Systematic synthesis and crystallographic characterisation of p-tert-butylcalix[4]arene derivatives bearing linear, achiral branched, and guerbet-type substituents

A systematic series of p-tert-butylcalix[4]arene derivatives bearing linear, achiral branched and Guerbet-type branched hydrocarbons at the lower rim were synthesised via Williamson etherification. Sodium hydride yielded tetra-substituted products, while potassium carbonate produced 1,3-di-substituted derivatives. All compounds were characterised by NMR, FTIR, and mass spectrometry.. Single crystals were obtained from tetra-O-alkylated derivatives with n-dodecyl, n-tetradecyl and 2-ethylbutyl hydrocarbon chains; Guerbet-type derivatives remained viscous oils, reflecting the inability of racemic β-branched architectures to crystallise. X-ray diffraction revealed invariant calix[4]arene core geometries but distinct supramolecular packing: linear chains form head-to-head bilayers through interdigitation, while 2-ethylbutyl disrupts bilayer packing, adopting staggered arrangements stabilised by C–H···π contacts. The 2-ethylbutyl derivative represents the first crystallographic characterisation of any branched-alkyl calix[4]arene, demonstrating that substituent topology fundamentally alters supramolecular organisation.