Die Kristallstruktur von CsTcO4 [1]

The Crystal Structure of CsTcO₄ CsTcO₄ crystallizes orthorhombic with a = 5.72₇, b = 5.92₁ and c = 14.34 Å. Z = 4, space group Pnma (Nr. 62, I.T.). The metal positions were refined by single crystal data, the oxygen positions first determined: the CsTcO₄ structure is a slight distortion of the scheelite arrangement (parameters: see text). The MADELUNG Part of Lattice Energy, MAPLE, ?Mean Effective Ionic Radii”?, MEIR, and Effective Coordination Numbers, ECoN, are calculated and discussed.     

Microsatellite structures in the context of human evolution

Six microsatellite - or short tandem repeat (STR) - systems with uniform repetitive sequences (HumTH01, HumCD4, HumFES/FPS, HumF13B, HumTPO, HumLPL) and three compound repeat systems (HumVWA, HumFIBRA, D21S11) were used, including data from the literature, to determine genetic distances among eight populations worldwide. The TH01- and VWA homologous loci in nonhuman primates (chimpanzees, gorillas, orangutans, rhesus monkeys, ring-tailed lemurs) were compared and found to be shorter than in humans. Microsatellites of lower complexity were most efficient for the separation of major ethnic groups. The loci of higher complexity showed a leveling of the diversity differences among populations, which could be attributed to higher mutation rates.     

MNDO study of reaction paths: Diboration of acetylene

The reaction of B₂H₄ with acetylene has been studied by the MNDO method. It is shown that the reaction is exothermic and proceeds in two steps. The first step is the formation of a three-center -complex and this is the rate-determining step of the reaction. The second step is the rearrangement of the -complex to the product and this step requires a very small amount of activation energy. The activation barrier for the diboration reaction is 12.8 kcal/mol.The proposed mechanism is significantly different from those proposed earlier and explains all experimental data relating to this reaction.     

Theoretical study of unimolecular rearrangements of vinylidenes to acetylenes

The rearrangement of vinylidene to acetylene has been studied in detail by the density functional method, using Becke's three‐parameter exchange functional and the gradient‐corrected functional of Lee, Yang, and Parr. The rearrangement of the anion, as well as that of fluoro‐substituted systems, has also been investigated, in order to determine the effect of fluorine substitution on the activation barrier to the 1,2‐hydrogen shift, as well as the relative migratory aptitudes of hydrogen and fluorine. Natural bond orbital analysis is invoked to gain insight into the mechanisms of the rearrangements. Basis size effects are also discussed, particularly in relation to anionic systems. The need to include diffuse functions in geometry optimizations of anionic systems is reinforced by the present calculations. © 2004 Wiley Periodicals, Inc. Int J Quantum Chem, 2005     

Molecular approaches to solar energy conversion with coordination compounds anchored to semiconductor surfaces

Strategies toward the realization of molecular control of interfacial charge transfer at nanocrystalline semiconductor interfaces are described. Light excitation of coordination compounds, based on (dpi)6 transition metals, anchored to wide band-gap semiconductors, such as TiO2, can initiate electron-transfer processes that ultimately reduce the semiconductor. Such photoinduced charge-separation processes are a key step for solar energy conversion. The thermodynamics and kinetic rate constants for three different interfacial charge separation mechanisms are discussed. Tuning the energetic position of the semiconductor conduction band relative to the molecular sensitizer has provided new insights into interfacial charge transfer. Supramolecular compounds that efficiently absorb light, promote interfacial electron transfer, and feature additional functions such as intramolecular electron transfer when bound to semiconductor surfaces have also been studied. New approaches for enhancing charge-separation lifetimes for solar energy conversion are presented.     

The application of INAA to the geochemical analysis of single diamonds

Instrumental neutron activation analysis (INAA) has been applied to the analysis of 62 small (0.01–0.5 carat), single, inclusion-bearing and inclusion-free diamonds from South Africa, Brazil and Colorado. Up to 40 elements were detected at the ppb and ppt levels in individual diamonds of the eclogitic (basaltic affinity) and the peridotitic (ultramafic) paragenesis. The data obtained in this study can be used to distinguish between diamonds from the eclogitic and peridotitic parageneses and provides geochemical information on the environment in which diamonds crystallize. Further, the technique may prove to be useful in fingerprinting diamonds of different provenance areas.