Electronic transitions and electronic structure of bis(tropolonato) copper(II)

The electronic structure of bis (tropolonato) copper(II) (abbreviated to troCu(II)) has been investigated by use of a polarized electronic absorption spectrum in the stretched PVA film together with unpolarized spectra in fluid and rigid media. Comparison of the polarized absorption spectrum and MO calculations shows that troCu(II) takes a transoid structure in the PVA film. The complex troCu(II) exhibits shorter molecular axis polarized bands at 387 (pi pi(2)*), 267(pi pi(9)*) and 220(pi pi(13)*) nm and longer axis polarized ones at 338(pi pi(3)*) and 252.9(pi pi(11)*) nm, All these bands are due to pi pi* transitions localized on the ligand moieties. In addition to these bands, troCu(II) shows a band around 316 nm which can be assigned to ligand-to-metal (or metal-to-ligand) intramolecular charge transfer transition. A single crystal X-ray diffraction analysis shows that troCu(II) forms a sandwich-type van der Waals dimer in the crystalline state. In the dimer state, a considerable charge migration occurs from the oxide ion to the carbonyl oxygen, but each monomer still maintains a transoid structure.