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Peripheral Substituents (peripheral + substituent)

Distribution by Scientific Domains

Chemistry	75%

Selected Abstracts

Studies on Nickel(II) Complexes with Amide-Based Ligands: Syntheses, Structures, Electrochemistry and Oxidation Chemistry

EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 12 2008
Jyoti Singh
Abstract The present work discusses the nickel chemistry in a set of amide-based open-chain ligands with subtle differences in the backbone or terminal amine substituents. The ligands coordinate to the Ni2+ ion through the Namide and Namine atoms maintaining a square-planar geometry. Absorption spectra and NMR studies reveal that the solid-state square-planar geometry is retained in solution. The electrochemical results suggest that the NiIII/NiII redox couple primarily depends on the N4 donors, which is composed of two Namide and twoNamine atoms and not on the peripheral substituents. All four ligands with variable backbone and substituents are equally competent in stabilizing the NiIII state. On the basis of electrochemical findings, chemical oxidations were carried out, and they reveal generation of the NiIII state in two cases, whereas decomposition was observed in others. Preliminary alkene epoxidation reactions suggest that the present nickel complexes transiently stabilize the higher oxidation state of the nickel ion that possibly participates in the oxidation of the substrates.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008) [source]

Synthesis and Structure,Efficiency Relations of 1,3,5-Benzenetrisamides as Nucleating Agents and Clarifiers for Isotactic Poly(propylene),

MACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 2 2010
Frank Abraham
Abstract This paper presents the synthesis and properties of 1,3,5-benzenetrisamides with a particular focus on structure-efficiency relationships of nucleation and optical property enhancement of isotactic poly(propylene) (i -PP). A family of twenty 1,3,5-benzenetrisamide derivatives was synthesized, in which the direction of the amide linkage between the core and the peripheral substituents, as well as their length (C-3 to C-6) and flexibility were systematically varied. Dissolution- and recrystallization temperatures of the additives in the polymer melt, the crystallization temperature of i -PP, and the optical properties clarity and haze were determined in the additive concentration range from 200 to 2,500,ppm. Within the reported series of compounds, few exhibited very good nucleating and clarification abilities, only one with outstanding characteristics, whereas other, very closely related derivatives were found to be incapable to nucleate or clarify i -PP, although, intriguingly, most are structural isomers. We conclude that it is the particular chemical structure of the additive that determines its crystallization/self-assembly process, and, therewith, the structure of the heterogeneous nuclei, and at a higher hierarchical level the morphology of the poly(propylene) solid state and its final properties; and, hence, that a predictive understanding is still elusive. [source]

NMR-based analysis of structure of heteroleptic triple-decker (phthalocyaninato) (porphyrinato) lanthanides in solutions

MAGNETIC RESONANCE IN CHEMISTRY, Issue 7 2010
Kirill P. Birin
Abstract A novel approach for the structural analysis of heteroleptic triple-decker (porphyrinato)(phthalocyaninato) lanthanides(III) in solutions is developed. The developed approach consists in molecular mechanics (MM+) optimization of the geometry of the complex taking into account the lanthanide-induced shift (LIS) datasets. LISs of the resonance peaks in 1H NMR spectra of a series of symmetric complexes [An4P]Ln[(15C5)4Pc]Ln[An4P], where An4P2, is 5,10,15,20-tetrakis(4-methoxyphenyl)porphyrinato-dianion, [(15C5)4Pc]2, is 2,3,9,10,16,17,24,25-tetrakis(15-crown-5)phthalocyaninato-dianion and Ln = La, Ce, Pr, Nd, Sm, Eu, are analyzed. Analysis of LISs showed two sets of protons in the molecule with opposite signs of shift. Two-nuclei analysis of LISs testifies isostructurality of the whole series of investigated complexes in solution despite contraction of the lanthanide ions. Model-free separation of contact and dipolar contributions of LISs was performed with one-nucleus technique and did not show changes in contact and dipolar terms within the investigated series. MM+ optimization of the molecular structure allowed the interpretation of features of LIS for each particular group of protons. Parameterization of MM + -optimized model of molecule with values of structure-dependent dipolar contributions of LIS allows the development of the precise structural model of the triple-decker complex in solution. This approach allows the determination of the geometry and structure of the sandwich macrocyclic tetrapyrrolic complexes together with conformational analysis of flexible peripheral substituents in solutions. The developed method can be applied with minor modifications for the determination of structural parameters of other types of lanthanides(III) complexes with tetrapyrrolic ligands and also supramolecular systems based on them. Copyright © 2010 John Wiley & Sons, Ltd. [source]

(2R,4S)-7-Bromo-2-phenyl-2,3,4,5-tetrahydro-1,4-epoxynaphtho[1,2- b]azepine, (2RS,4SR)-7-bromo-2-(4-chlorophenyl-2,3,4,5-tetrahydro-1,4-epoxynaphtho[1,2- b]azepine and (2RS,4SR)-2-(4-fluorophenyl)-2,3,4,5-tetrahydro-1,4-epoxynaphtho[1,2- b]azepine: hydrogen-bonded structures in two and three dimensions

ACTA CRYSTALLOGRAPHICA SECTION C, Issue 4 2009
Alirio Palma
(2R,4S)-7-Bromo-2-phenyl-2,3,4,5-tetrahydro-1,4-epoxynaphtho[1,2- b]azepine, C20H16BrNO, (I), exhibits evidence of a modest degree (ca 10%) of inversion twinning, while both (2RS,4SR)-7-bromo-2-(4-chlorophenyl)-2,3,4,5-tetrahydro-1,4-epoxynaphtho[1,2- b]azepine, C20H15BrClNO, (II), and (2RS,4SR)-2-(4-fluorophenyl)-2,3,4,5-tetrahydro-1,4-epoxynaphtho[1,2- b]azepine, C20H16FNO, (III), crystallize as genuine racemic mixtures. The molecules of (I) are linked into sheets by a combination of one C,H...O hydrogen bond and two C,H...,(arene) hydrogen bonds, while those of (II) are linked into sheets of ,-stacked hydrogen-bonded chains. A combination of one C,H...O hydrogen bond and four independent C,H...,(arene) hydrogen bonds links the molecules of (III) into a three-dimensional framework. The significance of this study lies in its finding, via comparison with the structures of some closely-related epoxybenzazepine analogues, of significant changes in crystal structures consequent upon small changes in the peripheral substituents. [source]