Copper(II) Complexes With Lignin Model Compound Vanillin

Bojan Kozlevčar,* Branka Mušič, Nina Lah, Ivan Leban, and Primož Šegedin
Faculty of Chemistry and Chemical Technology, University of Ljubljana, Aškerčeva 5, P.O. Box 537, SI-1001 Ljubljana, Slovenia

Three copper(II) coordination compounds with vanillinate ion trans-[Cu(C8H7O3)2(H2O)2]·2H2O 1, [Cu(C8H7O3)2(H2O)2] 2 and [Cu(C8H7O3)2(H2O)2]·2H2O 3 were synthesized and characterized. The structure analysis of air-unstable complex 1 reveals trans arrangement of two vanillinate ligands around copper(II) ion, coordinated via methoxy (Cu-O3 2.3266(14) Å) and deprotonated hydroxy group (Cu-O4 1.9383(13) Å). In the octahedral coordination sphere, two water molecules are also present (Cu-Ow1 2.0113(15) Å). Copper(II) ions in air-stable vanillinate complexes 2, 3 and 1a ([Cu(C8H7O3)2(H2O)2]; partially decomposed 1), that show very similar vibrational and electronic spectra, represent isolated paramagnetic centers (μeff > 1.73 BM). The most significant differences in IR spectra are above 3000 cm-1 for 1a (partial decomposition of 1 and different H-bonding), and in electronic spectra for non-typical orange coloured 2 with respect to yellow-green 1a and 3.

Key words: copper, vanillin, lignin, model, structure