In Situ Hydrogenation and Crystal Chemistry Studies of Co2Si Type Compounds MgPd2 and Pd2Zn

The hydrogenation properties of the intermetallic compounds MgPd₂ and Pd₂Zn, crystallizing in the Co₂Si type, were studied by in situ thermal analysis (DSC) under hydrogen pressure. Pd₂Zn does not show any reaction with hydrogen while MgPd₂ reversibly forms the hydride MgPd₂H. Neutron diffraction on the deuterides reveals the compositions MgPd₂D_0.861(6) (ambient) and MgPd₂D_0.97(1) [308(2) K, 2.56(5) MPa deuterium] with hydrogen (deuterium) occupying distorted [MgPd₅] octahedral voids. Quantum mechanical calculations support the structure models and show the hydrogenation to be exergonic for MgPd₂ and endergonic for Pd₂Zn. MgPd₂H releases hydrogen under normal conditions or vacuum. Heating under hydrogen pressure leads first reversibly to MgPd₂H_≈0.2 and subsequently irreversibly to MgPd₃H_≈1 and MgH₂. MgPd₂, Pd₂Zn, and MgPd₂H were classified in a structure map. Trends of axial ratio changes upon hydrogenation of TiNiSi type and ZrBeSi type compounds are discussed.     

Hydrogen-induced atomic rearrangement in MgPd3

The hydrogenation behavior of MgPd₃ has been studied by in situ X-ray powder diffraction and by neutron powder diffraction. At room temperature and p ≈500 kPa hydrogen pressure its structure is capable of incorporating up to one hydrogen atom per formula unit (α-MgPd₃H_≈1), thereby retaining a tetragonal ZrAl₃-type metal atom arrangement. Upon heating to 750 K in a hydrogen atmosphere of 610 kPa it transforms into a cubic modification with AuCu₃-type metal atom arrangement (β-MgPd₃H_≈0.7). Neutron diffraction on the deuteride reveals an anion deficient anti-perovskite-type structure (β-MgPd₃D_0.67, a=398.200(7) pm) in which octahedral sites surrounded exclusively by palladium atoms are occupied by deuterium. Complete removal of hydrogen (480 K, 1 Pa) stabilizes a new binary modification (β-MgPd₃, a=391.78(2) pm) crystallizing with a primitive cubic AuCu₃-type structure. Mechanical treatment (grinding) transforms both α and β modifications of MgPd₃ into a cubic face-centered solid solution Mg_0.25Pd_0.75 showing a random distribution of magnesium and palladium atoms.     

Versuche zur Hydrierung kubischer ternärer intermetallischer Phasen

Hydrogenation Reactions of Cubic Ternary Compounds The Zintl compound LiAlSi reacts at temperatures above 535°C and a pressure of 80–82 bar with hydrogen. A new phase with the formula LiAlSi_0.9 has been found. The reaction is reversible, at DTG measurements Proved. The new phases MgPd₂Ga and MgPd₂In, which have been characterised by X-ray investigation, decompose under hydrogen atmosphere irreversibly to Pd₁₁Ga₉, PdH and MgPd₃.     

Crystal Structure and Formation of TlPd3 and its new Hydride TlPd3H

TlPd₃ was synthesised from the elements in evacuated silica tubes at 600 °C. Alternatively, TlPd₃ was yielded by reduction of TlPd₃O₄ in N₂ gas atmosphere. Reduction of the oxide in H₂ gas atmosphere resulted in the formation of the new hydride TlPd₃H. The structure of tetragonal TlPd₃ (ZrAl₃ type, space group I4/mmm, a = 410.659(9) pm, c = 1530.28(4) pm) was reinvestigated by X‐ray and also by neutron powder diffraction as well as the structure of its previously unknown hydride TlPd₃H (cubic anti‐perovskite type structure, space group Pm\bar{3} m, a = 406.313(1) pm). In situ DSC measurements of TlPd₃ in hydrogen gas atmosphere showed a broad exothermic signal over a wide temperature range with two maxima at 280 °C and at 370 °C, which resulted in the product TlPd₃H. A dependency of lattice parameters of the intermetallic phase on reaction conditions is observed and discussed. Results of hydrogenation experiments at room temperature with gas pressures up to 280 bar hydrogen and at elevated temperatures with very low hydrogen gas pressures (1–2 bar) as well as results of dehydrogenation of the hydrides under vacuum will be discussed.     

Catalytic hydrogenation of styrene-g-natural rubber (ST-g-NR) in the presence of OsHCl(CO)(O2)(PCy3)2

OsHCl(CO)(O₂)(PCy₃)₂, was used as a catalyst for hydrogenation of styrene-g-natural rubber copolymer (ST-g-NR). Univariate experiments were conducted to explore the effect of variables on the rate of hydrogenation by measuring the hydrogen consumption as a function of time using a gas-uptake apparatus. From the kinetic results, the hydrogenation of ST-g-NR was observed to exhibit a first-order dependence on [CC]. The rate of hydrogenation showed a first-order dependence on the catalyst concentration and a first-order shift to zero-order dependence on hydrogen pressure with increasing hydrogen pressure. The rate of hydrogenation was also found to decrease with an increase in rubber concentration. The addition of a small amount of acid provided a beneficial effect on the hydrogenation rate of the grafted natural rubber. The hydrogenation rate of ST-g-NR was dependent on the reaction temperature and the apparent activation energy over the range of 120-160 °C was found to be 83.3 kJ/mol.     

Nanostructured ruthenium on γ-Al2O3 catalysts for the efficient hydrogenation of aromatic compounds

Free and trioctylamine (TOA)-stabilized ruthenium nanoparticles have been prepared by decomposition of the metal precursor Ru(η⁶-cycloocta-1,3,5-triene)(η⁴-cycloocta-1,5-diene) under mild conditions (room temperature, hydrogen atmospheric pressure). The nanoparticles have been deposited on γ-Al₂O₃ supports having different surface area. The resulting systems are active in the hydrogenation of methyl benzoate to methyl cyclohexanoate with a reaction rate decreasing in the order Ru(TOA)/γ-Al₂ O₃ (high surface area, catalyst D) > Ru(TOA)/γ-Al₂O₃ (catalyst C) > Ru/γ-Al₂O₃ (high surface area, catalyst B) > Ru/γ-Al₂O₃ (catalyst A). Catalysts A-D are long lived and can be reused without loss of activity; they are considerably more active than a commercial ruthenium on γ-Al₂O₃ sample. High Resolution Transmission Electron Microscopy analyses of such systems show that the nanoparticles are homogeneously dispersed on the support and that the size distribution decreases in the order catalyst A, 2.9 nm > catalyst B, 2.8 nm > catalyst C, 2.4 nm > catalyst D, 2.3 nm. Based on the easy hydrogenation of the aromatic ring to the cyclohexane derivative, an efficient synthesis of 4-carbomethoxyformylcyclohexane, important starting material in the preparation of pharmaceutical products, from the largely available methyl 4-formylbenzoate, has been set up in the presence of catalyst D.     

Hydrogenation of palladium rich compounds of aluminium, gallium and indium

Palladium rich intermetallic compounds of aluminium, gallium and indium have been studied before and after hydrogenation by powder X-ray diffraction and during hydrogenation by in situ thermal analysis (DSC) at hydrogen gas pressures up to 39 MPa and temperatures up to 700 K. Very weak DSC signals and small unit cell increases of below 1% for AlPd₂, AlPd₃, GaPd₂, Ga₅Pd₁₃, In₃Pd₅, and InPd₂ suggest negligible hydrogen uptake. In contrast, for both tetragonal modifications of InPd₃ (ZrAl₃ and TiAl₃ type), heating to 523 K at 2 MPa hydrogen pressure leads to a rearrangement of the intermetallic structure to a cubic AuCu₃ type with an increase in unit cell volume per formula unit by 3.6-3.9%. Gravimetric analysis suggests a composition InPd₃H_≈0.8 for the hydrogenation product. Very similar behaviour is found for the deuteration of InPd₃.     

Hydrogenation of arenes, alkenes and alkynes catalyzed by a sol–gel entrapped mixture of [Rh(cod)Cl]2 and Na[HRu3(CO)11]

A sol–gel entrapped 1:3 mixture of [Rh(cod)Cl]₂ and Na[HRu₃(CO)₁₁] catalyzes the hydrogenation of various unsaturated substrates by two distinguishable mechanisms. Under 13.8 bar H₂ and 20 °C methylated arenes react rapidly to give cycloalkane derivatives. XRD and TEM studies showed that under these conditions the hydrogenation proceeds without the generation of free metal particles. The hydrogenation of non-methylated arenes, as well as that of alkenes and alkynes, require a temperature of 80–120 °C at which the entrapped complexes form metallic nano-particles of 3–5 nm. Chloroarenes are also hydrodechlorinated at 120 °C, but require a hydrogen pressure of ≥25 bar. At both temperature ranges the catalysts are reusable at least four times. The high efficiency of the hydrogenation process at 20 °C is rationalized by a synergistic effect between the two different metal atoms of the combined catalyst. This may be related to a remote control model through a hydrogen spillover mechanism.     

Structural variations and hydrogen storage properties of Ca5Si3 with Cr5B3-type structure

The structure and phase variation of Ca₅Si₃ upon hydrogenation were systematically investigated using combined neutron powder diffraction (NPD), neutron vibrational spectroscopy (NVS), and first-principles calculations. The hydrogen absorption equilibrium was first attained with formation of Ca₅Si₃H(D)_0.53 (I4/mcm) with H exclusively located in Ca₄-tetrahedral sites. More hydrogen absorbed into the system under higher pressure leads to dissociations into CaH₂ (an amorphous hydride at higher pressures) and CaSi. The hydrogen-induced formation of an amorphous phase under higher pressures is very unusual in Cr₅B₃-type compounds and the observed formation of CaH₂ upon hydrogen absorption confirmed the proposed composition equilibrium between A₅Tt₃ (A = Ca, Sr; Tt = Si, Ge, Sn) and AH₂.     

3, 3, 3-Trifluoropropyl(methyl)cyclosiloxanes

The catalytic rearrangement of the cyclopentasiloxanes _mD_5-m, where represents a 3, 3, 3-trifluoropropyl(methyl)siloxane link and D a dimethylsiloxane link, and m=2–5 has been studied by the method described previously [1]. The rate of rearrangement and the rate of formation of a linear polysiloxane rise with an increase in m from 2 to 4. The equilibrium concentration of the linear polysiloxane formed from _mD_5-m and from _mD_4-m (m=0–4) [1] is inversely proportional to the molar fraction of links in the ring and rises with an increase in the total concentration of siloxane links in solution. Results have been obtained on the kinetics of the formation of the cyclosiloxanes _mD_n (where m=0–5, n=0–5, and m+n=3-6) during the rearrangement of the cyclopentasiloxanes _mD_5-m. It has been established that at equilibrium a mixture of cyclosiloxanes _mD_n containing practically constant ratios of tetramers, pentamers, and hexamers (m+n=4, 5, and 6) is obtained, regardless of the composition and structure of the initial cyclosiloxane and of the conditions of rearrangement (polymerization). The cyclopentasiloxanes _mD_5-m are less active in the process of rearrangement than the cyclotetrasiloxanes _mD_4-m. The activity of the cyclosiloxanes in rearrangement in the presence of a base rises in the sequence D₄D_{3 2}D₃<₃D₂<₄D < ₂D₂ < ₃D.For part II, see [1].     

Structural resolution and mechanistic insight into hydrogen adsorption in flexible ZIF-7

Flexible metal–organic frameworks offer a route towards high useable hydrogen storage capacities with minimal swings in pressure and temperature via step-shaped adsorption and desorption profiles. Yet, the understanding of hydrogen-induced flexibility in candidate storage materials remains incomplete. Here, we investigate the hydrogen storage properties of a quintessential flexible metal–organic framework, ZIF-7. We use high-pressure isothermal hydrogen adsorption measurements to identify the pressure–temperature conditions of the hydrogen-induced structural transition in ZIF-7. The material displays narrow hysteresis and has a shallow adsorption slope between 100 K and 125 K. To gain mechanistic insight into the cause of the phase transition correlating with stepped adsorption and desorption, we conduct powder neutron diffraction measurements of the D₂ gas-dosed structures at conditions across the phase change. Rietveld refinements of the powder neutron diffraction patterns yield the structures of activated ZIF-7 and of the gas-dosed material in the dense and open phases. The structure of the activated phase of ZIF-7 is corroborated by the structure of the activated phase of the Cd congener, CdIF-13, which we report here for the first time based on single crystal X-ray diffraction measurements. Subsequent Rietveld refinements of the powder patterns for the gas-dosed structure reveal that the primary D₂ adsorption sites in the dense phase form D₂–arene interactions between adjacent ligands in a sandwich-like adsorption motif. These sites are prevalent in both the dense and the open structure for ZIF-7, and we hypothesize that they play an important role in templating the structure of the open phase. We discuss the implications of our findings for future approaches to rationally tune step-shaped adsorption in ZIF-7, its congeners, and flexible porous adsorbents in general. Lastly, important to the application of flexible frameworks, we show that pelletization of ZIF-7 produces minimal variation in performance.

Hydrogen induced flexibility in MOFs can be leveraged to increase useable gas storage capacities. Here hydrogen adsorption isothermal and in situ powder neutron diffraction measurements combine to reveal the mechanism driving flexibility in ZIF-7.     

Inclusion complexes of the natural product gossypol. Clathrate type inclusion complexes of gossypol with carbonyl group containing guests

The crystal structures of 2:1 inclusion complexes of gossypol with methyl propionate (GPMEP) and ethyl acetoacetate (GPEAA) have been determined by X-ray structure analysis. The crystals of GPMEP, C₃₀H₃₀O₈l/2 C₄H₈O₂, are monoclinic, space groupC2/c,a=11.079(3),b = 30.724(7), c = 16.515(5) Å, = 90.46(2)°,V = 5621(3) Å,Z = 8,D _x = 1.33 g cm^–3. The structure has been refined to the finalR value of 0.059 for 1899 observed reflections. The crystals of GPEAA, C₃₀H₃₀O₈l/2 C₆H₁₀O₃, are monoclinic, space groupC2/c,a=11.095(2),b=30.604(9),c = 16.955(5) Å, = 88.27(2)°,V = 5754(3) Å,Z = 8,D _x = 1.35 g cm^–3. The structure has been refined to the finalR value of 0.056 for 2502 observed reflections.In contrast to previously investigated inclusion complexes of gossypol the host molecules do not form centrosymmetric dimersvia hydrogen bonds. In the crystal structures the racemic gossypol is separated into enantiomers forming alternating bimolecular layers. Nearly perpendicular to these chiral bilayers run elongated cavities enclosed on each side by layers of opposite chirality. The surface of these layers is hydrophobic, the polar groups are hidden inside the layer. Guest molecules which are hydrogen bonded to the host are included in cylindrically shaped cavities. Possible hydrogen bonds between host and guest are analysed for this isostructural class of complexes.     

A hirshfeld surface analysis,crystal structure and physicochemical characterization of 1-ethylpiperazinium trichlorocadmate(II)

A novel organic–inorganic hybrid material, C₆H₁₅N₂CdCl₃.H₂O, was synthesized, and its structure was determined at room temperature in the monoclinic space group P2₁/n with the following parameters: a = 10.3829 (17), b = 7.7459 (12), c = 14.905 (2) Å, β = 98.801 (15), and Z = 4. Its crystal structure is characterized by one-dimensional polymeric chains of edge-sharing CdCl₅N distorted octahedra. These chains are linked to the water molecules via OH … Cl hydrogen bonds to form layers parallel to the (b, a + c) plane. The crystal structure was stabilized by an extensive network of NH … Cl, OH … Cl and NH … O hydrogen bonds. The differential scanning calorimetry (DSC) reveals that the title compound is stable until 101.6 °C.The optimized geometry parameters, normal mode frequencies, and corresponding vibrational assignments of the present compound were theoretically examined by DFT/B3LYP method with the Lanl2dz basis set. The FT-IR spectrum of the polycrystalline sample was examined and compared to the calculated spectrum. The calculated results showed that the optimized geometry could well reproduce the crystal structure and that the theoretical vibrational frequency values were in good agreement with their experimental counterparts.     

The standard transported entropy of chloride ion in H2O and D2O

Transported entropies of the chloride ion, , in H₂O and in D₂O at 25°C and at concentrations ranging from 0.001 to 0.04m have been determined from the measurements of the steady-state (final) thermoelectric powers of the silver-silver chloride thermocell. Experimental data was extrapolated to infinite dilution to obtain the standard transported entropy . The concentration dependence of is examined and the solvent-isotope effect on the transported entropy is investigated. Thermodynamic data on the entropy of transfer of chloride ion from H₂O to D₂O is used to estimate the difference of the standard ionic entropy of transport in H₂O and D₂O for chloride ion.     

Anisotropic exchange interactions in dinuclear systems (Ln = Dy, Tm, Yb): Magnetometry and Dual Mode X-band Electron Paramagnetic Resonance spectroscopic study

A recently developed experimental and theoretical procedure is used in order to calculate the magnitude and anisotropy of interaction between a lanthanide and a 3d-metal ion. The general formula of the molecular compounds is [Ln(H₂O)₃(dmf)₄(μ-CN)Fe–(CN)₅] · nH₂O where 1  n  1,5 and dmf = N,N′-dimethylformamide, abbreviated as [LnFe] from now on. The main parts of this procedure are (a) the evaluation of the effective g-parameters of the lanthanide ion with the help of EPR measurements. (b) The use of dual mode EPR spectroscopy to define the anisotropic exchange interactions with the help of an anisotropic Hamiltonian model. (c) Use of the same magnetic model to fit magnetization and susceptibility data in order to verify the EPR findings.It was possible to define some trends concerning the exchange components of the [DyFe] dimer according to which the antiferromagnetic isotropic exchange constant is smaller than 4 cm⁻¹ and the anisotropic components are [D_exc, E_exc] = [6(1), 0.0] cm⁻¹. Also for the case of [TmFe] and [YbFe] dimers the antiferromagnetic isotropic exchange constant is smaller than 0.3 cm⁻¹ while the anisotropic components are [D_exc, E_exc] = [12.0, 0.0] cm⁻¹ and [D_exc, E_exc] = [0.4(1), 0.0] cm⁻¹, respectively.     

Nachweis von Wasserstoff (Deuterium) in Metall-Wasserstoff-Systemen mit Hilfe der SIMS-Technik

Summary The results obtained from measurements of the secondary ion yields of VH _n (VD _n )-samples as a function of the D₂ partial pressure and of the Ar⁺ primary ion current density are discussed. The use of D₂ instead of H₂ gas and the observation of H- and D-specific mass peaks in standardized spectra allow to determine only the hydrogen (deuterium) specific effects, and to represent graphically the secondary ion yields of different species (H⁺, D⁺, V⁺, VH⁺, V ₂ ⁺ , V₂H⁺ ...) — the intensities differ by more than 5 orders of magnitude — in a relative mode elucidating the influences of bulk hydrogen (deuterium) and of hydrogen adsorbed from the residual gas atmosphere.     

Labelling Studies to Determine Product Formation from Reactions of CO and Hydrogen Catalysed by Ru Clusters and Rh Complexes

Reaction of CO with hydrogen in the presence of [Ru₃(CO)₁₂], KI and N-methylpyrrolidone produces small amounts of methanol under mild conditions. Using D₂ the methanol is CD₃OD confirming that it is a product of CO hydrogenation. In the presence of added H₂O, CH _x D_1-y OH/D (y=0–3) are produced. Carrying out the same reaction in the presence of MeI water and RhCl₃·xH₂O (x=3–4) produces ethanoic acid in a slow reaction which continues for at least 64 h. The effects of different reaction parameters are discussed and labelling using ¹³CH₃I shows that some of the ethanoic acid originates from sources other than MeI whilst labelling with D₂, CD₃I, and/or D₂O suggest that some originates from CO and H₂. Electrospray mass spectrometry and high pressure infra-red spectroscopic studies show that the main species present in catalytic solutions are [HRu₃(CO)₁₁]⁻, [HRu₄(CO)₁₃]⁻ and [Ru(CO)₃I₃]⁻ for methanol carbonylation, [Ru(CO)₃I₃]⁻ and [RhI₂(CO)₂]⁻ for ethanoic acid production. A reaction carried out in the absence of [Ru₃(CO)₁₂] gave similar results to a reaction in which it was added, suggesting that the entire process may be catalysed by rhodium complexes alone. Electronic Supplementary Material  Supplementary material for this article is available at and is accessible for authorized users.

Stereo-specific synthesis of hydroanthracene-dicarboximides

Compound 3, N-((1S)-1-cyclohexylethyl)-9,10-dihydro-9,10-ethanoanthracene-(11S,12S)-dicarboximide-1,2,3,4-octahydro, was obtained by ruthenium-assisted hydrogenation of the hydroanthracene-dicarboximide 2 under mild conditions (3 bar H₂ and room temperature). In contrast to other related compounds, dicarboximides 2 and 3 were stereo-selectively obtained, confirmed by both solid state (X-ray diffraction) and solution (NMR). This selectivity denoted a hindered rotation around the N-CH axis together with the aromatic hydrogen bond acceptor behaviour of the hydroanthracene skeleton towards a methylene of the cyclohexyl group of the imide moiety. In addition, the nature of the metallic species involved in the hydrogenation process was also investigated.     

Inclusion compounds of (±) gossypol. Structure of the gossypol-n-valeric acid (1/2) coordinato-clathrate

The crystal structure of the inclusion compound of gossypol withn-valeric acid as a guest molecule has been determined by X-ray structure analysis. The crystals of C₃₀H₃₀O₈·(C₅H₁₀O₂)₂, are triclinic, space group ,a=6.912(2),b=14.506(3),c=19.387(4) Å, =78.85(2)°, =83.92(3)°, =86.78(3)°V=1895(1) ų,Z=2,D _x=1.267 g cm^–3, (CuK )=0.768 mm^–1,T=292 K. The structure has been solved by direct methods on intensity data collected for a twinned crystal and refined to the finalR value of 0.062 for 1606 observed reflections and 470 refined parameters.Gossypol-n-valeric acid (1/2) coordinato-clathrate is not isostructural with any of the previously investigated gossypol inclusion compounds but shows some structural similarities to gossypol-acetic acid (1/1). The host and one of the carboxylic acid molecules are connected via hydrogen bonds into molecular assemblies of a column type which are further bonded to centrosymmetric dimers of the secondn-valeric acid molecule. In effect, host and guest molecules are assembled into layer-type H-bonded aggregates. Structural features common to gossypol-n-valeric acid (1/2) and other earlier reported gossypol inclusion compounds are discussed.Supplementary Data relevant to this article have been deposited with the British Library under the number SUP 82194 (9 pages)     

A very simple synthesis of K3[Re(NO)(CN)5] · 2 H2O directly from [ReO4]−: Existence of two structural isomers in aqueous medium as indicated by13C N.m.r. spectroscopy

Summary Perrhenate(VII) was reductively nitrosylated using an excess of CN^–, OH^– and NH₂OH · HCl, and from the reaction mixture K₃[Re(NO)(CN)₅] · 2H₂O has been isolated. Its aqueous solution behaves as a 31 electrolyte and its¹³C n.m.r. spectrum in D₂O solution suggests that the complex molecule forms two types of isomeric structure arising from the two different modes of intramolecular hydrogen (deuterium) bonding of the two lattice water (D₂O in the bulk solvent) molecules.