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

The template reaction of isonitrosoacetylacetone (Hisoaac) with o-amin ophenol in the presence of (MeCO2)2Ni.4H2O (2:2:1 molar ratio) in etha nol led to the formation of the octahedral Schiff base complex (Hisoap h)2Ni.3H2O (1). The 1:1:1 molar ratio reaction produced the mixed-liga nd complex (Hisoaph)Ni(O2CMe).H2O (II). Refluxing a solution of trans I in chloroform led to formation of the cis complex (111). The expecte d reactivity of I with nickel(II) and copper(II) ions was confirmed (I V 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 0]- represent the anions of the Sch iff base with N- and 0-coordinated oximato groups to metal ions, respe ctively. Refluxing the chloroform solution of VI changed the site of i ntermolecular hydrogen bonding (VII). The cis octahedral modification of VI, (HisoethN)2M.nH2O (VIII) (M = Ni(II), n = 3), as well as its co rresponding square-planar palladium(II) complex (IX) (M = Pd(II), n = 0) were characterized. The suggested structures of the metal complexes are based on analytical, chemical, spectral and magnetic moment evide nce. An interpretation is presented for the phenomenon of chelate isom erism in the same molecule of nickel(II) and palladium(II) complexes o f vicinal oxime-imine ligands.