Cryst. Growth Des., 2009, 9 (7), pp 2999–3002

Guest Molecules Confined in Amphipathic Crystals as Revealed by X-ray Diffraction and MAS NMR†
Angiolina Comotti*‡, Silvia Bracco‡, Piero Sozzani‡, Samuel M. Hawxwell#, Chunhua Hu# and Michael D. Ward*#

Abstract
Multinuclear 1H−13C heterocorrelated (HETCOR) NMR spectroscopy combined with X-ray diffraction revealed the unusual dual properties of identical guest molecules confined in two crystallographically distinct host cavities within single crystals based on hexagonal frameworks comprising guanidinium ions and organomonosulfonates. The environments of the two cavities differ substantially, as one is lined by the highly polar quasihexagonal guanidinium-sulfonate network, while the other is defined by walls consisting of nonpolar aromatic groups. The effect of these different environments on the NMR properties of the guest molecules is evident from chemical shift data and two-dimensional HETCOR spectra. The large magnetic susceptibility effect due to ring currents of the aromatic hosts enables determination of the host−guest distances and suggests intermolecular CH···π interactions. The 13C relaxation times reveal the molecular dynamics of the guests in two nanoscale environments that differ with respect to shape and dimensionality.