Boron-doped diamond: Investigation of the stability of surface-doping versus bulk-doping using cyclic cluster model calculations

Boron-doped bulk diamond and the boron-doped hydrogen terminated (001) surface of diamond were investigated using the cyclic cluster model. Structure and stability of the hydrogen-terminated (001) surface were calculated and compared with experimental and other theoretical results from the literature. Boron-doping was modeled by substitution of a carbon atom by a boron atom in different positions with increasing distance from the surface up to boron-doped bulk diamond. In agreement with experiments on nanoclusters, boron is most stable in the first surface layers. (c) 2008 Wiley Periodicals, Inc. J Comput Chem, 2008.     

Synthese und Strukturen der ersten mehrkernigen Mangan‐Guanidin‐Komplexe und der ersten Mangan‐Komplexe mit mono‐protonierten Bis‐Guanidinliganden

Syntheses and Structures of the First Polynuclear Manganese Guanidine Complexes and of the First Manganese Complexes Containing Mono‐Protonated Bis‐Guanidine Ligands Metallation of two differently alkylated bis‐guanidine ligands containing a central pyridine functionality, namely N²,N⁶‐bis(1,3‐dimethylimidazolidin‐2‐ylidene)pyridine‐2,6‐diamine (DMEG₂py {N₇C₁₅H₂₃}, L¹ ) and N²,N⁶‐bis(1,1,3,3‐tetramethyl‐guanidine)pyridine‐2,6‐diamine (TMG₂py {N₇C₁₅H₂₇}, L² ), with manganese(II) bromide and chloride leads to the formation of the novel complexes [MnBr₃(TMG₂pyH)] ([MnBr₃(N₇C₁₅H₂₈)], ( 1 )), [MnBr₂(DMEG₂pyH)₂]²⁺ ([MnBr₂(N₇C₁₅H₂₄)₂]²⁺, ( 2 )), and [Mn₂X₃(DMEG₂py)₂]⁺ ([Mn₂X₃(N₇C₁₅H₂₃)₂]⁺; ( 3a ): X = Cl; ( 3b ): X = Br). 2 and 3 have been isolated as tetrahalomanganate salts. Single crystal X‐ray analyses show that all of them contain the manganese atoms in unusual pseudo‐tetrahedral coordination environments. 3a· 1/2[MnCl₄] and 3b· 1/2[MnBr₄] are isostructural and crystallize in the monoclinic space group C2c. The complex cations 3 exhibit a binuclear structure with two terminal and one bridging halide ion, respectively. The compounds 1 and 2 are mononuclear species crystallizing in the orthorhombic space group P2₁2₁2₁ in the case of 1 and in the triclinic space group in the case of 2· [MnBr₄]. The ability of L¹ and L² to bind either two manganese ions naked or only one of them in the mono‐protonated stage is the most remarkable property of these ligands. Further striking features are the spatial arrangements of the pyridine‐to‐manganese bonds which deviate significantly from the situation expected for nitrogen donor functions in sp² hybridized stages. Moreover, regarding each chelating ligand portion as a component which occupies one coordination site of the metal atom, a pseudo‐tetrahedral metal coordination is identified. To our knowledge, 1 and 2 are the first manganese complexes containing mono‐protonated bis‐guanidine ligands, whereas 3a and 3b are the first polynuclear manganese‐guanidine compounds known so far.     

The influence of X-ray resonant Raman scattering effects on the detection of copper(II) tetrasulphonated phthalocyanine (CuTSPc) thin-films deposited on gold electrodes

The influence of X-ray resonant Raman scattering on the detection capabilities of copper(II) tetrasulphonated phthalocyanine (CuTSPc) thin-films on gold electrodes has been investigated by means of synchrotron radiation X-ray fluorescence. In particular the paper focuses on the influence of the excitation energy in the relative narrow energy region of 9.2 to 11.7 keV on the detection limits and the peak-to-background ratios of copper.     

Biotinylated nanodiamond: simple and efficient functionalization of detonation diamond

We have developed a simple and efficient method for the covalent functionalization of detonation nanodiamond. After homogenization of the surface by borane reduction, the surface was modified with (3-aminopropyl)trimethoxysilane. Subsequent grafting of biotin yielded covalently biotinylated nanodiamond, which was characterized by FTIR spectroscopy, X-ray powder diffractometry, thermogravimetry, and elemental analysis. The activity was tested with horseradish peroxidase-labeled streptavidin. The surface loading of biotin was found to be 1.45 mmol g-1. The new material opens the way to covalently bonded diamond bioconjugates for labeling, drug delivery, and other applications.     

Structural importance of secondary interactions in molecules: origin of unconventional conformations of phosphine-borane adducts

The series of phosphine-borane adducts, Ph2(H3C--C[triple chemical bond]C)P--B(C6F5)3 (8 c), Ph(H3C--C[triple chemical bond]C)2P--B(C6F5)3 (8 b) and (H3C--C[triple chemical bond]C)3P--B(C6F5)3 (8 a), was prepared. The X-ray crystal structure analyses revealed close to eclipsed conformations for all members of this series with average dihedral angles theta(C-P-B-C) of 8.1 degrees (8 c), 12.3 degrees (8 b) and 20.3 degrees (8 a). Quantum chemical analysis of these compounds revealed the importance of a subtle interplay between competing attractive and repulsive secondary interactions, causing the surprising eclipsed conformational preference for systems of this degree of complexity. Some cyclic phosphine-borane adducts were studied for comparison.     

N-K electron energy-loss near-edge structures for TiN/VN layers: an ab initio and experimental study

We study N-K-edge electron energy-loss near-edge structures for well-defined TiN/VN bilayers grown on a MgO(100) substrate by both calculations and experiments. The structural relaxations and the electronic structure of TiN/VN multilayers are calculated using the Vienna Ab Initio Simulation Package computer code, which uses density functional theory to describe the electronic interaction. The effects of the core hole created in the excitation process are included in the calculations. For VN, off-stoichiometric effects due to nitrogen vacancies are modelled. The partial density of states (PDOS) for the N-K edge of atoms in the vicinity of the TiN/MgO interface revealed that two new peaks appear between 7 and 9 eV instead of a broad shoulder typical for the bulk. For the VN/TiN interface, the PDOS is modified only slightly, owing to similar bonding on both sides of the interface, and is thus very similar to the respective bulk spectra. An experimental spectrum taken at the VN/TiN interface is, however, well described by an average of the simulated spectra for VN and TiN bulk (interface). Such a finding is characteristic of an intermixed interface.      

Functionalized phosphorus analogues of the beta-diketiminato ligand systems: bis(N-arylphosphinimino)acetonitrile-derived complexes of rhodium and iridium

Staudinger reaction of dppm-CN (5) gave the corresponding bis(N-phenylphosphinimino)acetonitrile system (6). Deprotonation with LDA furnished the corresponding anionic ligand 9. Its reaction with [(CO)(2)RhCl](2) gave the corresponding kappa(2)N,N'-chelate complex 11. X-Ray diffraction revealed a non-planar boat-like conformation of the six-membered chelate ring in the crystal. Treatment of 9 with [(nbd)RhCl](2) gave the six-membered chelate complex 12 which features a different twist-like structure in the solid state, as does 13, which was formed by reacting 9 with [(cod)IrCl](2).