Influence of a Pyrazyl Linker on the Physicochemical Properties of Homodinuclear Bis(cyclen) and Bis(cyclam) Complexes
Résumé
CuII and NiII complexes of bis(cyclen)pyrazine and bis(cyclam)pyrazine, [Cu2L1]4+, [Ni2L1]4+, [Cu2L2]4+, [Ni2L2]4+, have been isolated and characterised by UV/Vis and EPR spectroscopy. Complex [Cu2L1]4+ was characterised by X-ray diffraction. The crystallographic structure indicated that the two metal cations are held in a square-pyramidal geometry, the central nitrogen pyrazine atoms occupying the apical position of each metal centre. In solution, the EPR spectrum of [Cu2L1]4+ revealed the presence of two isomers, one of which was the previous crystallised complex. For [Ni2L2]4+, the electrochemical studies have highlighted the presence of two distinct geometries for the complex (type III and type V). From the electronic point of view, EPR and electrochemical measurements indicated that in these complexes the pyrazine bridge behaves as a poorly efficient exchange bridging ligand between the two metal centres.