Studies in the stereochemistry of zinc(II). VI. Zinc complexes with quadridentate Schiff bases

Zinc complexes have been prepared with Schiff bases formed from salicylaldehyde and polymethylenediamines with chains of 2-9 carbon atoms. The anhydrous zinc complexes of ligands with 2-3 carbon chains readily form 1 : 1 adducts with water or bases such as pyridine; the ultraviolet and infrared spectra of these anhydrous compounds indicate that they are polymeric with bridging oxygen atoms, the zinc being 5-coordinate. The zinc complexes of ligands with carbon chains of four or more atoms do not form adducts, even in pyridine solution, and their spectra show that none of the oxygen atoms is bridging, the zinc being 4-coordinate. The stereochemistry of the zinc appears to be determined solely by steric effects: when the ligand is such that 4-coordination can produce a tetrahedral environment, further coordination does not occur; when 4-coordination cannot produce a tetrahedral environment, 5- coordination always occurs.