Ru Zn Research Articles

Cementite-type Y3Ru

Abstract Single crystals of Y3Ru were obtained as a side product during phase analytical studies of yttrium-rich compounds in the system Y–Ru–Zn. The structure of Y3Ru was refined from single-crystal X-ray diffractometer data: Fe3C type, Pnma, a = 732.51(7), b = 925.61(8), c = 633.66(10) pm, wR = 0.0639, 811 F 2 values, 23 variables. The ruthenium atoms have coordination number 9 in form of a strongly distorted tricapped trigonal yttrium prism with Ru–Y distances ranging from 275–391 pm. The second substructure concerns empty Y6 octahedra (d(Y–Y) = 344–396 pm). Electronic structure calculations show a net charge transfer from yttrium to ruthenium and underpin the essentially covalent Y–Ru bonding. A phase-pure sample of Y3Ru was synthesized from the elements by arc-melting. Temperature-dependent magnetic susceptibility studies of this sample reveal Pauli paramagnetism (3.6(1) × 10−5 emu mol−1 at T = 300 K).

Novel Reaction-Adsorption Method for Preparation of Ru–Zn–La/ZrO2 Catalysts with High Catalytic Performance for Selective Hydrogenation of Benzene

A novel wet-chemistry reaction-adsorption strategy via the facile acid–base interaction under mild conditions is demonstrated to fabricate the state-of-the-art Ru–Zn–La/ZrO2 catalysts for selective hydrogenation of benzene to cyclohexene. The catalyst preparation process is systematically investigated and verified with the combination of various characterization techniques. Preloading of lanthanide salts and alkali treatment after calcination not only favor the introduction of ruthenium and zinc species in the later stages but also help enhance the dispersion of the catalysts. The reaction rate constants (k1 and k2) decrease with the increment of the Zn/Ru molar ratio, and the selectivity at 40% conversion (S40) is positively correlated with the k1/k2 ratio, demonstrating the role of Zn species in retarding the hydrogenation activity of Ru and improvement of the selectivity to cyclohexene. In general, the catalytic behavior is dependent on the particle size of Ru, the La-to-Ru electron transfer effect, the content of Zn species, and the surface hydrophilicity of catalyst. These factors are generated by using different precursors and various predesigned La/Ru molar ratios in the preparation recipe. Moreover, a passivation treatment before the hydrogenation reaction can promote the cyclohexene selectivity of the catalyst Ru–Zn–La/ZrO2 (1.6 La/Ru) to 80.6% at a benzene conversion of 43.7%, which meets the industrial requirement. Notably, the specific activity of the catalyst is as high as 1224 gBZ·gRu–1·h–1, over 10 times higher than the industrial criterion. This work provides new insights into the design of Ru-based catalysts for benzene hydrogenation and other hydrogenation reactions as well.

Doped Ru to enable next generation barrier-less interconnect

An effective method for the formation of a Zn-doped Ru liner is demonstrated that realizes a self-forming barrier to achieve low resistivity interconnects for future back-end of line interconnect nodes. The “Ru–Zn” exhibits significantly improved adhesion to the dielectric and better electrochemical nucleation as compared to those of pristine Ru. In addition, time-dependent dielectric breakdown (TDDB) measurements indicate the inhibition of Cu ions drifting into the dielectric that precedes the TDDB failure. Complementary analysis using x-ray absorption spectroscopy, transmission electron microscope, and energy dispersive spectroscope suggests that the “Ru–Zn” forms an interfacial Zn–Si–O compound, and Zn, being more electronegative than Cu, protects the latter from oxidation. Calculation using density function theory also indicates that the Zn–Si–O compound adopts an intercalated structure at the interface of Ru/dielectric in which Zn occupies the interstitial sites within the Si–O lattice. We propose a twofold mechanism for improved TDDB performance: (1) the intercalated Zn atoms effectively block the diffusion of Cu ions through the dielectric and (2) Zn provides the cathodic protection of Cu that prevents the generation of mobile Cu ions that accelerate the TDDB.

Bonding and Reactivity of a Pair of Neutral and Cationic Heterobimetallic RuZn2 Complexes.

A combined experimental and computational study of the structure and reactivity of two [RuZn2Me2] complexes, neutral [Ru(PPh3)(Ph2PC6H4)2(ZnMe)2] (2) and cationic [Ru(PPh3)2(Ph2PC6H4)(ZnMe)2][BArF4] ([BArF4] = [B{3,5-(CF3)2C6H3}4]) (3), is presented. Structural and computational analyses indicate these complexes are best formulated as containing discrete ZnMe ligands in which direct Ru–Zn bonding is complemented by weaker Zn···Zn interactions. The latter are stronger in 2, and both complexes exhibit an additional Zn···Caryl interaction with a cyclometalated phosphine ligand, this being stronger in 3. Both 2 and 3 show diverse reactivity under thermolysis and with Lewis bases (PnBu3, PCy3, and IMes). With 3, all three Lewis bases result in the loss of [ZnMe]+. In contrast, 2 undergoes PPh3 substitution with PnBu3, but with IMes, loss of ZnMe2 occurs to form [Ru(PPh3)(C6H4PPh2)(C6H4PPhC6H4Zn(IMes))H] (7). The reaction of 3 with H2 affords the cationic trihydride complex [Ru(PPh3)2(ZnMe)2(H)3][BArF4] (12). Computational analyses indicate that both 12 and 7 feature bridging hydrides that are biased toward Ru over Zn.

Clover leaf-shaped supramolecules assembled using a predesigned metallo-organic ligand

A series of clover-like supramolecular structures were designed and synthesized using a combination of Ru–Zn, Ru–Co, Ru–Mn or Ru–Ni metal ions. These structures with distinct redox properties may have further applications as functional materials.

Zn-Promoted C-H Reductive Elimination and H2 Activation via a Dual Unsaturated Heterobimetallic Ru-Zn Intermediate.

Reaction of [Ru(PPh3)3HCl] with LiCH2TMS, MgMe2, and ZnMe2 proceeds with chloride abstraction and alkane elimination to form the bis-cyclometalated derivatives [Ru(PPh3)(C6H4PPh2)2H][M′] where [M′] = [Li(THF)2]+ (1), [MgMe(THF)2]+ (3), and [ZnMe]+ (4), respectively. In the presence of 12-crown-4, the reaction with LiCH2TMS yields [Ru(PPh3)(C6H4PPh2)2H][Li(12-crown-4)2] (2). These four complexes demonstrate increasing interaction between M′ and the hydride ligand in the [Ru(PPh3)(C6H4PPh2)2H]− anion following the trend 2 (no interaction) < 1 < 3 < 4 both in the solid-state and solution. Zn species 4 is present as three isomers in solution including square-pyramidal [Ru(PPh3)2(C6H4PPh2)(ZnMe)] (5), that is formed via C–H reductive elimination and features unsaturated Ru and Zn centers and an axial Z-type [ZnMe]+ ligand. A [ZnMe]+ adduct of 5, [Ru(PPh3)2(C6H4PPh2)(ZnMe)2][BArF4] (6) can be trapped and structurally characterized. 4 reacts with H2 at −40 °C to form [Ru(PPh3)3(H)3(ZnMe)], 8-Zn, and contrasts the analogous reactions of 1, 2, and 3 that all require heating to 60 °C. This marked difference in reactivity reflects the ability of Zn to promote a rate-limiting C–H reductive elimination step, and calculations attribute this to a significant stabilization of 5 via Ru → Zn donation. 4 therefore acts as a latent source of 5 and this operational “dual unsaturation” highlights the ability of Zn to promote reductive elimination in these heterobimetallic systems. Calculations also highlight the ability of the heterobimetallic systems to stabilize developing protic character of the transferring hydrogen in the rate-limiting C–H reductive elimination transition states.

Transforming PPh3into bidentate phosphine ligands at Ru–Zn heterobimetallic complexes

The reaction of [Ru(PPh3)3Cl2] with excess ZnMe2 led to P-C/C-H bond activation and P-C/C-C bond formation to generate a chelating diphenylphosphinobenzene ligand as well as a cyclometallated (diphenylphosphino)biphenyl group in the final product of the reaction, [Ru(dppbz)(PPh2(biphenyl)')(ZnMe)] (1; dppbz = 1,2-bis(diphenylphosphino)benzene); PPh2(biphenyl)' = cyclometallated PPh2(biphenyl). The mechanism of reaction was studied and C-C coupling to give a bidentate 2,2'-bis(diphenylphosphino)biphenyl (BIPHEP) ligand was suggested to be one of the key steps of the process. This was confirmed by the reaction of [Ru(BIPHEP)(PPh3)HCl] with ZnMe2, which also gave 1. An analogous set of steps took place upon addition of ZnMe2 to [Ru(rac-BINAP)(PPh3)HCl] (rac-BINAP = racemic(2,2'-bis(diphenylphosphino)-1,1'-binaphthyl) to give [Ru(dppbz)(PPh2(binaphthyl)')ZnMe] (3). H2 and the C-H bond of PhC[triple bond, length as m-dash]CH added across the Ru-Zn bond of 1, and also reversed the phosphine cyclometallation, to give [Ru(dppbz)(Ph2P(biphenyl))(H)2(H)(ZnMe)] (4) and [Ru(dppbz)(Ph2P(biphenyl))(C[triple bond, length as m-dash]CPh)2(H)(ZnMe)] (5) respectively.

Influence factors on activity of Ru–Zn catalysts in selective hydrogenation of benzene

Selective hydrogenation of benzene is an atom economic green route to produce cyclohexene. The control of Zn species is the key to the catalytic performance of Ru–Zn catalysts. The influences of ZnO crystals on selective hydrogenation of benzene were explored. A series of Ru–Zn catalysts with different Zn contents and ZnO morphologies were prepared by changing the amount of NaOH in the co-precipitation process. The catalysts were characterized by N2 physisorption, X-ray powder diffraction (XRD), inductively coupled plasma optical emission spectrometer (ICP-OES), scanning electron microscope (SEM), temperature-programmed reduction (H2-TPR) and Malvern laser particle size analyzer. It is found that with increasing the amount of NaOH, the Zn content first increased then decreased, and the ZnO crystals changed from relatively thicker pyramidal-shaped crystals to slimmer needle-shaped crystals. The catalyst had the highest Zn content (22.1%) and strongest interaction between ZnO crystals and Ru particles at pH10.6 of the solution after reduction. As a result, it had the lowest activity. The activity of Ru–Zn catalysts is affected by both the Zn content and the interaction between ZnO crystals and Ru particles. The effect of reduction time was also investigated. Prolonging the reduction time caused no significant growth of ZnO crystals but the aggregation of catalyst particles and growth of Ru nanocrystals, thus resulting in the decrease of catalytic activity.

Selective hydrogenation of benzene to cyclohexene over Ru–Zn/ZrO2 catalysts prepared by a two-step impregnation method

Supported Ru–Zn/ZrO2 catalysts are successfully prepared by a two-step impregnation method (Zn deposition–calcination–Ru deposition), and their catalytic performances for selective liquid-phase hydrogenation of benzene are investigated. Physical properties of the catalysts are characterized by N2 adsorption, atomic absorption spectroscopy, X-ray diffraction, temperature-programmed reduction, transmission electron micrographs, dynamic light scattering and X-ray photoelectron spectroscopy. Effects of the Zn content, concentration of alkaline treatment (NaOH) after hydrogen reduction, and hydrogen reduction temperature on the properties of Ru–Zn/ZrO2 catalysts with a fix Ru loading of 10.0 wt% are studied. It is found that the optimal ZnO content is 10.5 wt% in the first-step impregnation (ZnO–ZrO2), and that the alkaline treatment after hydrogen reduction is very important for obtaining the optimal Zn content in the ultimate catalyst. Over the optimal Ru–Zn/ZrO2 catalyst with 10.0 wt% Ru and 2.78 wt% Zn, the selectivity to cyclohexene can reach 80% at the benzene conversion of 50% under the reaction condition (1200r/min, 150°C, 5MPa H2). The specific activity of the catalyst is about 4 times higher than those of Ru–Zn catalysts prepared by coprecipitation. The recycle catalytic performance of the optimal Ru–Zn/ZrO2 catalyst is also explored. There is no significant decrease of catalytic performance after four recycles, indicating good stability of the catalyst prepared by the two-step impregnation method.

Ru-Zn heteropolynuclear complexes containing a dinucleating bridging ligand: synthesis, structure, and isomerism.

Mononuclear complexes in- and out-[Ru(Cl)(trpy)(Hbpp)](+) (in-0, out-0; Hbpp is 2,2'-(1H-pyrazole-3,5-diyl)dipyridine and trpy is 2,2':6',2″-terpyridine) are used as starting materials for preparation of Ru-Zn heterodinuclear out-{[Ru(Cl)(trpy)][ZnCl2](μ-bpp)} (out-2) and heterotrinuclear in,in- and out,out-{[Ru(Cl)(trpy)]2(μ-[Zn(bpp)2])}(2+) (in-3, out-3) constitutional isomers. Further substitution of the Cl ligand from the former complexes leads to Ru-aqua out,out-{[Ru(trpy)(H2O)]2(μ-[Zn(bpp)2])}(4+) (out-4) and the oxo-bridged Ru-O-Ru complex in,in-{[Ru(III)(trpy)]2(μ-[Zn(bpp)2(H2O)]μ-(O)}(4+) (in-5). All complexes are thoroughly characterized by the usual analytical techniques as well as by spectroscopy by means of UV-vis, MS, and when diamagnetic NMR. CV and DPV are used to extract electrochemical information and monocrystal X-ray diffraction to characterize complexes out-2, in-3, out-3, and in-5 in the solid state. Complex out-3 photochemically isomerizes toward in-3, as can be observed by NMR spectroscopy and rationalized by density functional theory based calculations.

Effect of transition metals (Cr, Mn, Fe, Co, Ni, Cu and Zn) on the hydrogenation properties of benzene over Ru-based catalyst

The influence of transition metals on the hydrogenation properties of benzene over Ru-based catalysts had been investigated in the presence of ZnSO4 acting as the reaction modifier. It was found that the (Zn(OH)2)3(ZnSO4)(H2O)x salt (x=1 or 3) chemisorbed on Ru surface played a key role in improving the selectivity of Ru catalysts to cyclohexene. The promoter Cr in Ru–Cr(x) catalysts existed as Cr2O3. The amount of the (Zn(OH)2)3(ZnSO4)(H2O)x salt (x=1 or 3) chemisorbed on Ru surface slightly decreased with the increase of the amount of Cr2O3, resulting in a slight decrease of the selectivity to cyclohexene for the Ru–Cr(0.42) catalyst. Co and Ni promoters were present as Co3O4 and Ni(OH)2 in the Ru–Co(x) and Ru–Ni catalysts, respectively. Increasing amounts of Co3O4 and Ni(OH)2 increased the chemisorption of (Zn(OH)2)3(ZnSO4)(H2O)x salt (x=1 or 3), leading to a slight decrease in activity and a slight increase in selectivity of the Ru–Co(x) and Ru–Ni(x) catalysts to cyclohexene. The promoters Mn, Fe and Zn existed as Mn3O4, Fe3O4 and ZnO, respectively, in the Ru–Mn(x), Ru–Fe(x) and Ru–Zn(x) catalysts. These could react with ZnSO4 to form the (Zn(OH)2)3(ZnSO4)(H2O)x salt (x=1 or 3). The amount of chemisorbed (Zn(OH)2)3(ZnSO4)(H2O)x salt (x=1 or 3) was significantly increased with the content of Mn3O4, Fe3O4 and ZnO, resulting in a prominent decrease in activity and a significant increase in cyclohexene selectivity of the Ru–Mn(x), Ru–Fe(x) and Ru–Zn(x) catalysts. The Ru–Mn(0.23), the Ru–Fe(0.47) and the Ru–Zn(0.27) catalysts provided maximum cyclohexene yields of 55.3%, 56.7% and 53.4%, respectively. The Cu promoter in the Ru–Cu(0.49) catalyst was present as CuO. Part of the CuO could react with the ZnSO4 in the slurry to form a Cu4(SO4)(OH)6(H2O) salt. The presence of the chemisorbed Cu4(SO4)(OH)6(H2O) and (Zn(OH)2)3(ZnSO4)(H2O)x (x=1 or 3) salts improved the selectivity of the Ru–Cu(0.49) catalyst to cyclohexene.

Ru–Zn supported on hydroxyapatite as an effective catalyst for partial hydrogenation of benzene

Design and preparation of efficient and greener catalytic systems for partial hydrogenation of benzene to cyclohexene is an interesting topic in green chemistry. In this work, Ru and Ru–Zn catalysts supported on hydroxyapatite (HAP), which is nontoxic and abundant in nature, were prepared via the simple ion-exchange method. The catalysts were characterized by powder X-ray diffraction (XRD), transmission electron spectroscopy (TEM), X-ray photoelectron spectroscopy (XPS) and nitrogen adsorption–desorption methods. The influences of Ru/Zn molar ratio, reaction temperature, pressure, reaction time, and amount of modifier NaOH on the partial hydrogenation of benzene were studied in detail. It was demonstrated that metallic nanoparticles of less than 2 nm were dispersed uniformly on the surface of the HAP, and the bimetallic Ru–Zn/HAP catalysts showed high activity and selectivity. The yield of cyclohexene could reach 33% over Ru–Zn/HAP at the optimized conditions, and the catalyst could be reused at least four times without obvious loss of the activity and selectivity.

Effect of alcohols as additives on the performance of a nano-sized Ru–Zn(2.8%) catalyst for selective hydrogenation of benzene to cyclohexene

In liquid phase hydrogenation of benzene, Ru–Zn(2.8%) catalyst (Ru–Zn catalyst with the Zn mass percentage of 2.8%) exhibited the excellent selectivity to cyclohexene for the nano-size effect and the chemisorbed ZnSO4·3(ZnOH)2⋅7H2O salt formed by the promoter ZnO reacting with ZnSO4. It is found that the cyclohexene yield of Ru–Zn(2.8%) catalyst generally increased with the molecular weight of PEG (Polyethylene glycol) in the presence of ZnSO4. PEG-10000 (Polyethylene glycol with the molecular weight of 10,000) as an additive made Ru–Zn(2.8%) catalyst give the highest cyclohexene yield of 62.3% in presence of ZnSO4 for the following two reasons. Firstly, the addition of PEG-10000 in presence of ZnSO4 could make more Zn2+ chemisorbed on the surface of the catalyst. The Zn2+ ions chemisorbed could be beneficial for stabilizing the formed cyclohexene, accelerating the desorption and hindering the re-adsorption of cyclohexene on the surface of the catalyst. Secondly, the PEG-10000 added might form two molecular hydrogen bonds in eight-numbered rings with the cyclohexene in the liquid phase, which could stabilize the cyclohexene in the liquid phase and hinder the re-adsorption. 2g of this catalyst with 0.2g PEG-10000 as an additive pretreated in presence of ZnSO4 gave a selectivity to cyclohexene of 78.6% and the best cyclohexene yield of 64.5% at the benzene conversion of 82.0% at 15min. Moreover, this catalyst had an excellent stability since ZrO2 and PEG-10000 could effectively inhibit the agglomeration of Ru–Zn(2.8%) catalyst.

Effect of (Zn(OH)2)3(ZnSO4)(H2O)5 on the performance of Ru–Zn catalyst for benzene selective hydrogenation to cyclohexene

A series of Ru–Zn catalysts with different Zn contents were prepared by co-precipitation. The catalysts were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Auger electron spectroscopy (AES) – Ar+ sputter, transmission electron micrographs (TEM)–energy dispersion scanning (EDS) and temperature-programmed reduction (TPR). The performances of the catalysts for benzene selective hydrogenation to cyclohexene were investigated in the presence of 0.6mol/L of ZnSO4. The results showed that the Ru and Zn in Ru–Zn catalyst were in metallic Ru and ZnO respectively and the ZnO was rich on the surface. The ZnO alone could not improve the selectivity to cyclohexene of Ru–Zn catalyst. However, the ZnO on the surface could react with ZnSO4 to form a (Zn(OH)2)3(ZnSO4)(H2O)5 salt. The (Zn(OH)2)3(ZnSO4)(H2O)5 salt chemisorbed played a key role in improving the selectivity to cyclohexene of Ru–Zn catalysts. After Ru–Zn(8.6%) catalyst was pretreated 22h in ZnSO4 solution at 140°C and 5MPa H2, a cyclohexene selectivity of 81.4% at a benzene conversion of 54.0% was achieved at 10min and a maximum cyclohexene yield of 58.9% was reached. Moreover, the activity was stable above 50% and the cyclohexene selectivity and yield were steadily above 76% and 40% on this catalyst in the first six recycles, respectively.

NMR investigations of the solution structures of Ru–Zn complexes tethered by oligo(aminoethylglycine) chains

[Ru(bpy)3]2+ complexes derivatized with two aminoethylglycine (aeg) chains bearing pendant bipyridine ligands coordinate Zn2+ to form a coordinative interchain crosslink. Although [Zn(bpy)2]2+ is both redox and spectroscopically silent, when bound to [Ru(bpy)3]2+ by the aeg strands it causes quenching of the emissive Ru complex excited state. 1H NMR spectroscopy is used to monitor changes in the structure and environment of the Ru complex during a titration as Zn2+ is added. Using spectral assignments from 1 and 2D NMR spectra, the spectrophotometric titrations reveal that Zn2+ binding causes significant shifts of the peaks assigned to the protons on the [Ru(bpy)3]2+ core that are closest to the Zn2+. These shifts reveal changes in the local environment that are likely a combination of electrostatic interactions between the two dication metal complexes and strain induced by the metal ion crosslinking the strands.

Photophysical properties of Kuratowski-type coordination compounds [MIIZn4Cl4(Me2bta)6] (MII = Zn or Ru) featuring long-lived excited electronic states

The syntheses of Kuratowski-type pentanuclear clusters featuring {MZn(4)Cl(4)} cores (M(II) = Ru or Zn) that incorporate triazolate ligands are described. The coordination compounds are characterized by single-crystal X-ray diffraction, X-ray powder diffraction (XRD), FTIR- and UV-vis spectroscopy. [Ru(II)Zn(4)Cl(4)(Me(2)bta)(6)]·2DMF (Me(2)bta(-) = 5,6-dimethyl-1,2,3-benzotriazolate) (1) crystallizes in the cubic system, while [Zn(5)Cl(4)(ta)(6)] (ta(-) = 1,2,3-triazolate) (3) crystallizes in the tetragonal system. Both compounds feature structurally similar cluster topologies in which the central octahedrally coordinated metal ion is coordinated to six triazolate ligands. Each triazolate ligand is coordinated with two zinc ions (μ(3)-bridging mode), leading altogether to a pentanuclear cluster of T(d) point group symmetry. Photophysical investigations reveal that compound [Zn(5)Cl(4)(Me(2)bta)(6)]·2DMF (2) shows a short-lived excited electronic state, which can be populated with high quantum yield. The isostructural compound [Ru(II)Zn(4)Cl(4)(Me(2)bta)(6)]·2DMF (1), on the other hand, shows a long-lived photoexcited state, owing to an internal singlet to triplet conversion of the electronic states, as revealed by time-resolved fluorescence spectroscopy. Insights gained from these studies open up novel design strategies towards photocatalytically active metal-organic frameworks incorporating photoactive Kuratowski-type secondary building units such as MFU-4 (Metal-Organic Framework Ulm University-4).

Ru9Zn7Sb8: A Structure with a 2 × 2 × 2 Supercell of the Half-Heusler Phase

The title compound Ru(9)Zn(7)Sb(8) was synthesized via a high-temperature reaction from the elements in a stoichiometric ratio, and its structure was solved by a single-crystal X-ray diffraction method. The structure [cubic, space group Fm3m, Pearson symbol cF96, a = 11.9062(14) Å (293 K), and Z = 4] adopts a unique 2a(hh) × 2a(hh) × 2a(hh) supercell of a normal half-Heusler phase and shows abnormal features of atomic coordination against the Pauling rule. The formation of this superstructure was discussed in light of the valence electron concentration per unit cell. It is a metallic conductor [ρ(300 K) = 16 μΩ·m], and differential scanning calorimetry revealed that Ru(9)Zn(7)Sb(8) undergoes a transformation at 1356(1) K and melts, by all indications, congruently at 1386 K. At room temperature, its thermal conductivity is about 3 W/m·K, which is only one-quarter of that of most normal half-Heusler phases. Ru(9)Zn(7)Sb(8) as well as its analogues of iron-, cobalt-, rhodium-, and iridium-containing compounds are expected to serve as a new structure type for exploring new thermoelectric materials.

Low-Dimensional Structure and Magnetism of the Quantum Antiferromagnet Rb4Cu(MoO4)3 and the Structure of Rb4Zn(MoO4)3

Single crystals of the quantum low-dimensional antiferromagnet Rb(4)Cu(MoO(4))(3) and the nonmagnetic analogue Ru(4)Zn(MoO(4))(3) have been synthesized by a flux-growth method. Detailed structural studies indicate that the Cu(II)-O network separated by a MoO(4) layer has a strongly anisotropic hybridization along the a-axis, forming a quasi-one-dimensional (1-d) chain of Cu(II) S = 1/2 spins. Furthermore, our low-temperature thermodynamic measurements have revealed that a quantum paramagnetic state with Wilson ratio approximately 2 remains stable down to at least 0.1 K, 100 times lower than the intrachain antiferromagnetic coupling scale. The low-temperature magnetic and thermal properties are found to be consistent with theoretical predictions made for a 1-d network of S = 1/2 spins.

Hydrogenation of cyclohexene over Ru–Zn/Ru(0 0 0 1) surface alloy: A first principles density functional study

In this work, the hydrogenation of cyclohexene over Ru–Zn/Ru(0 0 0 1) surface alloy was investigated by a DFT study so as to improve the understanding of the catalytic mechanism of the partial hydrogenation of benzene to cyclohexene over Ru–Zn alloy catalyst. Calculation results show that the presence of Zn atoms on the surface alloy results in not only a direct decrease in sites for the chemisorption of cyclohexene but also a depressed adsorption capability of the neighboring surface Ru sites. For an adsorbed cyclohexene molecule, whether the subsequent hydrogenation can be readily performed actually is determined by the relative position among the Zn atom, the H atom, and the adsorbed cyclohexene molecule. In most cases, the hydrogenation is forbidden because of the repulsion from Zn atoms to the nearby H atoms. Only in the specific situations in which the H atom participating in the reaction is not immediately close to the Zn atom, can the hydrogenation be accomplished with a relatively lower activation energy compared with the reactions on the Ru(0 0 0 1) surface. From the perspectives of adsorption and reaction kinetics, Ru-based catalyst modified by metallic Zn is no longer suitable for the hydrogenation of cyclohexene, which is supposed to be crucial to the improvement of cyclohexene yield in the partial hydrogenation of benzene over Ru–Zn alloy catalyst.

Partial hydrogenation of benzene to cyclohexene on a Ru–Zn/ m-ZrO 2 nanocomposite catalyst

A Ru–Zn/ m-ZrO 2 nanocomposite catalyst for benzene partial hydrogenation to cyclohexene was prepared by coprecipitation of ruthenium trichloride and zirconium oxychloride with ammonia, followed by hydrogen reduction in an aqueous zinc sulfate solution. By use of transmission electron microscopy (TEM), powder X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS), the reduction of zinc cation to metallic zinc and the transformation of zirconium hydroxide to monoclinic zirconia were proposed and explained. The hydrogenation parameters, such as the amount of zinc sulfate in the pretreatment process, the hydrogenation temperature, the stirring rate, and the hydrogen pressure, influenced the yield of cyclohexene. The pronounced positive effect of metallic zinc in enhancing the cyclohexene yield was discussed.