Cavity Size Effect on Host-Guest Property of Tiara-like Structural Mn(SR)2n Nanoclusters Probed by NMR Spectroscopy

The lack of detect technology hinders the understanding of host-guest (H-G) chemical properties for thiolate-protected tiara-like structural nanoclusters (Mn(SR)2n). In this work, NMR spectroscopy is demonstrated as a powerful tool to probe the H-G structure of Mn(SR)2n both experimentally and theoretically. A low-field shifting and wide chemical shift (CS) signal of the H nucleus in CH2Cl2 is observed in the NMR spectrum of the mixture of CH2Cl2 and Pd8(PET)16 (PET is 2-phenylethanethiol), agreeing with the theoretical results that a deshielding area appears in the central cavity of Pd8(SR)16. All Mn(SR)2n own similar nucleus-independent chemical shift maps and deshielding cavities, which means that the H nucleus in small molecules trapped by Mn(SR)2n should have consistent low-field shifted CSs. However, such a phenomenon was only observed in the NMR spectrum of the mixed solution of Pd8(SR)16 and CH2Cl2, indicating that Pd8(SR)16 is the only one in the series of Pdn(SR)2n (n = 4~16) analogues that can capture a CH2Cl2, the H-G properties of Mn(SR)2n are highly dependent on their cavity sizes, and a guest molecule only inserts into the matching cavity of Mn(SR)2n. We anticipate that the realization of such convenient probe strategy will give a deeper understanding of the H-G properties of Mn(SR)2n.