Dolbecq Anne, Compain Jean-Daniel, Mialane Pierre, Marrot Jérôme, Sécheresse Francis, Keita Bineta, Holzle Luis Roberto Brudna, Miserque Frédéric, Nadjo Louis
Institut Lavoisier de Versailles, UMR 8180, Université de Versailles Saint-Quentin en Yvelines, 45 Avenue des Etats-Unis, 78035 Versailles cedex, France.
Chemistry. 2009;15(3):733-41. doi: 10.1002/chem.200800719.
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.
基于O(3)PCH(2)PO(3)(4-)配体和{Mo(V)(2)O(4)}二聚单元的两种新化合物已被合成并进行了结构表征。(NH(4))(18)[(Mo(V)(2)O(4))(6)(OH)(6)(O(3)PCH(2)PO(3))(6)] x 33 H(2)O (1)中的十二核钼(V)多金属氧酸盐物种是一个具有假S(6)对称性的椅式构象的环己烷样环。在固态中，这些环并排排列，从而界定出大的矩形空隙。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)中的六核阴离子具有三角形框架并包封了一个甲基砷酸根配体。(31)P NMR光谱分析表明2在各种水性介质中具有稳定性，而1的稳定性取决于溶液中存在的阳离子的性质。已证明在CH(3)AsO(3)(2-)离子存在下1会转化为2。这种行为表明1可作为合成Mo(V)/二膦酸盐体系的新前体。这两种配合物作为Pt和Pd金属盐的还原剂以及所得Pt(0)和Pd(0)纳米颗粒的封端剂都非常有效。所获得的纳米颗粒的尺寸既取决于多金属氧酸盐（POM；即1或2）的性质，也取决于[金属盐]/[POM]的比例。在所有情况下，X射线光电子能谱(XPS)测量都揭示了稳定纳米颗粒的Mo(VI)物种的存在以及Mo(V)部分的不存在。Pt纳米颗粒的漫反射FTIR光谱表明两种体系的封端Mo(VI) POM相同且包含二膦酸根配体。胶体溶液没有显示出任何沉淀，并且纳米颗粒在几个月内保持良好分散。对2研究了Mo(V)物种的电化学还原。单独的循环伏安法以及与循环伏安法联用的电化学石英晶体微天平表明在此还原过程中电极表面有薄膜沉积。
