Stepwise Assembly of Ag₄₂ Nanocalices Based on a Mo^VI-Anchored Thiacalix[4]arene Metalloligand

Abstract

Metalloligand strategy has been well recognized in the syntheses of heterometallic coordination polymers; however, such a strategy used in the assembly of silver nanoclusters is not broadly available. Herein, we report the stepwise syntheses of a family of halogen-templated Ag42 nanoclusters (Ag42c–Ag42f) based on MoVI-anchored p-tert-butylthiacalix­[4]­arene (H4TC4A) as a metalloligand (hereafter named MoO3–TC4A). X-ray crystallography demonstrates that they are similar C3-symmetric silver–organic nanocalices capped by six MoO3–TC4A metalloligands, which are evenly distributed up and down the base of 42 silver atoms. These nanoclusters can be disassembled to six bowl-shaped [Ag11(MoO3–TC4A)­(RS)3] secondary building units (SBUs, R = Et or nPr), which are fused together in a face-sharing fashion surrounding Cl– or Br– as a central anion template. The electrospray mass spectrometry (ESI-MS) indicates their high stabilities in solution and verifies the formation of the MoO3–TC4A metalloligand, thereby rationalizing the overall stepwise assembly process for them. Moreover, Ag42c shows lower cytotoxicity and better activity against the HepG-2 cell line than MCF-7 and BGC-823. These results not only exemplify the effectiveness of a thiacalix[4]­arene-based metalloligand in the assembly of silver nanoclusters but also give us profound insight about the step-by-step assembly process in silver nanoclusters