Achirality in the low temperature structure and lattice modes of tris(acetylacetonate)iron(iii)

Tris(acetylacteonate) iron(III) is a relatively ubiquitous mononuclear inorganic coordination complex. The bidentate nature of the three acetylacteonate ligands coordinating around a single centre inevitably leads to structural isomeric forms, however whether or not this relates to chirality in the solid state has been questioned in the literature. Variable temperature neutron diffraction data down to T = 3 K, highlights the dynamic nature of the ligand environment, including the motions of the hydrogen atoms. The Fourier transform of the molecular dynamics simulation based on the experimentally determined structure was shown to closely reproduce the low temperature vibrational density of states obtained using inelastic neutron scattering

A Muon Spectroscopic and Computational Study of the Microscopic Electronic Structure in Thermoelectric Hybrid Silicon Nanostructures

Phenylacetylene-capped silicon nanoparticles (Phenyl-SiNPs) have attracted interest as a novel thermoelectric material. Here, we report a combined muon spectroscopic (μSR) and computational study of this material in solution to investigate the microscopic electronic structure of this system. For comparison, the model molecular compound tetrakis(2-phenylethynyl)silane has also been investigated. μSR measurements have shown that the muon isotropic hyperfine coupling constant, A μ, which depends on spin density at the muon, is greatly reduced for the Phenyl-SiNPs system when compared to the model compound. Results have also demonstrated that the temperature dependence of A μ for the Phenyl-SiNPs is of opposite sign and proportionally larger when compared to the model compound. Ab initio DFT methods have allowed us to determine the muon addition site in the model compound, while a wider computational study using both DFTB+ and CASTEP offers a qualitative explanation for the reduced coupling seen in the Phenyl-SiNPs system and also the contrasting temperature dependence of A μ for the two materials. Calculations suggest an increase in the density of electronic states at the energy level of the highest occupied molecular state for the Phenyl-SiNPs, even in the presence of an organic cap, suggesting a mechanism for enhanced electron transport in this system when compared to the tetrakis model compound

Hybrid silicon nanostructures with conductive ligands and their microscopic conductivities

Silicon nanoparticles (SiNPs) functionalized with conjugated molecules promise a potential pathway to generate a new category of thermoelectric materials. While the thermoelectric performance of materials based on phenyl-acetylene capped SiNPs has been proven, their low conductivity is still a problem for their general application. A muon study of phenyl-acetylene capped SiNPs has been recently carried out using the HiFi spectrometer at the Rutherford Appleton Laboratory, measuring the ALC spectra as a function of temperature. The results show a reduction in the measured line width of the resonance above room temperature, suggesting an activated behaviour for this system. This study shows that the muon study could be a powerful method to investigate microscopic conductivity of hybrid thermoelectric materials

Molecular sensors using a resonance Raman template

The potential use of resonance Raman spectroscopy as a molecular sensing tool is illustrated using a metalloporphyrin template and pyridine as an analyte. The equilibrium binding constant for the axial binding of pyridine to zinc tetraphenylporphyrin has been measured using resonance Raman spectroscopy. Although no new peaks are observed and the porphyrin peaks do not shift position, the quantification is made possible by the selective resonance enhancement of the template vibrations. The value for log k was determined by resonance Raman to be 3.65 ± 0.32, which compares well with previously published values estimated using absorption data. Values for log k were determined for a series of related compounds, the picolines, and these also compare favourably with those previously reported

Solid state effects in the IR spectrum of Octahydridosilasesquioxane

Infrared spectrum of Octahydridosilasesquioxane, in the solid state, is reported and analyzed to show the presence of significant solid state effects. This is in marked contrast with the reported Raman spectroscopic studies of this compound in the solid state where no evidence for such a proliferation of these effects were found. It is found that the normal modes with radial motion of the atoms in their normal coordinate are distinguishable from other vibrations by the distinct correlations between the band intensity and the solid state splitting observed in the IR spectrum. This new insight suggests an interchange of the literature assignments of the two modes v(27) and v(29) in the IR spectrum and a different origin to the doublet of bands in the Raman spectrum at 883 and 897 cm(-1). (C) 2003 Elsevier B.V. All rights reserved

Intermolecular Fermi resonance

The exceptionally broad feature at similar to3025 cm(-1) observed in the Raman spectrum of chloroform dissolved in liquid sulfur dioxide is shown to be due to the triple combination mode, nu(1)+nu(2)+nu(3), of sulfur dioxide gaining intensity by mixing with the fundamental C-H stretching mode of chloroform. Investigation of a number of similar systems shows that this broadening is unique to this system and is certainly not heterogeneous broadening due to C-H hydrogen bonding to SO2. This therefore is probably the first observation of the phenomenon of intermolecular Fermi resonance, between molecularly distinct species. (C) 2003 American Institute of Physics

Laying the foundation for understanding muon implantation in DNA: ab initio DFT calculations of the nucleic acid base muonium adducts

Muon spin relaxation studies with DNA and related materials have shown distinct differences in the behaviour of double stranded DNA compared to single stranded DNA and the free bases. Studies are now in progress to completely characterise the muonium adducts of all the bases of relevance to DNA and RNA. In order to assist in the assignments and to gain an insight into the electronic structures and physical properties of the bases, ab initio DFT calculations have been performed. The hyperfine frequencies exhibited by the Mu adducts of adenine, cytosine, guanine, thymine and uracil were found to span a sufficiently wide range to allow the opportunity for distinction between addition sites within each base and between these bases when incorporated in the DNA strand. The results are presented and discussed