Solid-state NMR and computational studies of tetratolyl urea calix[4]arene inclusion compounds

Abstract

Solid-state guest dynamics of tetratolyl tetraurea calix[4]arene tetrapentylether dimeric capsules filled with different types of aromatic guests such as benzene-d₆, fluorobenzene-d₅ and 1,4-difluorobenzene were studied. Upon inclusion, all guest moieties revealed complexation-induced shifts varying from 2.8 ppm to 5.1 ppm. All guest molecules were shown to undergo distinct motions, ranging from mere C₆-rotations of benzene-d₆ to (ill-defined) 180° phenyl flips of fluorobenzene-d₅. In all cases, dynamic heterogeneities were identified based on ²H lineshape deconvolution. In addition, by combination of both a computed nucleus independent chemical shift (NICS) map and explicit ¹⁹F and ²H ab initio DFT chemical shift calculations, the preferred orientation of the guest molecules within the host was derived.