Cluster chemistry: XXIX. Preparation of cluster complexes containing aryldiazo ligands: Crystal structure of [HRu3(μ-N2C6H4)(μ3-PhAsCH2AsPh2)(CO)8]

Hydrogenation of [Ru₃(CO)₁₀(L₂)] (L₂ = dppm or dpam) affords [HRu₃(μ₃-PhECH₂EPh₂)(CO)₉] (E = P or As), which is deprotonated by K[HBBu₃^s] . Reactions of the anions with [PhN₂] [PF₆] give [Ru₃(μ-N₂Ph)(μ₃-PhECH₂EPh₂)(CO)₉], which undergo facile cyclometallation reactions when heated, as revealed by an X-ray structure of the title complex.     

Chemical vapor detection using single-walled carbon nanotubes

Single-walled carbon nanotubes possess unique properties that make them a potentially ideal material for chemical sensing. However, their extremely small size also presents technical challenges for realizing a practical sensor technology. In this tutorial review we explore the transduction physics by which the presence of molecular adsorbates is converted into a measurable electronic signal, and we identify solutions to the problems such as nanotube device fabrication and large, low-frequency noise that have inhibited commercial sensor development. Finally, we examine strategies to provide the necessary chemical specificity to realize a nanotube-based detection system for trace-level chemical vapor detection.     

Heat capacity studies of the iron oxyhydroxides akaganéite (β-FeOOH) and lepidocrocite (γ-FeOOH)

The iron oxides and iron oxyhydroxides exist as several different polymorphs, and a thermodynamic understanding of these polymorphs can provide us with an understanding of their relative stability and chemical reactivity. This study provides heat capacity measurements for lepidocrocite (γ-FeOOH) over the temperature range (0.8 to 38) K and akaganéite (β-FeOOH) over the range (0.7 to 302) K. Fits of the heat capacity of the two samples below T = 15 K showed similar behavior to previously published fits of goethite (α-FeOOH), which required a linear term and an anisotropic gap parameter to model accurately the antiferromagnetic spin–wave contributions. The akaganéite measurements were compared to previously reported measurements all of which showed significant disagreement. It is believed that the measurements reported here are the most reliable. Also, the presence of adsorbed water contributes significantly to the heat capacity of akaganéite, and the standard molar entropy at T = 298.15 K of the hydrated form was calculated to be (81.8 ± 2) J · mol^?1 · K^?1.     

Heat capacity,third-law entropy,and low-temperature physical behavior of bulk hematite (α-Fe2O3)

The constant pressure heat capacity of a bulk hematite powder was measured using a Quantum Design physical properties measurement system (PPMS). The results of two series showed good precision and agreed well with measurements reported by Westrum and Grønvold. The standard molar entropy at T = 298.15 K was calculated to be (87.32 ± 2) J · mol^?1 · K^?1 for Series 1 and (87.27 ± 2) J · mol^?1 · K^?1 for Series 2, which are in good agreement with the value of (87.40 ± 0.2) J · mol^?1 · K^?1 (originally 20.889 cal · deg^?1 · mole^?1) calculated by Westrum and Grønvold. No anomaly was observed for the Morin transition, and theoretical fits below T = 15 K required a ferromagnetic T^3/2 term.     

Stir-bar sorptive extraction and thermal desorption-ion mobility spectrometry for the determination of trinitrotoluene and l,3,5-trinitro-l,3,5-triazine in water samples

Stir-bar sorptive extraction (SBSE) is interfaced to ion mobility spectrometry (IMS) for the rapid detection of trace analytes, with the explosives, trinitrotoluene (TNT) and l,3,5-trinitro-l,3,5-triazine (RDX) shown as examples. SBSE retains its inherent advantages as a sensitive, straightforward, solventless, and inexpensive method. Additionally, the new SBSE-IMS technique exhibits excellent sensitivity, has onsite field analysis capabilities and provides the potential to detect and quantitate analytes that are difficult to accomplish using gas chromatography (GC) or high-performance liquid chromatography (HPLC). The SBSE-IMS technique is shown to be an effective method for the low-level detection of TNT and RDX from water with method standard deviation of 8.6% for TNT and 6.6% for RDX. The short desorption time of 60 s and analysis time of less than 20 ms along with limits of detection of 0.1 ng/mL for TNT and 1.5 ng/mL for RDX and render the method potentially useful for trace analysis. Desorption profiles showing the kinetics of analyte transfer from the stir-bar into the IMS are shown and discussed; the SBSE-IMS configuration shows very rapid desorption from the stir-bar, with the analytes completely transferred in most cases, in under 1 min.     

Synthesis of substituted 2-amino-4-quinazolinones via ortho-fluorobenzoyl guanidines

A novel route to 12 substituted 2-amino-4-quinazolinones is described. Starting from 2,6-difluoro-4-methoxybenzonitrile, substitution of one of the fluorine atoms either directly or indirectly with heterocycles (e.g., pyridyl, thiazolyl, pyrazolyl) followed by hydrolysis of the nitrile gave a series of o-fluorobenzoic acid derivatives. Condensation with a set of six N,N-disubstituted guanidines followed by base-promoted ring closure afforded 2-amino-4-quinazolinone derivatives.     

Competition Between Thiol and Phosphine Ligands During the Synthesis of Au Nanoclusters

Reduction of a mixture of Ph₃PAuCl and CH₃(CH₂)₅SH with NaBH₄ yields predominately phosphine encapsulated nanoclusters with Au cores <1 nm, similar to the product isolated when the alkane thiol is not present in the reaction. When Et₃N is added to a solution of Ph₃PAuCl and CH₃(CH₂)₅SH, a Au–S bond is formed, and the subsequent reduction of this thiolate results in the formation of >2 nm core thiol encapsulated Au nanoclusters as the majority product. This latter reduction has been examined in more detail through in situ ³¹P NMR experiments, and a solution exchange reaction is observed wherein the PPh₃ generated by the reduction displaces thiol from the surface of the nanocluster product. This thiol displacement occurs with loss of a Au atom from the nanocluster core, as observed by NMR. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.