Synthesis, characterization, X-ray structure and spectroscopic study of platinum(II) complexes with tridentate diazene ligands having O,N,S donor set

At room temperature, 2-hydroxy-1-(2′-alkylthiophenylazo)naphthalenes and 1-hydroxy-2-(2′-alkylthiophenylazo)napthalenes (HL) slowly react with di-μ-chloro-bis(η3-2-methylallyl)platinum(II) in chloroform and afford complexes of the type [PtII(L)Cl]. Potassium tetrachloroplatinate also reacts with the HL group of ligands in acetonitrile medium under reflux condition and produces complexes of the type [PtII(L)Cl]. All the platinum complexes [PtII(L)Cl] have been successfully isolated in pure form and characterized by spectroscopic techniques. The solid state structures of [PtII(L3)Cl] (3) and [PtII(L9)Cl] (9) have been determined by single crystal X-ray diffraction. The crystal structures have revealed that diazene ligands bind to the metal ion as monoanionic terdentate O,N,S donors and the fourth coordination position is occupied by a halide ion. All the platinum(II) complexes absorb strongly in the ultraviolet and visible region. The TD-DFT (time-dependent density functional theory) calculation has been carried out for better understanding of the electronic structure of platinum(II) complexes and the nature of spectral transitions. The low energy absorptions are attributed to intraligand charge transfer transitions having admixtures of metal-to-ligand charge-transfer transitions whereas the high energy absorptions are due to ILCT and LLCT transitions. The reactivity of [PtII(L)Cl] with iodine and methyl iodide has been studied.

Graphical abstractSynthesis and characterization of divalent square-planar platinum(II) complexes of two sets of ligands, viz., 2-hydroxy-1-(2′-alkylthiophenylazo)naphthalenes and 1-hydroxy-2-(2′-alkylthiophenylazo)napthalenes have been described.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Synthesis of square planar platinum(II) complexes having O,N,S coordination sphere is reported. ► Two representative Pt(II) complexes have been structurally characterized. ► The reactivity of the complexes towards iodine has been described. ► TD-DFT study on a selected complex is reported.