An efficient method for solution-phase parallel synthesis of 2-quinoxalinol salen Schiff-base ligands

A solution-phase parallel method for the synthesis of 2-quinoxalinol salen ligands was designed and optimized. The synthesis begins with commercially available 1,5-difluoro-2, 4-dinitrobenzene (DFDNB) and employs a sequence of five straightforward and high-yielding reaction steps. Simple laboratory techniques with low sensitivity to water or air for solution-phase parallel reactions were coupled with convenient workup and purification procedures to give high-purity and yield a small ligand library of 20 compounds. The final step, a Schiff-base condensation of an aldehyde with the diaminoquinoxaline results in a new category of ligands for metal coordination or of potential bioactivity, based on the skeleton 2,2'-(1E,1'E)-(quinoxaline-6,7-diylbis(azan-1-yl-1-ylidene))bis(methan-1-yl-1-ylidene)diphenol. The approach described here is easily adaptable for parallel synthesis of a larger library.     

Uranyl stabilized Schiff base complex

Uranyl Schiff base complex [(UO(2))(2)(Salpro)(OH)(Solvent)(2)] (1) in the presence of excess of ethylenediamine (EDA) does not undergo nucleophilic addition (hydrolysis) and substitution (transamination) reactions due to an extended chelation [2N, 3O + OH] by the flexible backbone.     

One-pot metal templated synthesis for the preparation of 2-quinoxalinol salen metal complexes

Metal complexes of 2-quinoxalinol salen (salqu) ligands can be prepared in a one-pot metal templated synthesis resulting in significantly enhanced yields than if the ligand were prepared and isolated prior to introducing the metal for complexation. Using this method, 12 salqu metal complexes have been prepared and characterized from +2 metal ions.     

Comprehensive T-matrix reference database: A 2006–07 update

This paper presents an update to the comprehensive database of T-matrix publications authored by us previously and mostly includes the publications that appeared since 2005. It also lists several earlier publications not included in the original database.     

Sh-matrices method applied to light scattering by finite circular cylinders

We present a rigorous analytical solution describing light scattering by a finite circular cylinder of arbitrary dimensions. This solution uses a modification of the extended boundary condition method (EBCM) that is based on the introduction of the so-called Sh-matrices. The Sh-matrices depend only on the shape of particles and do not depend on the particle size or optical constants. The Sh-matrices can be used to find the transition-matrix (T-matrix), that contains all the scattering information from the particle system. The solution is confirmed by corresponding discrete-dipole approximation (DDA) and traditional EBCM calculations.     

Formation of association ions in the photoionization of alkyl halides

The methyl and ethyl chlorides and bromides, as well as methyl iodide, were photoionized in the vacuum ultraviolet at 300 K in a mass spectrometer over the pressure range 0.5 to approximately 100 millitorr. Under these conditions, stabilized parent ion dimers are found in CH₃Br, CH₃I, and C₂H₅Br, but not in the chlorides. Lower limits for the dissociative lifetimes of the ion–molecule collision complexes were estimated and are as follows: (CH₃Br)₂⁺, 1.6 μs; (CH₃I)₂⁺, 1.9 μs; and (C₂H₅Br)₂⁺, 5.4 μs. An increase in photon energy (internal energy content of the reactant ion) decreases the dissociative lifetime of the collision complex in CH₃I.     

Actinide cyanometallates

Simple salts of the tetracyanoplatinate (TCP) anions with the general formula M[Pt(CN)₄] _x ·H₂O have been described for over 200 years. A major structural feature of these compounds are pseudo one dimensional Pt···Pt interactions between the square planar tetracyanoplatinate anions. These interactions form quasi one-dimensional chains in the solid state and are believed to be the source of their unique spectroscopic and emission properties. The lanthanides offer the ability to tune the Pt···Pt spacing of these pseudo one dimensional chains, predictably by taking advantage of the lanthanide contraction. Here, we describe the emission and structural characteristics of new actinide tetracyanometallates.     

Steric modifications tune the regioselectivity of the alkane oxidation catalyzed by non-heme iron complexes

Iron complexes with the tetradentate N-donor ligand N,N'-di(phenylmethyl)-N,N'-bis(2-pyridinylmethyl)-1,2-cyclohexanediamine (bbpc) are reported. Despite the benzyl groups present on the amines, the iron compounds catalyze the oxygenation of cyclohexane to an extent similar to those employing less sterically encumbered ligands. The catalytic activity is strongly dependent on the counterion, with the highest activity and the strongest preference for alkane hydroxylation correlating to the most weakly coordinating anion, SbF(6)(-). The selectivity for the alcohol product over the ketone is amplified when acetic acid is present as an additive. When hydrocarbon substrates with both secondary and tertiary carbons are oxidized by H(2)O(2), the catalyst directs oxidation toward the secondary carbons to a greater degree than other previously reported iron-containing homogeneous catalysts.