As part of our studies on simple inorganic models of interest for the development of the bioinorganic chemistry of uranium, 2) we have started investigation on a dioxouranium(VI) complex with 8-hydroxyquinoline azodye derivatives which appear to be suitable models due to the pretence of dioxouranium(VI) for oxygen donors in biological systems. The chemistry of quinoline and its derivatives has attracted special interest due to their therapeatic properties.3) Quinoline sulphonamides have been used in treatment of cancer, 4) turberculosis, 5) and malaria.
6)Azo compounds based on quinoline play a central role as chelating agents for a large number of metal ions, as they form a stable six-membered ring after complexation with the metal ion and can also be used as analytical reagents.7) Dimethylformamide (DMF) or DMF/water mixtures as solvent can be used due to: i) hydrolytic reactions of highly charged metal ions; ii) insolubility of the ligand or of one or more of the complexes to be formed. DMF is an aprotic solvent which readily dissolves many water-soluble salts as well as other sparingly soluble substances.
8)In continuation of our earlier work, 9,10) we report herein the synthesis of quinoline azodyes (Chart 1) and the stability constants of Mn 2ϩ , Co 2ϩ , Ni 2ϩ and Cu 2ϩ complexes with quinoline azodyes at different temperatures. Ionization potential and substituent effects on the dissociation and stability constants are also investigated. Furthermore, the corresponding thermodynamic functions of complexation are evaluated and discussed. Moreover, the stoichiometries of these complexes are determined conductometrically at 298 K.
ExperimentalPreparation of the Ligands 8-Hydroxy-7-quinolinecarboxaldehyde was prepared according to El-Sonbati and El-Bindary.11) The standard chemical aniline and 4-alkyl-anilines (alkyl: CH 3 , OCH 3 , Cl, NO 2 ; Aldrich Chemical Co.) were used without any further purification. The experimental technique has been described previously.
1,2,11)The novel 5-(4Ј-derivatives phenyldiazo)-8-hydroxy-7-quinolinecarboxaldehyde) (HL n ) were prepared from aniline or its p-substituted derivatives (10 mmol) was dissolved in hydrochloric acid (20 mmol/25 ml distilled H 2 O). The hydrochloric compound was diazotized below Ϫ5°C with a solution of sodium nitrite (0.8 g, 10 mmol, 30 ml distilled H 2 O). The diazonium chloride was coupled with an alkaline solution of oxine (1.7 g, 10 mmol) in 20 ml of ethanol. The crude dye was collected by filtration and was crystallized from DMF, then dried in a vacuum dessicator over P 2 O 5 .Reagents and Materials Metal ion solutions (0.0001 M) were prepared from Analar metal chlorides in bidistilled water and standardized with EDTA.12) The ligand solutions (0.001 M) were prepared by dissolving the accurate weight of the solid in DMF (Analar). Solutions of 0.001 M HCl and 1 M KCl were also prepared in bidistilled water. A carbonate-free sodium hydroxide solution in 40% (v/v) DMF-water mixture was used as titrant and standardized against oxalic acid (Analar).Pot...