The redox, magnetic, structural, and electron transfer properties of the cobalt(III) and cobalt(II) complexes of an encapsulating ligand based on 3,13-dithia-6,10,16,19-tetraazabicyclo[6.6.6]icosane(NSsar) have been investigated. The cobalt(II) complex [Co(HNSsar)] crystallizes in the orthorhombic crystal system, space group Pmcn with a = 8.804(2) A,b = 12.554(2) A,c = 21.021(8) A, and Z = 4. The structure was refined to R = 0.050. The average Co-N bond length is 2.102(7) A, and a marked elongation in one Co-S bond (2.495(2) A) in comparison with the other (2.288(2) A) is apparent. The solution magnetic moment of the Co(II) complex [Co(AMNSsarH)] was found to be 2.88 µ. a value inconsistent with either a high- or low-spin condition for this species. The Co(III)/Co(II) reduction potentials for the range of NSsar complexes were established using cyclic voltammetric methods. The reduction potentials E° (V vs SHE) ranged from +0.022 V for [Co(NONSsar)] to -0.156 V for [Co(HNSsar)]. The Marcus cross correlation was used to calculate the self-exchange rates (k) of the NSsar complexes from the bimolecular rate information obtained after cross reactions between the cobalt(III) complexes [Co(XNSsar)] with the cobalt(II) complex [Co(AMMENsarH)] (X = Am. k = 0.72(0.20) × 10 M s; X = CL, k = 0.84(0.20) × 10 M s; X = H, k = 1.84(0.30) × 10 M s; X = AZA, k = 1.12(0.22) × 10 M s) or with [Co(diCLNsar)] (X = CL, k = 1.71(0.16) × 10 M s). The self exchange rate for [Co(AMMENsarH)] was determined by polarimetric methods to be 0.15 M s. The self exchange electron transfer rates for [Co(AMNSsarH)] and [Co(HNSsar)] were determined directly, using NMR methods, as 1.70(0.5) × 10 M s and 1.22(0.16) × 10 M s, respectively. The contributions of the inner-sphere reorganization energies for these NSsar complexes have been investigated.