Molecular Structures of Dipeptide-Palladium(II) Conjugated Complexes

The chiral tridentate 2,6-pyridinedicarboxamide ligand L1H2 bearing two dipeptide chains (-L-Ala-L-Pro-NHBu) was designed. Complexation of L1H2 with Pd(OAc)2 was demonstrated to afford the dipeptidepalladium(II) conjugated complex [(L1)Pd(MeCN)] (1) with an ancillary acetonitrile ligand. In the crystal packing of 1, a right-handed helical-like molecular arrangement was observed, wherein each assembly is connected through continuous intermolecular hydrogen bonds together with water molecules. The dipeptidepalladium(II) conjugated complex 1 was studied as a metalloreceptor through metal coordination to accommodate a guest ligand, 4-aminopyridine, resulting in the formation of the dipeptidepalladium(II) conjugated complex [(L1)Pd(4APy)] (2). Each preorganized helical molecule of 2 is packed in a right-handed helical-like molecular arrangement in the crystal packing. The dipeptidepalladium(II) conjugated complex 2 was found to exhibit emission with a maximum at 652 nm in the solid state.