Yingnan Chi

Lanthanide−Organic Cation Frameworks with Zeolite Gismondine Topology and Large Cavities from Intersected Channels Templated by Polyoxometalate Counterions

A family of organic-inorganic hybrid frameworks, {[Ln(H(2)O)(4)(pdc)](4)} [XMo(12)O(40)].2H(2)O (Ln = La, Ce, and Nd; X = Si and Ge; H(2)pdc = pyridine-2,6-dicarboxylate), have been prepared under hydrothermal conditions and characterized by single crystal X-ray diffraction analyses, elemental analyses, IR, and thermal gravimetric analyses. Single crystal X-ray diffraction reveals that all six compounds are isostructural, and each consists of a zeolite-like four-connected three-dimensional cationic framework {[Ln(H(2)O)(4)(pdc)](4)}(4+) and ball-shaped Keggin type [XMo(12)O(40)](4-) as templates. Interesting channels exist in the cationic framework with the gismondine topology, and these channels intersect each other to form large cavities, which array in a zigzag fashion and are occupied by nanosized [XMo(12)O(40)](4-) counterions. Moreover, these compounds display strong photoluminescent properties in the solid state at room temperature.

Structural variability of Cd(II) and Co(II) mixed-ligand coordination polymers: effect of ligand isomerism and metal-to-ligand ratio

A series of seven mixed-ligand coordination polymers, namely {[Cd4(H2L1)4(suc)4]·3H2O}n (1), {[Cd4(H2L1)3(suc)4]·5H2O}n (2), {[Cd2(HL1)2(suc)]·8H2O}n (3), {[Cd(H2L2)(suc)]·3H2O}n (4), {[Cd(H2L3)(suc)]·3H2O}n (5), {[Co(H2L1)(chdc)(H2O)]·H2O}n (6), {[Co(H2L2)(chdc)(H2O)]}n (7) have been produced by the reaction of three 2-amino-4,6-dipyridylpyrimidine isomers (H2L1, H2L2, H2L3) and secondary ligand 1,4-succinic acid (H2suc) or 1,4-cyclohexanedicarboxylic acid (H2chdc) with Cd(II) and Co(II) salts under hydrothermal conditions. All these compounds have been structurally determined by elemental analysis, IR and single-crystal X-ray diffraction. The three isomers are introduced in a mixed-ligand system for the first time. For the H2L1–H2suc–Cd(II) system, it is found that the structures of compounds 1–3 exhibiting a 1-D double-chain, a rare 1-D quadruple nano-chain and a 2-D network with (6,3) topology, respectively, are influenced by the ratio of metal-to-ligand. When H2L2 and H2L3 were used instead of H2L1, two 1-D chains (compounds 4 and 5) were obtained. Although they have the same molecular formula and structure motif, their supramolecular networks constructed by hydrogen-bondings and π–π stacking interactions are different. When H2L1 and H2L2 were introduced into the Co(NO3)2–H2chdc system, compounds 6 and 7 were successfully isolated, and display a zigzag chain and a helical chain, respectively. Interestingly, the cis- and trans-conformations of H2chdc were separated completely in the two compounds. The results reveal that both the coordination structure and the supramolecular assembly could be directed by the ligand isomers. Furthermore, several intriguing water clusters have been observed in these mixed-ligand compounds, such as a novel (H2O)10cluster in 2, a 2-D water net formed by (H2O)8clusters in 3, a 1-D undulated water chain in 4 and a chair-shaped (H2O)6cluster in 5. The solid-state properties of compounds 1–7 such as thermal stability and fluorescence have also been investigated.

pH-Dependent syntheses of copper–quinoxaline–polyoxotungatate hybrids: variable role of Keggin-type polyanion in different pH conditions

Four new hybrids based on the Keggin-type polyoxometalate, formulated as (Hbm)3(PW12O40)·4H2O (1) (bm = benzimidazole, which is synthesized in situ by quinoxaline), [Cu6(qx)9(PW12O40)2] (2), [Cu3(qx)5(PW12O40)(H2O)] (3) and [Cu4(qx)4(HPCuIIW11O39)]·1.5H2O (4) (qx = quinoxaline), were hydrothermally synthesized and structurally characterized by routine techniques and single-crystal X-ray diffraction. In 1, the [PW12O40]3− (PW12) clusters only act as counteranions and combine with the protonated organic ligand by electrostatic interactions. In 2, a 63 topological 2D layer is formed with the PW12 as the template. In 3, the PW12 anions link with four metal–organic chains via Cu–O weak interactions to construct a 3D framework. In 4, the Cu(II)-substituted Keggin unit as a hexadentate inorganic ligand coordinates with four Cu(I) ions from metal–organic chains and two O atoms from neighboring POMs to form a sandwich-like 2D layer. The structure difference of compounds 1–4 reveals that the self-assembly process is pH-dependent and the Keggin-type POM plays different role in different pH conditions.

Three New Imidazole-Functionalized Hexanuclear Oxidovanadium Clusters with Exceptional Catalytic Oxidation Properties for Alcohols

Cluster cat: Three new imidazole-functionalized neutral hexanuclear vanadium clusters have been prepared, one of which shows exceptional catalytic activity in the selective aerobic oxidation of alcohols (see scheme). Furthermore, these new polyoxovanadium clusters can be readily recycled and reused with unchanged catalytic activity. A plausible catalytic cycle is also proposed.

Cation-Induced Synthesis of New Polyoxopalladates

Seven polyoxopalladate compounds, [Pd(15)(SeO(3))(10)(μ(3)-O)(10)](10-), with Na(+) (1) and K(+) (2) as counterions, and Na(6)[M(II){Pd(12)(SeO(3))(8)(μ(4)-O)(8)}]·nH(2)O (M = Co (3), Zn (4), Ni (5), Cu (6), Mn (7); n = 7-9), have been prepared and characterized by SXRD, FT-IR, UV-vis, EA, TGA, and ESI-MS. These compounds comprise two distinct cluster configurations, {Pd(15)} and {M(II)Pd(12)}, which reveals the possibility of obtaining desired noble metal clusters with a certain nuclearity by using different cations as potential structural directing or template agents in synthesis. All compounds showed apparent absorptions in the visible light region, while 3 and 7 were found to show paramagnetic behavior typical of mononuclear Co(II) and Mn(II) complexes with zero-field splitting.

Self-assembly of polyoxometalates, Pt nanoparticles and metal–organic frameworks into a hybrid material for synergistic hydrogen evolution

A polyoxometalate (POM), Pt nanoparticles (NPs) and a metal–organic framework (MOF, NH2-MIL-53) self-assemble into a hybrid material, PNPMOF, that displays synergistic activity for visible-light-driven catalytic hydrogen evolution (the PNPMOF is far more active than any of the three functional components alone). The POM has four targeted functions in this hybrid material: it reduces H2PtCl6 to Pt NPs, stabilizes the Pt NPs, induces a strong electrostatic association of the negatively charged Pt NPs with the protonated NH2-MIL-53 sites on the particle surfaces, and facilitates the catalytic reduction reaction itself. The NH2-MIL-53 in this work protects the light sensitive 2-aminoterephthalate groups in the pores from oxidation by the POMs, while the surface protonated NH2 units on the MOF particle surfaces strongly bind the negatively charged POM-stabilized Pt NPs.

[{Ni4 (OH)3 AsO4 }4 (B-α-PW9 O34 )4 ](28-) : A New Polyoxometalate Structural Family with Catalytic Hydrogen Evolution Activity.

A new structural polyoxometalate motif, [{Ni4 (OH)3 AsO4 }4 (B-α-PW9 O34 )4 ](28-) , which contains the highest nuclearity structurally characterized multi-nickel-containing polyanion to date, has been synthesized and characterized by single-crystal X-ray diffraction, temperature-dependent magnetism and several other techniques. The unique central {Ni16 (OH)12 O4 (AsO4 )4 } core shows dominant ferromagnetic exchange interactions, with maximum χm T of 69.21 cm(3)  K mol(-1) at 3.4 K. Significantly, this structurally unprecedented complex is an efficient, water-compatible, noble-metal-free catalyst for H2 production upon visible light irradiation (photosensitizer=[Ir(ppy)2 (dtbbpy)][PF6 ]; sacrificial electron donor=triethylamine or triethanolamine). The highest turnover number of approximately 580, corresponding to a best quantum yield of approximately 4.07 %, is achieved when using triethylamine as electron donor in the presence of water. The mechanism of this photodriven process has been probed by time-solved luminescence and by static emission quenching.

Symmetry breaking of α-[H2W12O40](6-) depends on the transformation of isopolyoxotungstates.

Two enantiotopic 1D chain compounds, [Cu3(L1)3(H2O)2(H2W12O40)]·4H2O (1a,b; L1 = 2-(4,6-bis(pyridin-2-yl)pyridin-2-yl)pyridine), crystallizing in the chiral space group P212121 were prepared and spontaneously resolved in the absence of any chiral source. Interestingly, compounds 1a,b can be prepared from a [W7O24](6-) aqueous solution, [(n-C4H9)4N]4[W10O32], or Na10[H2W12O42], but when [H2W12O40](6-) aqueous solution was the starting material, the achiral compound [CuL1]2[H4W12O40]·5H2O (2) was obtained. When a terpyridine ligand (L2) having a coordination mode similar to that of L1 was used, the mesomeric dimer [Cu3(L2)3(H2O)(H2W12O40)]2·4H2O (3) was obtained from [W7O24](6-) aqueous solution or Na10[H2W12O42], but from [H2W12O40](6-) aqueous solution only compound [Cu2(L2)2Cl2]2[W10O32] (4) was isolated. It is notable that in compounds 1a,b and 3 the symmetry of the α-[H2W12O40](6-) cluster is broken by asymmetric coordination with metal-organic units in a similar mode. As the asymmetric subunit based on a tridecorated [H2W12O40](6-) cluster can be obtained from several isopolyoxotungstate sources except for [H2W12O40](6-), we speculate that the symmetry breaking of α-[H2W12O40](6-) depends on the transformation of isopolyoxotungstates. Furthermore, during the transformation a possible reaction intermediate as the precursor for 1a,b, compound [Cu3(L1)3(H2O)3(H4W11O38)] (5), has been presented and characterized by density functional theory (DFT) calculations.

Controlled solvothermal synthesis of novel organic functionalized polyoxovanadates

Four novel organic functionalized polyoxovanadates are solvothermally synthesized by altering the reaction temperature and using different organoarsonic acids. These POVs are fully characterized and the phase transitions between different POVs structures are confirmed by X-ray diffraction analyses. Such a transition is temperature-dependent and thus controlled synthesis of new POVs can be achieved.

Controllable Assembly of Vanadium-Containing Polyoxoniobate-Based Three-Dimensional Organic–Inorganic Hybrid Compounds and Their Photocatalytic Properties

The controllable synthesis of two vanadium-containing polyoxoniobate-based three-dimensional organic-inorganic hybrid compounds, [Co(pn)2]4[HPNb10V(IV)2O40(V(IV)O)4]·17H2O (1) and [Co(pn)2]5[PNb12O40(V(IV)O)6](OH)7·15H2O (2), where pn = 1,2-diaminopropane, is realized by changing the hydrothermal temperature or adding N-(aminoethyl)piperazine as an additive. Both compounds 1 and 2 are structurally characterized by single-crystal/powder X-ray diffraction and IR and X-ray photoelectron spectroscopy. Compound 1 features a new divanadium-substituted Keggin polyoxoniobate capped by four vanadyl groups, and the polyanion in 2 exhibits the highest coordination number (10-connected) in polyoxoniobate chemistry. Moreover, the photocatalytic activities of 1 and 2 for hydrogen evolution are preliminarily assessed.