Complexes of nickel with tetradentate ligands formed by ring opening of 1-benzoyl-3,5-dimethyl-5-(1′-benzoylhydrazido)pyrazoline

The condensation of acetylacetone with benzoylhydrazine in a 1:2 mol ratio in methanol to prepare acetylacetone bis(benzoylhydrazone) (H(3)bbhac) resulted in the formation of the cyclized product 1-benzoyl-3,5-dimethyl-5-(1'-benzoylhydrazido)-pyrazoline (bzpyzn). The pyrazoline structure has been confirmed by X-ray crystallography. In methanol, treatment of bzpyzn with Ni(O2CCH3) (.) 4H(2)O in a 1:1 mol ratio under aerobic conditions results in the pyrazoline ring opening and formation of a complex with the deprotonated acetylacetone bis(benzoylhydrazone) (bbhac(3-)). The room temperature magnetic moment (1.71 mu(B)) of [Ni(bbhac)] is consistent with an S = 1/2 spin state. However, the EPR spectral features indicate that [Ni(bbhac)] is on the borderline between an authentic nickel(III) complex and a nickel(II) stabilized ligand radical. In our attempts to grow single crystals of [Ni(bbhac)], the transformation of the central -CH= moiety of the acetylacetone residue in bbhac(3-) to a keto group has been realized. The molecular structure of the resulting nickel(II) complex of the formula [Ni(bbhacO)] has been determined by X-ray crystallography. (C) 2004 Elsevier Ltd. All rights reserved.