2,2'-bis(3-(2-pyridyl)-1-methyltriazolyl)biphenyl: A tetracoordinating wrapping ligand inducing similar skew coordination geometries at copper(I) and copper(II)

The synthesis of a new wrapping ligand, 2,2'-bis(3-(2-pyridyl)-1-methyl-1,2,4-triazol-5-yl)biphenyl (mbptb) is described. This ligand induces similar, about 45 degrees-crossed (skew) coordination geometries at both the Cu(I) and the Cu(II) ion. Both [Cu-I(mbptb)]ClO4 and [Cu-II(mbptb)](ClO4)(2) were characterized by X-ray structure determinations, UV/vis spectroscopy, and electrochemical measurements. The electronic spectrum of the orange Cu(I) complex shows two metal-to-ligand charge transfer bands at 442 and 340 nm, with extinctions epsilon of 1300 and 2600 M(-1) cm(-1) respectively, corresponding to excitations into the lowest and the second lowest unoccupied ligand MO. The turquoise Cu(II) compound shows a broad d-d transition with a maximum at 799 nm (epsilon = 73.4 M(-1) cm(-1)) with a shoulder at 690 nm, as well as a ligand-to-metal charge transfer transition at 344 nm (epsilon = 55 M(-1) cm(-1)). The Cu-II/Cu-I potential (in acetonitrile) is 0.53 V (NHE).