ELECTRON-EXCHANGE REACTIONS AND REDOX AND MAGNETIC-PROPERTIES OF THE COBALT(III) AND COBALT(II) COMPLEXES OF THE ENCAPSULATING LIGAND 13-DITHIA-6,10,16,19-TETRAAZABICYCLO[6.6.6]ICOSANE (N4S2SAR) - CRYSTAL-STRUCTURE OF THE COBALT(II) COMPLEX [CO(HN4S2SAR)](CLO4)2

The redox, magnetic, structural, and electron transfer properties of t he cobalt(III) and cobalt(II) complexes of an encapsulating ligand bas ed on 13-dithia-6,10,16,19-tetraazabicyclo[6.6.6]icosane (N4S2sar) hav e been investigated. The cobalt(II) complex [Co(HN4S2sar)]2+ crystalli zes in the orthorhombic crystal system, space group Pmcn with a = 8.80 4(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 leng th is 2.102(7) angstrom, and a marked elongation in one Co-S bond (2.4 95(2) angstrom) in comparison with the other (2.288(2) angstrom) is ap parent. The solution magnetic moment of the Co(II) complex [Co(AMN4S2s arH)]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) red uction 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 f or [Co(HN4S2sar)]3+/2+. The Marcus cross correlation was used to calcu late the self-exchange rates (k11) of the N4S2sar complexes from the b imolecular rate information obtained after cross reactions between the cobalt(III) complexes [Co(XN4S2sar)]n+ with the cobalt(II) complex [C o(AMMEN6sarH)]3+ (X = AM, k11 = 0.72(0.20) x 10(3) M-1 s-1; X = CL, k1 1 = 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 f or [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(AMN4S2 sarH)]4+/3+ and [Co(HN4S2sar)]3+/2+ were determined directly, using NM R 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 e nergies for these N4S2sar complexes have been investigated.