Hybrid α-Diimine/Bis(chalcogenoether) Ligands for Copper(I) and Copper(II) Complexes: Hybrid α-Diimine/Bis(chalcogenoether) Ligands for Copper(I) and Copper(II) Complexes

The new ligands L = 1,4-bis(2-methylchalcogenophenyl)-2,3-dimethyl-1,4-diaza-1,3-diene [chalcogen = O (1), S (2) or Se (3)] have been studied in their coordination behavior towards Cu-I and Cu-II. Whereas the O-ether containing ligand forms complex ions [Cu(L)(2)](n+) = 4(n+), with exclusive N-coordination (n = 1) or N and weaker O coordination (n = 2), the species with E = S or Se contain tetradentate ligands in [Cu(L)](+) (5(+), 6(+)) and [Cu(L)L'](n+) [n = 1, L' = TfO- (E = S) or n = 2 and L' = H2O (E = Se)]. Molecular structures in the crystals of 5(+) and 6(+) show distorted tetrahedral N coordination at the metal and innocently behaving alpha-diimine functions, in agreement with spectroscopic and computational data. The copper(II) ions [Cu(L)L'](2+) with one tetradentate ligand L = 2 or 3 exhibit a square-pyramidal configuration at the metal. Two isolated crystalline forms of 4(2+) show weak coordination (2.636-2.96 angstrom) of three or four ether oxygen atoms, resulting in 4+3 or 4+4 coordination arrangements for N and O donors, respectively. In agreement with the rather different Cu-I and Cu-II structures the electrochemical oxidation of the copper(I) complexes and the reduction of the corresponding Cu-II species reveal an ECEC behavior within a square scheme, whereas the reduction of the Cu-I compounds, most likely at the diimine site, proceeds irreversibly. UV/Vis spectroelectrochemical results showing intense MLCT and IL absorptions were analyzed with the help of TD-DFT calculations.