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.     

Time-dependent density-functional theory with a self-interaction correction

We discuss an implementation of the self-interaction correction for the local-density approximation to time-dependent density-functional theory. A variational formulation is given, taking care of the necessary constraints. A manageable and transparent propagation scheme using two sets of wave functions is proposed and applied to laser excitation with subsequent ionization of a dimer molecule.