Copper(II) complexes of the isomeric tetraazamacrocyclic ligands 1,11-and 1,8-bis(2-pyridylmethyl)-1,4,8,11-tetraazacyclotetradecane and of the 1,4,8,11-tetraazacyclotetradecane-5,12-dione analogue at neutral and basic pH

The regioselective synthesis of the new N,N'-dialkylated tetraazamacrocycle 1,11-bis(2-pyridylmethyl)-1,4,8,11-tetraazacyclotetradecane, L-1, has been achieved. The copper(II) complexes of L-1 and of the isomeric ligand 1,8-b is(2-pyridylmethyl)-1,4,8,11-tetraazacyclotetradecane, L-2, have been isola ted and their crystal structures determined. The structure of [CuL2](2+)(CH 3CO2-)(2), reveals planar N-4 co-ordination of the copper by the macrocycle , which adopts the trans-III configuration, and with the pendant pyridine n itrogens occupying the elongated axial sites. In contrast, in [CuL1](2+)(Cl O4-)(2), the copper is 5-co-ordinated by the four nitrogen atoms of the mac rocycle, which adopts the trans-I configuration, and one pendant pyridine n itrogen, forming a distorted square pyramid with the pyridine nitrogen at t he apex. The new macrocyclic dioxotetraamine 1,8-bis(2-pyridylmethyl)-1,4,8 ,11-tetraazacyclotetradecane-5,12-dione, L-3, has also been prepared. The c rystals obtained upon reaction of L-3 with copper(II) perchlorate under neu tral conditions have been shown by X-ray diffraction analysis to contain tw o distinct macrocyclic units containing copper ions. In the first a single copper centre is co-ordinated by the two trans-orientated amino nitrogens o f the macrocycle, the two pyridine nitrogens and one deprotonated amide nit rogen, forming a distorted trigonal bipyramid. The second has a 2:1 metal:l igand stoichiometry and, in the unit cell, bridges two complexes of the fir st type. In contrast, crystallisation under basic conditions leads to a 1:1 complex in which the two amides are deprotonated and the copper ion is bou nd within the macrocycle, weakly co-ordinated by the two pyridine nitrogens in elongated axial sites. The behaviour of the three complexes in solution has been studied by ESR, UV-visible absorption spectroscopy and by cyclic voltammetry.