Coordination diversity in palladium(II)-picolinamide ligand complexes: structural and quantum chemical studies

Abstract

The separation of different metal ions can be successfully accomplished by using picolinamide-based ligands. We herein report the first X-ray structure of picolinamide-based ligands of the type C5H4NCONR2 (where R=iC3H7 (L1) and iC4H9 (L2)) and C5H4NCONHR (R=tC4H9 (L3)) with palladium(II) ion. We have synthesized and characterized the structures of two palladium complexes, [PdCl2(L1)2] (1) and [PdCl2L3] (3). In 1, ligand L1 forms a 2 : 1 complex with palladium(II) chloride, whereas in 3, the ligand L3 forms a 1 : 1 complex. Further, in 1, the ligand L1 acts as a monodentate ligand and is bound only through pyridyl-N atom, whereas in 3, the ligand L3 acts as a bidentate chelating ligand and is bound through both the pyridyl-N and amido-O atoms to the Pd(II) center. Electronic structure calculations are carried out to understand the experimental coordination diversity in the Pd complexes. Our calculations clearly suggest that a combination of steric hindrance of the ligand and the electronic effect of metal ions may modulate the coordination preferences.