Lanthanide picrate complexes and picric acid adduct of a calix[4]arene diamide. Syntheses and structures of [Tm(LH–2)A], [Ce(LH–2)(MeOH)2A]·HA, [PrLA3] and L·2HA {L = 5,11,17,23-tetra-tert-butyl-25,27-bis(diethylcarbamoylmethoxy)-26,28-dihydroxycalix[4]arene, HA = picric acid}

Abstract

Reactions of 5,11,17,23-tetra-tert-butyl-25,27-bis(diethylcarbamoylmethoxy)-26,28-dihydroxycalix[4]arene (L) with lanthanide picrates produced 1 : 1 metal–calixarene complexes incorporating one, two or three picrate moieties, depending on the reaction conditions and the lanthanide used. Dichloromethane solutions of L have been found to extract picric acid (HA) from aqueous solution, resulting in the formation of an L·2HA adduct. Single crystal structure determinations have been carried out on [Tm(LH_–2)A]·2.5CH₂Cl₂, [Ce(LH_–2)(MeOH)₂A]·HA·H₂O, [PrLA₃]·2CH₂Cl₂·1.5H₂O and L·2HA·EtOH. The possible variations of these formulae, depending on the charge distribution within the complexes, are discussed. The calixarene is found in a distorted cone conformation in each case. The intense colour of some of these complexes appears to correlate with the disposition of a picrate moiety close to a calixarene phenyl ring, consistent with calixarene→picrate charge-transfer absorption. The UV /VIS spectroscopic studies suggest that at least some aspects of the solid-state structures are maintained in solution.