Synthesis of Binuclear Bismacrocyclic Iron(II) Complex by the Aerobic Oxidation of Iron(II) Complex of 1,4,8,11-Tetraazacyclotetradecane

The aerobic oxidation of the Fe(II) complex of 1,4,8,11-tetraazacyclotetradecane, [Fe(cyclam), in MeCN in the presence of a few drops of leads to low spin Fe(III) species [Fe(cyclam). The Fe(III) cyclam complex is further oxidized in the air in the presence of a trace of water to produce the deep green binuclear bismacrocyclic Fe(II) complex . The Fe(II) ions of the complex are six-coordinated and the bismacrocyclic ligand is extensively unsaturated. crystallizes in the monoclinic space group with a= 13.099 (1) , b= 10.930 (1) , c= 17.859 (1) , = 95.315 , and Z= 2. The structure was solved by heavy atom methods and refined anisotropically to R values of R= 0.0633 and = 0.0702 for 1819 observed reflections with F > (F) measured with Mo K radiation on a CAD-4 diffractometer. The two macrocyclic units are coupled through the bridgehead carbons of -diimitie moieties by a double bond. The double bonds in each macrocycle unit are localized. The average bond distances of , , and are 1.890 (5), 2.001 (5), and 1.925 (6) , respectively. The complex is diamagnetic, containing two low spin Fe(II) ions in the molecule. The complex shows extremely intense charge transfer band in the near infrared at 868 nm with = 25,000 . The complex shows a one-electron oxidation wave at +0.83 volts and two one-electron reduction waves at -0.43 and-0.72 volts vs. Ag/AgCl reference electrode. The complex reacts with carbon monoxide in to form carbonyl adducts, whose value (2010 ) indicates the -accepting property of the present bismacrocyclic ligand.