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Structural and supramolecular diversity of asymmetric carbohydrazones

Hydrazones, as structurally adaptable and functionally diverse systems, assume a number of practical roles as e.g. cytotoxic agents, molecular switches and anion receptors [1]. Moreover, hydrazones and their complexes are a versatile tool for investigating intermolecular interactions due to their tautomeric and conformational flexibility [2]. In this wide class of compounds, carbohydrazones have a special place, since they can be realized as mono- and disubstituted derivatives [3]. The possibility of tailoring them in asymmetric fashion, producing compounds with two structurally and chemically distinct subunits, offers a rich platform for testing them as supramolecular building blocks. To investigate carbohydrazones in this context, multifunctional asymmetric compounds bearing hydroxyaryl and pyridyl moieties, representing acidic and basic subunits, respectively, were prepared and structurally characterized. Title compounds were synthesized by stepwise functionalization of carbohydrazide. Depending on crystallization conditions, multiple polymorphs and/or solvates of the same compound could be isolated. Despite the expected supramolecular diversity, solid-state geometric features of those molecules are quite robust: all compounds crystallize as keto-imino tautomers in an anti conformation, with strong intramolecular OHaryl···Nimino hydrogen bond dictating the orientation of hydroxyaryl subunit. Pyridyl moiety is invariably taking part in interactions with hydrogen bond donors, while packing in whole is defined by delicate competition between carbamide homosynthon and carbonyl-hydroxyl heterosynthon.

asymmetric carbohydrazones ; supramolecular chemistry ; tautomers

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