Catalytic reaction of methyl formate with amines to formamides

A feasible procedure of using methyl formate as cheap reagent for the conversion of aliphatic and aromatic amines into formamides with high yields is reported. The improved amine formylation method proceeds mainly at room temperature and in presence of bicyclic guanidines as catalysts. A verifiable key intermediate of outstanding formylating activity is generated from methyl formate and the catalyst in the reaction mixture.     

Development of mullite and mullite/Al2O3 precursor sols for electrophoretic deposition of oxidation protection coatings

Mullite and mullite/Al₂O₃ precursor sols have been developed for the deposition of oxidation barrier coatings on carbon fibre reinforced composites using a combination of sol–gel synthesis and electrophoresis.The sols were synthesised by controlled hydrolysis and condensation of TEOS (tetraethoxysilane) and Al(OBu^s)₃ (aluminium tri-sec-butylate). The main objective was the definition of synthesis conditions which yield sols suitable for the electrophoretic deposition (EPD). Measurements of the Electrokinetic Sonic Amplitude were used to investigate the electrokinetic properties of the sols in the as-prepared state and depending on the later addition of H₂O. ²⁹Si CP/MAS NMR spectra of dried precursor samples were recorded to study the homogeneity of Al/Si mixture. The progress of crystallisation with increasing temperature of heat treatment was examined by XRD. Oxidation protection coatings on C/C–SiC composites were prepared by EPD.Whereas a low H₂O to TEOS ratio during the sol synthesis was advantageous for a low mullite formation temperature, a high H₂O to TEOS ratio was necessary to enable the EPD. The synthesis of a sol with a low H₂O to TEOS ratio in the first step and the later modification of this sol by the addition of water was a successful method to combine the required electrokinetic properties and mullitisation temperatures below 1200 °C.     

Uncertainty relations for general phase spaces

We describe a setup for obtaining uncertainty relations for arbitrary pairs of observables related by a Fourier transform. The physical examples discussed here are the standard position and momentum, number and angle, finite qudit systems, and strings of qubits for quantum information applications. The uncertainty relations allow for an arbitrary choice of metric for the outcome distance, and the choice of an exponent distinguishing, e.g., absolute and root mean square deviations. The emphasis of this article is on developing a unified treatment, in which one observable takes on values in an arbitrary locally compact Abelian group and the other in the dual group. In all cases, the phase space symmetry implies the equality of measurement and preparation uncertainty bounds. There is also a straightforward method for determining the optimal bounds.     

Equation of state of cubic hafnium(IV) nitride having Th3P4 -type structure

Pressure dependence of the specific volume, V(P), of the recently discovered high-pressure compound Hf₃N₄ having cubic Th₃P₄-type structure (c- Hf₃N₄) has been measured at room temperature up to 43.9 GPa in a diamond anvil cell using energy-dispersive X-ray powder diffraction combined with synchrotron radiation. A least-square fit of the Birch-Murnaghan equation of state to the experimental V(P)-data yielded for c- Hf₃N₄ the bulk modulus of and its first pressure derivative of . For fixed at 4 the bulk modulus of c- Hf₃N₄ was determined to be . The obtained B₀-value is only insignificantly below that estimated in preliminary measurements. Existing theoretical predictions for B₀ scatter around the present experimental data. The observation of a high bulk modulus of c- Hf₃N₄ supports the suggestion that this compound could have high hardness.     

The Parent Diarsene HAs=AsH as Side‐on Bound Ligand in an Iron Carbonyl Complex

The terminal diarsene HAs=AsH ligand attracts special interest concerning its bonding relation in comparison to its isolable relative, ethene. Herein, by the methanolysis of [{Fe(CO)₄}As(SiMe₃)₃] ( 1 ) the synthesis of [{Fe(CO)₄}(η²‐As₂H₂)] ( 2 ) is reported, containing a parent diarsene as unprecedented side‐on coordinated ligand. Following this synthetic route, also the D‐labeled complex [{Fe(CO)₄}(η²‐As₂D₂)] ( 2D ) could be isolated. The electronic structure and bonding situation of 2 was elucidated by DFT calculations revealing that 2 is best described as an olefin‐like complex. Moreover, the reactivity of 2 towards the Lewis acids [{M(CO)₅}(thf)] (M=Cr, W) was investigated, leading to the complexes [Fe(CO)₄AsHW(CO)₅]₂ ( 3 ) and [{Fe(CO)₄}₂AsH{Cr(CO)₅}] ( 4 ), respectively.     

The Family of A6M2O6 Oxometalates: Synthesis and Crystal Structure Determination of Cs6Mn2O6, Magnetic Exchange within Dimeric Poly‐oxoanions,and Classification of Crystal Structures

The new compound Cs₆Mn₂O₆ was synthesized via the azide/nitrate route. According to single‐crystal X‐ray analysis (P1 ; a = 695.74(7), b = 733.24(7), c = 735.12(7) pm, α = 78.559(4), β = 62.685(3), γ = 88.788(4)°; 2705 independent data, R₁ = 0.041), the anionic part of the compound consists of dimeric Mn₂O₆ units, formed by edge sharing of two MnO₄ polyhedra of a shape intermediate between tetrahedral and square planar. The crystal structure is singular, however, can be related to several oxides of the same general formula by group‐subgroup symmetry descent. The magnetic properties of Cs₆Mn₂O₆ have been simulated by an antiferromagnetic dimer model of spin S = 2 entities, considering a small temperature dependence of the spin exchange parameters.     

On Verdigris,Part III: Crystal Structure,Magnetic and Spectral Properties of Anhydrous Copper(II) Acetate,a Paddle Wheel Chain

Pure anhydrous Cu(CH₃COO)₂ was obtained both, by thermal dehydration of Cu(CH₃COO)₂ · H₂O and by drying a commercially purchased mixture of Cu(CH₃COO)₂ · H₂O and Cu(CH₃COO)₂ in a nitrogen atmosphere using P₂O₅ as drying agent. The crystal structure was solved ab initio from synchrotron X‐ray powder diffraction (XRPD) data at 150 °C and from laboratory XRPD data at ambient conditions and found to be isotypic to anhydrous chromium(II), molybdenum(II) and rhodium(II) acetate. Cu(CH₃COO)₂ crystallizes in space group P1 (no. 2) with lattice parameters of a = 5.1486(3) Å, b = 7.5856(6) Å, c = 8.2832(6) Å, α = 77.984(4)°, β = 75.911(8)°, γ = 84.256(6)° at ambient conditions. Cu₂(CH₃COO)₄ paddle wheels with short (2.6 Å) Cu–Cu distances form chains in a direction, which is the main motif in the crystal structure. Due to their identical structural main motif Cu(CH₃COO)₂ · H₂O and Cu(CH₃COO)₂ exhibit a similar bluish‐green color, almost identical UV/Vis spectra and comparable magnetic properties. The temperature dependent magnetic susceptibility also indicates only weak inter‐dimer spin exchange between neighbouring Cu₂(CH₃COO)₄ paddle wheels.     

Numerical investigations on autogenous shrinkage of cement paste and mortar

Autogenous shrinkage of cement paste and concrete is defined as the macroscopic length change occurring with no moisture transferred to the exterior surrounding environment. It is a result of chemical shrinkage affiliated with the hydration of cement particles and the ongoing process of self-desiccation. The process of self-desiccation can be modeled starting from the formation of the capillary pore space during hydration in the cement paste. In this proposal a working model will be introduced explaining the difficulties to obtain the autogenous shrinkage strains directly from a simulated or measured microstructure of cement paste. In a second step the autogenous shrinkage of a hardening cement mortar was described on a mesoscopic level. It based on measurements on cement paste. The mortar simply consists of cement paste and a defined fraction of spherical aggregates with a known modulus of elasticity. Furthermore the influence of the interfacial transition zone (ITZ) is studied in numerical simulations. The results of these finite-element-calculations are introduced and compared with testing results of the autogenous shrinkage of hardening mortar samples. (© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Rydberg-Rydberg collisions: resonant enhancement of state mixing and penning ionization

In rubidium Rydberg states, the collision nD_(5/2)+nD_(5/2)-->(n-2)F_(7/2)+(n+2)P_(3/2) is nearly resonant in the vicinity of n=43. As a result, over a short range of n centered around n approximately 43 the Rydberg-Rydberg interaction potential is quite large and turns from repulsive to attractive [Phys. Rev. A 75, 032712 (2007)10.1103/PhysRevA.75.032712]. We use state-selective field ionization to investigate the effect of this resonance on instantaneous excitation of mixed two-particle states, state-mixing collisions, and Penning ionization. We find that these processes depend on the magnitude and sign of the two-particle interaction potential, and thus on n near the resonance. The large magnitude of the observed state mixing provides evidence for many-body effects.