Electronic Structure of (2,2′-Bipyridine)(Catecholato)Copper(II)

Abstract

The polarized absorption spectrum of (2,2′-bipyridine)(catecholato)- copper(?) ([Cu(cat)(bpy)]) has been measured in the stretched poly(vinyl alcohol) (PVA) film at room temperature. It is found that the 312, 295 and 215 nm bands of [Cu(cat)(bpy)] are due to transitions localized on the bipyridine (bpy) moiety, and the 306 and 247 nm bands on the catecholate (cat) moiety. The observed 322 nm band can be regarded as an intramolecular interligand CT (LL'CT) transition from cat to bpy. The 207 nm band can be interpreted as superimposition of the two localized excitations cat and bpy, respectively, and LL'CT excitation. This implies that the two π -electronic systems of [Cu(cat)(bpy)], existing almost independently on the two ligands, can interact significantly. The complex [Cu(cat)(bpy)] shows d-d bands at 750, 625 and 550 nm, and intramolecular CT bands between the ligands and metal at 425, 335 and 245 nm.