Reactivity of uranyl ion with quinquedentate chelating hydrazine derivatives. Part 2. 2,6-Diacetylpyridine bis(4-methoxybenzoylhydrazone)

Abstract

The new quinquedentate chelating ligand 2,6-diacetylpyridine bis(4-methoxybenzoylhydrazone)(H₂dapmb) reacts with uranyl nitrate and perchlorate to give the monocationic species [UO₂(Hdapmb)][NO₃](1) and [UO₂(Hdapmb)][ClO₄](2) respectively, and in the presence of nitric and perchloric acid solutions to give the adducts [UO₂(H₂dapmb)][NO₃]₂(5) and [UO₂(H₂dapmb)][ClO₄]₂(6) respectively. The six-co-ordinate isomeric form [UO₂(H₂dapmb)(ONO₂)][NO₃](4) has been isolated under different experimental conditions. All the complexes have been fully deprotonated to neutral species [UO₂(dapmb)](3), under a range of experimental conditions. Complex (3) can be isolated in two different crystalline forms, α and β, depending on the experimental conditions. All the species have been characterized by a number of analytical and physico-chemical measurements, including the determination of the crystal structure of the two isomers of (3). The red (α) form is monoclinic, space group P2₁/c, with a= 8.229(5), b= 10.564(6), c= 29.662(9)Å, and β= 101.05(8)°, while the orange (β) form is orthorhombic, space group P2₁2₁2₁, with a= 15.266(8), b= 14.953(6), and c= 10.790(6)Å. An accurate structure determination was carried out for the monoclinic modification (automatic diffractometer, Mo-K_α radiation; 2 342 observed reflections; R= 0.040), while the investigation of the orthorhombic form was undertaken merely to ascertain whether or not its configuration was the same as that of the monoclinic form. The geometry of [UO₂(dapmb)] in the two forms is very similar, the only significant difference being the conformation of a carbon atom in a methoxy-group. Seven-fold co-ordination of U^VI was found, with the five donor atoms in the equatorial plane and the linear UO₂ group normal to the plane. Interconversion reactions on the various compounds have been studied.