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 Ag 42 nanoclusters (Ag42c−Ag42f) based on Mo VI -anchored p-tertbutylthiacalix[4]arene (H 4 TC4A) as a metalloligand (hereafter named MoO 3 −TC4A). X-ray crystallography demonstrates that they are similar C 3 -symmetric silver−organic nanocalices capped by six MoO 3 −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 (MoO 3 −TC4A)(RS) 3 ] secondary building units (SBUs, R = Et or n Pr), 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 MoO 3 −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.

Oxocarbon Anions Templated in Silver Clusters

“…One of the well-known strategies is to use macrocyclic ligands that form porous organic cages, which show a good perspective in adjusting the inner pore size and encapsulating well-dispersed metal aggregates. , In this context, the macrocycle with donor atoms such as O, N, or S atoms reveals great affinity to the attached guest cluster and great stability due to the high steric hindrance of the aromatic rings. , However, the size and the geometry of the encapsulated clusters or NPs are constrained by the host molecules in this macrocyclic template-directed strategy. In the past few decades, the anion-template strategy has been explored and applied to synthesize high-nuclearity silver clusters because the Ag­(I) ions exhibit a soft acceptor characteristic and flexible coordination to display structural diversity, arousing the interest of synthetic scientists. − The rationale for this strategy is to use the anion as the central template core leading to the aggregation of Ag­(I) ions, which are further stabilized by the ligands such as monothiolate, ,,,,− ,− dithiolate, ,,, diphosphine, , phosphonate, carboxylate, ,,,,,,,, alkynyl ligands, ,,,,,,− metalloligand, , and their combinations. Since there are no external constraints, the cluster nuclearity can be greatly increased.…”

“…In the past few decades, the anion-template strategy has been explored and applied to synthesize high-nuclearity silver clusters because the Ag(I) ions exhibit a soft acceptor characteristic and flexible coordination to display structural diversity, arousing the interest of synthetic scientists. 5−7 The rationale for this strategy is to use the anion as the central template core leading to the aggregation of Ag(I) ions, which are further stabilized by the ligands such as monothiolate, 11,12,15,18,21−25,34−37 dithiolate, 9,20,29,30 diphosphine, 19,22 phosphonate, 8 carboxylate, 12,17,18,21,24,26,27,34,37 alkynyl ligands, 8,10,14,16,17,19,26−28 metalloligand, 31,32 and their combinations. Since there are no external constraints, the cluster nuclearity can be greatly increased.…”

Anion-templated silver thiolated clusters affected by carboxylate ligands

“…In particular, the template method is usually used to prepare structurally determined silver nanoclusters, and anion templates of various sizes become the key factor for inducing molecular assembly. [19][20][21][22] At present, the commonly used templates are (i) halogen anion templates that were initially used, such as F − , Cl − , Br − , etc. ; 23,24 (ii) other widely used templates, such as S 2− , NO 3 − , CO 3 2− , SO 4 2− , CrO 4 2− , etc.…”

Silver Clusters Coprotected by Different Diphosphine and Thiol Ligands

“…Also, the physical properties of the clusters can be turned by functional anionic templates. − At present, some silver clusters encapsulating anionic templates have been reported. The commonly used templates are S 2– , SO 4 2– , CO 3 2– , Cl – , Br – , and polyoxometalates (POM), etc. − Specific examples are [(V 10 O 28 )@Ag 44 (EtS) 20 (PhSO 3 ) 18 (H 2 O) 2 ] n , [Ag 62 S 13 ( t BuS) 32 ]­(BF 4 ) 4…”