Square planar Pd(II) complexes derived from 1-ethyl-3-phenylthiourea, 3-mercapto-4-methyl-1,2,4-triazole and 2-mercapto-5-methyl-1,3,4-thiadiazole: Syntheses, spectral, structural characterization and photoluminescence properties

Abstract

The reaction of PdCl2 with 1-ethyl-3-phenyl-thiourea (Heptu), 3-mercapto-4-methyl-4H-1,2,4-triazole (Hmmtrz) and 2-mercapto-5-methyl-1,3,4-thiadiazole (Hmthd) respectively, yielded three new complexes [Pd(eptu)2] (1), [Pd(Hmmtrz)4]Cl2 (2) and [Pd(Hmthd)4]Cl2·2CHCl3 (3). These complexes have been isolated in pure form and characterized by elemental analyses, IR, NMR and single crystal X-ray diffraction technique. In all compounds the metal ion adopts a square-planar geometry. Two nitrogen and two sulfur atoms from the monoanionic eptu ligand in complex 1 are bonded to Pd(II) centre in trans fashion. Complexes 2 and 3 are salt-like and the metal centre is bonded through four neutral ligands. The electrical neutrality in these complexes is maintained by the presence of two chlorides as counter ions. Migration of hydrogen, within the ligand framework in complexes 2 and 3, from sulfur to nitrogen is observed that resulted in the thione form of the ligand and its coordination to the metal centre in both the complexes. Complex 2 is stabilized by intermolecular C-H⋯N and intramolecular N-H⋯Cl hydrogen bonding leading to an extended structure. Complex 3 is stabilized by intermolecular C-H⋯S hydrogen bonding. Complexes 1-3 are fluorescent materials which upon excitation at 31 000, 38 600 and 32 300 cm-1 exhibit an emission at 25 200, 27 000 and 26 700 cm-1, respectively. © 2016 Elsevier B.V. All rights reserved.