Guanggang Gao

CO2 Coordination by Inorganic Polyoxoanion in Water

Two inorganic polyoxoanions react with carbon dioxide in aqueous solution to yield two polymeric chainlike complexes, where an activated CO2 molecule covalently bonds to polyoxoanions in a linear mu-eta1,eta1-OCO style. For the first time, the CO2 coordination is realized by an economic and environmentally friendly approach.

Copper-complex-linked polytungsto-bismuthate (-antimonite) chain containing sandwich Cu(II) ions partially modified with imidazole ligand.

Two sandwich-type complexes Na9n(Cu(im)4(H2O)2)1.5n(Cu(im)4(H2O))n[{Cu(im)4}{Na(H2O)2}3{Cu3(im)2(H2O)}(XW9O33)2]2n .(xH2O)n (im=imidazole, X=Bi (1), Sb(2), x=42.5 (1), 40 (2)) have been synthesized and structurally characterized. Basic frameworks of 1 and 2 are built from sandwich-type [{Na(H2O) 2} 3{Cu3(im)2(H2O)}(XW9O33)2](9-) (X=Bi or Sb) anions and [Cu(im) 4](2+) cations. The Cu(2+) and Na(+) ions in the central belt are coordinated by alpha-[XW9O33](9-) units, im, and water molecules to form {CuO4(im)}, {CuO4(H2O)}, and {NaO4(H2O)2} groups in which Cu (2+) ions are partially modified with im ligands. These groups connect alternately forming a six-membered ring including six alpha-[XW9O 33](9-) units. Neighboring anions are further linked by [Cu(im) 4](2+) cations to display an unprecedented anionic chain, which is first observed in sandwich-type tungsto-bismuthate (-antimonite) system. Two kinds of isolated copper complexes and sodium ions are located as counterions, which cause three-dimensional packings of 1 and 2 to present interesting cage structures. The magnetic properties for 1 and 2 both indicate dominant antiferromagnetic interactions among trinuclear Cu(II) clusters.

Cobalt(II)/nickel(II)-centered Keggin-type heteropolymolybdates: syntheses, crystal structures, magnetic and electrochemical properties.

New Keggin-type cobalt(II)/nickel(II)-centered heteropolymolybdates, (C3H5N2)6[Co(II)Mo12O40]10H2O (1) and (NH4)3(C4H5N2O2)3[Ni(II)Mo12O40] (2), were isolated and characterized by IR, UV-vis, single-crystal X-ray diffraction, thermogravimetric, magnetic, as well as electrochemical analyses. The polyanion in the two compounds displays the well-known alpha-Keggin structure, which is composed of four Mo3O13 units formed by edge-sharing octahedra. Four Mo3O13 units connect each other by vertices, and the Co(2+) or Ni(2+) is located in the center. Magnetic measurements show that the central Co(2+) and Ni(2+) are in high spin states (with S = 3/2 and S = 1, respectively) exhibiting paramagnetic behaviors. Cyclic voltammetric experiments for 1 represent a quasi-reversible one-electron redox Co(3+)/Co(2+) couple and two four-electron reversible redox processes ascribed to Mo centers, while 2 only shows two four-electron redox processes attributed to Mo centers in pH = 0.5 H2SO4 solution.

New approach to the synthesis of an organopolymolybdate polymer in aqueous media by linkage of multicarboxylic ligands.

The reaction of molybdates with multicarboxylic ligands resulted in the crystalline materials of [Na 8(Mo (VI) 10O 32EDTA)(H 2O) 35] n ( 1) and (NH 4) 8 n [Mo (VI) 10O 32PDTA] n (H 2O) 30 n ( 2) (EDTA = 1,2-diaminoethanetetraacetate; PDTA = 1,3-diaminopropanetetraacetate). In the two compounds, decamolybdate clusters are covalently linked by multicarboxylic ligands to form unusual meso-helical chains. For the first time, the synthesis of an organopolyoxometalate polymer is realized in aqueous media, which opens a green chemical approach to the fabrication of polyoxometalate-based polymers. The photochromic properties of 1 in the poly(vinyl alcohol) film displayed reddish-brown coloration upon UV irradiation, providing a new coloration material for photochromic films.

The first ε-Keggin core of molybdogermanate in extended architectures of nickel(II) with N-donor ligands: syntheses, crystal structures and magnetic properties

By using both bipyridyl and acyclic amine ligands, two extended inorganic–organic hybrids based on e-Keggin type of molybdogermanate capped with four nickel(II)-organic cations, [GeMoV8MoVI4O36(µ2-OH)4{Ni(pda)(H2O)}2{Ni(pda)}{Ni(pda)(bpe)}(bpe)0.5]n (1) and [GeMoV8MoVI4O36(µ2-OH)4{Ni(pda)}2{Ni(pda)(bpy)0.5}{Ni(pda)(bpy)}]n · 7nH2O (2) (pda = 1,2-propanediamine, bpe = 1,2-bis(4-pyridine)-ethane, bpy = 4,4′-bipyridine), have been synthesized and structurally characterized, and their magnetic properties have also been investigated at temperatures of 2–300 K. These two compounds represent the first example of e-Keggin type molybdogermanate clusters employed as an effective building block to construct extended frameworks by the linkage of bidentate organic N-donor ligands, and the inorganic metal–oxygen clusters together with organic N-donor ligands form 1D chain and 2D layered structures.

Effects of film structure on electrochromic properties of the multilayer films containing polyoxometalates

Multilayer films of tungstophosphate anion (P(2)W(18)) and poly(allylamine hydrochloride) (PAH) were fabricated on quartz and ITO substrates by layer-by-layer self-assembly method. These films were characterized by UV-vis spectroscopy, cyclic voltammetry (CV), chronoamperometric (CA), chronocoulometry (CC) and atomic force microscopy (AFM). The effects of film structure on multilayer electrochromic properties were investigated. The electrochromic responses of the composite films were related to the surface coverage of anion and multilayer thickness. It was found that higher concentration of polycation and anion, or adding salt to the polycation solution used for multilayer film preparation led to thicker and denser film structure which improved optical contrast and coloration efficiency whereas prolonged response time.

Electrochromic ultra-thin films based on cerium polyoxometalate

Ultra-thin multilayer films consisting of polyoxotungsceriumate cluster K17[CeIII(P2W17O61)2]·30H2O [Ce(P2W17)2] and polyallylamine hydrochloride were fabricated on quartz and ITO substrates by a layer-by-layer self-assembly method. The multilayer films were characterized by UV-vis spectra, cyclic voltammetry (CV) and chronoamperometric (CA) measurement. Compared with other polyoxometalates, the electrochromic film exhibits suitable response times, low operation potentials, high optical contrast and thermal stability, which provide valuable information for exploring the possibility of application to polyoxometalate-based electrochromic materials.

New fabrication of lanthanide complexes based on the polyoxometalate ligand of the [α(1,4)-GeW10O38]12− anion

New-type two lanthanide complexes based on a germanotungstate ligand, Na12[Ln4(α(1,4)-GeW10O38)2 (H2O)6]·nH2O (Ln = Dy (1); Er (2)) which contain four trivalent lanthanide ions and two [α(1,4)-GeW10O38]12− units, have been synthesized and structurally characterised, and their magnetic properties have also been investigated. Each lanthanide ion resides in the vacant site of the [α(1,4)-GeW10O38]12− fragment through bonding to five oxygen atoms, four of which are from the WO6 octahedra, while the other one is from the central GeO4 tetrahedron group.

Electrochromic and pH-Sensitive Multilayer Films Based on Nickel-Substituted Dawson-Type Polyoxometalate

An ultrathin multilayer film consisting of polyoxometalate cluster a-K 8 [P 2 W 1 7 O 6 1 Ni 1 1 (H 2 O)].18H 2 O(P 2 W 1 7 Ni) and polyallylamine hydrochloride (PAH) was fabricated on quartz and indium tin oxide substrates by layer-by-layer self-assembly. The multilayer films, (P 2 W 1 7 Ni/PAH) n , were characterized by UV-visible spectra, cyclic voltammetry, chronoamperometry, atomic force microscopy, and in situ spectroelectrochemical measurements. The multilayer film exhibits both suitable response time and low operation potential due to the presence of nickel-substituted polyoxometalate, providing valuable information for exploring the possible application of polyoxometalate-based electrochromic materials. Further, P 2 W 1 7 Ni embedded in a self-assembled polyelectrolyte matrix can also be used as a pH sensor because of the pH dependence of its electrochemical response.

Polyoxometalate-based gasochromic silica

Materials capable of gasochromic behavior are still rare. In this paper, amorphous gasochromic hybrid silica material containing phosphomolybdic acid (PMo12) is prepared by the sol–gel technique. The structure and properties of the material are investigated by cyclic voltammetry, thermal gravimetric analysis, FT-IR spectra, X-ray diffraction, UV-Vis spectra and X-ray photoelectron spectra. The structural integrity of phosphomolybdic acid has been preserved after incorporation into the porous silica framework. Furthermore, the PMo12–SiO2 hybrid material shows sensing activity for H2S and SO2 gases at room temperature based on the color change.