 1 2 of −0.38 to −0.54 V vs. s.c.e, which is more negative than that of the corresponding CuN 4 complex without thiolate ligand. The | A∥| values ((193–201) × 10 -4 cm -1) observed in the ESR spectra of the CuN 4S complexes are relatively smaller than those of the corresponding CuN 4 complexes. Thus, the negative shift of E 1 2 and the decrease of | A∥| upon coordination of the thiolate ligand to the CuN 4 moiety may be due to electron donation from the thiolate ligand.