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
Abstract
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