Spectroscopic properties of ironthiosemicarbazone compounds. Structure of [Fe(C7H7N4S)2]·1.25H2O

The reaction of FeCl3 and HL, where HL=C7H8N4S, pyridine-2-carbaldehyde thiosemicarbazone, at physiological pH values in air gives rise to a powder of composition C14H16Cl0.3FeN8O1.2S2 which contains iron(II)– and iron(III)–thiosemicarbazone species. This fact confirms the reducing character of the ligand in neutral and basic media. The [Fe(C7H7N4S)2]·1.25H2O compound has been isolated. The crystal structure consists of discrete monomeric cationic entities containing low-spin iron(II) ions in a distorted octahedral environment. The metal ion is bonded to one sulfur and two nitrogen atoms of each thiosemicarbazone molecule. The powdered X-band EPR spectra of C14H16Cl0.3FeN8O1.2S2 show a significant variation with temperature which can be explained considering an ‘exchange narrowing’ phenomenon, in good accordance with the presence of antiferromagnetic interactions. The Mössbauer measurements are in good agreement with the existence of one iron(II) and two iron(III) low-spin species, with relative areas of 69, 17 and 14%, respectively.