Double‐Decker Paramagnetic {(K)(H3Hhp)2}⋅2− Radical Dianions Comprising Two [30]Trithia‐2,3,5,10,12,13,15,20,22,23,25,30‐Dodecaazahexaphyrins and a Potassium Ion

Reduction of free‐base [30]trithia‐2,3,5,10,12,13,15,20,22,23,25,30‐dodecaazahexaphyrin (H₃Hhp) yields {cryptand[2.2.2](K)}₂{(K)(H₃Hhp)₂}?4C₆H₄Cl₂ ( 1 ) containing double‐decker {(K)(H₃Hhp)₂} ^{? 2?} radical dianions, whose structure was elucidated using X‐ray diffraction. Potassium ion forms 12 short (K⁺)???N(H₃Hhp) contacts with two H₃Hhp macrocycles in the 3.048–3.157 Å range. Dianions have S=1/2 spin state manifesting an effective magnetic moment of 1.64 μ_B at 300 K and a narrow Lorentzian electron paramagnetic resonance signal. Quantum chemical calculations support the ionic nature of the (K⁺)‐N(H₃Hhp) interactions and the nearly equal distribution of the ?1.5 charge over each macrocycle. H₃Hhp takes the role of an aza‐crown ether in free‐base reduced state and forms a new type of double‐decker complex.     

A procedure for meaningful unsupervised clustering and its application for solvent classification

Artificial neural networks have proven to be a powerful tool for solving classification problems. Some difficulties still need to be overcome for their successful application to chemical data. The use of supervised neural networks implies the initial distribution of patterns between the pre-determined classes, while attribution of objects to the classes may be uncertain. Unsupervised neural networks are free from this problem, but do not always reveal the real structure of data. Classification algorithms which do not require a priori information about the distribution of patterns between the pre-determined classes and provide meaningful results are of special interest. This paper presents an approach based on the combination of Kohonen and probabilistic networks which enables the determination of the number of classes and the reliable classification of objects. This is illustrated for a set of 76 solvents based on nine characteristics. The resulting classification is chemically interpretable. The approach proved to be also applicable in a different field, namely in examining the solubility of C₆₀ fullerene. The solvents belonging to the same group demonstrate similar abilities to dissolve C₆₀. This makes it possible to estimate the solubility of fullerenes in solvents for which there are no experimental data      

Radical cations of branched alkanes in solutions: time-resolved magnetic field effect and quantum chemical studies

Radical cations of heptane and octane isomers, as well as several longer branched alkanes, were detected in irradiated n-hexane solutions at room temperature by the method of time-resolved magnetic field effect (TR MFE). To identify radical cations, the hyperfine coupling constants as determined by simulation of the TR MFE curves were compared to the constants calculated using the density functional theory (DFT) approach. The g-values of the observed radical cations were close to that of the 2,2,3,3-tetramethylbutane radical cation studied earlier by optically detected electron spin resonance (ESR) and TR MFE techniques. No evidence of the decay of the radical cations of branched alkanes to produce olefin radical cations was found, which was further supported by the observation of positive charge transfer from the observed radical cations to cycloalkane molecules. The lifetimes of the radical cations of the branched alkanes were found to be longer than tens of nanoseconds.     

Transition-Metal Nitride Core@Noble-Metal Shell Nanoparticles as Highly CO Tolerant Catalysts

Core–shell architectures offer an effective way to tune and enhance the properties of noble-metal catalysts. Herein, we demonstrate the synthesis of Pt shell on titanium tungsten nitride core nanoparticles (Pt/TiWN) by high temperature ammonia nitridation of a parent core–shell carbide material (Pt/TiWC). X-ray photoelectron spectroscopy revealed significant core-level shifts for Pt shells supported on TiWN cores, corresponding to increased stabilization of the Pt valence d-states. The modulation of the electronic structure of the Pt shell by the nitride core translated into enhanced CO tolerance during hydrogen electrooxidation in the presence of CO. The ability to control shell coverage and vary the heterometallic composition of the shell and nitride core opens up attractive opportunities to synthesize a broad range of new materials with tunable catalytic properties.     

Heat- and mass-transport in aqueous silica nanofluids

Using the transient hot wire and pulsed field gradient nuclear magnetic resonance methods we determined the thermal conductivity and the solvent self-diffusion coefficient (SDC) in aqueous suspensions of quasi-monodisperse spherical silica nanoparticles. The thermal conductivity was found to increase at higher volume fraction of nanoparticles in accordance with the effective medium theory albeit with a smaller slope. On the other hand, the SDC was found to decrease with nanoparticle volume fraction faster than predicted by the effective medium theory. These deviations can be explained by the presence of an interfacial heat-transfer resistance and water retention by the nanoparticles, respectively. We found no evidence for anomalous enhancement in the transport properties of nanofluids reported earlier by other groups.     

Quantum cellular neural networks

We have previously proposed a way of using coupled quantum dots to construct digital computing elements—quantum-dot cellular automata. Here we consider a different approach to using coupled quantum-dot cells in an architecture which, rather than reproducing Boolean logic, uses a physical near-neighbor connectivity to construct an analog cellular neural network.     

Migratory insertion of the R2P group into a nitrogen-nitrogen bond - a novel type of rearrangement in phosphorus-nitrogen ligand chemistry. 3. The rearrangement of triphosphinohydrazide ligand -N(PPh2)-N(PPh2)2 to triphosphazenide anion {[(Ph2P-N]2PPh2}- in the coordination sphere of divalent cobalt and nickel

Hydrazine dihydrochloride reacts with 3 equiv of Ph2PCl in tetrahydrofuran in the presence of triethylamine to give tris(diphenylphosphino)hydrazine (1) in 70% yield. Each nitrogen atom in 1 has a trigonal-planar environment according to X-ray analysis. Thermolysis of 1 at 130 degrees C results in the formation of two products: bis(diphenylphosphino)amine and octaphenylcyclotetraphosphazene. The interaction of free ligand 1 with NiBr2 affords a simple adduct [(Ph2P)2N-NH-PPh2]NiBr2, while its anionic (hydrazide) form undergoes rearrangement in a coordination sphere of divalent cobalt and nickel involving migratory insertion of the Ph2P group into a nitrogen-nitrogen bond. The reaction of 1 with cobalt bis(trimethylsilyl)amide, [(Me3Si)2N]2Co, yields the complex of phosphazenide-type (Me3Si)2N-Co[(Ph2PN)2PPh2] (2) in 86% yield. A similar reaction of 1 with nikelocene proceeds with substitution of one Cp ring to form durable 18-electron complex CpNi[(Ph2PN)2PPh2] (3).     

Dissipation of classical energy in nonlinear quantum systems

We show using two simple nonlinear quantum systems that the infinite set of quantum dynamical variables, as introduced in quantized Hamilton dynamics [O. V. Prezhdo and Y. V. Pereverzev, J. Chem. Phys. 113, 6557 (2000)], behave as a thermostat with respect to the finite number of classical variables. The coherent classical component of the evolution decays by coupling to the chaotic quantum reservoir. The classical energy, understood as the part of system energy expressible through the average values of coordinates and momenta, is transferred to the quantum energy expressible through the higher moments of coordinates and momenta and other quantum variables. At long times, the classical variables reach equilibrium, and the classical energy fluctuates around the equilibrium value. These phenomena are illustrated with the exactly solvable Jaynes-Cummings model and a nonlinear oscillator.     

Electrical properties of liquid crystal nano-colloids analysed from perspectives of the ionic purity of nano-dopants

The concentration of mobile ions in liquid crystals doped with nano-objects is analysed in the framework of the Langmuir isotherms assuming an ionic contamination of nano-dopants. The level of the ionic purity of nano-dopants is described by means of the dimensionless contamination factor. The applicability of the proposed approach is verified by fitting the broad variety of the existing experimental data. A good agreement between theoretical predictions and experimental data indicates the feasibility of the idea to consider nano-dopants partially contaminated. In addition, it provides the way to deduce a set of important parameters (the surface density of the adsorbing sites, the contamination factor and the ratio of the adsorption constant to the desorption constant) directly from electrical measurements.