Atmospheric gamma-rays of 1–200 GeV over Hyderabad

Using a stack of hypersensitized nuclear emulsions, exposed under 10.2 g.cm^?2 of residual atmosphere over Hyderabad, India, gamma-rays of energy > 1 GeV have been studied. It is found that the observed differential energy spectrum can be best represented by two power law spectra, one for energies less than 30 GeV and the other for higher energies but with the same spectral index of 2.6; however the intensities at energies greater than 30 GeV are about three times higher than what would be expected from the extrapolation of the spectrum at lower enerjies. The implication of this observation has been examined. The neutral pion production spectrum over Hyderabad has been derived from the gamma-ray spectrum. Using this information the energy spectrum of atmospheric electrons has been deduced and a comparison made with the observed spectrum below the geomagnetic threshold energy over Hyderabad; therefrom an upper limit of 0.5 particles/(m².sr.sec.) has been deduced for the flux of re-entrant albedo electrons above 2 GeV.     

Rietveld refinement of the cocrystal 2,4‐dihydroxybenzoic acid–N′‐(propan‐2‐ylidene)nicotinohydrazide (1/1)

A further example of using a covalent‐bond‐forming reaction to alter supramolecular assembly by modification of hydrogen‐bonding possibilities is presented. This concept was introduced by Lemmerer, Bernstein & Kahlenberg [CrystEngComm (2011), 13 , 55–59]. The title structure, C₉H₁₁N₃O·C₇H₆O₄, which consists of a reacted niazid molecule, viz.N′‐(propan‐2‐ylidene)nicotinohydrazide, and 2,4‐dihydroxybenzoic acid, was solved from powder diffraction data using simulated annealing. The results further demonstrate the relevance and utility of powder diffraction as an analytical tool in the study of cocrystals and their hydrogen‐bond interactions.     

Synthesis of novel heterocycles from 2-amino-3-(cyanomethylsulfonyl)thiophene

The synthesis and selected reactions of 2-amino-3-(cyanomethylsulfonyl)thiophene is reported. In particular, cyclization reaction of the versatile aminothiophene yielded a number of novel thieno[3,2-b][1,4]-thiazine 1,1-dioxides, as well as the analogous thieno[2,3-e][1,3,4]thiadiazine 4,4-dioxide. Reaction of the thienothiazine system with hydrazine was subsequently explored, which resulted in either ring-opening of the thiazine and formation of an aminopyrazole or solely ring cleavage depending on the thiazine substituent. Additionally, the synthesis of bis(2-amino-3-thienyl)sulfone and the corresponding bis-acetamide is described.     

An interesting synthesis of thieno[2,3‐d][1,2,3]thiadiazole via decomposition/recyclization of 3‐methoxycarbonyl‐1H‐thieno‐[2,3‐e][1,3,4]thiadiazine 4,4‐dioxide

Attempted hydrolysis of the ester of 3‐methoxycarbonyl‐1H‐thieno[2,3‐e][1,3,4]thiadiazine 4,4‐dioxide ( I ) under acidic conditions gave the ring‐contracted thieno[2,3‐d][1,2,3]thiadiazole ( V ) instead of the expected carboxylic acid. In addition to a discussion of the reaction, a plausible mechanism is presented.     

Comparison of time-dependent density-functional theory and coupled cluster theory for the calculation of the optical rotations of chiral molecules

A comparison of the abilities of time-dependent density-functional theory (TDDFT) and coupled cluster (CC) theory to reproduce experimental sodium D-line specific rotations for 13 conformationally rigid organic molecules is reported. The test set includes alkanes, alkenes, and ketones with known absolute configurations. TDDFT calculations make use of gauge-including atomic orbitals and give origin-independent specific rotations. CC rotations are computed using both the origin-independent dipole-velocity and origin-dependent dipole-length representations. The mean absolute deviations of calculated and experimental rotations are of comparable magnitudes for all three methods. The origin-independent DFT and CC methods give the same sign of [alpha]D for every molecule except norbornanone. For every large-rotation ketone and alkene for which DFT and CC yield the incorrect sign as compared to liquid-phase experimental data, the corresponding optical rotatory dispersion (ORD) curve is bisignate, suggesting that the two models cannot reliably reproduce the relative excitation energies and antagonistic rotational strengths of multiple competing electronic states that contribute to the total long-wavelength rotation. Several potential sources of error in the theoretical treatments are considered, including basis set incompleteness, vibrational and temperature effects, electron correlation, and solvent effects.     

Structural and magnetic properties of the Kagomé antiferromagnet YbBaCo4O7

The mixed-valent compound YbBaCo₄O₇ is built up of Kagomé sheets of CoO₄ tetrahedra, linked in the third dimension by a triangular layer of CoO₄ tetrahedra in an analogous fashion to that found in the known geometrically frustrated magnets such as pyrochlores and SrCr_9xGa_12−9xO₁₉ (SCGO). We have undertaken a study of the structural and magnetic properties of this compound using combined high-resolution powder neutron and synchrotron X-ray diffraction. YbBaCo₄O₇ undergoes a first-order trigonal→orthorhombic phase transition at 175 K. We show that this transition occurs as a response to a markedly underbonded Ba²⁺ site in the high-temperature phase and does not appear to involve charge ordering of Co²⁺/Co³⁺ ions in the tetrahedra. The symmetry lowering relieves the geometric frustration of the structure, and a long-range-ordered 3-D antiferromagnetic state develops below 80 K.     

One‐Dimensional Spin Chains from CuII Ions and 2,5‐Bis(pyrazol‐1‐yl)‐1,4‐dihydroxybenzene

The purple colored coordination polymer [1 Cu]_n was obtained from 2,5‐bis(pyrazol‐1‐yl)‐1,4‐dihydroxybenzene and CuBr₂ in aqueous ammonia. The crystal structure of [1 Cu]_n was determined from high resolution X‐ray powder diffraction data using the method of simulated annealing. In the solid state, [1 Cu]_n features largely independent linear chains, all of them being oriented parallel to the c‐axis of the crystal. The Cu ions are coordinated in a square‐planar fashion by two nitrogen atoms and two anionic oxygen donors. Magnetic susceptibility and magnetization measurements indicate the Cu ions in [1 Cu]_n to be antiferromagnetically coupled with a coupling constant of about 20 K.     

Transition metal catalysed dehydrogenation of amine-borane fuel blends

Mixtures containing ammonia-borane and sec-butylamine-borane remain liquid throughout the hydrogen release process that affords tri(N-sec-butyl)borazine and polyborazylene. Concentrated solutions with metal catalysts afford >5 wt% H(2) in 1 h at 80 °C and addition of (EMIM)EtSO(4) ionic liquid co-solvent eliminates competing formation of insoluble linear poly(aminoborane) (EMIM = 1-ethyl-3-methyl-imidazolium).