Synthesis and structural characterisation of new iron(III) complexes with biologically relevant pyrazolyl thiosemicarbazones

New iron(III) complexes of 5-methyl-3-formylpyrazole-N(4)-dipropylthiosemicarbazone (HMPzNPr2) and 5-methyl-3-formylpyrazole-N(4)-dibutylthiosemicarbazone (HMPzNBut2), [Fe(MPzNPr2)2]NO3·H2O (I) and [Fe(MPzNBut2)2]ClO4·H2O (II), respectively, have been synthesised for the first time and physico-chemically characterised by magnetic measurements (polycrystalline state), electronic, IR and EPR spectra. Both are cationic complexes containing two monodeprotonated tridentate ligands with NNS donor sites and an anionic counterpart; the complex species behave as 1:1 electrolytes in MeOH. IR spectra (4000–200 cm−1) indicate the co-ordination to central iron(III) via the pyrazolyl (tertiary) ring nitrogen, azomethine nitrogen and thiolato sulphur atom. EPR data (RT and LNT) reveal the presence of a spin-paired iron(III) cation with d2xz d2yz d1xy configuration. X-ray crystallographic data of I and II (both P1̄, triclinic) have authenticated a FeN4S2 octahedral co-ordination in both the complex ions, as envisaged from spectral data. In both species, the two azomethine nitrogen atoms are trans to each other, while the pyrazolyl ring nitrogen atoms and the thiolato sulphurs are in cis positions.