A new series of dioxouranium(VI) complexes of a potential ONNO tetradentate donor 2-aminobenzoylhydrazone of butane-2,3-dione (L₁H₂) have been synthesized. At pH 2·5–4·0, the donor (L₁H₂) reacts in the keto form and complexes of the type [UO₂(L₁H₂)(X)₂] (X⁻=Cl⁻, Br⁻, NO₃⁻, NCS⁻, ClO₄⁻, CH₃COO⁻, 1/2SO₄²⁻) are obtained. At higher pH (6·5–7), the complex of the enol form having the formula [UO₂(L₁)(H₂O)] has been isolated. On reaction with a monodentate lewis base (B), both types of complexes yield adducts of the type [UO₂(L₁)(B)]. All these complexes have been characterised adequately by elemental analyses and other standard physicochemical techniques. Location of the bonding sites of the donor molecule around the uranyl ion, status of the uranium-oxygen bond and the probable structure of the complexes have also been discussed.

Chelating behaviour of some tetradenate ONNO donors derived fromq- aminobenzoylhydrazide and some diketones toward oxo-vanadium(IV) ion is reported. The donors react with oxometal cation depending on the pH of the reaction medium. The product containing the neutral keto and the binegative enol form of the donors have the formulae [VO(H₂L)(SO₄)] (at pH 3.0)(┘1) and [VO(L)(H₂O)] (at pH 6.0)(┘2) respectively [H₂L = (2-NH₂)C₆H₄CONH: C(R) (CH₂)_mC(R): NNH CO C₆H₄(2−NH₂); H₂L = H₂DA(R= CH₃,m = 0), H₂BA(R = C₆H₅,m = 0), H₂AA(R = CH₃,m = 2)]. Both (┘1) and (┘2) react with a neutral monodentate donor B(B = pyridine, aniline etc.) yielding mixed-ligand complexes [VO(L)(B)]. Influence of the axial coordination on the V-O₍₁₎ bond is discussed and a monomeric distorted octahedral donor environment for the oxovanadium(IV) ion has been suggested