The relationship of some copper (II) complexes of facultative tetrathioethers to the coordination environment in the "blue" copper proteins.

The facultative potentially tetradentate thioether ligands 1,2-bis(methylthioethylthio)ethane (2,2,2), 1,3-bis(2-methylthioethylthio)propane (2,3,2) and 1,2-bis(3-methylthiopropylthio)ethane (3,2,3) react with copper(II) salts to form Cu2(2,2,2)Cl4, Cu3(ligand)X6 (ligand = 2,3,2 and 3,2,3 X = Cl; ligand = 2,2,2 2,3,2 and 3,2,3 X = Br), and Cu(ligand)(ClO4)2. The stoichiometry and structures of these complexes are discussed in terms of the steric demands of the ligand and the nature of the halide. The [Cu(2,3,2)(ClO4)] ClO4 and [Cu(3,2,3)(ClO4) [ClO4 complexes have electronic spectra which exhibit the intense 600 nm band characteristic of the "blue" copper proteins. In fact, the spectrum of [Cu(2,3,2)(ClO4)]ClO4 is very similar to that of pseudomonas aeroginosa azurin.