Tridentate and unsymmetrical tetradentate Schiff base ligands from salicylaldehydes and diamines: Their monomeric and dimeric nickel(II) complexes

Abstract

A series of ligands has been formed by the 1 : 1 molar condensation of salicylaldehyde (sl) with the diamines, propane-1,3-diamine (p), butane-1,4-diamine (b) and 2,5-dimethylhexane-2,5-diamine (d). The potentially tridentate ligands are o-[N-(3- aminopropyl)formimidoyl]phenol (Hslp), o-[N-(4- aminobutyl)formimidoyl]phenol (Hslb) and o-[N-(4-amino-1,1,4- trimethylpentyl)formimidoyl]-phenol (Hsld), respectively. These form the bis-nickel(II) complexes Ni(slp)₂, Ni(slb)₂ and Ni(sld)2. All appear to have octahedral structures in the solid. Ni(slb)₂ occurs in yellow and green forms in the solid. In solution Ni(sld)₂ occurs in equilibrium between tetrahedral (amines uncoordinated) and an octahedral centrosymmetric form with facially bound sld ligands. Ni(slp)₂ reacts with bis(5-chloro-salicylaldehyde)nickel(II) to give the unsymmetrical four-coordinate nickel complex formed from the 1 : 1 : 1 molar condensation of salicylaldehyde, propane-1,3-diamine and 5- chlorosalicylaldehyde. A dimeric, amido bridged complex has been produced by the vacuum thermolysis of Ni(slp)₂. Mass spectroscopic evidence is cited for the formation of the analogous dimeric complexes from Ni(slb)₂ and Ni(sld)₂.