Abstract
Treatment of 5,11,17,23-tetrakis[(p-carboxyphenyl)azo]-25,26,27,28-tetrahydroxy calix[4]arene (2) with HCl in DMF or NaOH in MeOH produced 5,11,17,23-tetrakis[(p-carboxyphenyl)azo]-25,26,27,28-tetrahydroxycalix[4]-arene·4DMF (2·4DMF) and 5,11,17,23-tetrakis[(p-carboxyphenylsodium)azo]-25,26,27,28-tetrahydroxycalix[4]- arene (3), respectively, which were characterized by elemental analysis, IR, UV-vis, 1H NMR and 13C NMR. An X-ray analysis of 2·4DMF revealed that its calix[4]arene core adopts a flattened cone conformation in which opposed phenyl groups take parallel or sharply inclined positions. The intra- and intermolecular hydrogen-bonding interactions and the π···π interactions form a 2D hydrogen-bonded wavelike network. Compound 2 had a unique reversible color change in a wide pH range from 1 to 13.5 and showed interesting pH sensing properties.
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