The ligand dissociation constants and the formation constants of Cu(II) piperidine-2-carboxylic acid chelates have been measured in varying proportions of methanol-water, ethanol-water, acetone-water, isopropanol-water and dioxane-water at 30°C and 0.10 M ionic strength. The results are discussed with reference to the change in the dielectric constant of water in the presence of the organic solvent, change in structure and hydrogen bonding in water, relative solvent basicity and proton solvation by the organic solvent. The relatively greater contribution to the stability of the metal chelate by the O-M link as compared to the N-M link has been suggested on the basis of the observed solvent effects on stabilities.

The proton ligand constants of 4-chloro and 4-amino picolinic acid N-oxide and the formation constants of corresponding binary chelates of Cu(II) and Ni(II) have been measured at 30°C and 0.1M ionic strength in varying percentages of dioxane-water, acetone-water, ethanol-water and isopropanol-water. The results are discussed with reference to the change in dielectric constants of water in the presence of organic solvent, change in the structuredness of water, change in hydrogen bonding ability of the organic solvent in water, solvent basicity and proton solvation by organic solvent. The values have been compared with aqueous and mixed aqueous systems of picolinic acid N-oxide and 4-methoxy picolinic acid N-oxide.