The electronic structure of tris(bipyridine)chromium(III) perchlorate

Abstract

The sharp-line excitation spectrum of [Cr(bpy) 3] (ClO 4) 3·HbpyClO 4 (bpy=2,2′-bipyridine) revealed an unusually large 2E g splitting of 165 cm −1, which was attributed to an extensive π interaction of the bipyridine with the Cr(III) d orbitals. Ligand field calculations based on the exact geometric positions of the coordinated nitrogen atoms yielded values for the angular overlap parameters of −2283 cm −1 for e π and 342 cm −1 for e ππ. The latter represents the extent of phase coupling between the two nitrogen atoms in a bipyridine molecule. These values lead to an interpretation of the π interaction in terms of two strongly electron-withdrawing empty bipyridine molecular orbitals of different symmetry type.