New dioxocyclam ligands appended with 2-pyridylmethyl pendant(s): synthesis, properties and crystal structure of their copper(II) complexes (dioxocyclam = 1,4,8,11-tetraazacyclotetradecane-12,14-dione)‡

Two new dioxocyclam ligands, 4-(pyridin-2-ylmethyl)-1,4,8,11-tetraazacyclotetradecane-12,14-dione (L1) and 4,8-bis(pyridin-2-ylmethyl)-1,4,8,11-tetraazacyclotetradecane-12,14-dione (L2), have been synthesized and characterized. The solution chemistry of the CuII complexes with these ligands have been studied by potentiometric and spectroscopic titration, cyclic voltammetry (CV), UV/VIS and ESR spectral techniques. The CuII complex of L2 has been isolated as single crystals and the structure has been determined by X-ray diffraction analysis to be [CuL2][ClO4]2 1. In complex 1, the CuII atom is five-co-ordinate with the two pendant pyridyl nitrogens and the two tertiary amines forming a distorted trigonal-bipyramidal configuration in which the backbone oxygen O(2) co-ordinates to CuII while the two amido nitrogen groups remained non-deprotonated and non-co-ordinated. To our knowledge, this is the first example of CuII complexes of dioxotetraamines in which the backbone oxygen co-ordinates to the central metal by twisting the backbone.