Studies on cobalt(III) complexes of a cyanoethyl derivative of an isomeric hexamethyl tetraazamacrocyclic ligand

Abstract

A 14-membered hexamethyl-tetraazamacrocycle, viz. Me₆[14]diene.2HClO₄ (L.2HClO₄), afforded a mixture of isomeric ligands, Me₆[14]anes, upon reduction with NaBH₄ and extraction by CHCl₃ at pH > 12. These ligands were separated by fractional crystallization from xylene and were designated as ‘tet-a’ and ‘tet-b.’ The interaction of ‘tet-b’ with excess acrylonitrile was fairly stereoselective and formed an N-pendent derivative, ‘tet-bx’, in which two cyano-ethyl groups were attached to trans N-atoms that are sterically less crowded. Aeration of ‘tet-bx’ and cobalt(II) acetate salt in methanol, followed by its treatment with HCl, yielded a bluish-green product, viz. trans-[Co(‘tet-bx’)Cl₂]Cl. trans-[Co(‘tet-bx’)Cl₂]Cl underwent axial substitution reactions with KSCN and KNO₃ and subsequent axial substitution and anion exchange reactions with NaNO₂, KBr, and KI to produce six-coordinated octahedral complexes, viz. bluish-green trans-[Co(‘tet-bx’)(NCS)₂]Cl, light-blue trans-[Co(‘tet-bx’)(NO₃)₂]Cl, yellow trans-[Co(‘tet-bx’)(NO₂)₂]NO₂, green trans-[Co(‘tet-bx’)Br₂]Br, and red trans-[Co(‘tet-bx’)I₂]I. These complexes were characterized using different modern analytical and spectroscopic techniques. The antibacterial activities of the N-pendent ligand and its cobalt(III) complexes on four types of selected bacteria were investigated.