English abstract
In this project two types of Schiff-base ligands were produced from the condensation reactions of 2-acetylpyridine with various forms of aroylhydrazides and thiosemicarbazides. These ligands are the aroylhydrazones HAPBH and HAPBBH, and the thiosemicarbazones HAPATSC and HAPETSC. The bismuth(III) complexes with these aroylhydrazones and thiosemicarbazones were synthesised by either stepwise or template reactions and were isolated as orange-yellow crystalline materials. The reactions of bismuth(III) with the aroylhydrazones appeared to be strictly dependent on the M : L stoichiometric ratio while those of bismuth(III) with the corresponding thiosemicarbazones were not. The chemical formulations of the ligands and the corresponding complexes isolated as solids were established by microanalyses. IR spectroscopy showed vibrations of the characteristic azomethine bond of Schiff bases in the range ~1580-1600 cm .
Single-crystal X-ray analyses were performed on the compounds HAPATSC ligand, [Bi(APBH)(EtOH)(n-NO3)(n--NO3)], [Bi(APBBH)(EtOH)(n-NO3)2] and [Bi(HAPETSC)(APETSC)(n-NO3)]NO3. The X-ray crystal structure of HAPATSC revealed that this thiosemicarbazone adopted the EE conformation stabilised by intramolecular hydrogen-bonding interactions between the imine nitrogen and the terminal amino group [N-H"N, H-N = 2.189(15) Å]. For bismuth(III) complexes the geometries at the bismuth(III) metal centre are irregular mainly because of ligand stereochemical constraints and the presence of the inert pair of electrons (6s) on the bismuth(III) atom. The different coordination modes of NO3 to the bismuth(III) centre could be distinguished readily with vibrational spectroscopy since they display different symmetries. Of all the bismuth(II) compounds, the most interesting is probably the thiosemicarbazone compound [Bi(HAPETSC)(APETSC/n'-NO3)]NO3 which possess two inequivalent coordinated thiosemocarbazone ligands, one neutral as the thione tautomer and the other uninegative in the thiolate form. Although the two ligands were under the same reaction conditions, only one ligand underwent tautomerism whereas the other did not. This observation emphasizes the coordination flexibility and versatility of thiosemicarbazones.
To compare and contrast the chemistry of main-group metals with that of transition metals, iron(III) was reacted with the thiosemicarbazone ligands HAPATSC and HAPETSC. The reactions produced the iron(II) complexes [Fe(HAPATSC)2](C104)2•H20 and Fe(HAPETSC)2](C104)2, regardless of the M:L molar ratios. Surprisingly, the thiosemicarbazones did not undergo metal-assisted tautomerism for electroneutrality of the complexes. The existence of the ligands in the thione form was confirmed by IR spectroscopy which proveed the presence of the N-H and C=S bonds by their characteristic vibrations. In the case of [Fe(HAPATSC)2](C104)2-H20, X-ray crystallography provided a definit the structure of this complex. As revealed by magnetic susceptibility measurements and Mössbauer spectroscopy, both [Fe(HAPATSC)2](C104)2:H20 and [Fe(HAPETSC)2](CIO4)2 are diamagnetic in the temperature range 300–4 K. The electronic spectra of these low-spin iron(II) compounds are dominated by MLCT absorptions in the range 500-560 nm which obscure the spin-allowed d-d bands. These absorptions are responsible for the intense pink and rosy colours of these compounds
