Synthesis, spectral characterization and structural investigation on some 4-amino antipyrine containing Schiff base Cu(II) complexes and their molecular association

Compounds [Cu(L-1)(2)] (1) and [Cu(L-2)(2)] (2), where L-1 and L-2 are Schiff base ligands of 4-aminoantipyrine and substituted salicylaldehydes, were synthesized and characterized using various spectroscopic techniques such as elemental analysis, UV-Vis, IR, and NMR. The single crystal X-ray structures for L-1, L-2, and their corresponding Cu(II) complexes assembled in a 1:2 metal to ligand ratio were analyzed for their various weak H-bonding and dimeric association. The structural analysis of compounds 1 and 2, being the first crystal structures in this series, deserves special attention to help further the understanding in this area of structure-reactivity correlation studies. Further these compounds, composed of very similar chemical composition with a small difference in the substituent on the salicylaldehyde moiety, influenced through various weak inter- and intramolecular H-bonding and C-H center dot center dot center dot pi interactions, rearrange the geometry around Cu(II) from a tetrahedrally distorted square planar geometry in [Cu(L-1)(2)] (1) to square planar in [Cu(L-2)(2)] (2). Steric strain imposed by the methyl substitution on the 4-aminoantipyrine moiety of the Schiff base ligand, causing this small change of the Cu(II) geometry, along with various weak interactions is analyzed in detail. (c) 2006 Elsevier Ltd. All rights reserved.