Synthesis and structure of bis(para-methoxyphenyl)selenoxide and its monohydrate. theoretical considerations of the hydration of diorganoselenium oxides

The title compound was prepared by base hydrolysis of (p-MeOC₆H₄)₂SeCl₂ in water and isolated as the crystalline monohydrate, (p-MeOC₆H₄)₂SeO·H₂O, in which the water molecule is associated via hydrogen-bonding. Water-free (p-MeOC₆H₄)₂SeO was obtained crystalline after drying and recrystallisation from toluene. Both crystal phases were investigated by single crystal X-ray diffraction. Preliminary DFT calculations at the B3LYP/LANL2DZdp level of theory suggest that the hydrogen bonded complexes R₂SeO·H₂O (R = H, Me, Ph) are by 2.79, 3.36 and 11.10 kcal mol^-1 more stable than the corresponding elusive diorganoselenium dihydroxides R₂Se(OH)₂. The hydrogen bond energies of R₂SeO·H₂O (R = H, Me, Ph) are 5.98, 7.18 and 5.89 kcal mol^-1.

Optimal vigilance level and hiring illegal immigrants

This paper assumes a Ricardian Economy and analyzes migration of illegal unskilled workers in a model of Cournot Duopoly where firms are producing homogenous and non-traded goods, and hiring illegal immigrants. The focus is on the behaviours of firms and the implications for the output, prices and employment of domestic workers in that industry. A two-stage simultaneous move game is set up: In Stage 1, for a given technology and vigilance level, each individual firm will decide whether to hire illegal immigrants. In Stage 2, each firm will choose the Cournot output level. Using this structure, we provide additional insights as to why firms hire illegal workers and what motivates these firms in their hiring practices. Furthermore the presence of illegal immigrants may create more employment for domestic workers and a social planner can be strategic in choosing optimal level of vigilance as we have shown that multiple solutions for optimal vigilance are possible and also Pareto ranked.

Synthesis and structure of tris(triphenyltin)benzene-1,3,5-tricarboxylate and its tri-DMSO adduct

The molecular structure of (Ph₃SnO₂C)₃C₆H₃ reveals distorted tetrahedral C₃O geometries for each tin atom. No intermolecular Sn...O associations occur between the molecules so that the trinuclear molecule may be considered monomeric. An increase in coordination number at tin is indicated by ¹¹⁹Sn NMR measurements conducted in d₆-DMSO solution and this has been confirmed by a structure analysis of (DMSO·Ph₃SnO₂C)₃C₆H₃·2 DMSO. In this structure, the tin atom geometries are distorted trigonal bipyramidal, existing within trans-C₃O₂ donor sets. Thus, while is it possible for the tin atoms to increase their coordination numbers in (Ph₃SnO₂C)₃C₆H₃, molecular aggregation to form polymeric arrays is precluded, most likely due to steric constraints.

Synthesis and structure of an ether-bridged double ladder compound: potential in host - guest chemistry

The synthesis of the first example of an organotin double ladder (6) containing a functional group within the spacer is reported. In the solid state, compound 6 shows an interlaminar cavity whose size and shape suggest the possibility of host–guest chemistry. ¹¹⁹Sn-NMR and ESMS show that compound 6 undergoes extensive dissociation in solution. ESMS of compound 6 to which have been added Li⁺, Na⁺, Mg²⁺ or Cu²⁺ show only minimal interaction.

Synthesis and structure of 1,3,5-tris(diorganohydroxysilyl)benzenes. Novel building blocks in supramolecular silanol chemistry

The 1,3,5-tris(diorganohydroxysilyl)benzenes 1,3,5-(HOR₂Si)₃C₆H₃ (TMSB, R = Me; TPSB, R = Ph) have been prepared and fully characterized by X-ray crystallography. The crystal structure of TMSB features pairwise connected layers, in which the molecules are involved in interlayer hydrogen bonding. The supramolecular hydrogen bond motif may be described as a 12-membered ring that adopts a chair conformation. TPSB forms an equimolar inclusion complex with water, which is associated via hydrogen bonding and apparently fills a void in the crystal packing. In this case, the supramolecular hydrogen bond motif may be described as an eight-membered ring. Two of the water molecules are also associated, giving rise to a water dimer entrapped in the silanol matrix. Besides the hydrogen bonds, the crystal structure of the TPSB·H₂O complex reveals intra- and intermolecular C-H··· π stacking of most of the phenyl groups. Electrospray mass spectrometry shows that TPSB undergoes supramolecular complex formation with a variety of N-donors such as 4-(dimethylamino)pyridine, N,N,N',N'-tetramethylethylenediamine, imidazole, 2-(dimethylamino)pyridine, and 2,2'-dipyridylamine.

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Synthesis and structure of new oligomethylene-bridged double ladders. How far can the layers be separated?

The synthesis of the α,ω-bis[dichloro(trimethylsilylmethyl)stannyl]alkanes, (Me₃SiCH₂)C1₂Sn(CH₂)_nSnCl₂(CH₂SiMe₃) (13, n=5; 14, n=6; 15, n=7; 16, n=8; 17, n=10; 18, n=12) and the corresponding oligomethylene-bridged diorganotin oxides [(Me₃SiCH₂)(O)Sn(CH₂)_nSn(O)(CH₂SiMe₃)]_m (19, n=5; 20, n=6; 21, n=7; 22, n=8; 23, n=10; 24; n=12) is reported. The reaction of the diorganodichlorostannanes 13–18 with the corresponding diorganotin oxides 19–24 provided the spacer-bridged tetraorganodistannoxanes {[(Me₃SiCH₂)ClSn(CH₂)_nSnCl(CH₂SiMe₃)]O}₄ (25, n=5; 26, n=6; 27, n=7; 28, n=8; 29, n=10; 30, n=12). Compounds 13–30 have been identified by elemental analyses and multinuclear NMR spectroscopy. Compounds 25, 27, 29 and 30 have also been characterised by single crystal X-ray diffraction analysis and electrospray mass spectrometry. For the latter the essential double ladder motif is maintained for all n in the solid state, but subtle changes in alignment of the ladder planes occur. Separation between the two layers of the double ladder ranges from approx. 8.7  Å (for 25, n=5) to approx. 15 Å (for 30, n=12). In solution there is some dissociation of the double ladders into the corresponding dimers. The degree of dissociation is favoured by increasing oligomethylene chain length n.

A comparative study of construction industry size and structure between the UK and Australia and the significance of industry fragmentation

While comparing both the size and structure between the UK and Australian construction industries, this study reveals that the UK construction industry is about two and a half times larger than the Australian construction industry, and both industries are dominated by the proportion of small firms. The issue of fragmentation is characteristic of the construction industries in these two countries, and beyond. This study then develops a self recruiting-subletting cost indifference point model to explain why fragmentation occurs. Although the high proportion of small firms in the construction industry has been criticised as it prevents the exploitation of economies of scale, the self recruiting-subletting cost indifference point model theoretically proposes that subletting is usually profitable for construction firms. Thus the size distribution of the construction industry has a propensity to skew towards small firms.

Growth and structure of prismatic boron nitride nanorods

Prismatic boron nitride nanorods have been grown on single crystal silicon substrates by mechanical ball-milling followed by annealing at 1300 °C. Growth takes place by rapid surface diffusion of BN molecules, and follows heterogeneous nucleation at catalytic particles of an Fe/Si alloy. Lattice imaging transmission electron microscopy studies reveal a central axial row of rather small truncated pyramidal nanovoids on each nanorod, surrounded by three basal planar BN domains which, with successive deposition of epitaxial layers adapt to the void geometry by crystallographic faceting. The bulk strain in the nanorods is taken up by the presence of what appear to be simple nanostacking faults in the external, near-surface domains which, like the nanovoids are regularly repetitive along the nanorod length. Growth terminates with a clear cuneiform tip for each nanorod. Lateral nanorod dimensions are essentially determined by the size of the catalytic particle, which remains as a foundation essentially responsible for base growth. Growth, structure, and dominating facets are shown to be consistent with a system which seeks lowest bulk and surface energies according to the well-known thermodynamics of the capillarity of solids.

Slow component of VO2 during level and uphill treadmill running : relationship to aerobic fitness in endurance runners

The aim of this study was to compare the oxygen uptake (VO^sub 2^) slow component (SC) during level and uphill running in endurance runners, and to identify associations between the SC and the following aerobic fitness indicators: peak VO^sub 2^, running speed associated with the peak VO^sub 2^ (Vpeak), running speed at the lactic threshold and the VO^sub 2^ fraction elicited at the lactic threshold. Fourteen male endurance-trained runners underwent several 6-min bouts of level (LTR) and 10.5% uphill treadmill running. VO^sub 2^ SC was calculated as the difference between mean VO^sub 2^ during the 6th and the 3rd minutes. The highest mean values for the SC were 181.9±240.2 mL*min^sup -1^ for level running at ~94% peak VO^sub 2^ and 105.4±154.6 mL*min^sup -1^ for uphill running at ~90% peak VO^sub 2^. The SC observed during the last bout of the LTR correlated with peak VO^sub 2^ and with Vpeak (-0.71 and -0.76, P<0.05, respectively). The results show that for endurance-trained runners the magnitude of the SC is not affected by the treadmill gradient and that within a homogeneous sample of endurance-trained runners the SC does not correlate with indicators of aerobic fitness.