Stepwise Assembly of Ag-42 Nanocalices Based on a Mo-VI-Anchored Thiacalix[4]arene Metalloligand

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 Ag-42 nanoclusters (Ag42c-Ag42f) based on Mo-VI-anchored p-tert-butylthiacalix[4]arene (H(4)TC4A) as a metalloligand (hereafter named MoO3-TC4A). X-ray crystallography demonstrates that they are similar C-3-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 [Ag-11(MoO3-TC4A)(RS)(3)] secondary building units (SBUs, R = Et or Pr-n), 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.