The nickel (II) complexes 3-hydroxy-3-penten-2-one oximato-N, O(3-methylimino-2-pentanone oximato-N,N')nickel(II), Ni(pen)(mei); 3-hydroxy-3-penten-2-one oximato-N, O(3-ethylimino-2-pentanone oximato-N,N')nickel(II), Ni(pen)(eti); 4-hydroxy-4-hexen-3-one oximato-N, O(4-methylimino-3-hexanone oximato-N,N')nickel(II), Ni(hex)(mei); and 4-hydroxy-4-hexen-3-one oximato-N,O(4-ethylimino-3-hexanone oximato-N,N')nickel(II), Ni(hex)(eti) have been synthesized from the corresponding alkyldione monoximes and amines and characterized by NMR, IR, MS, and elemental analysis. The latter three complexes have not been previously reported, and the characterization shows their structure to be contrary to that reported for Ni(pen)(mei) in earlier literature. Their formation suggests two separate courses of the alkyldione monoxime : reaction with amine;to form the imine and keto/enol tautomerization. The crystal structure of Ni(hex)(eti) has been determined : monoclinic, P2(1)/n, a = 8.2350(1) Angstrom, b = 14.0895(2) Angstrom, c = 13.7965(1) Angstrom, beta = 95.964(1)degrees, with four molecules per unit cell. The reactivity of the complexes is explained based on the crystal structure and H-1 NMR data.