Cavity Size Effect on Host-Guest Property of Tiara-like Structural M-n(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 (M-n(SR)(2n)). In this work, NMR spectroscopy is demonstrated as a powerful tool to probe the H-G structure of M-n(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 Pd-8(PET)(16) (PET is 2-phenylethanethiol), agreeing with the theoretical results that a deshielding area appears in the central cavity of Pd-8(SR)(16). All M-n(SR)(2n) own similar nucleus-independent chemical shift maps and deshielding cavities, which means that the H nucleus in small molecules trapped by M-n(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 Pd-8(SR)(16) and CH2Cl2, indicating that Pd-8(SR)(16) is the only one in the series of Pd-n(SR)(2n) (n = 4 similar to 16) analogues that can capture a CH2Cl2, the H-G properties of M-n(SR)(2n) are highly dependent on their cavity sizes, and a guest molecule only inserts into the matching cavity of M-n(SR)(2n). We anticipate that the realization of such convenient probe strategy will give a deeper understanding of the H-G properties of M-n(SR)(2n).