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 NaASO(2), 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 (K-1=4.1x10(6) and K-2=2.3x 10(5) 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 W-183 NMR spectroscopy in solution. The 10-line spectra recorded for each of them are consistent with an averaged C-2h molecular symmetry in solution.