Palladium(II) complexes of terdentate azo ligands with an O,N,S donor set: Synthesis, spectroscopic characterization, X-ray structure and TD-DFT calculations

Abstract

The reaction of 2-hydroxy-1-(2′-alkylthiophenylazo)naphthalenes (HL1–HL5) and 1-hydroxy-2-(2′-alkylthiophenylazo)naphthalenes (HL6–HL10) with sodium tetrachloropalladate in ethanol medium at room temperature leads to the formation of a new series of complexes of the type [Pd(L)Cl]. All the palladium compounds have been isolated in their pure form and characterized by spectral and elemental analysis data. The crystal structures of [PdL3Cl] (3) and [PdL6Cl] (6) have been determined by single crystal X-ray diffraction as representative cases. The crystal structures show that both complexes have distorted square–planar structures in which he palladium(II) centers are bonded to O1 of the naphtholato function, N2 of the diazene group and S1 at the 2′ position of the phenyl fragment. Therefore, the ligands bind palladium(II) in a tridentate monoanionic [O, N, S] fashion, which give rise to five- and six-membered chelate rings in each case. The fourth coordination site is occupied by a chloride ion. These complexes show intense absorption bands in the visible and UV region. The nature of the electronic transitions has been examined using (TD-DFT) formalism.