Ring-opening polymerization of l-lactide by organotin(IV)alkoxides,R2Sn(OPr)2: Estimation of the activation parameters

The ring-opening polymerization of l-lactide, l-LA, to give poly-l-lactide by R₂Sn(OPrⁱ)₂ compounds, where R = Buⁿ and p-XC₆H₄ (X = CF₃, F, H, Me and OMe) has been studied in benzene over a temperature range. There is a relatively small variation in ΔH^≠ as a function of R with all the values falling within the range 11 ± 2 kcal mol⁻¹. The entropy of activation, ΔS^≠, is consistently large and negative, −50 ± 5 eu, supporting the view that the ring-opening event, the enchainment step involves a highly ordered transition state. The crystal and molecular structures of the compounds Ph₂Sn(OPrⁱ)₂, (p-FC₆H₄)₂Sn(OPrⁱ)₂ and (p-Me₂NC₆H₄)₃SnOPrⁱ are also reported. While the latter compound is monomeric in the solid state the former are both dimeric with a pair of bridging OPrⁱ ligands.     

Germanium(II)‐, Zinn(II)‐ und Blei(II)‐Derivate des polycyclischen Alumosiloxans [Ph2SiO]8[Al(O)OH]4

Germanium(II)‐, Tin(II)‐ and Lead(II)‐Derivatives of the polycyclic Alumosiloxane [Ph₂SiO]₈[Al(O)OH]₄ Five new derivatives of the polycyclic alumosiloxane [Ph₂SiO]₈[Al(O)OH]₄ have been synthesized by replacement of the protic hydrogen atoms on the hydroxy‐groups attached to the aluminium atoms by the divalent group 14 elements germanium, tin and lead. The compounds can be divided in those with one metal atom per alumosiloxane moiety, [Ph₂SiO]₈[Al(O)OH]₂[AlO₂]M (M=Ge, Sn), and those with complete substitution of the protic hydrogen atoms by metal atoms like [Ph₂SiO]₈[AlO₂]₄M₂ (M= Sn, Pb). Always one element of the series Ge, Sn, Pb is missing in the two types of compounds. Crystal structure analyses of [Ph₂SiO]₈[Al(O)OH]₂[AlO₂]₂M · 2 C₄H₈O₂ (M= Ge ( 1 ), Sn ( 2a )), [Ph₂SiO]₈[Al(O)OH]₂[AlO₂]₂Sn · 2 THF ( 2b ) and [Ph₂SiO]₈[AlO₂]₄M₂ (M= Sn ( 3 ), Pb ( 4 )) have been performed elucidating either polycyclic basket‐type ( 1 , 2a , 2b ) or closed polyhedral structures ( 3 , 4 ).     

Direct evidence of the dependence of surface state density on the size of SnO2 nanoparticles observed by scanning tunnelling spectroscopy

In this work, we report a scanning tunnelling spectroscopy (STS) study of 30 and 10 nm tin dioxide nanoparticles. The STS spectra give a surface band gap of 2.5 eV for both samples and show that the density of surface states in the band gap is around 6 times higher for the 30 nm particles than for the 10 nm particles. This provides direct experimental evidence for our theoretical model, which predicts a decrease in the surface state density as the particle size decreases, and partly accounts for the improved sensitivity of gas sensing devices fabricated with nanoparticles.     

The effects of the spinodal microstructure on the electrical properties of TiO2-SnO2 ceramics

The electrical properties of ceramics within the TiO₂-SnO₂ system which exhibit spinodal decomposition were investigated under different annealing conditions. Changes in the lattice parameter and the phase evolution of the spinodal decomposition, measured in terms of the volume fraction transformed X(t), were examined as a function of annealing time using X-ray diffraction. The room temperature dielectric properties were measured and compared to dielectric mixing rules. Doping with pentavalent Nb was found to slow the decomposition kinetics and a high permittivity (ε_r>1000) was induced. The origin of the high permittivity is linked to the formation of an electrically heterogeneous structure which is derived from the spinodal microstructure. Lastly, it was observed that Nb-doped TiO₂-SnO₂ ceramics exhibited non-linear current-voltage behavior which can be attributed to the negative temperature coefficient of resistance effect.     

Quantum Chemical Investigation of Monostanna[n]cyclacenes

Semiempirical molecular orbital treatment at the level of PM3 type calculations has been performed on the Hückel-type monostannacyclacenes having tin atom at the fusion and periposition of arenoid rings. The effect of tin substitution is found to be moderately destabilizing, but it becomes less pronounced in larger systems. The heats of formation values of fusion- and peri-type monostannacyclacenes, in some cases, are more endothermic and, in some cases, less endothermic as compared to the cyclacenes having the same n (the number of arenoid rings) value. The frontier molecular orbital energies, cryptoannulenic effects, geometries, and dipole moments of these structures have also been examined.     

n-羟基苯甲酸(n=p,m,o)在一种新的活性基底上的SERS研究(英文)

将银纳米颗粒覆盖在覆有铟锡氧化物的导电玻璃上,可以将其作为一种新型的表面增强拉曼散射(SERS)活性基底。将三种羟基苯甲酸分子作为探针分子在这种新的基底上进行检测,得到了很好的SERS信号,从中可反映出大量分子振动信息     

SnCl2 mediated efficient N,N-dialkylation of azides to tertiary-amine via potential stannaimine intermediate

A base free one-pot conversion of azides to N,N-dialkylamine is described. A two-step reaction pathway has been postulated invoking the intermediacy of stannaimine. This new carbon-nitrogen bond formation strategy adds to the repertoire of tin(II) chemistry.     

Structure Motifs of Sodium Stannides on the Tin‐rich Side of the Phase Diagram

The flexibility of the Sn‐Sn bond is acknowledged by the structural variety of compounds which are formed between tin and electropositive metals as minority components. As demonstrated for Na/Sn, already in the case of simple, binary systems a plethora of different structural motifs becomes obvious. Although the phase diagram of sodium and tin has been studied extensively for many years, the series of sodium stannides could be complemented by several new representatives during the last few years.     

Bulk and surface properties of liquid Al-Mg, Au-Sn, and Mg-Tl compound forming alloys

We have used phenomenological models based on statistical mechanics to study the bulk and surface properties of Au-Sn, Al-Mg, and Mg-Tl binary liquid alloys. Our study reveals that the three alloys are weakly ordered systems with the most stable intermetallic complexes at temperatures of 823 K, 1073 K and 923 K been AuSn, Al₃Mg₂ and Mg₄Tl, respectively. An analysis of Warren-Cowley short-range order parameter indicates that the weakest intermetallic compound is Al-Mg while Au-Sn is observed to be more chemically ordered than Mg-Tl. Furthermore, our surface properties calculations shows that Mg-atom and Sn-atom segregate to the surface over the whole concentration range of Al-Mg and Au-Sn alloys, respectively. In Mg-Tl, there is a competing effect between Tl-atom being drawn into the bulk and at the same time Tl-atom wanting to segregate to the surface over the whole concentration range.     

Electronic properties of nanocrystalline tin oxide dispersed in monolithic mesoporous silica

This paper is devoted to the study of the electrical properties of nanocrystalline tin oxide dispersed in the mesoporous silica. By immersing the silica in precursor solutions with different concentrations and heat-treatment, different samples were obtained. With precursor concentrations increasing from 0.1 to 4.0 M, the resistivities of the samples decrease from 3.15×10⁶ to 2.43×10³ Ω cm. The resistivity changes with the measurement time, and the deviations from Ohm's law in the voltage–current (V–I) measurements illustrate the capacitance property of these nanocomposites. For this new kind of nanocomposites, the obtained results provide experimental evidence of the conducting mechanism for tin oxide nanoparticles.