Solvent influence upon complex formation between different 1,8-dioxo-octahydroxanthene derivatives and yttrium(III) cation in some non-aqueous solvents using conductometric method

Resumo

The complexation reactions between the yttrium(III) cation and (4-chlorophenyl, phenyl, 4-nitrophenyl, 4-methoxyphenyl, 4-methylphenyl) 9-substituted 1,8-dioxo-octahydroxanthene were studied in acetonitrile (AN) and methanol (MeOH) at different temperatures using the electrical conductivity measurements. The conductance data show that the stoichiometry of all formed complexes between the Y³⁺ cation and the studied ligands is 1: 1 [ML]. The order of stability of the complexes formed between the organic ligands and Y³⁺ cation in pure MeOH at 45°C was found to be: (3,6,6-Tetramethyl-9-(4-chlorophenyl)-1,8- dioxo-octahydroxanthene·Y³⁺) > (3,6,6-Tetramethyl-9-(4-methoxyphenyl)-1,8-dioxo-octahydroxanthene · Y³⁺) > (3,6,6-Tetramethyl-9-(4-phenyl)-1,8-dioxo-octahydroxanthene·Y³⁺) ≈ (3,6,6-Tetramethyl-9-(4- nitrophenyl)-1,8-dioxo-octahydroxanthene·Y³⁺) > (3,6,6-Tetramethyl-9-(4-methylphenyl)-1,8-dioxooctahydroxanthene ·Y³⁺). The values of the standard thermodynamic parameters (ΔH_c^°, ΔS_c^°) for formation of the complexes were obtained from temperature dependence of the formation constants of the complexes using the van’t Hoff plots. The experimental results show that the thermodynamics of the complexation reactions is influenced by the nature of solvent system and in most cases, the complexes are entropy stabilized.