Ferrocene-based thiosemicarbazones: Solvent effect on thiol-thione tautomerism and conformational polymorphism

Thiosemicarbazones are important molecules with tremendous biological significance. In the present study, effect of solvents of different nature and polarity on thiol-thione tautomerism in ferrocene-based thiosemicarbazones 1-3 has been evaluated though UV-vis spectroscopy. The resulting data shows a good correlation between the tautomer and the polarity of the solvent. The hydrogen bond donating or accepting ability of solvents does not play any major role in preferentially stabilizing one of the tautomer, if substituents are not considered. With this information, search for desmotrops of 1-3 was attempted in different solvents. However, in spite of desmotrops, an interesting case of conformational polymorphism in 1 has been discovered. Under slightly different conditions of crystal growth, two polymorphs of 1 have been obtained which are different owing to the different orientations of ferrocenyl and aryl substituents around the central N-iminothiourea moiety and have slightly different unit cell parameters. Interestingly, these two polymorphs have almost same 3D-cyrstal packing which is quite rare phenomenon in solid state chemistry. Additionally, the solid state self-assemblies of 2 and 3 are also discussed. (C) 2017 Elsevier B.V. All rights reserved.