SYNTHESES, STRUCTURE, AND REACTIVITY OF COBALT AND NICKEL-COMPLEXES OF 1,4,7-TRITHIACYCLODECANE - SELF-EXCHANGE RATES FOR CO(S6)2+/3+ COUPLES FROM CO-59 NMR-SPECTROSCOPY

Cobalt(II) and nickel(II) complexes of 1,4,7-trithiacyclododecane (4, [10]-aneS3) have been synthesized and characterized by single-crystal X-ray diffraction and electronic and EPR spectroscopy. Both complexes contain the [M(S3)2]2+ cation and crystallize in the monoclinic space group P2(1)/c (No. 14). Refinement of the species Ni(4)2(ClO4)2.2CH3NO2 (a = 10.484 (4), b = 15.272 (1), c = 9.445 (1) angstrom; beta = 101.49 (1)-degrees) converged at R = 0.0705 (R(w) = 0.0738) for 199 parameters using 1848 reflections with I > 2-sigma(I). Three S atoms from each ligand occupy a trigonal face in a distorted octahedral ion, where the average Ni-S bond length is 2.396 (7) angstrom. The cobalt complex is isomorphous with a = 10.463 (3) angstrom, b = 15.292 (4) angstrom, c = 9.720 (2) angstrom, and beta = 102.16 (1)-degrees. Refinement converged at R = 0.0829 (R(w) = 0.0812) for 199 parameters using 1545 reflections with I > 2-sigma(I). The Co-S distances all differ and cannot be distinguished as axial or equatorial bonds. Co-59 NMR signals show peaks at 2336 and 2268 ppm relative to [Co(CN)6]3- owing to cis and trans isomers, respectively. By use of NMR line broadening in the presence of the corresponding cobalt(II) ion, the self-exchange electron-transfer rates for the [Co(4)2]3+/2+ (4.3 x 10(5) M-1 s-1) and [Co(1)2]3+/2+ couples (1.3 x 10(5) M-1 s-1) (1 = 1,4,7-trithiacyclononane) have been determined. This is believed to be the first instance of such data being derived from this nucleus. Electrochemical data are consistent with the formation of M(III) and M(I) species, although for the latter in the case of nickel there is ESR evidence for a change in geometry.