Zintl ions, cage compounds, and intermetalloid clusters of Group 14 and Group 15 elements

For a long time, Zintl ions of Group 14 and 15 elements were considered to be remarkable species domiciled in solid-state chemistry that have unexpected stoichiometries and fascinating structures, but were of limited relevance. The revival of Zintl ions was heralded by the observation that these species, preformed in solid-state Zintl phases, can be extracted from the lattice of the solids and dissolved in appropriate solvents, and thus become available as reactants and building blocks in solution chemistry. The recent upsurge of research activity in this fast-growing field has now provided a rich plethora of new compounds, for example by substitution of these Zintl ions with organic groups and organometallic fragments, by oxidative coupling reactions leading to dimers, oligomers, or polymers, or by the inclusion of metal atoms under formation of endohedral cluster species and intermetalloid compounds; some of these species have good prospects in applications in materials science. This Review presents the enormous progress that has been made in Zintl ion chemistry with an emphasis on syntheses, properties, structures, and theoretical treatments.     

Laminar magnetohydrodynamic duct flow in the presence of a magnetic dipole

We study magnetohydrodynamic flow of a liquid metal in a straight duct. The magnetic field is produced by an exterior magnetic dipole. This basic configuration is of fundamental interest for Lorentz force velocimetry (LFV), where the Lorentz force opposing the relative motion of conducting medium and magnetic field is measured to determine the flow velocity. The Lorentz force acts in equal strength but opposite direction on the flow as well as on the dipole. We are interested in the dependence of the velocity on the flow rate and on strength of the magnetic field as well as on geometric parameters such as distance and position of the dipole relative to the duct. To this end, we perform numerical simulations with an accurate finite-difference method in the limit of small magnetic Reynolds number, whereby the induced magnetic field is assumed to be small compared with the external applied field. The hydrodynamic Reynolds number is also assumed to be small so that the flow remains laminar. The simulations allow us to quantify the magnetic obstacle effect as a potential complication for local flow measurement with LFV. (© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Using ultra-weak photon emission to determine the effect of oligomeric proanthocyanidins on oxidative stress of human skin

Exposure of skin to ultraviolet (UV) radiation triggers oxidative stress in skin tissue that can lead to erythema, early skin aging or even cancer. It is suggested that oligomeric proanthocyanidins (OPCs), phytonutrients that belong to the polyphenol family have an anti-oxidant/anti-inflammatory activity on the skin. Measuring ultra-weak photon emission (UPE) is a non-invasive, fairly-sensitive and convenient technique for continuously monitoring oxidative stress. The present study was undertaken to confirm anti-oxidant activity of the specific OPCs cream formulation in human skin by measuring UPE of skin. In the present study 25 healthy female subjects participated. As a baseline measurement of skin, UPE was recorded from the dorsal surface of the subjects’ hands before (spontaneous UPE) and after exposure to UV (UV-induced UPE). The effects of the OPCs cream on spontaneous and UV-induced UPE were measured using a fractionated UV exposure protocol. UV exposure resulted in an increase in UPE from both hands. Repeat UV exposure also resulted in a long-term increase of spontaneous UPE. This is likely due to depletion of anti-oxidant capacity of skin resulting in sensitization of skin to UV. It was assessed by measuring spontaneous UPE at 80 min after each UV exposure. Application of the OPCs cream immediately after UV exposure resulted in a significant (approx. 30%) decrease in UV-induced UPE. Topical OPCs cream application also reduced sensitization of skin to UV following repeated UV exposure (i.e., reduced long-term increase in spontaneous UPE). This study indicates that the specific OPCs cream formulation significantly decreases UV-induced oxidative stress in human skin based on UPE measurement. It therefore suggests that regular use of this OPCs cream might protect skin from harmful effects of UV.     

Reliability of stable carbon and oxygen isotope compositions of pedogenic needle fibre calcite as environmental indicators: examples from Western Europe

Stable carbon and oxygen isotope analyses were conducted on pedogenic needle fibre calcite (NFC) from seven sites in areas with roughly similar temperate climates in Western Europe, including the Swiss Jura Mountains, eastern and southern France, northern Wales, and north-eastern Spain. The δ(13)C values (-12.5 to-6.8 ‰ Vienna Pee Dee Belemnite (VPDB)) record the predominant C(3) vegetation cover at the sites. A good correlation was found between mean monthly climatic parameters (air temperature, number of frost days, humidity, and precipitation) and δ(18)O values (-7.8 to-3.4‰ VPDB) of all the NFC. Similar seasonal variations of δ(18)O values for monthly NFC samples from the Swiss sites and those of mean monthly δ(18)O values of local precipitation and meteorological data point out precipitation and preferential growth/or recrystallisation of the pedogenic needle calcite during dry seasons. These covariations indicate the potential of stable isotope compositions of preserved NFC in fossil soil horizons as a promising tool for palaeoenvironmental reconstructions.     

ChemInform Abstract: Endohedrally Filled [Ni@Sn9]4‐and [Co@Sn9]5‐Clusters in the Neat Solids Na12Ni1‐xSn17 and K13‐xCo1‐xSn17: Crystal Structure and 119Sn Solid‐State NMR Spectroscopy.

The title Zintl phases are prepared by reactions of the corresponding elemental alkali metals with pre‐prepared M‐Sn alloys (M: Ni, Co) at 550—880 °C for 48 h.     

Endohedrally Filled [Ni@Sn9]4− and [Co@Sn9]5− Clusters in the Neat Solids Na12Ni1−xSn17 and K13−xCo1−xSn17: Crystal Structure and 119Sn Solid‐State NMR Spectroscopy

A systematic approach to the formation of endohedrally filled atom clusters by a high‐temperature route instead of the more frequent multistep syntheses in solution is presented. Zintl phases Na₁₂Ni_1?xSn₁₇ and K_13?xCo_1?xSn₁₇, containing endohedrally filled intermetalloid clusters [Ni@Sn₉]^4? or [Co@Sn₉]^5? beside [Sn₄]^4?, are obtained from high‐temperature reactions. The arrangement of [Ni@Sn₉]^4? or [Co@Sn₉]^5? and [Sn₄]^4? clusters, which are present in the ratio 1:2, can be regarded as a hierarchical replacement variant of the hexagonal Laves phase MgZn₂ on the Mg and Zn positions, respectively. The alkali‐metal positions are considered for the first time in the hierarchical relationship, which leads to a comprehensive topological parallel and a better understanding of the composition of these compounds. The positions of the alkali‐metal atoms in the title compounds are related to the known inclusion of hydrogen atoms in the voids of Laves phases. The inclusion of Co atoms in the {Sn₉} cages correlates strongly with the number of K vacancies in K_13?xCo_1?xSn₁₇ and K_5?xCo_1?xSn₉, and consequently, all compounds correspond to diamagnetic valence compounds. Owing to their diamagnetism, K_13?xCo_1?xSn₁₇, and K_5?xCo_1?xSn₉, as well as the d‐block metal free binary compounds K₁₂Sn₁₇ and K₄Sn₉, were characterized for the first time by ¹¹⁹Sn solid‐state NMR spectroscopy.