Cobalt cage complexes with N3S3 donor sets and differing cavity sizes: A novel macrobicyclic cage with a contracted cap

Treatment of the cobalt(III) complex of the hexadentate tripodal N3S3 ligan d ten (4,4',4"-ethylidynetris(3-thiabutan-1-amine) with propanal and parafo rmaldehyde under basic conditions, followed by borohydride reduction and re oxidation of the metal center, leads largely to the encapsulated (red) meta l complex cation [Co(Me-2-N(3)S(3)sar)](3+) (Me-2-N(3)S(3)sar = 1,8-dimethy l-3,13,16-trithia-6,10,19-triazabicyclo[6.6.6]icosane). Unexpectedly, signi ficant amounts of the homologous (yellow) complex cation [Co(Me-2-N(3)S(3)a bsar)](3+) Me-2-N(3)S(3)absar = 1,8-dimethyl-3,13,16-trithia-6,10, 19-triaz abicyclo[6.6.5]nonadecane) were also obtained. This macrobicyclic complex h as a contracted cavity resulting from a cap containing one fewer methylene units than Me-2-N(3)S(3)sar. The structures of both cobalt(III) complexes h ave been determined by X-ray crystallography. [Co(Me2-N3S3sar)]Cl . ZnCl4. H2O crystallizes in the cubic space group P2(1)3 with Z = 4, a = 13.9683(11 ) Angstrom. [Co(Me-2-N(3)S(3)absar)](ClO4)(3) 0.5CH(3)CN . 0.5H(2)O crystal lizes in the triclinic space group P1 with Z = 4, a = 12.036(4) Angstrom, b = 15.932(9) Angstrom, c = 17.212(14) Angstrom, alpha = 64.93(7)degrees, be ta = 72.77(5)degrees, gamma = 88.91(7)degrees. The surprising structural re arrangement is examined, along with the spectral and redox properties of bo th cobalt complexes. The influence of the reduced cavity size in the absar type cage is reflected in a shift of the bands in the electronic spectrum o f both the cobalt(II) and cobalt(III) complexes to higher energy, and a mor e negative value for the Co(III/II) redox potential. The demetalation of th e complexes is also described.