Relation of coordination number to memory and threshold switching in chalcogenides

The paper reports a structural study of some memory and threshold chalcogenides in terms of coordination numberC, defined byC=8−N, and is the average coordination number for covalently bonded materials. The average number of nearest neighbours surrounding a central atom, obtained for As-Ge-Te (memory) and Se-Ge-Te (threshold) systems have been used to estimate the cohesive energies, assuming simple additivity of bond energies. The bonding pattern so obtained, explains certain properties of these glasses.     

Formation of diaryl(allyl)phosphine in π -allyl palladium(II) induced cleavage of triarylphosphines

A reverse migration of allylic group from palladium to phosphorus and the formation of diaryl(allyl)phosphine in the π -allyl palladium(II) induced cleavage of triarylphosphines has been demonstrated.     

The reaction of PPh3 with Di-μ-chlorobis(arylazooximato)dipalladium(II)

Summary Di--chlorobis(arylazooximato)dipalladiuni(II) compounds react with PPh₃ to give the four-coordinate complexes (5) and (4) in which the azooxime acts as a unidentate and bidentate ligand respectively. Hydrogen bonding in polar solvents such as MeOH or EtOHetc. stabilize (5) whereas, polar solvents such as Me₂CO, py and Et₂O convert (5) into (4). The equilibrium: (4) + PPh₃ (5) exists in PhH solution and equilibrium constants at 30°C have been calculated spectrophotometrically. The variation in equilibrium constants and the stabilities of (5) have been explained on the basis of electron-releasing and electron-withdrawing properties of substituents, R, in the azooxime ligand.     

Mössbauer study of a ferromagnetic metallic glass: Fe74Co10B16

Amorphous Fe₇₄Co₁₀B₁₆ (METGLAS 2605CO) has been studied in the temperature range of 77 K – 700 K by Mössbauer spectroscopy. Its crystallization temperature is found to be 665 ± 5 K and Curie temperature is estimated to be 760±10 K. The observed rapid decrease in reduced hyperfine fields can be explained well by Handrich's model for amorphous ferromagnets if one assumes a temperature dependent δ, a measure of fluctuations in the exchange interactions in such solids.     

Rotational-echo double resonance of uniformly labeled 13C clusters

The use of rotational-echo double resonance NMR to measure distances from an observed tightly coupled cluster of 13C spins to a distant 15N, 31P, or 19F is practical if 13C chemical shifts and homonuclear 13C-13C isotropic J interactions are refocused by a combination of rotor-synchronized 13C pi and pi/2 pulses. This scheme is illustrated by experiments performed on diluted and recrystallized L-[13C(3),15N]alanine and L-[13C(6),alpha-15N]histidine.     

Dielectric properties of CaCu3Ti4O12–silicone resin composites

CaCu₃Ti₄O₁₂ (CCTO)–silicone resin composites with various CCTO volume fractions were prepared. Relatively high dielectric constant (ε=119) and low loss (tanδ=0.35) of the composites with CCTO volume fraction of 0.9 were observed. Two theoretical models were employed to predict the dielectric constant of these composites; the dielectric constant obtained via the Maxwell–Garnett model was in close agreement with the experimental data. The dielectric constant of CCTO–silicone resin composites showed a weak frequency dependence at the measuring frequency range and the loss tangent apparently decreases with increase in frequency.     

Conjugate base catalysed one-pot synthesis of pyrazoles from β-formyl enamides

A novel one-pot synthesis of pyrazoles has been accomplished by the reaction of β-formyl enamides with hydroxylamine hydrochloride catalysed by potassium dihydrogenphosphate in acid medium.     

New flavonoid glycosides and other chemical constituents from Clerodendrum phlomidis leaves: isolation and characterisation

Phytochemical investigation of the plant Clerodendrum phlomidis Linn. F. (Lamiaceae) has now led to the isolation of two new flavonoid glycosides (1, 2) together with six known compounds identified as pectolinaringenin (3), pectolinaringenin-7-O-β-d-glucopyranoside (4), 24β-ethylcholesta-5,22E,25-triene-3β-ol (5), 24β-ethylcholesta-5,22E,25-triene-3β-O-β-D-glucopyranoside (6), (2S,3S,4R,10E)-2-[(2′R)-2′-hydroxytetracosanoylamino]-10-octadecene-1,3,4-triol (7) and andrographolide (8) mainly by spectroscopic analysis. Compounds 4 and 6–8 are reported for the first time from C. phlomidis.