1,3-bis(4-pyndyl)propane complexes of divalent metal halides and pseudohalides

Summary Coordination compounds formed by the interaction of 1,3-bis(4-pyridyl)propane (DPP) with some divalent metal halides and pseudohalides have been prepared and characterized by magnetic susceptibilities, electronic and i.r. spectral measurements down to 200 cm^–1 in the solid state. The i.r. spectra indicate that DPP acts mostly as a bidentate bridging ligand in these complexes. Moreover, the two pyridyl rings which are nonplanar in uncoordinated DPP become coplanar upon coordination. Tentative stereo chemistries of the complexes have been suggested in the solid state. The ligand field parameters Dq, B, , and ₂/₁ have been calculated for the cobalt(II) and nickel(II) complexes and are consistent with the proposed stereo chemistries.     

Extractive spectrophotometric determination of palladium using 2-(2-hydroxyimino-1-oxoethyl)furan

A rapid, simple, selective and sensitive method for the determination of palladium in trace amounts has been developed, based on the reaction of 2-(2-hydroxyimino-1-oxoethyl)furan [-isonitroso-2-acetyl-furan] with the metal ion in acetic acid. The intense yellow complex is quantitatively extractable into chloroform, whose absorbance is measured at 425 nm. The method is free from the interference of a large number of other metal ions. It obeys Beer's law in the range 0.0–3.8 g Pd mL^–1 with Sandell's sensitivity of 0.003 g Pd cm^–2. The ratios of metal to ligand in the extracted complex are 1:1 and 1:2. The analysis of various samples has been carried out with satisfactory and reproducible results.     

Pariser-Parr-Pople type SCF-MO-CI calculations on pentafluorobenzenes

The -electron densities at various atomic positions and the ground state bond orders have been calculated in several pentafluorobenzenes using Pariser-Parr-Pople method. The low lying excited energy states of these molecules obtained by a partial configuration interaction procedure involving only singly excited states are reported.

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Zusammenfassung Die -Elektronendichten an den verschiedenen Atomen sowie die Bindungsordnungen im Grundzustand sind in einer Reihe von Pentafluorbenzolen mittels der Methode von Pariser-Parr-Pople berechnet worden. Die untersten angeregten Zustände ergaben sich aus der Wechselwirkung mit einer beschränkten Anzahl einfach angeregter Konfigurationen.

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Résumé La méthode de Pariser-Parr-Pople a été utilisée pour calculer les densités électroniques et les indices de liaison dans l'état fondamental de plusieurs pentafluorobenzènes. Les états excités les plus bas de ces molécules ont été obtenus par interaction de configuration limitée aux états monoexcités.

     

MRINDO/S-CI calculation on the electronic spectra of higher azines

Summary MRINDO/S calculation completed by singly excited configuration interaction was performed on the higher aziness-triazine,s-tetrazine and pentazine. The results enable the main characteristics of the observed electronic spectra to be interpreted. The importance of outer (Rydberg) atomic orbitals is stressed and it is found that a few singlet-singlet transitions of the higher azines lead to an excited state with considerable Rydberg character.     

Extractive spectrophotometric determination of niobium(V) with 3-hydroxy-2-(2-thienyl)-4H-chromen-4-one

A coloured complex of niobium (V) with 3-hydroxy-2-(2-thienyl)-4H-chromen-4-one (HTC) is produced in perchloric acid medium (4 mol/L); it is quite stable and extractable into dichloromethane. Beer's law is obeyed in the range 0.0–1.9 g Nb(V) mL^–1. The molar absorptivity at _max=420 nm is 5.0357×10⁴ L mol^–1 cm^–1. Using Job's method and the mole ratio method, the ratio of metal to ligand (Nb:HTC) in the extracted species has been found to be 1:2. The effect of anions and foreign metals is described.     

Dependence ofT c on doping in oxygen-hole induced Jahn-Teller mediated superconductors

A bipolaronic model of high-T _c superconductivity, that is based upon the idea that a doped oxygenhole reduces the separation between the and levels of the neighbouring Cu-ion and hence causes a Jahn-Teller mixing between the two levels, is suggested. Within the BCS scheme, the bipolaron Hamiltonian is investigated for the superconducting order parameter and the critical temperatureT _c as a function of hole-doping. Under suitable approximation for the bipolaronic kinetic energy, the hole-doping dependence ofT _c shows a universal behaviour. For temperatures close toT _c and forT _c 1, obeys the BCS type of relation with pre-factor of (1–T/T _c )² related to the range of superconducting-phase against the doping axis.     

Thermal and physico-chemical studies on binary organic eutectic systems

The phase diagrams of binary systems of 4-aminoacetophenone (AAP) with each of benzoin (BN) and 4-nitrophenol (PNP) have been established by the thaw-melt method. This study shows the formation of eutectics. Accurate compositions of BN and PNP to form eutectic mixtures have been determined by the phase diagram study between BN?CAAP and PNP?CAAP in the entire range of compositions. The thermal properties of the eutectics, such as enthalpy of mixing, solid?Cliquid interfacial energy, entropy of fusion and excess thermodynamic functions were computed based on enthalpy of fusion values. The influence of undercooling on growth kinetics of pure components and their eutectics has been studied. The microstructural studies infer the influence of solid?Cliquid interfacial energy on the morphology of microstructures of eutectics.     

A Multivariate CLT for Decomposable Random Vectors with Finite Second Moments

Stein's method is used to derive a CLT for dependent random vectors possessing the dependence structure from Barbour et al. J. Combin. Theory Ser. B 47, 125–145, but under the assumption of second moments only. This allows us to derive Lindeberg–Feller type theorems for sums of random vectors with certain dependence structures. We apply the main theorem to the study of three problems: local dependence, random graph degree statistics and finite population statistics. In particular, we consider U-statistics of independent observations as well as of observations drawn without replacement.