Solid-state and solution studies of bis-carboxylate binding by bis-amidinium calix[4]arenes†

Bis-amidinium calix[4]arene receptors were shown to coordinate bis-carboxylate anions in DMSO solution; the crystal structure of the malonate salt of one of the receptors revealed a number of different amidinium–carboxylate interactions, demonstrating the propensity of these species to form complex hydrogen bonding networks.