Synthesis and characterisation of the nickel(II) and copper(II) complexes of new quinquedentate (N₃O₂) ligands and the crystal structure of aqua[3,15-diacetyl-9-methyl-5,9,13-triazaheptadeca-3,14-diene-2,16-dionato-(2-)- N⁵N⁹N¹³O²O¹⁶]nickel(II) dihydrate

Nickel(II) and copper(II) complexes of two new multidentate ligands have been prepared and characterised. Although containing seven potential donor atoms, steric constraints dictate that the ligands behave as quinquedentate (N₃O₂) species. The nickel(II) complexes are isolated in both hydrated and anhydrous forms, each characterised by its colour and spectroscopic properties. In solution the copper complexes are five-co-ordinate, while the co-ordination number of the nickel(II) complexes depends on the nature of the solvent. In CHCl₃ the complexes are five-co-ordinate but in MeOH they are six-co-ordinate. The crystal structure of the trihydrate form of one of the complexes shows the nickel(II) ion to have a six-co-ordinate, pseudo-octahedral geometry, with one water molecule in the primary co-ordination sphere. This complex undergoes extremely facile dehydration to produce the five-co-ordinate, anhydrous form.