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

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.