Highly Selective CO2 Electroreduction to CH4 by In†Situ Generated Cu2 O Single-Type Sites on a Conductive MOF: Stabilizing Key Intermediates with Hydrogen Bonding.

It is still a great challenge to achieve high selectivity of CH4 in CO2 electroreduction reactions (CO2 RR) because of the similar reduction potentials of possible products and the sluggish kinetics for CO2 activation. Stabilizing key reaction intermediates by single type of active sites supported on porous conductive material is crucial to achieve high selectivity for single product such as CH4 . Here, Cu2 O(111) quantum dots with an average size of 3.5 nm are in situ synthesized on a porous conductive copper-based metal-organic framework (CuHHTP), exhibiting high selectivity of 73 % towards CH4 with partial current density of 10.8 mA cm-2 at -1.4 V vs. RHE (reversible hydrogen electrode) in CO2 RR. Operando infrared spectroscopy and DFT calculations reveal that the key intermediates (such as *CH2 O and *OCH3 ) involved in the pathway of CH4 formation are stabilized by the single active Cu2 O(111) and hydrogen bonding, thus generating CH4 instead of CO.

Mg2+ incorporated Co-based MOF precursors for hierarchical CNT-containing porous carbons with ORR activity.

In this paper, we introduced light and abundant metal magnesium into a cobalt-based metal organic framework (Co-MOF, [(CH3)2NH2]2[Co3(bpdc)4]·5DMF·4CH3OH) (1, H2bpdc = 4,4'-biphenyldicarboxylic acid, DMF = N,N-dimethylformamide) as a heteroatom to synthesize Mg-Co bimetallic MOFs, namely [(CH3)2NH2]2[MgCo2(bpdc)4]·4DMF·5CH3OH (2) and [(CH3)2NH2]2[Mg1.2Co1.8(bpdc)4] 4DMF·4CH3OH·6H2O (3). Based on the formation of a rather low density framework after the introduction of the light Mg2+, such bimetallic MOFs exhibited higher gas adsorption abilities than the isostructural Co-based MOF 1. N2 adsorption measurements demonstrate that the BET surface area of 3 is 305.4 m2 g-1, exhibiting three times that of 1 (104.4 m2 g-1). Significantly, due to the introduction of the low-melting Mg2+, the Mg-Co MOFs could be further utilized as precursors for porous carbons only by calcination at a mild temperature of 600 °C which could exhibit a BET surface as high as 712.78 m2 g-1. Furthermore, after post-synthetic modification with a N/S heteroatom at 900 °C, the obtained hierarchical carbons exhibit superior activity in the oxygen reduction reaction (ORR) that is comparative to the commercial Pt/C catalyst. TEM results indicate that Co-embedded carbon nanotube (CNT)-containing hierarchically nanoporous carbons have been obtained. This study may offer a new avenue to prepare porous carbons utilizing Mg-containing bimetallic MOFs as sacrificial templates.

Fine decoration of carbon nanotubes with metal organic frameworks for enhanced performance in supercapacitance and oxygen reduction reaction.

Efficient electrode material is crucial for energy conversion from renewable sources such as solar electricity. We present a method for preparation of carbon nanotubes (CNTs) with zeolitic imidazolate frameworks (ZIFs, e.g., ZIF-8) via an in situ pyrolysis process. The resultant materials are completely new carbon composites with desirable hierarchical porosity and nitrogen-doped features. Electron microscopy images show that CNTs with small external diameters enable more uniform dispersion of ZIF-8-derived carbons, subsequently yielding a unique hierarchically porous structure. Such carbon shows superior activity in oxygen reduction reaction (ORR) and high performance of supercapacitance, making it a valuable metal-free electrode material and a competent alternative to the state-of-the-art Pt/C catalyst. The electrocatalytic performance of CNTs can be dramatically improved by the incorporation of ZIF-8-derived carbons, which is attributed to the combination of good conductivity, abundant accessible dopant species, as well as proper porosity. Our method offers a new avenue for constructing electrocatalysts by effective integration of ZIF-8-derived carbon and the CNTs skeleton.

Dual-Emission Luminescence of Magnesium Coordination Polymers Based on Mixed Organic Ligands.

Presented herein are two luminescent magnesium coordination polymers (Mg-CPs), namely [Mg2 (H2O)2 (2-NDC)4 (1,10-phen)2] (1) and [Mg2 (H2O)(1,4-NDC)2 (1,10-phen)] (2), in which 2-NDCH=2-naphthalenecarboxylic acid, 1,4-NDCH2 =1,4-naphthalene dicarboxylic acid, and 1,10-phen=1,10-phenanthroline. Based on the mixed ligands, the title compounds exhibit linker-based photoluminescence (PL) properties thanks to the unique configuration of the Mg(2+) ions. The two compounds show interesting dual emission on excitation of the different luminophores of the mixed linkers. In particular, the emissions of compound 2 could be tuned from green to yellow simply by varying the excitation energies. Furthermore, 2 could be excited by using a commercial λ=450 nm blue LED chip to generate white-light emission, which allows the fabrication of a white-light-emitting diode (WLED) with 20 lm W(-1) luminous efficacy. This work may provide a new method for designing tunable PL CPs by using the low-cost and abundant magnesium ion.

Single crystalline wurtzite ZnO/zinc blende ZnS coaxial heterojunctions and hollow zinc blende ZnS nanotubes: synthesis, structural characterization and optical properties.

Synthesis of ZnO/ZnS heterostructures under thermodynamic conditions generally results in the wurtzite (WZ) structure of the ZnS component because its WZ phase is thermodynamically more stable than its zinc blende (ZB) phase. In this report, we demonstrate for the first time the preparation of ZnO/ZnS coaxial nanocables composed of single crystalline ZB structured ZnS epitaxially grown on WZ ZnO via a two-step thermal evaporation method. The deposition temperature is believed to play a crucial role in determining the crystalline phase of ZnS. Through a systematic structural analysis, the ZnO core and the ZnS shell are found to have an orientation relationship of (0002)ZnO(WZ)//(002)ZnS(ZB) and [01-10]ZnO(WZ)//[2-20]ZnS(ZB). Observation of the coaxial nanocables in cross-section reveals the formation of voids between the ZnO core and the ZnS shell during the coating process, which is probably associated with the nanoscale Kirkendall effect known to result in porosity. Furthermore, by immersing the ZnO/ZnS nanocable heterojunctions in an acetic acid solution to etch away the inner ZnO cores, single crystalline ZnS nanotubes orientated along the [001] direction of the ZB structure were also achieved for the first time. Finally, optical properties of the hollow ZnS tubes were investigated and discussed in detail. We believe that our study could provide some insights into the controlled fabrication of one dimensional (1D) semiconductors with desired morphology, structure and composition at the nanoscale, and the synthesized WZ ZnO/ZB ZnS nanocables as well as ZB ZnS nanotubes could be ideal candidates for the study of optoelectronics based on II-VI semiconductors.

From selenidostannates to silver-selenidostannate: structural variation of chalcogenidometallates synthesized in ionic liquids.

Presented here are the ionothermal preparation and structural variation of selenidostannates, whose structures can be tuned by varying the combination of ionic liquids and auxiliary amines as mixed solvent, as well as changing the reaction temperature and time. Remarkably, a silver-selenidostannate compound featuring lamellar structure was achieved by unusual insertion of linear two-coordinate Ag(+) ions between the {Sn(3)Se(7)}(n)(2n-) double chains.

Ionothermal syntheses, crystal structures and properties of three-dimensional rare earth metal-organic frameworks with 1,4-naphthalenedicarboxylic acid.

Twelve isostructural rare earth metal-organic frameworks, namely, [Hmim][RE(2)Cl(1,4-NDC)(3)] (RE = La (1), Ce (2), Pr (3), Nd (4), Sm (5), Eu (6), Gd (7), Tb (8), Dy (9), Ho (10), Er (11), Y (12), Hmim = 1-hexyl-3-methylimidazolium, 1,4-NDCH(2) = 1,4-naphthalenedicarboxylic acid), have been ionothermally synthesized and structurally characterized. The structures feature three-dimensionally anionic frameworks of [RE(2)Cl(1,4-NDC)(3)](n)(n-) with channels in which the Hmim(+) cations are located. The current results are the first ionothermal synthesis of rare earth metal-organic frameworks based on 1,4-NDCH(2) which possess a previously unknown (4,7)-connected 3-nodal network with the Schläfli symbol of (3(2)·4(2)·5(2))(3(2)·4(9)·5(2)·6(8))(2)(4(3)·6(3))(2). Luminescent and magnetic properties of some of the title compounds have been studied. Thermogravimetric analyses indicated that all these compounds were thermally stable up to ca. 250 °C.

Thermomorphic behavior of the ionic liquids [C4mim][FeCl4] and [C12mim][FeCl4].

The iron-containing ionic liquids 1-butyl-3-methylimidazolium tetrachloroferrate(III) [C(4)mim][FeCl(4)] and 1-dodecyl-3-methylimidazolium tetrachloroferrate(III) [C(12)mim][FeCl(4)] exhibit a thermally induced demixing with water (thermomorphism). The phase separation temperature varies with IL weight fraction in water and can be tuned between 100 °C and room temperature. The reversible lower critical solution temperature (LCST) is only observed at IL weight fractions below ca. 35 % in water. UV/Vis, IR, and Raman spectroscopy along with elemental analysis prove that the yellow-brown liquid phase recovered after phase separation is the starting IL [C(4)mim][FeCl(4)] and [C(12)mim][FeCl(4)], respectively. Photometry and ICP-OES show that about 40 % of iron remains in the water phase upon phase separation. Although the process is thus not very efficient at the moment, the current approach is the first example of an LCST behavior of a metal-containing IL and therefore, although still inefficient, a prototype for catalyst removal or metal extraction.

First hexanuclear zirconium macrocycle sustained in a chair-like conformation by glycolic acids.

A discrete, hexanuclear zirconium metallocycle has been synthesized, isolated, and characterized by single-crystal X-ray diffraction. It is sustained in a chair-like conformation by glycolic acids. Formation and growth of the complex has been observed using in situ time-resolved dynamic light scattering measurements.

Two gallium antimony sulfides built on a novel heterometallic cluster.

Two gallium antimony sulfides, [Ni(en)(3)][Ga(2)Sb(2)S(7)] (1) and [(Me)(2)NH(2)](2)[Ga(2)Sb(2)S(7)] (2), have been prepared under mild solvothermal conditions. Both structures feature a two-dimensional network in which two GaS(4) tetrahedra and two SbS(3) trigonal pyramids are combined to form a heterometallic cluster of {Ga(2)Sb(2)S(9)} as a new secondary building unit. The thermal properties of 1 and 2 have been studied by thernogravimetric analysis, and the optical properties of 1 and 2 have been characterized by UV-vis spectra.

The first examples of lanthanide selenite-carboxylate compounds: syntheses, crystal structures and properties.

[Ln(8)(SeO(3))(4)(2,6-pdc)(8)(H(2)O)(10)].2H(2)O (Ln = La (1), Nd (2), Eu (3); 2,6-pdcH(2) = pyridine-2,6-dicarboxylic acid) represent the first examples of luminescent lanthanide selenite-carboxylate compounds. The compounds have been hydrothermally synthesized and structurally characterized. The structures feature two-dimensional (2D) host frameworks composed of Ln(8)(SeO(3))(4)(2,6-pdc)(8)(H(2)O)(10) clusters connected to each other via inter-cluster Ln(2)O(2) rhombic units along the b-axis and 12-membered Ln(4)O(2)(COO)(2) rings along the c-axis. Inter-layer H-bonding interactions between coordinated water molecules and carboxylate groups lead to three-dimensional architectures. Thermogravimetric analysis (TGA) indicated that the 2D networks were thermostable up to approximately 450 degrees C after losing both coordinated and lattice water molecules and underwent reversible process of dehydration and rehydration. Study on photoluminescent properties revealed that compounds 1, 2 and 3 were new rare-earth materials with violet, near-infrared, and red luminescence, respectively.

Heterododecanuclear Pt(6)Ln(6) (Ln = Nd, Yb) arrays of 4-ethynyl-2,2'-bipyridine with sensitized near-IR lanthanide luminescence by Pt --> Ln energy transfer.

Heterododecanuclear Pt(6)Ln(6) (Ln = Nd, Yb) complexes of 4-ethynyl-2,2'-bipyridine (HC[triple bond, length as m-dash]Cbpy), prepared using emissive Pt(Me(3)SiC[triple bond, length as m-dash]Cbpy)(C[triple bond, length as m-dash]Cbpy)(2) as an alkynyl bridging "ligand", afford sensitized near-infrared (NIR) lanthanide luminescence by Pt --> Ln energy transfer from both Pt(bpy)(acetylide)(2) and Pt(2)(dppm)(2)(acetylide)(2) chromophores.