SYNTHESIS OF BINUCLEAR BISMACROCYCLIC IRON(II) COMPLEX BY THE AEROBICOXIDATION OF IRON(II) COMPLEX OF 1,4,8,11-TETRAAZACYCLOTETRADECANE

The aerobic oxidation of the Fe(II) complex of 1,4,8,11-tetraazacyclot etradecane, [Fe(cyclam)(CH3CN)2](ClO4)2, in MeCN in the presence of a few drops of HClO4 leads to low spin Fe(III) species [Fe(cyclam)(CH3CN )2](ClO4)3. The Fe(III) cyclam complex is further oxidized in the air in the presence of a trace of water to produce the deep green binuclea r bismacrocyclic Fe(II) complex [Fe2(C20H36N8)(CH3CN)4](ClO4)4.2CH3CN. The Fe(II) ions of the complex are six-coordinated and the bismacrocy clic ligand is extensively unsaturated. [Fe2(C20H36N8)(CH3CN)4](ClO4)4 .2CH3CN crystallizes in the monoclinic space group P2(1)/n with a=13.0 99 (1) angstrom, b=10.930 (1) angstrom, c=17.859 (1) angstrom, beta=95 .315 (7)degrees, and Z=2. The structure was solved by heavy atom metho ds and refined anisotropically to R values of R=0.0633 and R(w)=0.0702 for 1819 observed reflections with F>4sigma(F) measured with Mo Kalph a radiation on a CAD-4 diffractometer. The two macrocyclic units are c oupled through the bridgehead carbons of beta-diimine moieties by a do uble bond. The double bonds in each macrocycle unit are localized. The average bond distances of Fe(II)-Ni(imine), Fe(II)-N(amine), and Fe(I I)-N(MeCN) are 1.890 (5), 2.001 (5), and 1.925 (6) angstrom, respectiv ely. The complex is diamagnetic, containing two low spin Fe(II) ions i n the molecule. The complex shows extremely intense charge transfer ba nd in the near infrared at 868 nm with epsilon=25,000 M-1 cm-1. The co mplex shows a one-electron oxidation wave at +0.83 volts and two one-e lectron reduction waves at -0.43 and -0.72 volts vs. Ag/AgCl reference electrode. The complex reacts with carbon monoxide in MeNO2 to form c arbonyl adducts, whose nu(co) value (2010 cm-1) indicates the pi-accep ting property of the present bismacrocyclic ligand.