engleski

Structural insights into complexes and polyoxomolybdate salts derived from asymmetric carbohydrazones

Hydrazones, as structurally adaptable and functionally diverse systems, assume a number of practical roles as e.g. cytotoxic agents [1] or anion receptors [2], while their Mo(VI) complexes have demonstrated their value as effective epoxidation (pre)catalysts [3]. In this wide class of compounds, carbohydrazones have a special place, owing to the structural versatility of their mono‐ and disubstituted derivatives [4]. The possibility of tailoring them in asymmetric fashion, creating in return systems with two different subunits, varying in chelating behaviour and acid‐base properties, offers a versatile platform for testing them as metalloorganic and supramolecular building blocks. To investigate carbohydrazones in this context, multifunctional asymmetric compounds bearing hydroxyaryl and pyridyl moieties were derived and tested for their chelating and anion receptor behaviour. Dioxomolybdenum(VI) complexes and carbohydrazonium polyoxomolybdates (POMs) were prepared by crystallization from solution and by mechanochemical synthesis. To explore alternative routes towards corresponding POM salts, dioxomolybdenum(IV) complex decomposition and salt metathesis reactions were explored as well. The results evidence that different reaction conditions, in particular solvent choice and water content, along with the starting carbohydrazone structure affect the reaction outcome and the structure of the products obtained. Whereas dioxomolybdenum(VI) complexes have their structures determined by strongly chelating hydroxyaryl subunit, structures of POM salts are shaped by delicate competition between CONH∙∙∙OPOM, NH+py∙∙∙OPOM and OHar∙∙∙OPOM intermolecular hydrogen bonds (Figure 1).

asymmetric carbohydrazones ; dioxomolybdenum(VI) complexes ; polyoxomolybdates

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