The synthesis of the compounds [Co(S2CSR)2(SR)]2, R = C2H5, n-C3H7, and Co(S2CSR)3, R = CH3, C2H5, n-C3H7, tert-C4H9, and C6H5CH2, is reported. The elimination of carbon disulfide from tris(ethyl thioxanthato)cobalt(III) to form tetrakis(ethyl thioxanthato)-μ-bis(ethylthio)-dicoball(III) has been directly confirmed and is shown to be a first-order reaction. The molecular structure of the latter compound was revealed in a single-crystal X-ray diffraction study. The molecule is a centrosymmetric dimer with two bridging ethyl mercaptide ligands [distances: Co–S, 2.242 (2), 2.250 (2) Å; nonbonded Co ⃛ Co, 3.321 (2) Å; angles: S–Co–S, 84.54 (5)°; Co–S–Co,95.34 (3)°] and four terminal thioxanthate groups [Co–S distances: 2.261 (2), 2.264 (2), 2.282 (2), and 2.290 (2) A; S–Co–S chelate ring angles: 75.68 (7)°, 76.05 (7)°]. The relationship between metal-metal bonding and the choice of stereoisomer for [M(S2CSR)2(SR)]2 complexes, M = Fe, Co, is discussed. The pmr spectra of solutions of the cobalt dimers are consistent with the structure found in the solid for the ethyl derivative. The methylenic protons attached to the bridging sulfur atoms exhibit large upfield shifts which may result from paramagnetic anisotropy effects. Voltammetric studies of the dimers indicate irreversible one-electron reduction and oxidation waves. The monomers exhibit reversible one-electron reduction waves. Electronic and selected infrared spectral absorptions are reported and assigned. A rationale is suggested for the low and varying redox potentials in nonheme proteins containing the Fe2S2 core.
ASJC Scopus subject areas
- Colloid and Surface Chemistry