Crystal Spectra of Metal Coordination Compounds. IV. Bis‐Acetylacetonato‐Copper (II)

The polarized crystal absorption spectrum of bis‐acetylacetonato‐copper (II) has been measured with light incident on three different crystal faces. Four absorption bands have been found and a consistent analysis made in terms of a strong rhombic (D2h) field from the ligands. The symmetries of the ground and excited states are not those predicted on the basis of simple crystal field theory and it has been suggested that strong metal‐ligand π bonding will account for the observed order of states. The slight differences between the positions of the bands in the crystal and in chloroform are accounted for by weak intermolecular interactions between adjacent molecules in the crystal.