The stability of chromium(III) complexes formed with nicotinic acid and quinolinic acid derivatives

In this study, the equilibrium reactions of chromium(III) ion with the total of nine ligands nicotinicacid (NA, HL), 2-aminonicotinic acid (2-ANA, HL), 4-aminonicotinic acid (4-ANA, HL), 2,3-Pyridinedicarboxylic acid (Quinolinicacid, 2,3-PDCA, H2L), 2,5-Pyridinedicarboxylic acid (2,5-PDCA, H2L), 2,6-Pyridinedicarboxylic acid (2,6-PDCA, H2L), 2-pyrazinecarboxylic acid (2-PzCA, HL), 2,3-Pyrazinedicarboxylic acid (2,3-PzDCA, H2L) and 2-Hydroxy-6-methylpyridine-3-carboxylic acid (2-H-6-MP-3-CA,H2L) with dissociable protons and their coordination forms with aqueous solution were investigated. The stability constants of the resulting coordination species were determined by potentiometric method in a 25°C 0.1 M in a 0.1 M KCl ionic medium. It was found that chromium(III) with HL type ligands formed CrL2+, CrL2+, CrL(OH)+, CrL2(OH) type complexes and with H2L type ligands formed CrL+, CrL2-, CrL(OH), CrL2(OH)2- type complexes from these nine ligands. Stability constants were calculated with the BEST program. In this study, from the results of stability constants (log Kf) the stability of the complexes in terms of ligands; among the ligands that are in the HL type for the 1:1 molar ratio, decrease in the following order: 4-ANA > 2-ANA > 2-PzCA > NA, and among the ligands that are in the H2L type, 2-H6-MP3-CA > 2,3-PDCA > 2,5-PDCA > 2,6-PDCA > 2,3-PzDCA, among the ligands thatare in the HL type for the 1:2 molarratio, 4-ANA > 2-ANA > NA > 2-PzCA, and among the ligands that are in the H2L type, 2-H6-MP3-CA > 2,3-PDCA > 2,5-PDCA > 2,6-PDCA > 2,3-PzDCA.