Determination of Stability Constant of Some Transition Metal Ions Chelates With Substituted Pyrazoles

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The stability constants of the complexes of Cu (II), Co (II) and Ni (II) ions with 3-(3’-nitrophenyl)-4-(4-chlorobenzoyl)-5-(2-hydroxyphenyl) pyrazole (L1), 3-(4’-chlorophenyl)-4-(4""-chlorobenzoyl)-5-(2-hydroxyphenyl) pyrazole (L2), 3-(4’-methoxyphenyl)-4-benzoyl-5-(2-hydroxyphenyl) pyrazole (L3), 3-(4-bromophenyl)-4-furoyl-5-(2-hydroxyphenyl) pyrazole (L4) have been determined by the pH-metric method at 0.1M ionic strength at 28 ± 0.10C in 70% dioxane-water mixture. The data obtained were used to estimate the values of proton-ligand (pK) and metal-ligand (logK) stability constants. It is observed that Cu (II), Co (II) and Ni (II) metal ions form 1:1 and 1:2 complexes with all the ligands.

Stability constants; Pyrazoles; metal chelates; dioxane-water