Complexes of Cu(II) with mixed-donor phenanthroline-containing macrocycles: analysis of their structural, redox and spectral properties in the context of Type-1 blue copper proteins biomimetic models

The macrocycles L1–L3 having N2S2O-, N2S2-, and N2S3-donor sets, respectively, and incorporating the 1,10-phenanthroline unit interact in EtOH and MeCN solutions with CuII to give 1:1 [M(L)]2+ complex species. The compounds [Cu(L1)(ClO4)]ClO4 (1), [Cu(L2)(ClO4)]ClO4.12H2O (2) and [Cu(L3)](ClO4)2 (3) were isolated at the solid state and the first two also characterised by X- ray diffraction studies. The conformation adopted by L1 and L2 in the cation complexes reveals the aliphatic portion of the rings folded over the plane containing the heteroaromatic moiety with the ligands encapsulating the metal centre within their cavity by imposing, respectively, a square-based pyramidal and a square planar geometry. In both complexes, the metal ion completes its coordination sphere by interacting with a ClO4 ligand. The compound [Cu(L3)2](PF6)2 (4) containing a 1:2 cation complex was also isolated at the solid state: EPR spectroscopy measurements suggest the presence of a CuN4 chromophore in this complex. The EPR and electronic spectral features of 1–4 have been studied and their redox properties examined in comparison with those observed for Type-1 blue copper proteins. The reactivity of L1–L3 has also been tested toward stoichiometric amounts of the CuI salt [CuCl(PPh3)3].