Mixed-ligand oxovanadium(IV) complexes with dipicolinic acid and several bidentate amino acids

The formation of ternary oxovanadium(IV) complexes involving dipicolinic acid (H2Dipic) as the primary ligand and a series of α-amino acids as secondary ligands was investigated. The amino acids studied included α-Alanine (HαAla), Proline (HPro), Serine (Hser), Threonine (HThr), Leucine (HLeu), Isoleucine (HIle), Valine (HVal), Tryptophan (HTrp), Asparagine (Asn), Glutamine (HGln), Methionine (HMet), and Phenylalanine (HPhe). Potentiometric titrations were conducted in 1.0 mol dm−3 NaCl at 25°C to determine the speciation of these systems. Experimental data were analysed using the least-squares program LETAGROP. It was necessary to first characterise the binary VO(IV)-Asn system, which revealed the formation of several species: VO(HL)2+, VO(L)+, VO(HL)22+, VO(HL)(L)+ and VO(L)2. For the ternary systems, the species VO(Dipic)(HL) and VO(Dipic)(L)− were identified, and their respective distribution diagrams were analysed. Furthermore, the relative stability parameters Δ log10 K, log10 X and %RS were determined to evaluate the stability of the ternary complexes relative to their binary counterparts.