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

Abstract

Coordination of the [Mo(3)S(4)(H(2)O)(9)](4+) cluster with the trivacant [AsW(9)O(33)](9-) ion gives the supramolecular complex [{(H(4)AsW(9)O(33))(4)(Mo(3)S(4){H(2)O}(5))}(2)](12-) (1) in good yield. The structure of 1 shows that two [H(4)AsW(9)O(33)](5-) subunits sandwich a single central [Mo(3)S(4)(H(2)O)(5)](4+) ion to give a basic monomeric unit [(H(4)AsW(9)O(33))(2){Mo(3)S(4)(H(2)O)(5)}](6-). In the solid state, a supramolecular dimeric association is evidenced that consists of two [(H(4)AsW(9)O(33))(2){Mo(3)S(4)(H(2)O)(5)}](6-) units held together by twelve hydrogen bonds and four SS contacts. Complex 1 reacts with NaAsO(2), AgNO(3) 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 {AsW(9)O(33)} subunits. Complex 3 is the first example of an Ag/{Mo(3)S(4)} combination in which the environment of the two equivalent Ag(+) cations is remarkable for containing two sulfur atoms belonging to {Mo(3)S(4)}, two oxygen and one central arsenic atom of the {AsW(9)O(33)} subunits. Potentiometric titration shows that the addition of Ag(+) ions is quantitative and occurs in two successive steps (K(1)=4.1 x 10(6) and K(2)=2.3 x 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 (183)W NMR spectroscopy in solution. The 10-line spectra recorded for each of them are consistent with an averaged C(2h) molecular symmetry in solution.

Noble Metals in Polyoxometalates

“…[19] The crystal structure of the guanidinium salt (CH 6 N 3 ) 5 , in which the two Ag + ions are each coordinated to oxygen atoms of the {AsW 9 O 33 } units and the S atoms of two {Mo 3 S 4 } clusters located in different monomeric units of the parent supramolecular assembly. [11] The incorporation proceeds in two successive steps as based on potentiometric titration studies, and the 183 W NMR spectrum is consistent with rapid hopping of both enclosed Ag + ions between two equivalent sites. , first reported by Mizuno et al, [20] has been shown to function as a size-selective cryptand that can incorporate Ag + and other metal ions.…”

“…Most studies have been carried out with the phosphorus-centered lacunary species, the products often being formulated as [PM 11 8À which would imply uncommon and presumably paramagnetic octahedral or square-pyramidal Pd II centers. Recent studies suggest a different explanation of these results in terms of the S-structure species that are described in Section 2.3.3.…”

“…Reaction of rhodium(III) with lacunary heteropolytungstates was first reported in 1979, [53] but the products, formulated as "[Rh(PW 11 5À with six different lacunary polytungstates were described. [54] Unfortunately this work did not exploit the development and use of techniques such as 183 W NMR spectroscopy and relied predominantly upon elemental analyses, electronic spectroscopy, and titrimetry.…”

“…[26c] Absorption of carbon monoxide by a material described as "K 5 [SiW 11 RhO 39 ]/Al 2 O 3 " (possibly containing the aqua deriv-ative, but otherwise uncharacterized) has been investigated by diffuse reflection infrared spectroscopy at temperatures up to 900 K. [55] High-yield syntheses of [PW 11 O 39 Rh III X] 5À (X = Cl, Br) have been achieved by hydrothermal reactions of the lacunary polytungstate with RhCl 3 in the presence of excess halide anion. [56] Salts of these complexes were characterized by elemental analysis, 31 confirmed by analytical ultracentrifugation and X-ray structure analysis of the potassium salt (Figure 6 d) 5À and dibenzyl under prolonged (5 h) photolysis at ambient temperature.…”

“…The electrophilic terminal oxo group undergoes attack by solvent water resulting in O-O coupling. [39] If the concentrations are increased in the hydrothermal reaction of [SiW 11 + from triphenylphosphine. [44] The comparative reactivity of several observed and hypothetical [XW 11 O 39 …”