Studies on Cr III-cellulose acetate complexes

Abstract

Cr III complexes with acetylated bagasse dissolving pulp (I) and acetylated bagasse kraft paper pulp(II) have been prepared and characterised by means of electronic and vibrational data. The electronic absorption spectra of Cr III with I and II exhibit absorption bands at 16 666 and 23 324 cm −1, which are assigned in octahedral symmetry to the transitions 4T 2g ← 4A 2g and 4T 1g ← 4T 2g, respectively. The third highest band, associated with the 4T 1g ← 4T 2g transition, is not observed, being obscured by charge transfer absorption. The ligand field parameters Dq and B have been calculated. The nephelauxetic parameter, β, has the value 0·67 suggesting strong covalency in the metal-ligand σ bond. Cr III-II complexes have higher optical absorbance than Cr III-I complexes. Since I has a greater acetyl content and lower D.P. than II, that is II has more unacetylated hydroxyl groups, then the hydroxyl groups must be more involved in chelation. The secondary cellulose acetate (SCA) acts as uninegatively charged bidentate ligand and coordinates via the O-atom of the hydroxyl group and the O-atom of the ester group to form stable five-membered rings.