Synthesis and characterization of the chromium(III) complexes of ethylene cross-bridged cyclam and cyclen ligands

Dichloro(4,10-dimethyl-1,4,7,10-tetraazabicyclo[5.5.2] tetradecane) chromium(III) chloride, Dichloro(4,10-dibenzyl-1,4,7,10-tetraazabicyclo[ 5.5.2] tetradecane) chromium(III) chloride, and Dichloro(4,11-dimethyl- 1,4,8,11-tetraazabicyclo[6.6.2] hexadecane) chromium)(III) chloride have been prepared by the reaction of anhydrous chromium(III) chloride with the appropriate cross-bridged tetra-azamacrocycle. Aquation of these complexes proved difficult, but Chlorohydroxo(4,11-dimethyl- 1,4,8,11tetraazabicyclo[6.6.2] hexadecane) chromium)(III) chloride was synthesized directly from chromium(II) chloride complexation followed by exposure or the reaction to air in the presence of water. The four complexes were characterized by X-ray crystal structure determination. All contain the chromium(III) ion in a distorted octahedral geometry and the macrocycle in the cis-V configuration, as dictated by the ethylene cross-bridge. Further characterization of the hydroxo complex reveals a magnetic moment of mu(eff) = 3.95 B.M. and electronic absorbtions in acetonitrile at lambda(max) = 583 nm (epsilon = 65.8 L/cm mol), 431 nm (epsilon = 34.8 L/cm mol) and 369 nm (epsilon = 17 L/cm mol). (C) 2008 Elsevier B.V. All rights reserved.