Selective Inclusion of Cu+ and Ag+ Electron-Rich Metallic Cations within Supramolecular Polyoxometalates Based on {AsW9O33}{Mo3S4} Combinations

Coordination of the [Mo3S4(H2O)9]4+ cluster with the trivacant [AsW9O33]9− ion gives the supramolecular complex [{(H4AsW9O33)4(Mo3S4{H2O}5)}2]12− (1) in good yield. The structure of 1 shows that two [H4AsW9O33]5− subunits sandwich a single central [Mo3S4(H2O)5]4+ ion to give a basic monomeric unit [(H4AsW9O33)2{Mo3S4(H2O)5}]6−. In the solid sate, a supramolecular dimeric association is evidenced that consists of two [(H4AsW9O33)2{Mo3S4(H2O)5}]6− units held together by twelve hydrogen bonds and four S⋅⋅⋅S contacts. Complex 1 reacts with NaAsO2, AgNO3 and CuI to give compounds 2, 3 and 4, respectively. X‐ray structural analysis reveals that the molecular arrangements of 2 to 4 are closely related to the parent structure of 1. {AsOH}2+, Ag+ and Cu+ ions are located on three distinct pairs of sites. Two hanging {AsOH}2+ groups in 2 are symmetrically attached to two opposite {AsW9O33} subunits. Complex 3 is the first example of an Ag/{Mo3S4} combination in which the environment of the two equivalent Ag+ cations is remarkable for containing two sulfur atoms belonging to {Mo3S4}, two oxygen and one central arsenic atom of the {AsW9O33} subunits. Potentiometric titration shows that the addition of Ag+ ions is quantitative and occurs in two successive steps (K1=4.1×106 and K2=2.3×105 L mol−1), which is consistent with the retention of the supramolecular cluster in solution. The structure of 4 reveals a single copper atom embedded in the central part of the dimer. The Cu+ cation is bound to four sulfur atoms to complete a cuboidal moiety. UV/Vis studies in solution indicate that the stability of the dimeric assemblies of 2, 3 and 4 is significantly enhanced by the presence of Cu+ or Ag+ ions, which act as additional coordination linkers within the supramolecular cluster. The anions 1 to 4 were characterised by 183W NMR spectroscopy in solution. The 10‐line spectra recorded for each of them are consistent with an averaged C2h molecular symmetry in solution. Polyoxometalate clusters: The dimeric complex [(H4AsW9O33)4{Mo3S4(H2O)5}]212− consists of two monomeric moieties, weakly bound through weak hydrogen‐bonding and van der Waals interactions. The resulting dimer exhibits supramolecular coordination sites that are able to specifically bind electron‐rich metallic cations, such as Ag+ and Cu+ (see figure).