Site occupancy and reactivity of nickel(II) and palladium(II) coordination compounds of vicinal oxime-imine ligands: an interpretation to the phenomenon of chelate isomerism in the same molecule

Abstract

The template reaction of isonitrosoacetylacetone (Hisoaac) with o-aminophenol in the presence of (MeCO 2) 2Ni·4H 2O (2:2:1 molar ratio) in ethanol led to the formation of the octahedral Schiff base complex (Hisoaph) 2Ni·3H 2O ( I). The 1:1:1 molar ratio reaction produced the mixed-ligand complex (Hisoaph)Ni(O 2CMe)·H 2O ( II). Refluxing a solution of trans I in chloroform led to formation of the cis complex ( III). The expected reactivity of I with nickel(II) and copper(II) ions was confirmed ( IV and V). The oximato group in I–V is N-coordinated. The square-planar (HisoethN)Ni(HisoethO) ( VI) was prepared as in I using 2-aminoethanol (Heth). [Hisoeth N] − and [Hisoeth O] − represent the anions of the Schiff base with N- and O-coordinated oximato groups to metal ions, respectively. Refluxing the chloroform solution of VI changed the site of intermolecular hydrogen bonding ( VII). The cis octahedral modification of VI, (HisoethN) 2M· nH 2O ( VIII) (M = Ni II, n = 3), as well as its corresponding square-planar palladium(II) complex ( IX) (M = Pd II, n = O) were characterized. The suggested structures of the metal complexes are based on analytical, chemical, spectral and magnetic moment evidence. An interpretation is presented for the phenomenon of chelate isomerism in the same molecule of nickel(II) and palladium(II) complexes of vicinal oxime-imine ligands.