A tetranuclear complex from the employment of pyridine-2,6-dimethanol in copper(II) nitrate chemistry: Synthetic,structural and magnetic studies

The use of pyridine-2,6-dimethanol (pdmH₂) in copper(II) nitrate chemistry is reported. The reaction of Cu(NO₃)₂·3H₂O with one equivalent of pdmH₂ in MeCN affords the known mononuclear complex [Cu(pdmH₂)₂](NO₃)₂ (1) in high-yield. The reaction of 1 and NaOMe in an 1:1 ratio, as well as the reaction between Cu(NO₃)₂·3H₂O, pdmH₂ and NaOMe in an 1:1:1 ratio, in MeOH gives the tetranuclear complex [Cu₄(NO₃)₂(pdmH)₄(H₂O)(MeOH)](NO₃)₂ (2) in moderate yields. The cation of 2 possesses a slightly distorted tetrahedral Cu₄ topology with a [Cu₄(μ₂-OR)₄]⁴⁺ core. The pdmH⁻ ions behave as η¹:η¹:η²:μ₂ ligands. Strong intramolecular hydrogen bonds and π–π stacking interactions provide thermodynamic stability on compound 2. Variable-temperature, solid-state dc magnetic studies were carried out on complex 2 in the 2.0–300 K range. The data indicate predominant antiferromagnetic exchange interactions and a resulting S = 0 ground state, which is expected for a solely, μ₂-alkoxide-bridged system with obtuse Cu–O–Cu bond angles that magnetically behaves as a Cu₄ ring. A simplified 1 − J model was found to be adequate to describe the variable-temperature dc susceptibility data. The data were fitted to the appropriate equation derived from the Hamiltonian H = −J₁(S₁ · S₂ + S₂ · S₄ + S₃ · S₄ + S₁ · S₃), giving the parameters J₁ = −99.5 cm⁻¹ and g = 2.11(4). The combined work demonstrates the ligating flexibility of the pdmH₂ chelate and its usefulness in the synthesis of oligo- and polynuclear Cu^II_x clusters with interesting structural and magnetic properties, without requiring the co-presence of carboxylate ligands.     

Synthesis, Characterization and Properties of a Novel Cationic Hexanuclear Cyclic Guanidinate Copper(I) Cluster of High Solubility in Non-polar Solvents

The reaction of copper(I) tetra-acetonitrile hexaflourophosphate with LiTEhpp (the lithium salt of 3,3,7,7-tetraethyl-1,3,4,6,7,8-hexahydro-2H-pyrimido[1,2-??)pyrimidine) at low temperature (?80?°C) in THF under Schlenk conditions, produces a cluster salt tetrakis(3,3,9,9-tetraethyl-1,5,7-triazabicyclo[4.4.0]dec-4ene)bis(hexafluorophosphate)-hexa-copper(I), [Cu₆(TEhpp)₄)](PF₆)₂(1). The cation is composed of an octahedral core of six copper(I) with four TEhpp ligands, each in a tri-coordinating fashion through two N atoms. This compound shows strong luminescent properties at liquid nitrogen temperature and is soluble in non-polar solvents such as toluene and hexane. The synthesis, spectroscopic properties and crystal structure are presented and discussed. The use of CuCl for the reaction with LiTEhpp yields a solution from which, in the presence of water, two mononuclear copper structures are produced in low yield, [Cu(II){(??-O-(HTEhpp)₂}₂Cl][Cu(I)Cl₂], 2, and Cu (TEhpp)₂Cl, 3.     

Acetonitrile Activation Promoted by Divalent Nickel Species with Bicyclic Guanidinate Ligands

Three compounds are described from reactions of divalent nickel species and bicyclic guanidinate ligands. These compounds encompass a variety of nuclearities with one being triangular and having an hour-glass shape and the formula Ni₃(tbn)₆·2LiCl, 1, where tbn is a bicyclic guanidinate anion with fused 5/6 membered rings. A dinuclear compound [(??²-Imeth)Ni(??-tbo)]₂Cl₂, 2, contains two fused 5/5 membered rings (tbo) that bridge two divalent nickel atoms and also contains a chelating unit in each metal center. The neutral Imeth (1-(2,3,5,6-tetrahydro-1H-imidazo[1,2-a]imidazol-1-yl)ethanimine) is an imino-containing ligand produced by the Ni(II) catalyzed reaction of tbo with acetonitrile. A mononuclear species, [(??²-hpp)Ni(hpp)(Hhpp)]Cl, 3, is obtained from reaction of NiCl₂ with the bicyclic guanidinate ligand with two fused six-member rings in contact with moisture. In all compounds each of the Ni atoms has a local square-planar arrangement common in d⁸ species.     

A Monte Carlo approach for estimating measurement uncertainty using standard spreadsheet software

Despite the importance of stating the measurement uncertainty in chemical analysis, concepts are still not widely applied by the broader scientific community. The Guide to the expression of uncertainty in measurement approves the use of both the partial derivative approach and the Monte Carlo approach. There are two limitations to the partial derivative approach. Firstly, it involves the computation of first-order derivatives of each component of the output quantity. This requires some mathematical skills and can be tedious if the mathematical model is complex. Secondly, it is not able to predict the probability distribution of the output quantity accurately if the input quantities are not normally distributed. Knowledge of the probability distribution is essential to determine the coverage interval. The Monte Carlo approach performs random sampling from probability distributions of the input quantities; hence, there is no need to compute first-order derivatives. In addition, it gives the probability density function of the output quantity as the end result, from which the coverage interval can be determined. Here we demonstrate how the Monte Carlo approach can be easily implemented to estimate measurement uncertainty using a standard spreadsheet software program such as Microsoft Excel. It is our aim to provide the analytical community with a tool to estimate measurement uncertainty using software that is already widely available and that is so simple to apply that it can even be used by students with basic computer skills and minimal mathematical knowledge.     

Metastable 11 K Superconductor Na(1-y)Fe(2-x)As(2)

The topochemical deintercalation of Na(+) ions from solid NaFeAs at room temperature in THF with iodine yields the superconducting phase Na(1-y)Fe(2-x)As(2) (T(c) ≈ 11 K). This metastable iron arsenide decomposes at 120 °C and is not accessible by high-temperature solid-state synthesis. X-ray powder diffraction confirms the ThCr(2)Si(2)-type structure, but reveals very small coherently scattering domains with a mean composition Na(0.9(2))Fe(1.7(1))As(2). HRTEM investigations show crystalline as well as strongly distorted areas with planar defects. The latter are probably due to sodium loss and disorder which is also detected by (23)Na solid state NMR. The (57)Fe-M?ssbauer spectrum of Na(1-y)Fe(2-x)As(2) shows one type of iron atoms in tetrahedral coordination. All results point to one crystallographic phase with very small domains due to fluctuations of the chemical composition. From electronic reasons we suggest the superconducting phase is presumably NaFe(2)As(2) in the ordered fractions of the sample.     

Evaluation of different carbon and nitrogen sources in production of rhamnolipids by a strain of Pseudomonas aeruginosa

Culture conditions involving variations in carbon and nitrogen sources and different C:N ratios were examined with the aim of increasing productivity in the process of rhamnolipid synthesis by Pseudomonas aeruginosa. In addition to the differences in productivity, the use of different carbon sources resulted in several proportions related to the types of rhamnolipids synthesized (monorhamnolipids and dirhamnolipids). Furthermore, the variation in nutrients, mainly the nitrogen source, resulted in different amounts of virulence factors, as phenazines and extracellular proteins. The data point out a new concern in the choice of substrate to be used for rhamnolipid production by P. aeruginosa: toxic byproducts.     

High-power blue/UV light-emitting diodes as excitation sources for sensitive detection

With advances in III-V nitride manufacturing processes, high-power light-emitting diode (LED) chips in the blue and UV wavelengths are now commercially available at reasonable cost and can be used as excitation sources in optical sensing. We describe the use of these high-power blue and UV LEDs for sensitive fluorescence detection, including chip-based flow cytometry, capillary electrophoresis (CE), and single-molecule imaging. By using a blue LED with a focusable power of approximately 40 mW as the excitation source for fluorescent beads, we demonstrate a simple chip-based bead sorter capable of enriching the concentration of green fluorescent beads from 63% to 95%. In CE experiments, we show that a mixture of analyte solution containing 30 nM 6-carboxyrhodamine 6G and 10 nM fluorescein can be separated and detected with excellent signal-to-noise ratio (approximately 17 for 10 nM fluorescein) using the collimated emission from a blue LED; the estimated mass detection limit was approximately 200 zmol for fluorescein. We also demonstrated ultrasensitive fluorescence imaging of single rhodamine 123 molecules and individual lambda-DNA molecules. At a small fraction of the cost of an Ar+ laser, high-power blue and UV LEDs are effective alternatives for lasers and arc lamps in fluorescence applications that demand portability, low cost, and convenience.     

Fe Supported Catalysts Prepared by The Sol-Gel Method. Characterization and Evaluation in Phenol Abatement

Iron supported catalysts containing 10 wt% of iron, as oxide, on TiO₂ and Al₂O₃ have been prepared by the sol gel method and the traditional method based of the impregnation of the support with the metal precursor on commercial and sol-gel supports. The samples were characterised by measuring the specific area (S _BET), temperature programmed reduction (TPR), infrared spectroscopy (FTIR), electrophoretic migration (IP), chemical oxygen demand (COD) and X-ray diffraction (XRD). The catalytic activity was measured in a batch reactor using ozone as oxidizing agent. It was found presence of highly dispersed iron oxide in the samples prepared by cogelation, whereas in those prepared by impregnation of the iron precursor, the dispersion was very poor. Catalytic activity indicates that phenol is degraded with a low mineralization to CO_2.     

CO2 Hydrogenation on Cu/Al2O3: Role of the Metal/Support Interface in Driving Activity and Selectivity of a Bifunctional Catalyst

Selective hydrogenation of CO₂ into methanol is a key sustainable technology, where Cu/Al₂O₃ prepared by surface organometallic chemistry displays high activity towards CO₂ hydrogenation compared to Cu/SiO₂, yielding CH₃OH, dimethyl ether (DME), and CO. CH₃OH formation rate increases due to the metal–oxide interface and involves formate intermediates according to advanced spectroscopy and DFT calculations. Al₂O₃ promotes the subsequent conversion of CH₃OH to DME, showing bifunctional catalysis, but also increases the rate of CO formation. The latter takes place 1) directly by activation of CO₂ at the metal–oxide interface, and 2) indirectly by the conversion of formate surface species and CH₃OH to methyl formate, which is further decomposed into CH₃OH and CO. This study shows how Al₂O₃, a Lewis acidic and non‐reducible support, can promote CO₂ hydrogenation by enabling multiple competitive reaction pathways on the oxide and metal–oxide interface.