Synthesis and crystal structure of copper(II) complexes with pyridoxal S-methylisothiosemicarbazone bearing a new coordination mode

Abstract

The reaction of copper(II) nitrate and pyridoxal S-methylisothiosemicarbazone (PLITSC) in the presence of ammonium thiocyanate resulted in the formation of two types of complexes. A dimeric complex of the formula [Cu(-PLITSC)NCS2](NCS)2·2MeOH was obtained in the presence of excess of ammonium thiocyanate, while in the presence of its nearly equimolar amount, crystals of a polymeric complex [Cu(-PLITSC)NCS]NO3∙MeOHn were formed. The complexes were characterized by elemental analysis, conductometry, IR spectroscopy, and their structures are unequivocally determined by single crystal X-ray crystallography. In both complexes, the copper atom is five-coordinated, situated in a deformed square-pyramidal environment. The basal plane of the square pyramid is defined by the oxygen atom of the deprotonated phenol group and terminal nitrogen atoms of the isothiosemicarbazide moiety of the Schiff base, as well as the nitrogen atom of the coordinated thiocyanate ion, while the apical site is occupied by the oxygen atom of the hydroxymethyl group of the neighboring asymmetric unit. This coordination mode of the PLITSC was hitherto unknown. A survey of the Cambridge Structural Database showed that the coordination of the hydroxymethyl group is rare within pyridoxal-based Schiff base metal complexes.