Meilin Wei

Three porous coordination polymers of Co2+ and dpdo ligands with channels hosting polyanion chains

Three porous coordination polymers, {[Co(dpdo)4(H2O)2][H(H2O)6](PMo12O40)} n (1), {[Co(dpdo)4(H2O)2][H3O(CH3OH)4](PMo12O40)} n (2) and {[Co(dpdo)4(H2O)2][K(CH3OH)4](PMo12O40)} n (3) (where dpdo is 4,4′-bipyridine-N,N′-dioxide), with special channels for the chain-like assembly of polymeric Keggin-type anions have been synthesized through self-assembly of Co2+ and dpdo ligands in acetonitrile/water or methanol/water solutions and characterized by single crystal X-ray diffraction. Based on layers constructed by [Co(dpdo)4(H2O)2]2 + and different bridging units for charge compensation between layers, the three compounds exhibit similar noninterwoven networks with large channels occupied by the poly-Keggin-anion chains. Thermogravimetric analyses suggest that the three supramolecular networks have different thermal stabilities based on different cationic bridging units.

Crystal structures and proton conductivities of two molecular hybrids based on decorated poly-Keggin-anion chains

Two proton-conductive molecular hybrid complexes, {[H(H2O)2][Sr(HINO)4(H2O)7(PW12O40)]} n (1) and {[H(H2O)2][Ca(HINO)4(H2O)5(PW12O40)]} n (2), were constructed by introducing alkaline-earth metal ions and [PW12O40]3– anions in the gallery of H-bonding networks based on isonicotinic acid N-oxide (HINO). Single-crystal X-ray diffraction analyses at 293 K reveal that both complexes crystallized in the orthorhombic space group Pnnm, and presented the same 3-D hydrogen-bonded networks with large 1-D channels. Interestingly, HINOs not only constructed 1-D hydrogen-bonded chains, but also coordinated to alkaline-earth metal ions to form decorated poly-Keggin-anions. In addition, decorated poly-Keggin-anion chains are also formed in the 1-D channels. Thermogravimetric analyses show no weight loss in the temperature range 20–70°C, indicating that all water molecules in the unit structure are not easily lost below 70°C. Surprisingly, the proton conductivities of 1 and 2 at 85–100°C under 98% relative humidity conditions reached good proton conductivities of 10−3 S cm−1.

Constructing porous lanthanide coordination polymers of 4,4′-bipyridine- N , N ′-dioxide templated by single- and double-Keggin anions

Three porous coordination polymers, {[Nd(dpdo)2(H2O)5(CH3OH)2](PMo12O40)(CH3OH)-(H2O)5} n (1), {[Tb(dpdo)4(H2O)3](PMo12O40)(H2O)2CH3CN} n (2) and {[Tb(dpdo)4(H2O)3]H(SiMo12O40)(dpdo)0.5(CH3CN)0.5(H2O)4} n (3) (where dpdo is 4,4′-bipyridine-N,N′-dioxide), templated by single- or double-Keggin polyanions were synthesized and characterized by single crystal X-ray diffraction. The compounds exhibit three different 3D non-interwoven frameworks with large cavities occupied by the single- or double-Keggin-type anions. Thermogravimetric analyses suggest different stability for the three metal-organic frameworks. The SHG (second harmonic generation) efficiency of 1 confirms its noncentric framework.

A porous Cu(II)-MOF containing [PW12O40]3− and a large protonated water cluster: synthesis, structure, and proton conductivity

A proton-conducting metal–organic framework (MOF), {[Cu4(dpdo)12][H(H2O)27(CH3CN)12][PW12O40]3}n (where dpdo is 4,4′-bipyridine-N,N′-dioxide) (1), was synthesized by the reaction of CuHPW12O40·nH2O and dpdo at room temperature. Single-crystal X-ray diffraction analysis at 293 K revealed that 1 crystallized in the cubic space group Im-3 and presented a non-interwoven 3-D framework with cubic cavities and guest molecules. A large ionic water cluster H+(H2O)27, consisting of a water shell (H2O)26 and an encaged H+(H2O) as a center core, was trapped in the cubic cavity of the MOF {[Cu4(dpdo)12(PW12O40)3]−}∞. Thermogravimetric analysis suggests that 1 has high thermal stability, indicating that such a non-interwoven 3-D framework with cubic cavities is a suitable host for researching protonated water clusters. Its water vapor adsorption isotherm at room temperature and pressure shows that the water vapor adsorbed in it was 65.1 cm3 g−1 at the maximum allowable humidity. It exhibits good proton conductivities of 10−5–10−4 S cm−1 at 100 °C in the relative humidity range 35–98%. Graphical Abstract

An ion crystal based on silver double helicates and Keggin polyanions

An ion crystal [Ag2L2][(n-C4H9)4N][PMo12O40] · H2O · 0.5CH3OH · 0.25 DMF (I) (DMF is N,N-dimethylformamide) has been synthesized by the complexation of metal double helix and Keggin polyanions in a DMF-CH3 OH solution and structurally characterized by elemental analysis, IR spectra, and single-crystal X-ray diffraction. In compound I [PMo12O40]3− anions and [(n-C4H9)4N]+ ions alternately arrange themselves in a special order in consistence with that of [Ag2L2]2+ metal helicates based on π-π stacking interactions, yielding a packing of complex cations and Keggin anions.

A complex based on a decorated Keggin-type cluster from Cu(II) and 4,4′-dimethyl-2,2′-bipyridine: synthesis, structure and proton conductivity

Abstract A proton-conductive complex based on decorated Keggin-type cluster, {[Cu(dmbipy)(H2O)3]2[SiW12O40]}·7H2O (where dmbipy is 4,4′-dimethyl-2,2′-bipyridine) (1), was synthesized by reaction of CuSiW12O40·nH2O and dmbipy at room temperature. The product was characterized by elemental analysis, infrared spectroscopy, and single-crystal X-ray diffraction analysis. Single-crystal X-ray diffraction analysis at 293 K revealed that 1 crystallized in the monoclinic space group C2/c and has a 3-D supramolecular network with 1-D hydrophilic channels constructed by a decorated Keggin-type cluster, [Cu(dmbipy)(H2O)3]2SiW12O40, and solvent water molecules via hydrogen-bonding interactions. Thermogravimetric analysis suggests that 1 has high-thermal stability and good water binding in 1-D hydrophilic channels from 20 to 100 °C. Compound 1 exhibits good proton conductivities (over 10−3 S cm−1) at 100 °C in the relative humidity range 35–98%.

Two new supramolecular compounds based on Ni(II)-Schiff-base and Keggin-type [PMo12O40]3−

Two polyoxometalate-templated nickel-Schiff-base compounds, {[Ni(L)2]2[PMo12O40][Cl] · 1.5DMF · H2O} n (1) and {[Ni(L)2]2[PMo12O40][Cl] · DMSO · CH3OH · 0.5H2O} n (2) (where L is 1,4-bis(4-imidazolyl)-2,3-diaza-1,3-butadiene), were synthesized in situ from Ni2+ and L in H2O/DMF/CH3OH or H2O/DMSO/CH3OH at room temperature and characterized by elemental analysis, infrared spectroscopy, and single-crystal X-ray diffraction analysis. The results of the single-crystal X-ray diffractions suggested that both compounds have the same packing of the Ni(II)-Schiff-base cation layer and Keggin anion layer. Thermogravimetric analyses suggested that two supramolecular compounds have similar thermal stabilities based on the same packing of the cation and anion layers.

A sandwich-type POM containing mixed cations: synthesis, thermal performance and proton-conducting properties

Abstract A new sandwich-type polyoxometalate, Na5H[N(CH3)4]2[Co(C3N2H4)2(H2O)4][Co4(H2O)2(PW9O34)2]·21H2O (1), has been synthesized. 1 is composed of a Weakley-type polyanion, [Co4(H2O)2(PW9O34)2]10−, four kinds of cations (five Na+, two [N(CH3)4]+, one [Co(C3N2H4)2(H2O)4]2+, and one H+), and 21 crystalline H2O molecules. The surface oxygen of the polyanion in 1, the crystalline water, and coordinated water molecules make an extended 3-D hydrogen-bonding network. Alternating current (AC) impedance experiments of 1 reveal good proton conductivity for 1 of 5.03 × 10− 4 S cm−1 at 25 °C under 98% relative humidity (RH). Activation energy of 1 calculated from Arrhenius plots is 0.358 eV, indicating Grotthuss mechanism is dominant in the proton transfer. Thermal decomposition behavior of 1 was examined by thermogravimetry/mass spectrometry (TG/MS) measurements.

Crystal structures and properties of two Cu(I) complexes based on Keggin-type clusters and diethyl 4,4′-dicarboxy-2,2′-biquinoline acid

Abstract Two proton-conductive Cu(I) complexes based on Keggin-type clusters, [Cu(debqdc)2]2[HPW12O40]·4H2O (1), and [Cu(debqdc)2]2[HPW12O40]·debqdc·4H2O (2), where debqdc is diethyl 4,4′-dicarboxy-2,2′-biquinoline, were simply synthesized at room temperature. The products were structurally characterized by elemental analyses, infrared spectroscopy, and single-crystal X-ray diffraction analyses. Single-crystal X-ray diffraction analyses revealed that both complexes crystallized in the triclinic space group P−1 and presented two three-dimensional supramolecular networks with one-dimensional hydrophilic channels via hydrogen-bonding interactions and π–π stacking interactions between the aromatic rings. In the [Cu(debqdc)2]+ ion, debqdc acts as a bidentate nitrogen donor ligand in the chelating fashion. The bulky debqdc ligand constrains the Cu(I) metal center within such a rigid environment in a tetrahedral geometry. The two complexes exhibit good proton conductivities (10−5 ~ 10−4 S cm−1) at 100 °C in the relative humidity range 35 ~ 98%. The luminescence behaviors of these complexes in the solid state at room temperature have also been investigated. Upon excitation at 285 nm, both 1 and 2 display three main emission peaks centered at 470, 520, and 568 nm, respectively.