Search results for "geometry."

Cover Feature: The Missing Link in the Magnetism of Hybrid Cobalt Layered Hydroxides: The Odd–Even Effect of the Organic Spacer (Chem. Eur. J. 3/2021)

2020

Coordination Chemistry of Cu2+ Complexes of Small N-Alkylated Tetra-azacyclophanes with SOD Activity

2018

A new tetraaza-pyridinophane macrocycle (L1) N-alkylated with two isopropyl and one methyl groups symmetrically disposed has been prepared and its behavior compared with those of the unsubstituted pyridinophane (L3) and the related compound with three methyl groups (L2). The protonation studies show that, first, a proton binds to the central methylated amine group of L1, while, second protonation leads to a reorganization of the protons that are at this stage attached to the lateral isopropylated amines. The X-ray structure of [HL1]+ agrees with the UV–vis and NMR studies as well as with the results of DFT calculations. The stability of the Cu2+ complexes decreases on increasing the bulkine…

Polymerizable and polymeric zwitterionic surfactants: 1. Synthesis and bulk properties

1991

Abstract The synthesis of a series of permanently zwitterionic surfactant monomers based on sulphobetaines and the preparation of their polymers is described. Solubilities, thermal properties and bulk structures of the zwitterionic polymers are studied with respect to their molecular architecture, and compared with cationic analogues. The various solubilities of the polymers can be correlated with their molecular geometry, enabling differentiation into distinct classes. This behaviour is paralleled by the observed bulk structures of the polymers where distinct classes of superstructures are present. However, independently of the molecular geometry, no thermal transition could be detected fo…

Oxygen atom transfer catalysis by dioxidomolybdenum(VI) complexes of pyridyl aminophenolate ligands

2021

Abstract A series of new cationic dioxidomolybdenum(VI) complexes [MoO2(Ln)]PF6 (2–5) with the tripodal tetradentate pyridyl aminophenolate ligands HL2-HL5 have been synthesized and characterized. Ligands HL2-HL4 carry substituents in the 4-position of the phenolate ring, viz. Cl, Br and NO2, respectively, whereas the ligand HL5, N-(2-hydroxy-3,5-di-tert-butylbenzyl)-N,N-bis(2-pyridylmethyl)amine, is a derivative of 3,5-di-tert-butylsalicylaldehyde. X-ray crystal structures of complexes 2, 3 and 5 reveal that they have a distorted octahedral geometry with the bonding parameters around the metal centres being practically similar. Stoichiometric oxygen atom transfer (OAT) properties of 5 with…

Speciation of tin(II) in aqueous solution: thermodynamic and spectroscopic study of simple and mixed hydroxocarboxylate complexes

2013

This contribution reports the results of potentiometric and Mossbauer investigations on the formation, stability, and structure of binary and ternary mono- and binuclear complexes of Sn2+ with three hydroxocarboxylic ligands (namely L = tartrate, malate, and citrate) and chloride at T = 298.15 K in different ionic media and ionic strengths (0.15 and 1.00 mol dm−3 in NaCl(aq) and 1.00 mol dm−3 in NaNO3(aq)). The stability constants of various simple Sn i H j L (2+−) and mixed Sn i H j L k Cl (2+−−) species obtained in the different experimental conditions are reported, and various speciation diagrams of the simple and mixed systems are shown in different conditions. The sequestering ability …

Synergy of Axial and Point Chirality to Construct Helical N -Heterotriangulene-Based Supramolecular Polymers

2018

Internodal elongation in the grapevine (<em>Vitis vinifera</em> L.) : leaf influences and role of the shoot apex

1996

<p style="text-align: justify;">The respective influences of the leaves and shoot apex on stimulation of internodal elongation were studied in the grapevine. Various defoliation or decapitation treatments were applied to the shoot of rooted hardwood cuttings grown in a controlled environment chamber.</p><p style="text-align: justify;">Concerning the foliar influences, the role of three sorts of leaves, in relation to their nodal position relative to the internode was analysed ; its own leaves, the leaves located below it and the young leaves neoformed above. The effects produced by excision of these different leaves show that the two adjacent leaves (below and above) of th…

Static properties of end-tethered polymers in good solution: A comparison between different models

2004

We present a comparison between results, obtained from different simulation models, for the static properties of end-tethered polymer layers in good solvent. Our analysis includes data from two previous studies--the bond fluctuation model of Wittmer et al. [J. Chem. Phys. 101, 4379 (1994)] and the off-lattice bead-spring model of Grest and Murat [Macromolecules 26, 3108 (1993)]. Additionally, we explore the properties of a similar off-lattice model simulated close to the Theta temperature. We show that the data for the bond fluctuation and the Grest-Murat model can be analyzed in terms of scaling theory because chains are swollen inside the Pincus blob. In the vicinity of the Theta point th…

Synthesis, Structural, Magnetic and Thermal Characterization of {[Cu(bipy)] 2 (μ‐HP 2 O 7 )(μ‐Cl)}·H 2 O

2008

Copper(II) hydroxide reacts with 2,2′-bipyridine (bipy) and sodium pyrophosphate in a 2:2:1 stoichiometric ratio under ambient conditions at pH 1.6 in water. The resulting neutral dinuclear CuII complex features a bridging set containing bridging monoprotonated pyrophosphate and a monoatomic chloro bridge (making this the first pyrophosphate bridged coordination complex containing an alternate, additional halide bridge between the metal centers). Single-crystal X-ray diffraction studies revealed the complex to be {[Cu(bipy)]2(μ-HP2O7)(μ-Cl)}·H2O. The structure consists of a dimeric copper(II) system with each metal ion in a square pyramidal geometry. The asymmetric [Cu(bipy)]2+ units are br…

119Sn Mössbauer spectroscopic studies of the products of the reaction of triorganotin(IV) derivatives with 6-thiopurine

1985

Abstract A structural study of the products of the reaction of R 3 Sn IV derivatives (R = Me, Bu n , Ph) with 6-thiopurine, 6-TPH 2 , and its sodium salt, 6-TPHNa, has been undertaken using Mossbauer spectroscopy and the point-charge model rationalization of the Mossbauer parameter nuclear quadrupole splitting. The synthetic reactions have been carried out at ca . 0 °C, 20 °C and 50 °C. The Mossbauer spectra of the complexes AlK 3 Sn(6-TPH) are consistent with the occurrence of two distinct tin(IV) sites in samples prepared at the lower temperature, while one only site appears by increasing the temperature of the reaction. Two tin sites constantly occur in the products of the reactions invo…