Dynamic Phenomena in Self‐Complementary {2}‐Metallocryptates Probed by Solution 133Cs‐NMR. New Insights into Ion Pairing Processes: X‐Ray Structure and Solid‐State NMR Spectra of a Meandering Species

Two self-complementary {2}-metallocryptates, differing in methyl and phenyl substituents, respectively, have been studied by X-ray analysis, and solid-state and solution NMR. Mixed Mg/Cs metal methyl complex 2 is a linear polymer in the solid state. The two different Cs sites are confirmed by 133Cs-solid-state NMR. By contrast, the analog mixed Mg/Cs metal phenyl complex 4 is a meandering polymer as shown by an actual X-ray analysis. The four non-equivalent Cs-sites in 4 are reflected in the solid-state NMR spectra. Solution 133Cs-NMR spectra of 4 reveal two independent dynamic processes: a fast exchange of Cs within contact ion-pairs and solvent-separated ion-pairs (CIP, SSIP), and a slower exchange of ‘inside’ endo Cs, surrounded by three ligands, and ‘outside’ exo Cs involved in the CIP/SSIP equilibrium. Complete line-shape analysis of variable-temperature 133Cs-NMR spectra of 4 yield kinetic parameters of =10.8 kcal/mol for the fast SSIP-CIP exchange and =13.2 kcal/mol for the slower endo/exo exchange of Cs. DOSY-NMR Measurements confirm the monomeric nature of 4 in solution.