Intercalating lithium into the lattice of silver nanoparticles boosts catalytic hydrogenation of carbon–oxygen bonds

Coinage metal nanoparticles with high dispersion can serve as highly efficient heterogeneous catalysts. However, owing to their low melting point, poor thermal stability remains a major obstacle towards their application under reaction conditions. It is a common practice to use porous inorganic templates such as mesoporous silica SBA-15 to disperse Ag nanoparticles (NPs) against aggregation but their stability is far from satisfactory. Here, we show that the catalytic activity for hydrogenation of dimethyl oxalate (DMO) to methyl glycolate (MG) over Ag NPs dispersed on SBA-15 silica can be further promoted by incorporation of alkali metal ions at small loading, which follows the inverse order of their cationic size: Li⁺ > Na⁺ > K⁺ > Rb⁺. Among these, 5Ag₁–Li_0.05/SBA-15 can double the MG yield compared to pristine 5Ag/SBA-15 under identical conditions with superior thermal stability. Akin to the effect of an ionic surfactant on stabilization of a micro-emulsion, the cationic charge of an alkali metal ion can maintain dispersion and modulate the surface valence of Ag NPs. Interstitial Li in the octahedral holes of the face center packed Ag lattice is for the first time confirmed by X-ray pair distribution function and electron ptychography. It is believed that this interstitial-stabilization of coinage metal nanoparticles could be broadly applicable to multi-metallic nanomaterials for a broad range of C–O bond activating catalytic reactions of esters.

Coinage metal nanoparticles with high dispersion can serve as highly efficient heterogeneous catalysts.     

Addition of atomic hydrogen to acetylene. Chain reactions of the vinyl radical

The main reaction products resulting from the addition of atomic hydrogen to acetylene are shown to be ethylene, 1,3-butadiene, and benzene. The mechanism involves chain reactions of the vinyl and butadienyl radicals, which regenerate atomic hydrogen. Some of the rate parameters are estimated.     

The canonical ensemble via symplectic integrators using Nosé and Nosé-Poincaré chains

Simulations that sample from the canonical ensemble can be generated by the addition of a single degree of freedom, provided that the system is ergodic, as described by Nosé with subsequent modifications by Hoover to allow sampling in real time. Nosé-Hoover dynamics is not ergodic for small or stiff systems and the addition of auxiliary thermostats is needed to overcome this deficiency. Nosé-Hoover dynamics, like its derivatives, does not have a Hamiltonian structure, precluding the use of symplectic integrators which are noted for their long term stability and structure preservation. As an alternative to Nosé-Hoover, the Hamiltonian Nosé-Poincaré method was proposed by Bond, Laird, and Leimkuhler [J. Comput. Phys. 151, 114 (1999)], but the straightforward addition of thermostatting chains does not sample from the canonical ensemble. In this paper a method is proposed whereby additional thermostats can be applied to a Hamiltonian system while retaining sampling from the canonical ensemble. This technique has been used to construct thermostatting chains for the Nosé and Nosé-Poincaré methods.     

Metal ion scrambling in hexanuclear M(6)(Et(2)NCO(2))(12) complexes (M = Co,Mg). Synthesis,solid state structure,and solution dynamics of heteronuclear Co(n)Mg(6-n)(Et(2)NCO(2))(12) complexes

Heteronuclear diethylcarbamato complexes of the form Co(n)()Mg(6)(-)(n)()(Et(2)NCO(2))(12) were prepared from the isostructural homonuclear precursors Mg(6)(Et(2)NCO(2))(12), 1, and Co(6)(Et(2)NCO(2))(12), 2, via a solvothermal methodology. Two materials were selected for single-crystal X-ray diffraction analysis: Co(1.6)Mg(4.4)(Et(2)NCO(2))(12) and Co(2.7)Mg(3.3)(Et(2)NCO(2))(12). Both compounds crystallize in the orthorhombic space group Ccca, as do 1 and 2. The molecular structure is best described as two trinuclear M(3) units cross-linked by diethylcarbamate ligands and twisted about one another, so that the complex has overall D(2) symmetry and is chiral. Each trinuclear unit consists of two terminal pentacoordinate metal ions and one central hexacoordinate metal ion. The X-ray diffraction data were unambiguous that the Co(2+) ions migrate exclusively to the pentacoordinate sites in the heteronuclear complexes, thus demonstrating that metal ion scrambling at the molecular level must occur. The composition of individual crystals can be continuously varied for Co(2+) mole fractions chi(Co) < 0.5, and the a and c unit cell distances are linearly related to chi(Co). This indicates that the compounds behave as solid solutions. There appears to be either a chemical or crystallographic phenomenon inherent in the synthetic methodology that prevents isolation of heteronuclear materials having chi(Co) > 0.5. Solution electronic spectroscopy and molecular weight measurements show that 2 can dissociate in chloroform and cyclohexane solution to give a dimeric complex 2'. This behavior contrasts with the stability of 1 in solution, as shown by NMR. The kinetic rate profile for formation of Co(n)Mg(6-n)(Et(2)NCO(2))(12) reveals saturation kinetics and is consistent with direct attack by 2' on 1 to give the heteronuclear complex via a higher nuclearity intermediate. This study illustrates a general method for the preparation of solids based on heteronuclear Werner-type complexes of the M(6)(Et(2)NCO(2))(12) structure type, and the mechanism by which such compounds can be formed from isostructural homonuclear precursors.     

The nature of unsupported uranium-ruthenium bonds: a combined experimental and theoretical study

Four new uranium-ruthenium complexes, [(Tren(TMS))URu(η(5)-C(5)H(5))(CO)(2)] (9), [(Tren(DMSB))URu(η(5)-C(5)H(5))(CO)(2)] (10), [(Ts(Tolyl))(THF)URu(η(5)-C(5)H(5))(CO)(2)] (11), and [(Ts(Xylyl))(THF)URu(η(5)-C(5)H(5))(CO)(2)] (12) [Tren(TMS)=N(CH(2)CH(2)NSiMe(3))(3); Tren(DMSB)=N(CH(2)CH(2)NSiMe(2)tBu)(3)]; Ts(Tolyl)=HC(SiMe(2)NC(6)H(4)-4-Me)(3); Ts(Xylyl)=HC(SiMe(2)NC(6)H(3)-3,5-Me(2))(3)], were prepared by a salt-elimination strategy. Structural, spectroscopic, and computational analyses of 9-12 shows: i) the formation of unsupported uranium-ruthenium bonds with no isocarbonyl linkages in the solid state; ii) ruthenium-carbonyl backbonding in the [Ru(η(5)-C(5)H(5))(CO)(2)](-) ions that is tempered by polarization of charge within the ruthenium fragments towards uranium; iii) closed-shell uranium-ruthenium interactions that can be classified as predominantly ionic with little covalent character. Comparison of the calculated U-Ru bond interaction energies (BIEs) of 9-12 with the BIE of [(η(5)-C(5)H(5))(3)URu(η(5)-C(5)H(5))(CO)(2)], for which an experimentally determined U-Ru bond disruption enthalpy (BDE) has been reported, suggests BDEs of approximately 150 kJ mol(-1) for 9-12.     

Extreme red shifted SERS nanotags

Surfaced enhanced Raman scattering (SERS) nanotags operating with 1280 nm excitation were constructed from reporter molecules selected from a library of 14 chalcogenopyrylium dyes containing phenyl, 2-thienyl, and 2-selenophenyl substituents and a surface of hollow gold nanoshells (HGNs). These 1280 SERS nanotags are unique as they have multiple chalcogen atoms available which allow them to adsorb strongly onto the gold surface of the HGN thus producing exceptional SERS signals at this long excitation wavelength. Picomolar limits of detection (LOD) were observed and individual reporters of the library were identified by principal component analysis and classified according to their unique structure and SERS spectra.     

Isolation of Elusive HAsAsH in a Crystalline Diuranium(IV) Complex

The HAsAsH molecule has hitherto only been proposed tentatively as a short‐lived species generated in electrochemical or microwave‐plasma experiments. After two centuries of inconclusive or disproven claims of HAsAsH formation in the condensed phase, we report the isolation and structural authentication of HAsAsH in the diuranium(IV) complex [{U(Tren^TIPS)}₂(μ‐η²:η²‐As₂H₂)] ( 3 , Tren^TIPS=N(CH₂CH₂NSiPrⁱ₃)₃; Prⁱ=CH(CH₃)₂). Complex 3 was prepared by deprotonation and oxidative homocoupling of an arsenide precursor. Characterization and computational data are consistent with back‐bonding‐type interactions from uranium to the HAsAsH π*‐orbital. This experimentally confirms the theoretically predicted excellent π‐acceptor character of HAsAsH, and is tantamount to full reduction to the diarsane‐1,2‐diide form.     

The competing roles of topology and spin density in the magnetic behavior of spin-delocalized radicals: Donor–acceptor annelated nitronyl nitroxides

The effects of acceptor–donor interactions in thienyl substituted benzimidazole-nitronyl nitroxides (TBNN) on the absorption spectroscopy, spin density distribution, magnetic behavior, and crystallographic packing were explored through spectroscopy, computation, and characterization of structure and magnetic properties in the crystalline phase. The electronic spectra of the radicals exhibit a strong broad absorption in the NIR (λ_max ～ 1000 nm) that exhibits solvatochromism consistent with charge transfer between the thienyl (donor) and benzonitronyl nitroxide (acceptor) dyads. Computational analysis allowed assignment of the transition as a HOMO–SOMO transition (TD-DFT UB3LYP/6-31G7). The TBNN radicals form highly disordered slipped π-stacks in the solid state that give rise to antiferromagnetic interactions consistent with 1D chain interactions. The magnetic behavior was well-fit to a Bonner–Fisher model to give exchange parameters of J = ?2 to ?10 cm^?1 depending on substitution. The weak exchange parameters are attributed to the degree of solid-state disorder, and the observed properties can be rationalized by the effects of substitution on the electronic structure and topology of the radicals.     

Repdigits as sums of three Pell numbers

In this paper, all base 10 repdigits expressible as sums of three Pell numbers are found.