Hydrothermal Synthesis and Crystal Structure of a Novel Polymolybdic(VI) Acid: {[H_3O]_2^+[Mo_2O_4(OH)_6]^(2-)}_n

A novel supramolecular polymolybdic（VI） acid was unexpectedly synthesized by the reaction of sodium molybdate with 1,2,4,5-benzenetetracarboxylic and trichloroacetic acids in 1：1：1 molar ratio under hydrothermal condition. The crystal belongs to tetragonal with space group P4/mbm, a = 0.88867（17）, b = 0.88867（17）, c = 0.55676（15） nm, Z = 3, V = 0.43969（17） nm^3, Dc = 4.486 g/cm^3,μ = 4.365 mm^-1, F（000） = 576, R = 0.0273 and wR = 0.0679. In the crystal, the Mo（VI） atoms are six- and five-coordinated in distorted octahedral and trigonal bipyramidal geometries, respectively. Furthermore, these Mo（VI） atoms, bearing different coordinated environments, are bridged by OH groups with disorder O atoms to form a twodimensional framework with pentagonal grids. It is worthy of notice that these adjacent twodimensional frameworks are extended into a three-dimensional supramolecular array with pentagonal large cavities＇by Van Der Waals＇ forces and hydrogen bonding interactions.

Studies on Organo-Phosphorus, -Arsenic and -Antimony Polytungstates and Polymolybdates(IX )——Preparation and Properties of o-Aminophenylarsenic Polymolybdates

In order to investigate the influence of organic groups on the types of organoarsenic polymolybdates, o-nitrophenylarsonic acid was reduced to o- aminophenylarsonic acid and then it reacted with sodium molybdate at pH = 3;. Three new salts were prepared and characterized:（ 1 ） （CN3H6）4[（o-NH2C6H4As）2Mo6O24], （ 2 ） Cs4[（o-NH2C6H4As）2Mo6O24], （3） [（CH3）4N]4[（o-NH2C6H4As）2Mo6O24].2H2O. The IR, UV spectra, thermal properties and electrochemical behaviors are reported. It is strange enough that when the o-nitro group was reduced to o-amino group, [（RAs）2Mo6O24]4- type of complexes was formed.

Studies on Organo-Phosphorus, -Arsenic and -Antimony Polytungstates and Polymolybdates (Ⅶ)——Preparation and Properties of p-Aminophenylarsenic Polymolybdates

In order to investigate the influence of organic groups on the types of organoarsenic polymolybdates, the reations of p-aminophenylarsonic acid with sodium molybdate were tested at pH=3-5. Six salts were prepared and characterized. (1) (CN3H8)4 [(p-NH3C6H4As)2Mo6O25] · H2O, (2) (CN3H6)4 [(p-, NH3C6H4As )2Mo6O25 ] · 6H20, (3) Cs4 [(p-NH3C6H4As)2Mo6O25] · 4H2O, (4) C(CH3)4N]4[(p-NH3C6H4As)2Mo6O25] · 5H2O, (5) [(n-C4H9)4N]3Na[(p-NH3C6H4As)2Mo6O25] · 2H2O, (6) Ba2 NH3C6H4As)2Mo6O25] · 10H2O. The IR, UV spectra, and electrochemical behavior are reported and discussed. They should belong to the same type as that for phenyl derivative or the nitrophenyl derivatives. But the ammo groups can accept protons, so that the anion' s charge decreases. Very similar to the tungsten congener (CN3H6)4[(p-NH3C,H4As)2W6O25] · 4H2O, [(RAs)2Mo6O25]4- type of complexes are formed.

Synthesis and Crystal Structure of an Inorganic-organic Hybrid Compound Containing a New Polymolybdate Cluster {Mo(12)}

A new low-nuclear polymolybdate cluster [Cu_4~Ⅱ（opr）_2（Mo_（12）O_（40））]_n·2n H_2 O was successfully isolated by the introduction of flexible multidentate 1,1A-（1,3-propanediyl）bis[2-（2-pyridyl）benzimidazole ligand（opr）,（NH_4）_6Mo_7O_（24）·4H_2O,and copper（Ⅱ） ions under hydrothermal conditions. Single-crystal X-ray analysis reveals that the complex crystallizes in the P2_1/n space group with a = 13.8437（5）,b =19.3953（6）,c =15.7681（6） A,β =112.698（4）o,V = 3905.9（2） A^3,Z = 4,D_c = 2.502 g/cm^3,μ = 3.020 mm^-1,F（000） = 2824,the final R = 0.0352,wR = 0.0523 and S = 0.783 for 7111 observed reflections with I 〉 2σ（I）. The structure of the compound contains a new type of low-nuclear（Mo_（12）O_（40））^8-polymolybdate cluster. These dodecamolybdate anions are linked together through sharing edges to form a 1D molybdenum oxide chain. Its photocatalytic performance for methylene blue（MB） was also studied under UV irradiation.

A strategy for highly dispersed Mo2C/MoN hybrid nitrogen- doped graphene via ion-exchange resin synthesis for efficient electrocatalytic hydrogen reduction

Molybdenum carbide/molybdenum nitride hybrid N-doped graphene （abbreviated as Mo2C/MoN/NG）, as an efficient electrocatalyst for the hydrogen evolution reaction （HER）, was synthesized via simple ion-exchange resin synthesis followed by a two-step annealing process, which increased the dispersion degree of the electrocatalyst＇s active sites on the support skeleton and simplified the synthetic conditions. Additionally, N-doped graphene （NG） enhanced the electron transfer and reduced the inner resistance. The material has a graphene-like morphology and highly dispersed Mo2C/MoN nanoparticles about 2 nm in diameter on the NG. X-ray photoelectron spectroscopy, X-ray diffraction, and high-resolution transmission electron microscopy revealed that Mo2C/MoN/NG consisted of Mo2C and MoN composited together. Finally, Mo2C/MoN/NG exhibited remarkable performance as an electrocatalyst for the HER with a small overpotential of 78.82 mV and a small Tafel slope of 39.3 mV.dec^-1 in a 0.5 mol.L-1 H2SO4 solution. Its activity was approximately 30% lower than that of 20% Pt/C and 60% higher than that of NG. Also, it exhibited a low onset overpotential of 24.82 mV, which is similar to the theoretical HER potential. Our work provides a foundation for advanced HER applications of molybdenum compounds.

Multicolor Photochromism of Polymolybdate-Citric Acid Composite Films

Photochromic polymolybdate-citric acid composite films were fabricated. It was found that after UV irradiation the composite films with different molar ratios of organic/inorganic components exhibited different colors. The UV-irradiated films showed dark blue, dark khaki and light sea green colors when the ratios were 1.0, 0.3 and 0.2, respectively. It was identified by Raman spectra that the polymolybdate species formed in the composite films after UV irradiation were sensitive to the ratios of the organic/inorganic components, thus resulting in the different colors of irradiated films. Citric acid played an important role during the photochromic process. Under UV light irradiation, it served as hole scavenger that suppresses the recombination of photogenerated electrons and holes to make the polymolybdates show UV light photochromism.

Studies on organo-phosphorus,-arsenic,and-antimony polytungstates and polymolybdates Ⅴ.Syntheses and structures of benzylarsonic polymolybdates

In order to investigate the influence of organic groups on the structural types of organoa- rsenic polymolybdates,benzylarsonic acid has been selected to react with sodium molybdate.Three new complexes have been synthesized and characterized:[C(NH_2)_3]_4 [(C_6H_5CH_2As)_2Mo_6O_(24)](1), Cs_4[(C_6H_5CH_2As)_2Mo_6O_(24)]·5H_2O(2)and[(n-C_4H_9)_4N]_3Na[(C_6H_5CH_2As)_2Mo_6O_(24)].6H_2O(3).Molecular structure of compound 1 has been determined by means of single-crystal X-ray diffraction studies.It is monoclinic,space group P2_1/n with cell dimensions of a=12.342(2),b=18.621(2),c=10.042(2), β=105.80(1)°,V=2220.5~3,z=2,μ=15.854cm^(-1),R=0.023.It is demonstrated that the structural types of benzylarsonic polymolybdates are the same as those for alkylarsonic polymolybdates but different from those for arylarsonic polymolybdates.Their elemental analyses,IR and UV spectra and electrochemical behaviors in aqueous solution have been reported.It is suggested that the arsenic- carbon bond has great influence on the structural types of organoarsenic polymolybdates.

Studies on organo-phosphorus, -arsenic and -antimony polytungstates and polymolybdates——II. Degradation method for preparing arylarsenic polytungstates

Six guanidinium salts of arylarsenic po1ytungstates have been prepared by the 'degradation method' using sodium metatungstate as a starting material instead of sodium tungstate, They belong to three types of complexes: [(RAs)_2W_6O_(25)H]^(5-) where R=C_6H_5(1),o-NO_2C_6H_4(2),m-NO_2C_6H_4(3), p-NO_2C_6H_4(4),[(RAs)_2W_6O_(25)]^(4-) where R=p-NH_2C_6H_4(5), and[(RAs)_2W_6O(25)]^(6-)where R=3,4,-C_6H_3 (NO_2)(OH)(6). Complex 1 is a known compound, prepared by the acidification building up method, i.e. conversion of sodium tungstate to polytungstate. Complex 1 and 6 prepared by the degradation method, i.e. from sodium metatungstate to lower polytungstate, are briefly reported in our previous re- port of this investigation. Complexes 2-5 are new compounds. Molecular structures of complexes 5 and 6 have been determined by means of single-crystal X-ray diffraction studies. It is especially em- phasized that the degradation method starting with metatungstate has the advantage in the simplification of reaction products. thus leading to their higher yields.