Two modes of chelation in Bis(4-iminopentane-2,3-dione 3-oximato)nickel(II)

The red, neutral, diamagnetic nickel complex formed by the reaction of bis(pentane-2,4-dionato)nickel(II) with nitrite and ammonium ions has been investigated by p.m.r., infrared, and mass spectrometry. It is proposed that this complex has a novel unsymmetrical structure in which the ligand [CH3COC(NO)C(NH)CH3]- exhibits two different modes of chelation in the same molecule. The modes differ in that an oximino nitrogen-to-nickel bond in one chelate ring is replaced by an oximino oxygen-to-nickel bond in the other. 2H-, 15N-, and 18O-labelled derivatives of the complex have been prepared and the isotopic shifts observed in the infrared spectra have been used to assign particular vibrational modes. An analogous unsymmetrical structure is also proposed for bis(1-ethoxyoarbonyl-2-iminopropan-1-one oximato)nickel(II).