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 (N4S2sar) have been investigated. The cobalt(II) complex [Co(HN4S2sar)]2+ crystallizes in the orthorhombic crystal system, space group Pmcn with a = 8.804(2) angstrom, b = 12.554(2) angstrom, c = 21.021(8) angstrom, and Z = 4. The structure was refined to R = 0.050. The average Co-N bond length is 2.102(7) angstrom, and a marked elongation in one Co-S bond (2.495(2) angstrom) in comparison with the other (2.288(2) angstrom) is apparent. The solution magnetic moment of the Co(II) complex [Co(AMN4S2sarH)]3+ was found to be 2.88 mu(B), a value in consistent with either a high- or low-spin condition for this species. The Co(III)/Co(II) reduction potentials for the range of N4S2sar complexes were established using cyclic voltammetric methods. The reduction potentials E-degrees (V vs SHE) ranged from +0.022 V for [Co(NON4S2sar)]3+/2+ to -0.156 V for [Co(HN4S2sar)]3+/2+. The Marcus cross correlation was used to calculate the self-exchange rates (k11) of the N4S2sar complexes from the bimolecular rate information obtained after cross reactions between the cobalt(III) complexes [Co(XN4S2sar)]n+ with the cobalt(II) complex [Co(AMMEN6sarH)]3+ (X = AM, k11 = 0.72(0.20) x 10(3) M-1 s-1; X = CL, k11 = 0.84(0.20) X 10(3) M-1 s-1; X = H, k11 = 1.84(0.30) X 10(3) M-1 s-1; X = AZA, k11 = 1.12(0.22) X 10(3) M-1 s-1) or with [Co(diCLN6sar)]2+ (X = CL, k11 = 1.71(0.16) X 10(3) M-1 s-1). The self exchange rate for [Co(AMMEN6sarH)]4+/3+ was determined by polarimetric methods to be 0.15 M-1 s-1. The self exchange electron transfer rates for [Co(AMN4S2sarH)]4+/3+ and [Co(HN4S2sar)]3+/2+ were determined directly, using NMR methods, as 1.70(0.5) x 10(3) M-1 s-1 and 1.22(0.16) x 10(4) M-1 s-1, respectively. The contributions of the inner-sphere reorganization energies for these N4S2sar complexes have been investigated.