Mössbauer Spectrometry as a Powerful Tool to Study Lithium Reactivity Mechanisms for Battery Electrode Materials

Hyperfine Interactions - The use of 57Fe as a local Mössbauer probe is of high interest for studying mechanisms induced by lithium insertion. In this way the substitutions Ti/Fe and Li/Fe have...     

Optimal scheduling of unit-time tasks on two uniform processors under tree-like precedence constraints

An O(n ³/(b+1)) time algorithm to obtain a minimum finish time schedule subject to tree-like precedence constraints for unit-time tasks on two uniform processors is obtained. It is assumed that the slower processor takesb time units for each one taken by the speedier one, for some integerb. It is also noted that a slight modification of this schedule yields a minimum mean flow time schedule.

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Zusammenfassung Es wird ein Algorithmus der Ordnung O(n ³/(b+1)) zur Ermittlung der frühesten Fertigstellungszeit für Schedulingprobleme mit 2 Prozessoren und baumartigen Präzendenzbeziehungen angegeben. Dabei wird angenommen, daßt die Durchführung jeder einzlnen Aufgabe gleich lange dauert, der langsamere Prozessor jedochb Zeiteinheiten (b ganzzahlig) zur Durchführung einer Aufgabe benötigt. Ferner wird gezeigt, dafß eine leichte Modifikation der Lösung eine Reihenfolge mit minimaler mittlerer Durchlaufzeit ergibt.

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This research is supported in parts by NSERC Grant A4619 and the Manufacturing Research Corporation of Ontario.

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On leave from Department of Computer Science, Technical University of Gdansk.     

Pyrazine control of the solid-state supramolecular chemistry of zinc phthalocyanine

Crystals of monoaxially coordinated T-shaped and H-shaped supramolecular zinc(II) phthalocyaninato complexes with pyrazine are obtained. In both types of molecules the central Zn atom of ZnPc complexes with pyrazine exhibits 4 + 1 coordination. The Zn atom is equatorially coordinated by four isoindole N atoms of Pc macrocycle and axially by N atom of pyrazine molecule. The interaction of the central Zn atom of ZnPc with the axial N atom of pyrazine leads to a deviation of Zn from the centre of cavity by 0.371(2) Å in the T-shaped complex and by 0.296(2) Å in the H-shaped complex. Thermogravimetric analysis of the crystals exhibits three slopes down, corresponding to the loss in succession of solvated pyrazine molecules, than the loss of ligated pyrazine molecules from the T-shaped complex and the finally the loss of the bridged pyrazine molecule from the H-shaped complex. Finally the thermal processing leads to the β-ZnPc as residue. The UV–Vis spectrum taken in solution shows the batochromic shift in the polar solvent like α-chloronaphthalene in relation to the spectrum in non-polar solvent like benzene.     

Synthesis,Structure, and UV–Vis Characterization of Antimony(III) Phthalocyanine: [(SbPc)2(Sb2I8)(SbBr3)]2

A new antimony(III)–phthalocyanine complex with the formula of [(SbPc)₂(Sb₂I₈)(SbBr₃)]₂ has been obtained in the reaction of pure antimony powder with phthalonitrile under the oxidation conditions by iodine monobromide vapors. The complex crystallizes in the centrosymmetric space group of the triclinic system. Both independent (SbPc)⁺ units exhibit non-planar conformation, since the Sb(III) is larger than the equilibrium cavity size of the ring and cannot be accommodated without its expansion; thus, the metal protrudes out of the cavity, forming a saucer shape. The centrosymmetric anionic unit of the crystal consists of two (Sb₂I₈)²⁻ interacted anionic units forming (Sb₄I₁₆)⁴⁻ anionic complex that interacts with two SbBr₃ molecules to form [Sb₆I₁₆Br₆]⁴⁻ anionic aggregate. Each [Sb₆I₁₆Br₆]⁴⁻ anionic aggregate is surrounded by four (SbPc)⁺ cations forming a supramolecular centrosymmetric (SbPc)₄[Sb₆I₁₆Br₆] complex. Translationally related (SbPc)₄[Sb₆I₁₆Br₆] molecules form a stacking structure along the [100] and [011] directions with N₄–N₄ distances of 3.55 and 3.53 Å, respectively, between the back-to-back-oriented saucer-shaped (SbPc)⁺ units. The interaction between the building units of the crystal was analyzed using the Hirshfeld surface and the analysis of the 2D fingerprint plots. The UV–Vis absorption spectra of crystal 1 were taken in CH₂Cl₂ and toluene solutions in the concentration range from 10⁻⁵ to 10⁻⁶ mol/L. No significant changes related to aggregation in solutions were observed. The Q-band in toluene solution is red shifted by ~15 nm in comparison to that in CH₂Cl₂ solution. Oxidation of (SbPc)₄[Sb₆I₁₆Br₆] yields Sb^VPc derivative. Both Sb^III and Sb^V phthalocyanine derivatives absorb near infrared light (600–900 nm), which should be intriguing from the point of view of potential use as photosensitizers for PDT and as an infrared cut filter for plasma display and silicon photodiodes.