Supramolecular structure and substituents effect on the spectral studies of dioxouranium(VI) azodyes complexes

The synthesis of several coordination azo compounds of dioxouranium(VI) heterochelates with bidentate azo compounds derived from 4-alkylphenylazo-5-sulfo-8-hydroxyquinoline (HLn) ligands, are described. The ligands and structural composition of azo complexes were confirmed and characterized by various physico-chemical techniques. The bonding sites of the azo compounds are deduced from IR and H-1 NMR spectra and the ligands were found to bond to the UO22+ ion in a bidentate fashion. The ligands obtained contain N=N and phenolic functional groups in different positions with respect to the quinoline group. IR spectra show that the azo compounds (HLn) acts as a monobasic bidentate ligand by coordinating via the azo nitrogen atom of azodye (-N=N-) and oxygen atom of the phenolic group forming thereby a six-membered chelating ring and concomitant formation of an intramolecular hydrogen bond. The v(3) frequency of UO22+ has been shown to be an excellent molecular probe for studying the coordinating power of the ligands. The values of v(3) of the prepared complexes containing UO22+ were successfully used to calculate the force constant, F-UO (in 10-8 N/angstrom) and the bond length R-UO (in angstrom) of the U-O bond. A strategy based upon both theoretical and experimental investigations has been adopted. The theoretical aspects are described in terms of the well-known theory of 5d-4f transitions. Wilson's, matrix method, Badger's formula, and Jones and El-Sonbati equations were used to calculate the U-O bond distances from the values of the stretching and interaction force constants. The most probable correlation between U-O force constant to U-O bond distance were satisfactorily discussed in term of Badger's rule and the equations suggested by Jones and El-Sonbati. The effect of Hamette's constant is also discussed. (C) 2011 Elsevier B.V. All rights reserved.