Synthesis, spectroscopy and cyclic voltammetry of new iron(III) complexes with 5-methyl-3-formyl pyrazole 3-hexamethyleneiminyl thiosemicarbazone (HMPz3Hex):: X-ray crystallographic identification of [Fe(MPz3Hex)2]ClO4 • 2H2O with an indication for unusual rotation about the azomethine double bond on complexation with iron(III)

New iron( III) complexes of 5-methyl-3-formylpyrazole 3-hexamethyleneiminylthiosemicarbazone ( HMPz3Hex), [ Fe( MPz3Hex) 2] X center dot nH(2)O ( where X Cl, NO3 or ClO4 and n 1 - 2) have been synthesized and physico-chemically characterized by magnetic data ( polycrystalline state), electronic, i.r. and e.p.r. spectral studies. The reported complexes are all cationic electrolytes ( 1: 1) containing two moles of monodeprotonated title ligand and an anionic counterpart. I.r. spectra ( 4000 - 200 cm(-1)) indicate coordination to the central iron( III) ion via the pyrazolyl ( tertiary) ring nitrogen, azomethine nitrogen and thiolato sulphur atoms of the primary ligand molecule. E.p.r. data ( r.t. and l.n.t.) show the presence of a low-spin iron( III) cation with d(xz)(2)d(xz)(2)d(xz)(1) configuration. Cyclic voltammograms of iron( III) complexes indicate a reversible Fe+3/Fe+2 couple. X-ray data of [ Fe( MPz3Hex)(2)] ClO4 center dot 2H(2)O ( P-1, triclinic) authenticate a FeN4S2 distorted octahedral coordination with the two azomethine nitrogens trans to each other; the pyrazolyl nitrogens and thiolato sulphurs are in cis-positions, indicating an unusual rotation about the azomethine ( C = N) double bond of the free HMPz3Hex during complexation with iron( III).