Synthesis, thermal, and photochemistry of some polypyridyl complexes of chromium (III) bound to macromolecules

Abstract

Polymer coordinated chromium(III) complexes [Cr(bpy)₂(PAA)₂]+, 1, [Cr(bpy)₂-(PMA)₂]⁺, 2, [Cr(phen)₂(PAA)₂]⁺, 3, and [Cr(phen)₂(PMA)₂]⁺, 4, [where bpy, phen, PAA and PMA are, respectively, 2,2'-bipyridine, 1,10-phenanthroline, poly(acrylic acid), and poly(methacrylic acid)] were synthesized. The polymer-chromium(III) complexes were characterized by elemental and spectroscopic analyses. Thermal substitution reactions of these macromolecular chromium(III) complexes in basic solutions lead to the replacement of the polypyridyl ligand by hydroxide ion while in strong acidic solutions the polymer complexes precipitate out. The photochemical reactions are qualitatively similar to that of the thermal reactions and the quantum yields are dependant on the pH of the medium. Further, lower quantum yields were observed for the aquation of the polymer complexes in comparison with the monomeric chromium(III) complexes and the results are discussed in terms of the effect of the polymer environment. Flash photolysis of 1 and 3 results in the formation of transients with maxima at 480 nm for 1 and 470 nm, 580 nm for 3. The decay of the transients were found to obey first order kinetics and the rate constants were determined. The transients were suggested to be the alkyl-chromium complexes. Flash photolysis of 2 and 4 does not produce transients which is interpreted to be due to the presence of a methyl group in the ligand which hinders the formation of the carbonchromium bond.