Hexa‐ and Dodecanuclear Polyoxomolybdate Cyclic Compounds: Application toward the Facile Synthesis of Nanoparticles and Film Electrodeposition

Abstract

Two new compounds based on O(3)PCH(2)PO(3)(4-) ligands and {Mo(V)(2)O(4)} dimeric units have been synthesized and structurally characterized. The dodecanuclear Mo(V) polyoxomolybdate species in (NH(4))(18)[(Mo(V)(2)O(4))(6)(OH)(6)(O(3)PCH(2)PO(3))(6)] x 33 H(2)O (1) is a cyclohexane-like ring in a chair conformation with pseudo S(6) symmetry. In the solid state, the wheels align side by side, thus delimiting large rectangular voids. The hexanuclear anion in Na(8)[(Mo(V)(2)O(4))(3)(O(3)PCH(2)PO(3))(3)(CH(3)AsO(3))] x 19 H(2)O (2) has a triangular framework and encapsulates a methylarsenato ligand. (31)P NMR spectroscopic analysis revealed the stability of 2 in various aqueous media, whereas the stability of 1 depends on the nature of the cations present in solution. It has been evidenced that the transformation of 1 into 2 occurs in the presence of CH(3)AsO(3)(2-) ions. This behavior shows that 1 can be used as a new precursor for the synthesis of Mo(V)/diphosphonate systems. The two complexes were very efficient both as reductants of Pt and Pd metallic salts and as capping agents for the resulting Pt(0) and Pd(0) nanoparticles. The size of the obtained nanoparticles depends both on the nature of the polyoxometalate (POM; i.e., 1 or 2) and on the [metallic salt]/[POM] ratio. In all cases, X-ray photoelectron spectroscopy (XPS) measurements have revealed the presence of Mo(VI) species that stabilize the nanoparticles and the absence of Mo(V) moieties. Diffuse-reflectance FTIR spectra of the Pt nanoparticles show that the capping Mo(VI) POMs are identical for both systems and contain the diphosphonato ligand. The colloidal solutions do not show any precipitate and the nanoparticles remain well-dispersed for several months. The electrochemical reduction of Mo(V) species was studied for 2. Cyclic voltammetry alone and electrochemical quartz crystal microbalance coupled with cyclic voltammetry show the deposition of a film on the electrode surface during this reduction.

Chemoselective Hydrogenation of Cinnamaldehyde over Pd/CeO2–ZrO2 Catalysts

“…and Pd 4? states are 335 and 340.6, 337.5 and 342.9, and 338.4 and 343.5 eV, respectively corresponding to the 3d 5/2-3/2 spin-orbit doublet [33][34][35][36]. The binding energy of Zr 3p also falls in the same range.…”

Molybdenum Complexes Bearing the Tris(1‐pyrazolyl)methanesulfonate Ligand: Synthesis, Characterization and Electrochemical Behaviour

“…The data revealed the tetraoxo 2+ bridging structure found in many compounds. [44,[45][46][47][48] The anionic Tpms group acts as a tridentate N,N,O ligand. The basal positions in each octahedron are occupied by the N11 and N14 atoms and the bridging O2 oxygen atoms and the two distorted octahedra share the common O2-O2 i edge; the apical positions are taken up by the oxido O1 and O12 atoms from the sulfonate group.…”

Characterization of tetra, dodeca and tetradeca MoV polyoxometalate wheels structured by etidronate ligands

“…Moreover, such nanosystems are obtained in a one-pot procedure, in water, at room temperature and without any additional surfactant. For example, by simply mixing the cyclohexanelike dodecanuclear compound mentioned above and Pd II cations in aqueous solution, NPs with diameter of 9-14 nm containing a Pd 0 core and capped by POMs are obtained [6]. Additionally, it has also been shown that Ag 0 [9] and Pt 0 [10] POM capped NPs can be obtained using this procedure.…”

“…A larger complex, a dodecanuclear wheel which adopts a cyclohexane-like ring in a chair conformation has been obtained in absence of any additional coordinating groups. Nevertheless, the presence of ammonium cations in the reacting medium is crucial for the obtaining of this species, highlighting the importance of the nature of the counterions on the resulting POM [6]. In addition to these cyclic systems, bicyclic compounds have also been obtained.…”

“…Focusing on polyoxomolybdate systems where all the molybdenum centers are reduced in their V oxidation state, a large number of species have been isolated both in organic or aqueous media. In all cases, these polyanions contain the dinuclear dicationic [ 8À has been obtained in presence of methyl arsenate, [6] while ellipsoidal octanuclear clusters have been isolated when the synthetic process is performed in presence of sulfite or carbonate [7]. A larger complex, a dodecanuclear wheel which adopts a cyclohexane-like ring in a chair conformation has been obtained in absence of any additional coordinating groups.…”