Synthesis and stability of new hexaazamacrocyclic dinuclear cobalt complexes and its oxidation reactions

Homodinuclear cobalt complexes with a new 26-membered unsymmetric macrocyclic ligand: 3,6,10,18,22,25,-hexaaza-31,32-dihydroxy-14,29-dimethyl-tricyclo[25,3,1,111,17] dotriaconta-l(30),12,14,16(32),27,28-hexaene (L or BTBP), have been synthesized and characterized with elemental analysis, FAB-MS and X-ray. The ligand maintains preorganized dinuclear integrity for cobalt(II) complexes, while facilitating the formation of non-bridged dicobalt centers. Potentiometric equilibrium studies indicate that a variety of protonated, mononuclear and dinuclear complexes are formed with Co(II) from pH 2 through 12 in aq. solution. The stability constants and species distribution as a function of pH of the 1:1 and 1:2 [ligand: Co(II)] complexes were determined in KCI supporting electrolyte (μ=0.100 M) at 25 °C. Dinuclear cobalt(II) complex could form a μ-peroxo adduct at 1 atm oxygen atmosphere with the oxygenation constant log KO2=3.19. The neutral homodinuclear complexes: [Co2C28H44N6O2(NO3)2]·12H2O has been synthesized and its crystal structure has been reported with triclinic system, a=8.3376(5), b=9.4501(6), c=14.1028(9) Å, α=73.9100(2), β=73.4940(2), γ=87.7310(2)° and Z=1. Each cobalt(II) ion is complexed by half of the coordination sites of the dinucleating macrocycle, and the anionic nitrate enters into the coordination sphere and completes a six-coordinated octahedron.