Syntheses, systematic potentiometry and structural studies of 26-membered hexaaza-diphenolate-based macrocyclic diiron complexes
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Homodinuclear ferrous complexes with a new 26-membered macrocyclic ligand: 3,6,10,18,22,25-hexaaza-31,32-dihydroxy-14,29-dimethyl-tricyclo[25,3,1,1, 11,17]dotriaconta-1(30),12,14,16(32),27,28-hexaene (L or BTBP), have been synthesized and characterized with elemental analysis, NMR, FAB MS and X-ray. The ligand maintains preorganized dinuclear integrity for iron(II) complexes, while facilitating the formation of non-bridged diiron centers. Potentiometric equilibrium studies indicate that a variety of protonated, mononuclear and dinuclear complexes are formed with Fe(II) and Fe(III) from p[H] 2 through 12 in aqueous solution. The stability constants and species distribution as a function of p[H] of the 1:1, 1:2 and 1:1:1 [ligand: Fe(II)/Fe(III) or ligand:Fe(II):Fe(III)] complexes were determined in KCl supporting electrolyte ( = 0.100 M) at 25C. Dinuclear iron(II) complex easily forms -peroxo adduct at 1 atm oxygen atmosphere with the oxygenation constant log K[O2] = 7.74. The neutral homodinuclear complexes [Fe2C28H44N6O2(CO 3)2)]12(H2O) forms triclinic crystals, of space group P1, with a = 8.318(10) , b = 9.443(12) , c = 14.066(18) , = 73.925(2), = 73.510(2), = 87.775(2) and Z = 1. Each iron(II) is complexed by half of the coordination sites of the dinucleating macrocycle, and the anionic carbonate enters into the coordination sphere and completes a six-coordinated octahedron. 2002 Elsevier Science B.V. All rights reserved.