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(m-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(m-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.