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-Kα 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 UVI 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.