Controllable assembly of a 3-D metal–organic supramolecular framework with the inclusion of a well-resolved 1-D water morph

Two mixed-ligand metal–organic complexes [Cd₂(adipato)(phen)₂(NO₃)₂(H₂O)₂](H₂O)₆ (1) and {[Cd(adipato)(phen)](H₂O)₃}_n (2) have been synthesized upon the reaction of Cd(II) nitrate with 1,10-phenanthroline (phen) and adipate under similar conditions. For 1, the adipato-bridged dinuclear entities are extended into a 3-D supramolecular architecture via hydrogen bonds and π–π stacking. Interestingly, a well-resolved 1-D water morphology consisting of alternate cyclic water tetramer and hexamer is detected as the guests in each channel of this 3-D lattice. Whereas 2 represents a layered coordination polymer in which the Cd^II centers are interlinked by adipate dianions via different coordination modes.     

A 3D heteropolynuclear network with 4,6-connected (44 · 62)(48 · 66 · 8) topology: Synthesis,structure, thermal and magnetic properties

This paper describes a novel heteropolynuclear coordination polymer [Cd₄Co₂(m-BDC)₆(HIm)₄]_n (1) (m-H₂BDC = 1,3-benzenedicarboxylic acid, Him = imidazole), which has been hydrothermally prepared and characterized by single-crystal X-ray diffraction, IR, ICP, XRPD, TGA, DSC, and element analysis. The overall architecture is constructed from alternate Co(II) and Cd layers arranged in ABAB mode, and affords a three-dimensional (3D) 4,6-conneccted (4⁴ · 6²)(4⁸ · 6⁶ · 8) topological network. Furthermore, magnetic property of 1 has also been studied in the temperature range of 5–300 K.     

A new (3,3,6)-connected achiral 3D supramolecular network containing unique helical chains based on 1H-benzimidazole-5,6-dicarboxylato and Pb(II)

A new 1D Pb(II) coordination polymer, {[Pb(Hbidc)(phen)]·H₂O}_n (1), has been synthesized by a solvothermal method based on 1H-benzimidazole-5,6-dicarboxylato (H₃bidc) and 1,10-phenanthroline (phen). Complex 1 features two types of helical chains, a 1D left- and right-handed double-stranded helical chain and a supramolecular helical chain, which interweave into a new (3,3,6)-connected achiral 3D supramolecular network. Notably, the supramolecular helical chains are induced by the different spatial orientations of the 1D double-stranded helical chains. The structure and properties of 1 have been determined by single crystal X-ray diffraction, powder X-ray diffraction (PXRD), elemental analysis (EA), thermogravimetric (TG) analysis and solid state fluorescence spectra.     

A novel luminescent 3D metal–organic framework possessing 4-fold interpenetrating (3,4)-connected net

A novel 3D polymer [Zn(L¹)(1,4-BDC)_0.5] (1) (HL¹ = 3,5-bis(pyridin-4-ylmethoxy)benzoic acid, 1,4-BDC = 1,4-benzenedicarboxylate anion) has been isolated under hydrothermal condition and characterized by single crystal X-ray diffraction. Compound 1 displays a 3D 4-fold interpenetrating (3,4)-connected net with (4 · 8²)(4 · 8⁵) topology. In addition, powder X-ray diffraction, photoluminescent property and thermogravimetric analysis for 1 are investigated in detail.     

Synthesis,structure and properties of a novel 3D pentanuclear [Zn5(OH)2]8 + cluster-based (3,4,11)-connected coordination polymer

A novel coordination polymer based on the multidentate N-donor ligand 1-((1H-1,2,4-triazol-1-yl)methyl)-3,5-bis(3-pyridyl)-1,2,4-triazole (3,3′-tmbpt) and 1,2,4,5-benzenetetracarboxylate anion (btec), namely, [Zn₅(3,3′-tmbpt)(btec)₂(OH)₂] (1), has been synthesized hydrothermally. Compound 1 displays a rare 3D (3,4,11)-connected framework based on a [Zn₅(OH)₂]^8 + cluster. The optical band gap and photoluminescent property of compound 1 have been studied.     

Construction of a new 3D Zn(II) coordination polymer with (4,6)-connected topology: Synthesis,structure and luminescence

A new coordination polymer of {[Zn₂(odpa)(IP)]·4H₂O}_n (1) (H₄odpa = 3,3′,4,4′-oxydiphthalic acid and IP = 1-H-imidazo[4,5-f][1,10]-phenanthroline), is reported. The 3D (4,6)-connected {4⁴∙6²∙8⁸∙12}{4⁴∙6²} topology net is formed by IP and odpa ligands in 1. Interestingly, the IP ligand acts as a tridentate mode and extends the resulting 3D feature. The luminescence study indicates that the title compound emits bright red fluorescence.     

A rare (3, 6, 10)-connected net containing both Zn2(COO)4 and Zn4(COO)8 units

A novel coordination polymer [Zn₃(btrc)₂(L1)]_n (1) (H₃btrc = 1, 2, 4-benzenetricarboxylic acid; L1 = 1, 3-bis(4-pyridyl)propane) has been synthesized under hydrothermal conditions. Single crystal X-ray diffraction study reveals that polymer 1 presents an unusual example of (3, 6, 10)-connected net with (4·6·7) (5²·6⁶·7⁷) (4¹⁶·5¹²·6⁴·7¹³) topology symbol, where btrc^3?, Zn₂(CO₂)₄, and Zn₄(CO₂)₈ units act as three-, six-, and ten-connecting nodes, respectively. In addition, the IR spectra, luminescence properties and thermogravimetric analysis of this polymer are investigated in this study.     

A novel 3D (4, 8)-connected metal-organic framework of scu topology with two types of 1D channel constructed by methylenediisophthalic acid (H4MDIP)

A novel coordination polymer 1 {[Zn₅(MDIP)₂(H₂O)₆(μ₃-OH)₂]·2H₂O}_n has been synthesized using methylenediisophthalic acid (H₄MDIP) under hydrothermal conditions. Single-crystal X-ray diffraction analysis indicates that 1 shows a 3D porous framework with two types of 1D channel. The structure is further simplified by topology analysis which indicates a (4, 8)-connected net with a Schläfli symbol of (4⁴.6²)₂(4¹⁶.6¹²) topology. Moreover, compound 1 displays a strong blue photoluminescent property.     

Two 3D coordination complexes containing metal-triazolate helical chains: Synthesis,structure, fluorescence and NLO properties

Two three-dimensional coordinationcomplexes containing metal-triazolate helical chains wereobtained. Their fluorescent andnonlinear optical properties were explored.

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Interaction of water with the clean and oxygen pre-covered Ir(1 1 1) surface

Adsorption and reaction of water on the clean and oxygen modified Ir(1 1 1) single crystal surfaces have been studied using temperature programmed desorption (TPD) and molecular beam reactive scattering (MBRS) techniques under ultrahigh vacuum (UHV) conditions. Water dissociates on the clean Ir(1 1 1) surface with a probability (estimated based on production of hydrogen) which decreases from 0.016 to 0.004 ± 0.0015 with increasing water coverages from 0.34 to 2.59 monolayer. Scattering experiments performed at various surface temperatures in the limit of zero coverage yield water dissociation probabilities in the range of 0.0005–0.012 (300–900 K) with an uncertainty expressed as ±20% of the dissociation probability. The apparent activation energy for water dissociation on clean Ir(1 1 1) is estimated to be 170 ± 5 kJ/mol employing MBRS techniques, which probably cannot be applied to TPD measurements with higher water coverages. We speculate that water dissociation occurs on the defects of the Ir(1 1 1) surface. Using isotopically labeled reactants, a strong interaction between adsorbed water and oxygen was found on Ir(1 1 1), indicated by a new water desorption feature at 235 K and scrambled oxygen and water desorption products.     

1D and 3D arrays of isomeric cadmium(II) diphosphonates constructed from N,N-dimethylaminomethane-1,1-diphosphonate ligand

Two isomeric cadmium(II) diphosphonates built up from corner-sharing CdO₆ octahedra and CPO₃ tetrahedra, with the same formula of [Cd(H₃L)₂] (H₄L = (CH₃)₂N–CH(PO₃H₂)₂), have been synthesized and structurally characterized. Compound 1 shows a 1D chain structure in which the adjacent Cd²⁺ ions are doubly bridged by two equivalent H₃L^? anions, whereas compound 2 exhibits a novel non-centrosymmetric 3D framework which is formed by a pillared-layer array, with one type of H₃L^? anions participating in the construction of a 2₁-symmetry layer and the other type of H₃L^? anions acting as pillars.     

Carbon monoxide adsorption and dissociation on Mn-decorated Rh(1 1 1) and Rh(5 5 3) surfaces: A first-principles study

Efficient CO activation on Rh particles promoted by Mn cocatalysts is important to the activity for the conversion of the syngas (CO and H₂) to hydrocarbon and oxygenates. To study the effect of the step edge and promotion of Mn cocatalysts on CO activation, we studied the CO dissociation on Mn-decorated Rh(1 1 1) and stepped Rh(5 5 3) surfaces using density functional theory calculations. We found that the presence of the step edge and Mn stabilizes the transition state and reaction products: compared to clean Rh(1 1 1), calculated barrier for CO dissociation on Mn-decorated Rh(5 5 3) is lowered by about 1.60 eV, and corresponding reaction energies with respect to CO in gas phase changes from endothermic (0.21 eV) to strong exothermic (−1.73 eV). The present work indicates that the addition of Mn cocatalysts and decrease of Rh particle sizes improves greatly the activity of CO dissociation.     

Effect of steric restrictions on the enhancement of miscibility through hydrogen bonding in blends of modified poly(α-methyl styrene) with polymers containing acceptor sites

Two series of copolymers have been prepared from α-methylstyrene and α-methylstyrene units modified by the incorporation of the hydrogen-bond donor units, methyl carbinol and trifluoromethyl carbinol, designated PαMS ( I ) and PαMS ( II ), respectively. It has been observed that if the concentration of the donor unit exceeds 4 mol %, one-phase blends can be prepared with a series of polymers containing hydrogen-bond acceptor sites such as poly(vinyl acetate), poly(vinyl pyrrolidone), poly(4-vinyl pyridine), and some poly(alkyl acrylate)s, none of which are miscible with the unmodified PαMS. All the one-phase blends formed are stable at temperatures above the glass transition temperature, T_g, of the blend, but eventually phase separate when the temperature is increased sufficiently. These lower critical cloud-point curves have been measured for a wide range of the blends and act as an indicator of the effectiveness of the hydrogen bonds in enhancing one-phase blend formation. The T_g's of the blends are in many cases higher than those calculated from the simple rule of mixtures and reflect the reduction in chain mobility in the blends caused by extensive hydrogen bonding. The results demonstrate the effect that specific interactions have in enhancing miscibility in binary polymer blends. © 1993 John Wiley & Sons, Inc.     

18-Crown-6 as a linker for (imino ester)2Pt centers providing their assembly into 1D arrays via hydrogen bonding

The platinum(II- and IV) complexes trans-[PtCl_n{HNC(OMe)Et}₂] (n = 2, 4) were assembled with 18-crown-6 into novel 1D arrays by hydrogen bonding thus forming 1:1 associates. The crystal structure determinations revealed the presence of the N–H?O and the non-conventional weak CH?O interactions between the imino hydrogen and the methyl hydrogens, respectively, of trans-[PtCl_n{HNC(OMe)Et}₂] and the oxygens of 18-crown-6.     

Structure Stability and Microwave Dielectric Properties of (1 − x) Ba(Mg1/2W1/2) O3 + xBa(Y2/3W1/3)O3 Ceramics

The structure stabilities of double perovskite ceramics‐ (1 ? x) Ba(Mg_1/2W_1/2)O₃ + xBa(Y_2/3W_1/3)O₃ (0.01 ≤ x ≤ 0.4) have been studied by X‐ray powder diffraction (XRD), scanning electron microscopy (SEM), and Raman spectrometry in this study. The microwave dielectric properties of the ceramics were studied with a network analyzer at the frequency of about 8–11 GHz. The results showed that all the compounds exhibited face‐centered cubic perovskite structure. Part of Y³⁺ and W⁶⁺ cations occupied 4a‐site and the remaining Y³⁺ and Mg²⁺ distributed over 4b‐site, respectively, and kept the B‐site ratio 1:1 ordered. Local ordering of Y³⁺/Mg²⁺ on 4b‐site and Y³⁺/W⁶⁺ cations on 4a‐site within the short‐range scale could be observed with increasing Y‐doping content. The decomposition of the double perovskite compound at high temperature was successfully suppressed by doping with Y on B‐site. However, Ba₂Y_0.667WO₆ impurity phase appeared when x > 0.1. The optimized dielectric permittivity increased with the increase in Y doping. The optimized Q × f value was remarkably improved with small amount of Y doping (x ≤ 0.02) and reached a maximum value of about 160 000 GHz at x = 0.02 composition. Further increasing in Y doping led to the decrease in Q × f value. All compositions exhibited negative τ_f values. The absolute value of τ_f decreased with increasing Y‐doping content. Excellent combined microwave dielectric properties with ε_r = 20, Q × f = 160 000 GHz, and τ_f = ?21 ppm/°C could be obtained for x = 0.02 composition.     

Two new three-dimensional (3,4)-connected lanthanide (III) coordination polymers based on 2-(3-Pyridyl)-1H-imidazole-4, 5-dicarboxylate: Structures and luminescent properties

Two new lanthanide (III) coordination polymers, namely, {[Eu₃(μ₃-HPyIDC)₄]·Cl}_n, (1) and {[Tb₂(μ₃-HPyIDC)₂(μ₂-Ox) (H₂O)₂]·4H₂O}_n (2) (H₃PyIDC = 2-(3-Pyridyl)-1H-4, 5-imidazoledicarboxylic acid; Ox = oxalate), were successfully synthesized under hydro(solvo)thermal conditions and structurally characterized. Compound 1 displays a 3D framework with new (3,4)-connected {4.8.10}₄{4.8⁴.12}₂{4².8⁴} topology built by 3-connected μ₃-HPyIDC⁻ nodes and 4-connected metal ions. Compound 2 exhibits a rare (3,4)-connected dmc topology, in which μ₃-HPyIDC⁻ anions are 3-connected nodes and metal ions are 4-connected nodes. Moreover, the thermal stabilities and luminescence of compounds 1–2 were also investigated.     

A first-principles study on the role of hydrogen in early stage of graphene growth during the CH4 dissociation on Cu(1 1 1) and Ni(1 1 1) surfaces

The influence of hydrogen for CH₄ dissociation on Cu(1 1 1) and Ni(1 1 1) surfaces has been investigated by using the density functional theory. The two possible reactions, i.e. H-abstraction reaction (CH_x + H → CH_x−1 + H₂) and direct dehydrogenation reaction (CH_x + H → CH_x−1 + 2H), are studied. Our results show that H-abstraction reaction has higher energy barrier than direct dehydrogenation reaction on Cu(1 1 1), while for Ni(1 1 1), only the direct dehydrogenation reaction is observed. The microkinetic analysis supports that H-abstraction reaction is less competitive than the direct dehydrogenation reaction at broad coverage of H atom on Cu(1 1 1) surface. The major intermediate changes from CH to CH₃ on Cu(1 1 1) and Ni(1 1 1) with the increase of H₂ partial pressure. Furthermore, the behavior of free C atoms on both clean and H pre-adsorbed metal surfaces is discussed. The adsorbed H atom hinders the polymerization of the C atoms on Cu(1 1 1), resulting in sufficient time for C relaxed to the most stable site and further lead to a prefect graphene pattern formation, while H atom has little effect on such process for Ni(1 1 1).     

Resistivity Enhancement and Transport Mechanisms in (1 − x)BaTiO3–xBi(Zn1/2Ti1/2)O3 and (1 − x)SrTiO3–xBi(Zn1/2Ti1/2)O3

Ceramics of composition (1?x)BaTiO₃–xBi(Zn_1/2Ti_1/2)O₃ (BT‐BZT) were prepared by solid‐state synthesis; they have been shown to exhibit excellent properties suited for high‐temperature dielectric applications. The X‐ray diffraction data showed a single‐phase perovskite structure for all the compositions prepared (x ≤ 0.1 BZT). The compositions with less than 0.075 BZT exhibited tetragonal symmetry at room temperature and pseudo‐cubic symmetry above it. Most notably, a significant improvement in insulation properties was measured with the addition of BZT. Both low‐field AC impedance and high‐field direct DC measurements indicated an increase in resistivity of at least two orders of magnitude at 400°C with the addition of just 0.03 BZT (~10⁷ Ω‐cm) into the solid solution as compared to pure BT (~10⁵ Ω‐cm). This effect was also evident in dielectric loss data, which remained low at higher temperatures as the BZT content increased. In conjunction with band gap measurements, it was also concluded that the conduction mechanism transitioned from extrinsic for pure BT to intrinsic for 0.075 BZT suggesting a change in the fundamental defect equilibrium conditions. It was also shown that this improvement in insulation properties was not limited to BT‐BZT, but could also be observed in the paraelectric SrTiO₃–BZT system.     

Densification,microstructural evolution and dielectric properties of Ba6 − 3x(Sm1 − yNdy)8 + 2xTi18O54 microwave ceramics

Utilizing different rare-earth cations R³⁺ to the Ba_6 − 3xR_8 + 2xTi₁₈O₅₄ compounds is one of effective route to tailor the dielectric constant, quality factor and temperature coefficient of frequency. In this study, densification, microstructural evolution, and microwave dielectric properties of Ba_6 − 3x(Sm_1 − yNd_y)_8 + 2xTi₁₈O₅₄ compound, with x ranging from 0.3 to 0.7; and y from 0 to 1.00, were investigated. The ceramics with x = 0.7 [Ba_3.9(Sm_1 − yNd_y)_9.4Ti₁₈O₅₄] has a higher densification compared with others, due to the formation of vacancy, in the perovskite-like tetragonal cavity of the tungsten bronze-type framework structure. Differential thermal analysis and density results show that the densification of Ba_6 − 3x(Sm_yNd_1 − y)_8 + 2xTi₁₈O₅₄ ceramics during sintering is primarily resulting from the solid state sintering process. The phase homogeneity for the Ba_6 − 3x(Sm_0.5Nd_o.5)_8 + 2xTi₁₈O₅₄ system is at least extended in the range of x between 0.3 and 0.7. Combining different rare-earth cations appears not alter the single phase range in tungsten bronze-type Ba_6 − 3xR_8 + 2xTi₁₈O₅₄ ceramics. The size of the columnar-grain in the microstructure increases with increasing the Nd/Sm ratio as well as the x value. Dielectric constant changes from 91.0 to 84.2 as the x increases from 0.3 to 0.7. Variation of the Nd/Sm ratio allows one to control the τ_f value to the nearly 0 ppm/°C.