POLARIZED CRYSTAL SPECTRA OF ACENTRIC COPPER COMPOUNDS. THREE CRYSTAL FORMS OF ETHYLENEBISACETYLACETONEIMINATO-COPPER(II)

Abstract

Abstract Polarized absorption spectra on one face of single crystals of anhydrate, hemihydrate and monohydrate crystal modifications of N,N′-ethylenebis(acctylacetoneiminato)copper(II) are reported. Polarized spectra of the anhydrous form from 4° K to 300° K are analyzed with the aid of an oriented-gas model. Absorptions at about 16.4 kK and 18.4 kK are ascribed to the mainly “d-d” transitions A 1(x 2-y 2) ← B 2(xy) and A 1(3z 2-r 2) ← B 2(xy) which are electronically allowed along y in C 2v (x). Vibronic components may also contribute to these transitions, as suggested by the temperature dependence of the integrated intensity along the x- and/or z-axes of the anhydrate in the 15 to 19 kK region. Similar methods and a comparison with the spectral frequencies of the monohydrate crystal suggest, but with less certainty, that the absorption at about 22.5 kK is not primarily associated with the “d-d” transitions. Crystal exciton effects for the anhydrate and hemihydrate spectra are also considered. Model calculations show a marginal possibility that excitons affect the polarization ratios to a measurable extent, but the main result that the molecular absorptions are mainly y-polarized is unchanged by consideration of intermolecular interactions.