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Synthesis and characterization of thioamide pentacyanoferrate(III) complexes

Cyano complexes have played an important role in the chemistry of coordination compounds since the discovery of Prussian blue in 1704. Mononuclear cyanometallates serve as valuable starting materials in the synthesis of polynuclear complexes in which the cyanide acts as a bridge between two metal centers. In particular, mononuclear heteroleptic cyano complexes of paramagnetic ions were used in the synthesis of heterometallic complexes with interesting magnetic properties. Belonging to the class of thioamide compounds with versatile applications in medicine, thiourea and thiourea based heterocycles were herein investigated as ligands. The reactions of aquapentacyanoferrate(III) with thiourea, 4- imidazoline-2-thione, 1-methyl-4-imidazoline-2- thione or ethyl 3-methyl-2-sulfanylidene- imidazole-1-carboxylate were studied in buffered aqueous media and the produced pentacyano(thioamide)ferrate(III) complexes were characterized by means of UV/Vis and EPR spectroscopy. The wavelength of the ligand-to-metal charge transfer band in the electronic absorption spectra supported the S-coordination of thioamides to iron(III). Stability constants of the obtained complexes were evaluated by spectrophotometric mole ratio method. Kinetic studies for the formation and dissociation of [Fe(CN)5(thioamide)]2– complexes were conducted by spectrophotometric measurements. Isolated salts of pentacyano(thioamide)ferrates(III) were characterized by elemental, thermogravimetric and ESI-MS analysis, IR and 57Fe-Mössbauer spectroscopy as well as by single-crystal X-ray diffraction. The crystal and molecular structure of (PPh4)2[Fe(CN)5(thiourea)] is the first reported structure of a mononuclear pentacyano(ligand)ferrate(III) complex in which the ligand is coordinated through the sulfur.

pentacyanoferrate(III) complexes ; thiourea ; thiourea based heterocycles

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