Synthesis and characterization of ethylenediamine platinum(II) complexes containing thiourea derivatives. X-ray crystal structures of [Pt(en)(2-imidazolidinethione)2](NO3)2 and [Pt(en)(1-phenyl-2-thiourea)2](NO3)2

Abstract

Reactions of ethylenediamineplatinum(II) nitrate with thiourea derivatives afford new complexes of the form [Pt(en)L2](NO3)2 [en = ethylenediamine, L = 1-benzyl-2-thiourea (bztu), 1-cyclohexyl-2-thiourea (chtu), 1,3-diethyl-2-thiourea (detu), 1,3-diisopropyl-2-thiourea (diptu), 1-ethyl-2-thiourea (etu), 1-heptyl-2-thiourea (htu), 2-imidazolidinethione (imt), 1-isopropyl-2-thiourea (iptu), 1-phenyl-2-thiourea (phtu), 1-(3-pyridyl)-2-thiourea (pytu), and 1-tert-butyl-2-thiourea (tbtu)]. These complexes are soluble in high polarity solvents and have been characterized by elemental analysis, IR spectroscopy and NMR spectroscopy. IR analyses reveal the characteristic vibrations of the functional groups and the nitrate counter ions. NMR studies show that the chemical shifts of proton and carbon signals of the bonded en are about the same, indicating the bonding of thioureas to the platinum(II) center exert limited trans effect on the en ligand. The observation that thioamide proton signals shift downfield and the thiocarbonyl carbon signals shift upfield as compared to the free thioureas suggests a decrease in thiocarbonyl bond order and an increase in thiocarbonyl carbon-amide nitrogen bond order upon coordination to the platinum(II) center. Good quality single crystals of [Pt(en)(2-imidazolidinethione)2](NO3)2 (7) and [Pt(en)(1-phenyl-2-thiourea)2](NO3)2 (9) are grown by slow evaporation of methanol solution at room temperature. Their molecular structures have been identified by the single crystal X-ray diffraction. Complex 7 crystallizes in the orthorhombic space group Pccn whereas 9 crystallizes in the monoclinic space group P2(1)/n. X-ray crystallographic analysis indicates that the geometry about the platinum atom is square-planar and the crystal packings are dominated by intermolecular en NH⋯O (NO3) and thioureas NH⋯O (NO3) hydrogen bonds. The two imidazole rings in 7 and the two phenyl rings in 9 are oriented above and below the PtN2S2 plane, respectively, to minimize the steric interaction.