Adduct formation of copper(II) chelates of 1-hydroxypyrazole 2-oxides with substituted pyridines

Equilibrium constants have been determined for the adduct formation of 10 copper(II) chelates of the derivatives of 1-hydroxypyrazole 2-oxide with nine substituted pyridines at room temperature in chloroform solution. These adducts were shown to have 1:1 stoichiometry. All the stabilities of the adducts were governed by: (1) σ-donating ability of the nitrogen atom in the substituted pyridines to the copper(II) chelates, (2) electron-attracting forces of substituents at the 3- and 4-positions of the phenyl ring in the chelate ligands, and (3) the magnitude of the polar substituent constant of the substituents in the pyrazole ring of the chelate ligands.