Synthesis and Characterization of the Cobalt Complexes of New BF₂⁺ Bridged, Anthracene Substituted Bis(a-Dioxime) Macrocycles

Abstract

The synthesis, characterization and structure are described for new cobalt complexes, with a BF₂ ⁺ bridged, bis(a-dioxime) ligand, based upon a sterically demanding framework derived from an anthracene Diels-Alder adduct. The ligand provides a deep cleft within which axial ligands and/or O₂ can bind. The crystal structures of the bis- and mono(BF₂ ⁺) bridged complexes have space groups P2₁/c and P I, respectively, with unit cell dimensions a = 12.662(2) Å, b = 16.430(3) Å, c = 10.438(3) Å, β = 103.51(2)°, a = 12.046(1)Å, b = I7.596(3)Å, c = 9.939(I)Å, a = 105.15(1)°, β = 102.87(1)°, and γ = 78.13(1), respectively. For both complexes Z = 2 and the residuals R and R _w were 0.070, 0.104, and 0.059, 0.075, respectively. ESR studies show that the cobalt(II) complexes have a strong tendency to bind two axial nitrogen bases, adopting a coordination number of six. The dioxygen affinity of the new cobalt(II) dioxygen carrier is limited by the competition between axial base binding and O₂ binding. This extends the understanding of correlations between electrode potentials and O₂ affinities and possible sources of apparent contradictions.

Key Words:

• Cobalt complex
• macrocycle
• dioxygen binding
• ESR study
• X-ray crystal structure