Titanium arsenide films from the atmospheric pressure chemical vapour deposition of tetrakisdimethylamidotitanium and tert-butylarsine

Thin films of titanium arsenide have been deposited from the atmospheric pressure chemical vapour deposition (APCVD) of [Ti(NMe(2))(4)] and (t)BuAsH(2) at substrate temperatures between 350-550 °C. Highly reflective, silver coloured films were obtained which showed borderline metallic-semiconductor resistivities. The titanium arsenide films were analyzed by scanning electron microscopy (SEM), Raman spectroscopy, wavelength dispersive analysis of X-rays (WDX), powder X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The films showed variable titanium to arsenic ratios but at substrate temperatures of 500 and 550 °C films with a 1 : 1 ratio of Ti : As, consistent with the composition TiAs, were deposited. Powder XRD showed that all of the films were crystalline and consistent with the formation of TiAs. Both nitrogen and carbon contamination of the films were negligible.     

Synthesis, spectral characterization, and structural investigation of mononuclear salen-type Cu(II) and Zn(II) complexes of a potentially octadentate N2O6 Schiff base ligand derived from binaphthol

A new potentially octadentate N₂O₆ Schiff base ligand, H₂L derived from the condensation of 2,2′-(1,1′-binaphthyl-2,2′-diylbis(oxy))dianiline and o-vanillin, along with its copper(II) and zinc(II) complexes, is synthesized and has been characterized by elemental analyses, IR, UV–vis, ¹H and ¹³C NMR spectra, as well as conductivity measurements. H₂L forms mononuclear complexes of 1:1 (metal:ligand) stoichiometry with Cu(II) and Zn(II), and conductivity data confirm the non-electrolyte nature of these complexes. The [ZnL] and [CuL] complexes display very different solid-state structures, as determined by X-ray crystallography. While the [ZnL] complex has a distorted octahedral geometry about the metal, the [CuL] complex displays a distorted square planar geometry about the copper, with long Cu–O(ether) distances of 2.667 Å.     

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Stabilization of coordinated carbonate in aqueous acidic solution: steric inhibition of protonation in Co(III) complexes containing chelated carbonate

The synthesis, characterization, X-ray crystal structures, and reactivity in aqueous acidic solution of the Co(III) carbonate complexes [Co(tpa)(O2CO)]ClO4.H2O, [Co(Me-tpa)(O2CO)]ClO4.0.5H2O, [Co(Me2-tpa)(O2CO)]ClO4.0.5H2O, and [Co(Me3-tpa)(O2CO)]ClO4 are reported (tpa = tris(2-pyridylmethyl)amine; Me-tpa, Me2-tpa, and Me3-tpa are derivatives of tpa containing one, two, and three 6-methylpyridyl rings, respectively). The complexes display very different spectroscopic and 59Co NMR properties, consistent with the decreasing ligand field strength of the tripodal amine ligands in the order tpa > Me-tpa > Me(2)-tpa > Me3-tpa. X-ray structural data show an increase in the average Co-N bond distances as the number of methyl groups on the tripodal amine ligand increases, and this is the result of steric interactions between the methyl groups and the carbonate ligand and between the methyl groups themselves. Rate data for the acid hydrolysis of [Co(tpa)(O2CO)]+ (I = 1.0 M (NaClO4), 25.0 degrees C) over the [HClO4] range of 0.10-1.0 M are consistent with a previously proposed mechanism involving protonation of the carbonate ligand prior to ring-opening, but the equilibrium constant for protonation is smaller in this case than those obtained previously, as is the equilibrium constant for proton transfer from the exo to the endo O atoms. Comparative rate data ([HCl] = 6.0 M, 25.0 degrees C) for the four complexes show that those containing methylated ligands undergo acid hydrolysis between 25 and 90 times more slowly than [Co(tpa)(O2CO)]+ under the same conditions, and it is proposed that this rate difference is a result of steric factors. Inspection of space-filling diagrams shows that one of the endo oxygen atoms is significantly sterically hindered by the methyl groups of the tripodal amine ligands, thus inhibiting protonation at this site and leading to slower observed rates of hydrolysis. The results obtained in this study are consistent with the endo oxygen atoms being the mechanistically important site of protonation in the acid hydrolysis of metal complexes containing chelated carbonate.     

Accuracy of the multipole expansion applied to a sphere in a creeping flow parallel to a wall

An example system is studied to discuss precision of the multipoleexpansion, applied to determine forces exerted on particlesby a viscous low-Reynolds-number fluid flow. A single spherein an ambient flow (pure shear, quadratic, and modulated shear)parallel to a close plane wall is considered. Forces and torquesexerted by the ambient flow on a motionless sphere are evaluated.Their precision is determined and related to a multipole orderof the truncation. Similar analysis is performed for a movingsphere with no ambient flow and for a freely moving sphere.Relative motion of the sphere with respect to the wall givesrise to strong lubrication interactions. It is analysed howthese interactions affect accuracy of the pure multipole expansion,and what are the smallest distances where it becomes insufficient.An alternative precise method is applied, in which lubricationexpressions are subtracted from the hydrodynamic forces andtorques, and the residue is evaluated as a fast-convergent seriesof inverse powers of the distance between the sphere centreand the wall. The accuracy of this procedure is carefully analysed.