Shape-persistent macrocycles - Self-assembly reactions and characterization by hyperpolarized 129Xe NMR spectroscopy

The use of three shape-persistent, conjugated macrocycles 2a-2c as ligands for self-assembly reactions is described. The macrocycles have been characterized through a combination of spectroscopic analyses and, for compounds 2b and 2c, X-ray crystallographic analysis. Whereas the reaction of 2a with the cis-Pt(II) species 3 successfully provides the porous solid 4a, the analogous reaction of 2b and 2c with 3 leads only to mixtures of products. The application of continuous-flow hyperpolarized Xe-129 NMR spectroscopy to investigate the solid-state pores of macrocycles 2b and 2c and the supramolecular complex 4a as a function of temperature is described. All three species show permanent porosity upon removal of co-crystallized solvent molecules. Using trends in the Xe-129 chemical shifts and temperature-dependent dynamics of Xe atoms in the solids, information is obtained on the nature of the pores in these systems. Using the Xe-129 NMR data for complex 4a, the effective heat of adsorption (Delta Hads) was calculated to be similar to 29 kJ mol(-1).