(Cyclen- and cyclam-pyridine)copper complexes:: The role of the pyridine moiety in CuII and CuI stabilisation

The protonation constants of cyclen- and cyclam-pyridine [1-(pyridin-2-ylmethyl)-1,4,7,10-tetraazacyclododecane (L-1) and 1-(pyridin-2-ylmethyl)-1,4,8,11-tetraazacyclotetradecane (L-2), respectively] and the stability constants (log beta(110)) of the corresponding copper complexes ([CuL1](2+) and [CuL2](2+)) were determined by potentiometric titrations. The complexes were subsequently isolated and characterised by X-ray diffraction, UV/Vis spectroscopy and electrochemical studies. The [CuL2](2+) complex adopts two distinct and stable geometries (trans I and III), which mainly differ by the macrocycle configuration. The trans III configurational isomer can be converted into the trans I one by electron transfer. ((c) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)