The Study Of Tris-Carboxylate Based Anion-Coordination-Driven Assembly Of Truncated Tetrahedrons And Double-Walled Tetrahedrons

Due to its structural diversity and functional richness,supramolecular assemblies have gained significant attention among researchers.Since anions play significant roles in many areas,including our lives and the environment,anion chemistry has gained great development in recent years.Anion-coordination-driven assembly(ACDA)has witnessed great potential in the construction of anionic supramolecular architectures.Several of discrete anion-based assemblies including helicates,tetrahedral cages,bicapped trigonal antiprisms and grid complexes have been successfully synthesized using ACDA.The anion in previous systems mainly focused on the high electron-density,inorganic phosphate(PO₄^3-)or sulfate(SO₄^2-)ion.To further examine the scope of anions in ACDA and enrich the resulted supramolecular structures by expanding the anion centers from oxoanion(phosphate or sulfate)to organic tris-carboxylates,an Archimedean solid(truncated tetrahedron)and a highly entangled double-walled tetrahedron featuring a ravel topology have been assembled with tris-bis(urea)ligands.This paper mainly includes the following contents:First,we previously reported that C₃ symmetric tris-bis(urea)ligands L¹(the central backbone is Triphenylamine),L²(the central backbone is Triphenyltriazine)and L³(the central backbone is Triphenylbenzene)can assemble with phosphate and sulfate to form a tetrahedral cage[A₄L₄](A=anion,L=ligand)and a pinwheel helices[A₃L₂].Based on ligand L¹,triphenylamine-based C₃-symmetry tris(bisurea)ligands L⁴ and L⁵ have been designed and synthesized.Liangds L^4/5 are then used to assemble with sulfate or phosphate to form anionic pinwheel helices[A₃L₂]and tetrahedra cage[A₄L₄],respectively.By mixing ligands L^1/4/5 and assembling with sulfate or phosphate,the phenomenon of narcissistic self-sorting has been demonstrated.Through NMR and MS analysis,it is found that the three ligands L^1/4/5 which assembled with sulfate or phosphate anion to produce exclusively the[A₃L₂]or[A₄L₄]complexes,containing only one of the three types of ligands rather than a statistic mixture.We report that narcissistic self-sorting is available for well-defined anion-coordination systems.Second,previous research of the anions has mainly focused on high electron-density,inorganic phosphate ion(PO₄^3-)and sulfate ion(SO₄^2-).Here we expand the anion center from phosphate to organic tris-carboxylates.A“truncated”tetrahedron complex(TPA)₁₂[(A¹)₄(L¹)₄]can be obtained by assembling the smallest trianion A¹ with ligand L¹.This is the first ever produced Archimedean-type polyhedron that based on anion-coordination.Moreover,the three-arm anions and ligands enable the generation of suitable peripheral cavities(or grooves)that can efficiently bind guests,including the tetraalkyl-ammonium or-phosphonium cations with long alkyl chains.The larger ligands L^2/3/4 can also assemble with A¹ in acetonitrile at room temperature to produce the truncated tetrahedral complexes.It is also observed that ligand L⁴ assembled with A² can produce the corresponding truncated tetrahedral.Third,we switch to the combination of larger anions A³(1,3,5-triazine-2,4,6-tris(4-benzoate))and A⁴(benzene-1,3,5-tris(4-benzoate))with the largest ligand(L⁴),from which the highly entangled double-walled tetrahedron(TEA)₁₂[(A^3/4)₄(L⁴)₄]can be isolated.Such a binding between inner-wall ligands and outer-wall anions results in a highly entangled structure which contains six closed loops in total and two of them form a Solomon link.From another point of view,on each of the double-walled faces,the entanglement of the H-bonded strands results in a trefoil knot.Therefore there are also four trefoil knots in the structure.It should be noted that the formation of the above Solomon links and trefoil knots are observed for the first time in anion-coordination-based systems.