The electrochemical reduction of an unsaturated mixed-metal cluster anion: Synthesis and x-ray crystal structure of [(Ph3P)2N][{Os3H(CO)10}2Ag]

The unsaturated mixed-metal cluster anion [{Os₃H(CO)₁₀}₂Ag]^? has been prepared by the reaction of [(Ph₃P)₂N][Os₃H(CO)₁₁] with Ag[PF₆], and the anion has been shown by an X-ray analysis to consist of an Ag^I atom linking together two “Os₃H(CO)₁₀” fragments. The electrochemistry of this complex has been investigated and it has been shown to undergo two one-electron reductions.     

Testing heteroscedasticity by wavelets in a nonparametric regression model

In the nonparametric regression models, a homoscedastic structure is usually assumed. However, the homoscedasticity cannot be guaranteed a priori. Hence, testing the heteroscedasticity is needed. In this paper we propose a consistent nonparametric test for heteroscedasticity, based on wavelets. The empirical wavelet coefficients of the conditional variance in a regression model are defined first. Then they are shown to be asymptotically normal, based on which a test statistic for the heteroscedasticity is constructed by using Fan's wavelet thresholding idea. Simulations show that our test is superior to the traditional nonparametric test.     

Spinning Sidebands in Slow-Magic-Angle-Spinning NMR Spectra Arising from TightlyJ-Coupled Spin Pairs

Complex spinning sidebands are observed in magic-angle-spinning (MAS) NMR spectra arising from isolated tightlyJ-coupled spin pairs under slow spinning conditions. Such spinning sidebands are sensitive to the magnitude and relative orientation of the chemical-shift tensors, the dipolar-coupling tensor, and the sign of the indirect spin–spin (J) coupling. We show that it is possible to extract information concerning such NMR parameters from an analysis of the observed spinning sidebands. As an example, numerical simulations are carried out to reproduce observed³¹P MAS NMR spectra of a phosphole tetramer (1) ando-bis(diphenylphosphino)benzene (2), so that invaluable information concerning the orientations of the phosphorus chemical-shift tensors and the sign ofJ(³¹P,³¹P) can be deduced. Simulations are carried out by numerically evaluating the spin-density matrix of the spin system.     

Synthesis and crystal structure of nickel(Ⅱ) and zinc(Ⅱ) complexes with 2,4-bis(3,5-dimethylpyrazol-1-yl)-6-methoxyl-1,3,5-triazine

2,4-Bis(3,5-dimethylpyrazol-1-yl)-6-methoxyl-1,3,5-triazine(bpt) has been synthesized by using a new, simple and general method with high yields. Reactions of bpt with Ni(CIO4)2 · 6H2O and Zn(CIO4)2 · 6H2O in methanol gave mononuclear complex [Ni(bpt)2] · (CIO4)2 · H2O and ternary complex [Zn(mpt)2(dmp)](CIO4)2 respectively, where mpt (2,4-dimethoxy-6-(3,5-dimethyl-pyrazol-1-yl)-1,3,5-triazine) and dmp(3,5-dimethylpyrazole) are the alcoholysis products of bpt in the presence of Zn2+ ion. A possible mechanism for this catalytic reaction was proposed. X-ray crystal structure for ligand bpt, Ni and Zn complexes are reported. The protonated form of the ligand bpt crystallizes as its perchlorate salt including one molecule of water, [Hbpt · H2O · CIO4]. The proton is located on one pyrazole N-atom. [Hbpt ?H2O ?CIO4], in which [Hbpt]+ is in cis-cis conformation, are packed in slipped stacks of approximately parallel layers. The π-π overlap interactions between the non-protonized pyrazoles of the adjace     

Quantitative analysis of Earth’s field NMR spectra of strongly-coupled heteronuclear systems

In the Earth’s magnetic field, it is possible to observe spin systems consisting of unlike spins that exhibit strongly coupled second-order NMR spectra. Such spectra result when the J-coupling between two unlike spins is of the same order of magnitude as the difference in their Larmor precession frequencies. Although the analysis of second-order spectra involving only spin-½ nuclei has been discussed since the early days of NMR spectroscopy, NMR spectra involving spin-½ nuclei and quadrupolar (I > ½) nuclei have rarely been treated. Two examples are presented here, the tetrahydroborate anion, , and the ammonium cation, . For the tetrahydroborate anion, ¹J(¹¹B,¹H) = 80.9 Hz, and in an Earth’s field of 53.3 μT, ν(¹H) = 2269 Hz and ν(¹¹B) = 728 Hz. The ¹H NMR spectra exhibit features that both first- and second-order perturbation theory are unable to reproduce. On the other hand, second-order perturbation theory adequately describes ¹H NMR spectra of the ammonium anion, , where ¹J(¹⁴N,¹H) = 52.75 Hz when ν(¹H) = 2269 Hz and ν(¹⁴N) = 164 Hz. Contrary to an early report, we find that the ¹H NMR spectra are independent of the sign of ¹J(¹⁴N,¹H). Exact analysis of two-spin systems consisting of quadrupolar nuclei and spin-½ nuclei are also discussed.     

石墨炔原子催化剂的崭新道路:基于自验证机器学习方法的筛选策略

近年来, 原子催化剂(ACs)引起了广泛的研究关注. 目前该领域的长足发展受限于贵金属的使用和单原子催化剂(SACs)的性能有限. 本文总结了利用密度泛函理论(DFT)和机器学习(ML)方法筛选高效的基于石墨炔(GDY)的原子催化剂的工作. 研究表明, Pd, Co, Pt和Hg可以形成稳定的零价过渡金属-石墨炔组合(TM-GDY), 而镧系-过渡金属的双原子催化剂(Ln-TM DAC)组合通过f-d轨道耦合作用可以获得有效的催化性能提升. 进一步分析表明, 主族元素与过渡金属和镧系金属的结合可以通过p轨道耦合保持高电活性, 从而构成高度稳定的GDY-DAC系统, 机器学习算法也揭示了s,p轨道的作用. 此外, 理论算法技术在筛选催化水分解析氢反应(HER)的高效组合上也表现出了优越性, 创新性地预测了石墨炔-原子催化剂在实际催化反应中的潜能. 本综合评述可为未来设计新型原子催化剂提供新的思路与策略.     

Analysis of the Symmetry of Crystal Packing Forces by Methyl Proton Tunneling: A Strategy for the Unambiguous Assignment of the Magnetic Jahn – Teller Effect in Molecules

Intrinsic and extrinsic forces behind the distortion in metal atom clusters can be readily distinguished provided that the clusters are embedded in a suitable ligand environment and that the tunneling of the protons in the peripheral ligands is then analyzed by inelastic neutron scattering. For the [Cr₃O(OOCCH₃)₆(H₂O)₃]Cl⋅6 H₂O model system studied, the tunneling process is very sensitive to the local environment. Thus a tool is available to allow a better assessment of the cause of structural distortions.     

锑掺杂二氧化锡（ATO）纳米颗粒：共沸蒸馏干燥法制备及隔热性能

以五水合四氯化锡、三氯化锑为原料,乙醇为溶剂,氨水为沉淀剂,乙酸异戊酯为共沸溶剂,共沸蒸馏干燥前驱体溶胶,650℃煅烧后制备了单分散不同锑掺杂量的掺锑二氧化锡（ATO）纳米颗粒。结果表明,锑含量对颗粒粒径、光电性质具有重要影响,10mol%锑掺杂量时,样品具有最低的电阻率以及最优良的光学性质（最高的可见光透过率与近红外屏蔽效果）,电学性质。ATO与聚氨酯复合涂膜玻璃隔热测试表明,涂层薄膜具有优良的隔热效果,能够有效地减小热量的传递与扩散。     

Hydrogen and deuterium atoms in octasilsesquioxanes: experimental and computational studies

The rate of detrapping of atomic hydrogen from several octasilsesquioxanes is the same for dissolved and solid samples and is independent of the presence of other species such as free radicals or oxygen; varying the cage substituents leads to only minor differences in the activation parameters. Hydrogen atoms are found to be more strongly stabilized in homosubstituted octasilsesquioxanes compared with singly Ge-substituted cages. A kinetic isotope effect observed for the detrapping of H and D from MeT(8) is ascribed to the difference in the zero-point energies of the trapped atoms. There is a secondary H/D isotope effect in the temperature dependence of the (29)Si-superhyperfine splitting constants in the range 228-353 K. Cage relaxation has a substantial effect on the detrapping barrier but little influence on the intracage potential. Calculations using a rigid cage approximation give satisfactory agreement with zero-point parameters extracted from experimental data. Different model chemistries yield qualitatively different pictures of the dependence of the hyperfine coupling constant of the trapped H atom upon the detrapping coordinate. Within an isotropic approximation of the vibrational displacements, the B3LYP data give fairly close agreement with the experimental temperature dependence, subject to a shift of the absolute value related to known weaknesses of the method. For the Si(7)Ge cage, it is found that the transition state in which the H atom passes through a Ge-containing face is strongly favored, accounting for the larger detrapping rate parameters observed experimentally for this species.     

Novel integrated paired emitter-detector diode (PEDD) as a miniaturized photometric detector in HPLC

A novel low power, low cost, highly sensitive, miniaturized light emitting diode (LED) based flow detector has been used as optical detector for the detection of sample components in high performance liquid chromatography (HPLC). This colorimetric detector employs two LEDs, one operating in normal mode as a light source and the other is reverse biased to work as a light detector. Instead of measuring the photocurrent directly, a simple timer circuit is used to measure the time taken for the photocurrent generated by the emitter LED (lambda(max) 500 nm) to discharge the detector LED (lambda(max) 621 nm) from 5 V (logic 1) to 1.7 V (logic 0) to give digital output directly without using an A/D converter. Employing a post-column reagent method, a Nucleosil 100-7 column (functionalized with iminodiacetic acid (IDA) groups) was used to separate a mixture of transition metal complexes, manganese(II) and cobalt(II) in 4-(2-pyridylazo)-resorcinol (PAR). All optical measurements were taken by using both the in-built HPLC variable wavelength detector and the proposed paired-emitter-detector-diode (PEDD) optical detector configured in-line for data comparison. The concentration range investigated using the PEDD was found to give a linear response to the Mn(II) and Co(II) PAR complexes. The effects of flow rate and emitter LED light source intensity were investigated. Under optimised conditions the PEDD detector offered a linear range of 0.9-100 microM and LOD of 0.09 microM for Mn-PAR complex. A linear range of 0.2-100 microM and LOD of 0.09 microM for Co-PAR complex was achieved.