Synthesis, characterization and single crystal structures of chiral Schiff base and its tetranuclear palladium complex with Pd[sbnd]O[sbnd]Pd bridging and Pd[sbnd]Pd bonds

Abstract

A new chiral Schiff base ligand 2-{N-[(2S)-(1-hydroxy-3-phenylpropan-2-yl]ethanimidoyl} phenol ((S)H2L) was obtained by acid catalyzed condensation of (2S)-(−)-2-amino-3-phenyl-1-propanol with 2′-hydroxyacetophenone. The palladium complex was prepared by treating a solution of (S)H2L in acetone with a solution of Na2PdCl4 in water in 1:1 M ratio. The new ligand and its complex were characterized by FT-IR, 1H, 13C{1H} NMR spectroscopy, polarimetry and elemental analysis and their molecular structures were determined by single crystal X-ray diffraction. Both the compounds crystallizes in monoclinic system in the space group P21. There exists an intra [OH⋯N (1.62(5) Å)] and intermolecular [OH⋯O (1.53(5) Å) and CH⋯O (2.59 Å)] hydrogen bonding and secondary interactions in the crystal of (S)H2L. The structure of the palladium complex was found very interesting wherein the ligand coordinated to metal center as tridentate dianionic (O−, N, O−) fashion, (S)-L, resulting in a tetranuclear palladium cluster, [Pd4((S)-L)4]. In these supramolecular structures phenolate oxygen coordinated to Pd(II) ion as PdO terminal bonds [1.934(12) - 1.977(11) Å] and the alkoxide oxygen coordinated as PdOPd bridging bonds [1.993(11) - 2.012(12) Å]. The PdN bond lengths found were in the range of 1.949(13) to 1.919(12) Å. There exists two asymmetric tetranuclear complex molecules in its crystal lattice. There exists very strong metal-metal bond interaction, Pd(2)Pd(3) [3.0410(18) Å] and Pd(6)Pd(7) [3.0517(19) Å] respectively in the two asymmetric units.