Structural Characterization of Encapsulation Reactions Based on the Tris(ethane-1,2-diamine)cobalt(III) Ion

Abstract

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 N_o 1735 'observed' reflections] and Δ,Λ-[Co(N^t-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 N_o 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 N_o 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 N_o 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 N_o 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 N_o 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.