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The supramolecular complexes between bis-pyridinium- 4-oxime and distinctive cyanoiron platforms

The inter-ionic metalo-organic hybrid materials are interesting systems because of the opportunity to obtain a synergy of distinctive properties of both components combined into one supramolecular assembly with new optical and electrochemical properties. Recently, mono- and bis-pyridinium-4- oxime were recognized as electron acceptors for the formation of colored, supramolecular, inter- ionic charge-transfer complexes with hexacyanoferrate(II) as a donor [1]. Herein, the bis-pyridinium-4-oxime cation, toxogonin (TOXO), as the most potent electron acceptor, is used for construction of a new type material containing hexacynoferrate or nitroprusside anionic platform. The crystal structures of two complexes, (TOXO)2[FeII(CN)6]·3.5 H2O (Fig. 1) and (TOXO) [FeII(CN)5(NO)]·3 H2O, are resolved, yielding valuable insights into the interactions responsible for the supramolecular complex assembly. The solvent- or temperature-induced dehydration of (TOXO)2[FeII(CN)6]·3.5 H2O results in the loss of crystallinity and the irreversible color change, indicating the molecular-level charge-transfer perturbation. In this work, the supramolecular chemistry of the photochromic nitroprusside anion has been extended to its association with the biologically active and pharmacologically important ligand. The formation of the supramolecular (TOXO)[FeII(CN)5(NO)] assembly in aqueous solution are monitored by the UV/Vis and 1H-NMR spectroscopy. The optical and structural properties of the complexes are provided employing FT-IR, Mössbauer and diffuse reflectance spectroscopy. The color, composition and spectroscopic analysis of the complexes provide insights into binding of the cationic and anionic counterparts.

pyridinium oxime ; hexacyanoferrate(II) ; supramolecular complexes

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