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

Abstract

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.