On the basis of structural comparisons involving intermediates and side products of encapsulation reactions as well as several cage complexes, the efficiency of the base- catalysed reaction between formaldehyde, nitromethane and [Co(en)3]3+ (en = ethane-1,2-diamine) to give [Co((NO2)2sar)]3+ appears to be explicable in terms of the 'interlocking' of constituent parts without appreciable concomitant bond length or bond angle distortions. Thus, the structures of the podand ligand complexes Λ-[Co(NO2sen)]Cl3.2H2O [orthorhombic, space group P 212121, a 18.755(6), b 11.598(4), c 9.164(3) Ǻ; R 0.038 for No 1735 'observed' reflections] and Δ,Λ-[Co(Nt-Me,NO2sen)]Cl3.4H2O [monoclinic, P21/n, a 18.613(5), b 9.301(3), c 13.779(4) Ǻ, β 107.10(2)°; R 0.051 for No 26441 show very close configurational and conformational similarities to those of the cage complexes Δ,Λ-[Co(NO2azasar)]Cl3.3H2O [monoclinic, P 21/c, a 9.339(3), b 15.479(9), c 17.360(7)Ǻ, β 114.15(3)°; R 0.048 for No 2612], Δ,Λ-[Co((NO2)2sar)]Cl3.2H2O [triclinic, Pī , a 13.592(3), b 10.024(3), c 9.772(3)Ǻ, α 62.89(2),β 82.96(3), γ 85.15(2)°; R 0.045 for No 5646] and Δ,Λ-[Co((OH)2sar)]Cl3.3H2O [monoclinic, P21/c, a 15.97(1), b 8.758(4), c 16.760(4)Ǻ, β 98.72(4)°; R 0.052 for No 2400], as well as to published structures of [Co(en)3]3+, [Co(tame)2]3+ [tame = 1,1,1-tris- ( aminomethyl )ethane = ethylidynetris ( methanamine )] and other cage complexes. Some of these similarities may be associated with common hydrogen-bonding patterns in the solids resulting from anion ' chelation' by adjacent NH moieties in the metal ion coordination spheres. Necessary caution in relating structural and electronic properties is implied by the structure determination for Δ,Λ [Co(Cl,ClCH2absar)](NO3)3 [monoclinic, P 21/c, a 14.750(6), b 9.264(3), c 17.959(7) Ǻ, β 95.80(3)°; R 0.061 for No 1431], one of the products of molecular rearrangement following nitrosation of [Co((NH2)2sar)]3+. Despite marked electronic spectral and electrochemical differences with its parent complex, [Co(Cl,ClCH2absar)](NO3)3 contains cobalt(III) in a coordination environment which remains similar to those in more symmetrical cage complexes.

The syntheses of complexes containing the [Ni( sar )]2+/3+ and [Ni((NH3)2sar)]4+ ions are described along with an X-ray crystal structure analysis of the salt [Ni((NH3)2sar)] (NO3)4.H2O ( sar is 3,6,10,13,16,19-hexaazabicyclo[6.6.6] icosane ; (NH3)2sar2+ is its 1,8-diammonio derivative). The NiIII ion is a powerful oxidant, with E′ = 0.90 V (v. n.h.e. at 298 K, I = 0.2, aqueous trifluoromethanesulfonate medium), but is relatively stable in dilute aqueous acid. Both the NiII and NiIII complexes of sar have been resolved into their enantiomeric forms, and their absorption, optical rotatory dispersion and circular dichroism spectra recorded and partly analysed. The electron self-exchange rate between enantiomeric forms in the different oxidation states has been measured by a stopped-flow circular dichroism method, and ket = (5.3�0.3)×103 dm3 mol-1 s-1 at 298 K, I = 0.2 (NaCF3SO3). The activation parameters, ΔH‡ 22�4 kJ mol-1 and ΔS‡ -100�12 J K-1 mol-1, and the rate constants are consistent with the comparatively small rearrangements required in the structures of the two ions relative to the optimal cavity radius for the cage of 2.05(1) Ǻ.