The hydroxo-complex [NBu 4 ] 2 [{Ni(C 6 F 5 ) 2 (μ-OH)} 2 ] reacts with β-ketonimines in a 1:2 molar ratio to give the mononuclear anionic nickel (II) derivatives of general formula [NBu 4 ] [Ni(C 6 F 5 ) 2 {R γ COCHC(=NR)Me}] (R γ =Me, R=Ph, p-ClC 6 H 4 , p-BrC 6 H 4 , o- MeC 6 H 4 , p-MeC 6 H 4 , o-MeOC 6 H 4 , p- MeOC 6 H 4 ; R γ = Ph, R = Ph, p-ClC 6 H 4 , p-BrC 6 H 4 , o-MeC 6 H 4 , p- MeC 6 H 4 , o-MeOC 6 H 4 , p-MeOC 6 H 4 ). All the complexes have been characterized by partial elemental analyses, conductance measurements, thermal analysis (thermogravimetry, differential thermogravimetry and differential scanning calorimetry) and spectroscopic (IR, Vis-UV, and 1 H- and 1 9 F-NMR) methods.