Synthesis and characterization of the cobalt(III) complexes of two pendant-arm cross-bridged cyclams

The cobalt(III) complexes of 4,11-diacetato-1,4,8,11-tetraazabicyclo6.6.2]hexadecane (1), Co(1)]PF₆, and 4,11-diacetamido-1,4,8,11-tetraazabicyclo6.6.2]hexadecane (2), Co(2)]PF₆]₃, have been synthesized and characterized. The crystal structure of Co(1)]PF₆ consists of an octahedral cobalt(III) cation coordinated to all four ligand nitrogen donors in the macrobicycle’s cavity, as well as to the deprotonated carboxylate oxygen atoms of both pendant arms. Analytical and spectroscopic data indicates that the ligand in Co(2)]PF₆]₃ is not deprotonated, suggesting coordination through the amide carbonyl oxygens. Study of the electronic spectra of these novel complexes and comparison with data from related cobalt(III) complexes characterizes the ligands as strong field with Δ₀=24,040 and Δ₀=24,250 cm⁻¹ for 1 and 2, respectively. Cyclic voltammograms were obtained for both complexes with large variations observed due to the differences in ligand charge and coordination.