Electronic structure of M(BH4)4, M = Zr, Hf, and U, by variable photon-energy photoelectron spectroscopy and density functional calculations

Photoelectron (PE) spectra have been obtained for the M(BH(4))(4) (M = Zr, Hf and U) molecules in the 20-60 eV photon-energy range, and for M = U, also in the 90-120 eV region. Derived branching ratios (BR) and relative partial-photoionization cross sections (RPPICS) of the valence bands are used to confirm band assignment and demonstrate d-orbital covalency for all three compounds and f-orbital covalency for U(BH(4))(4). Core ionizations are identified and used to confirm resonance features in the RPPICS. The absorption spectrum of Zr(BH(4))(4) between 20 and 60 eV shows 4p absorption at 35.5 eV, coincident with the 4p-4d resonance in the RPPICS of the 1e and 2t(2) ionization bands of Zr(BH(4))(4). Less intense absorption bands at 32.5 and 33.8 eV correspond with shape resonance features in the 1a(1) and 1t(2) PE bands. The RPPICS of the f band of U(BH(4))(4) shows two strong resonant features between 95 and 120 eV. Direct photoemission of the 5f electrons from U(BH(4))(4) results only in the observation of the (2)F(5/2) ion state of [U(BH(4))(4)](+), but in the 5d-5f resonant region, a weak band corresponding to the (2)F(7/2) ion state is also observed. The splitting of the 1t(2) band of U(BH(4))(4) is attributed to a small contribution of U 6p semi-core electrons to this MO. Density functional calculations give a good estimate of the pattern of ionization energies, although the calculated absolute values are lower than the experimental values, the first IE by 0.5 eV for Zr(BH(4))(4) and Hf(BH(4))(4) and 1.0 eV for U(BH(4))(4). The MO compositions are in very good agreement with the deductions made from the BR and RPPICS analyses.     

A comparison of the solid-state structures of a series of phenylseleno-halogen and pseudohalogen compounds,PhSeX (X = Cl,CN, SCN)

Structural and spectroscopic data on the series of compounds “PhSeX”, where X = Cl, CN or SCN, are reported and compared with previously reported data on “PhSeX” systems (X = Br and I). The chloro-compound displays a “square” motif, Ph₄Se₄Cl₄, in the solid state, linked by long Se–Se bonds [2.993(3)–3.035(3) Å], and forms a loosely held network of Se₄ and Cl₄ squares in its extended structure. In contrast, the pseudohalogen derivatives, PhSeCN and PhSeSCN, consist of essentially monomeric units, which form chains held together by weak Se?N interactions in the solid state. These Se?N interactions are much shorter in PhSeCN, 3.023(3)–3.065(4) Å, than in PhSeSCN, 3.348(4) Å. Weaker Se?N contacts are also present between the chains. The structure of PhSeSCN described here is the first reported crystallographic study of a selenium thiocyanate compound. Spectroscopic studies suggest that all three compounds exist as monomers in solution. The results reported herein illustrate the subtle differences in the solid-state structures of PhSeX compounds.     

Determination of vicinal hydroxyl groups in poly(vinyl alcohol) (PVA)

An accurate procedure for the determination of 1,2-diol groups in styrene glycol and poly-(vinyl alcohol) has been demonstrated. The diols are cloven with periodate and the excess of this is determined by means of standard arsenite solution.     

The chemisorption of carbon monoxide on Ni(110) studied by electron energy loss spectroscopy

The vibrational spectrum of carbon monoxide chemisorbed on Ni(110) at 300K has been recorded as a function of surface coverage. At low and intermediate coverage the adsorbate is bonded either to single nickel atoms (linear site) or to two nickel atoms in contact (B₂ site). As the coverage approaches unity the spectrum changes rapidly until at saturation virtually all adsorbed molecules are of B₂ type.     

pH-sensitive holograms for continuous monitoring in plasma

Conventional electrochemical methods of determining the pH of body fluids have drawbacks. Newer optical methods offer the promise of miniaturisation and continuous in vivo measurements without drift. This report examines the ability of a holographic sensor based on a thin-film, biocompatible hydrogel (approximately 10 μm) of poly(2-hydroxyethyl methacrylate) and ionisable 2-(dimethylaminoethyl) methacrylate to accurately measure the pH of blood plasma ex vivo. It is found that the sensors behave in a fully reversible manner. After an initial calibration with buffers, they can measure pH over extended periods (more than 40 h). Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

The synthesis and structural characterisation of an homologous series of group 14 1-chloro-2,2-difluorovinyl compounds

A series of group 14 1-chloro-2,2-difluorovinyl compounds Ph₃E(CClCF₂) (E=Ge, Sn, Pb) has been prepared using the low temperature reactions of 1-chloro-2,2-difluorovinyllithium (LiCClCF₂), generated in situ from CF₃CH₂Cl (HCFC-133a) and n-butyllithium. These new materials have been fully characterised, including for E=Ge and Sn, by single crystal X-ray studies. This is the first time that any main-group 1-chloro-2,2-difluorovinyl compounds have been crystallographically studied.     

Interpretations of the differential cross-sections for pp → π−π+

The differential cross-sections for $\text{p}$p → π^?π⁺ in the momentum range 0.8 to 2.4 GeV/c (centre-of-mass energy 2.02 to 2.57 GeV) are analysed in terms of the possible existence of s-channel resonances. The systematics of the dip structures and the s-dependence of dσ/dt are presented.