Cyanocobalt(III) complexes of penta- and tetradentate-coordinated macrocyclic hexaamines

Abstract

The pendent-arm macrocyclic hexaamine trans-6,13-dimethyl-1,4,8,11-tetraazacyclotetradecane-6,13-diamine (L) may coordinate in tetra-, penta- or hexadentate modes, depending on the metal ion and the synthetic procedure. We report here the crystal structures of two pseudo-octahedral cobalt(III) complexes of L, namely sodium trans-cyano(trans-6,13-dimethyl-1,4,8,11-tetraazacyclotetradecane-6,13-diamine)cobalt(III) triperchlorate, Na[Co(CN)(C13H30N6)](ClO4)3 or Na{trans-[CoL(CN)]}(ClO4)3, (I), where L is coordinated as a pentadentate ligand, and trans-dicyano(trans-6,13-dimethyl-1,4,8,11-tetraazacyclotetradecane-6,13-diamine)cobalt(III) trans-dicyano(trans-6,13-dimethyl-1,4,8,11-tetraazacyclotetradecane-6,13-diaminium)cobalt(III) tetraperchlorate tetrahydrate, [Co(CN)2(C14H32N6)][Co(CN)2(C14H30N6)](ClO4)4.4H2O or trans-[CoL(CN)2]trans-[Co(H2L)(CN)2](ClO4)4.4H2O, (II), where the ligand binds in a tetradentate mode, with the remaining coordination sites being filled by C-bound cyano ligands. In (I), the secondary amine Co-N bond lengths lie within the range 1.944 (3)-1.969 (3) A, while the trans influence of the cyano ligand lengthens the Co-N bond length of the coordinated primary amine [Co-N = 1.986 (3) A]. The Co-CN bond length is 1.899 (3) A. The complex cations in (II) are each located on centres of symmetry. The Co-N bond lengths in both cations are somewhat longer than in (I) and span a narrow range [1.972 (3)-1.982 (3) A]. The two independent Co-CN bond lengths are similar [1.918 (4) and 1.926 (4) A] but significantly longer than in the structure of (I), again a consequence of the trans influence of each cyano ligand.