The structures and energy minimization analyses of the macrotricyclic cage complex [Co(nosartacn)]³⁺ and its precursor [Co(taetacn)]³⁺

Abstract

The crystal structures of (-)₄₈₇-[Co(taetacn)] (ClO₄)₃ [taetacn = 1,4,7-tri(2-aminoethy1)-1,4,7-triazacyclononane] and (+)₄₉₀-[Co(nosartacn)] (S₂O₆)_3/2.4H₂O (nosartacn = 9-nitro-1,4,7,11,14,19- hexaazatricyclo[7.7.4.2^4.14]docosane) have been determined. Crystals of the former complex (1) are cubic, space group P2₁3, a 13.168(5) Å, whereas the latter (2) are orthorhombic, space group C222₁, a 10.22(1), b 6.944(8), c 32.33(1) Å. The structures were refined by blocked-matrix least-squares methods to R factors of 0.040 and 0.050 on 952 and 2318 F respectively. The absolute configurations and conformations are described as Δ(λδ) for (1) and Λ(λδ) for (2). Molecular mechanics studies of conformers of both complexes show that the solid-state geometries are the most energetically favourable, and that other possible conformers are destabilized by coupling of the five-membered chelate rings through the tertiary nitrogen atoms.