Tetrabenzylcyclen as a receptor for fluoride

A tetraazacyclic ligand, tetrabenzylcyclen (L), was synthesized using an improved method with a higher yield by treatment of cyclen with benzylchloride in the presence of potassium carbonate. The reaction of L with an aqueous solution of fluorosilicic acid yielded a mixed-anionic salt with the composition [H3L][F][SiF6]$4H2O (1). The single crystal X-ray study revealed that the macrocyclic trication essentially changes the conformation compared to the free ligand in order to tightly accommodate the fluoride inside and to keep the hexafluorosilicate anions and water molecules outside in the solid state complex

Preparation, structure and properties of pyridinium/bipyridinium hexafluorosilicates

Pyridinium hexafluorosilicates with the compositions (LH)2[SiF6] (where L = 2,6-bis(hydroxymethyl)-pyridine (I), 4,5-bis(hydroxymethyl)-2-methylpyridine-3-ol (II)), monohydrate (LH)2[SiF6]H2O (L = 2-bromo-6-methylpyridine (III)) and (LH2)[SiF6] (L = 4,40-bipyridine (IV), 2,20-bipyridine (V)) were separated as crystalline products of interaction of fluorosilicic acid with different pyridines. All compounds were characterized by elemental analysis, IR, NMR 19F and mass-spectrometry, solubility data, and X-ray crystallography. The structural study revealed the details of the anion binding and solid state supramolecular architectures provided by the combination of the plethora of intermolecular interactions including strong charge assisted and conventional hydrogen bonds of NH F, OH F types along with O Br contacts and p–p interactions. The relationship between the salts structure and physico-chemical properties is discussed

Nitrides as ammonia synthesis catalysts and as potential nitrogen transfer reagents

In this article, an overview of the application of selected metal nitrides as ammonia synthesis catalysts is presented. The potential development of some systems into nitrogen transfer reagents is also described

Resilience management during large-scale epidemic outbreaks

Assessing and managing the impact of large-scale epidemics considering only the individual risk and severity of the disease is exceedingly difficult and could be extremely expensive. Economic consequences, infrastructure and service disruption, as well as the recovery speed, are just a few of the many dimensions along which to quantify the effect of an epidemic on society's fabric. Here, we extend the concept of resilience to characterize epidemics in structured populations, by defining the system-wide critical functionality that combines an individual’s risk of getting the disease (disease attack rate) and the disruption to the system’s functionality (human mobility deterioration). By studying both conceptual and data-driven models, we show that the integrated consideration of individual risks and societal disruptions under resilience assessment framework provides an insightful picture of how an epidemic might impact society. In particular, containment interventions intended for a straightforward reduction of the risk may have net negative impact on the system by slowing down the recovery of basic societal functions. The presented study operationalizes the resilience framework, providing a more nuanced and comprehensive approach for optimizing containment schemes and mitigation policies in the case of epidemic outbreaks

Room temperature antiferromagnetic order in superconducting X_yFe_{2-x}Se_ 2, (X= Rb, K): a powder neutron diffraction study

Magnetic and crystal structures of superconducting X yFe 2-xSe 2 (X= Rb and K with Tc=31.5 K and 29.5 K) have been studied by neutron powder diffraction at room temperature. Both crystals show ordered iron vacancy pattern and the crystal structure is well described in the I4/m space group with the lattice constants a=8.799, c=14.576 and a=8.730, c=14.115 A, and the refined stoichiometry x=0.30(1), y=0.83(2) and x=0.34(1), y=0.83(1) for Rb- and K-crystals respectively. The structure contains one fully occupied iron position and one almost empty vacancy position. Assuming that the iron moment is ordered only on the fully occupied site we have sorted out all eight irreducible representations (irreps) for the propagation vector k=0 and have found that irreps tau_2 and tau_7 well fit the experimental data with the moments along c-axis. The moment amplitudes amounted to 2.15(3) mu_B, 2.55(3) mu_B for tau_2 and 2.08(6) mu_B, 2.57(3) mu_B for tau_7 for Rb- and K-crystals respectively. Irrep tau_2 corresponds to the Shubnikov group I4/m' and gives a constant moment antiferromagnetic configuration, whereas tau_7 does not have Shubnikov counterpart and allows two different magnetic moments in the structure.Comment: 5 pages, 1 table, 4 figure

[[alternative]]Host-Guest Complexes of crown-ethers with HN-Proton Donr Molecules

[[abstract]]Crown ethers were reacted with HN-proton-donor molecules to obtain crystalline molecular host-guest complexes. It was found that complexes with crown ethers of different structure are formed, depending on the linear dimensions and mode of steric shielding of active centers of the proton-donor molecules.[[notice]]補正完畢[[incitationindex]]SC

Crystal structures and solubility of 4,4´-bipyridinium and 2-brom-5-methylpyridinium hexafluorosilicates

Hexafluorosilicates with heterocyclic cations are convenient models for the estimation of H-bonds influence on structural characteristics and properties of this onium salts. As a part of our systematic investigation here we describe results of X-ray structure analysis and solubility data determination of the hexafluorosilicates (4,4´-DipyH2)SiF6 (I) and (2-Br-6-CH3C5H3NH)2SiF6·H2O (II)

Preparation, Characterization, And Electronic Structure Of Asymmetric Isonaphthalimide: Mechanism Of Dual Fluorescence In Solid State

The asymmetric isonaphthalene imide, 3-[(4-nitrophenyl)imino]-1H,3H- benzo[de]isochromen-1-one was obtained by condensation of 1,8-naphthoylchloride with p-nitroaniline in the presence of pyridine. The crystal structure and vibrational and electronic absorption spectra are reported. The emission spectrum of the crystalline phase demonstrates dual luminescence, with short and long wavelength components, while only the short wavelength component is present in chloroform solution. The geometrical and electronic structures of the ground and excited states of the molecule are investigated using density functional theory methods. Dual fluorescence is explained in terms of the excited states of different nature. The spectroscopic properties of newly synthesized compounds for possible biosensor applications are discussed. © 2013 American Chemical Society

Structure of the 18-crown-6 complex with ammonium hexafluorosilicate and water

The crystalline host–guest type complex [(18-crown-6ċNH4)2][SiF6]ċ4H2Ohas been obtained as the result of the interaction of SiF4ċ2NH3 with 18-crown-6 (18C6) in an aqueous medium. Crystal data: monoclinic, space groupC 2 c, a=26.541(2), b=8.363(2), c=20.469(2) Å, β = 122.43(1)°and Z=4. The final R-value is 0.070 for 3253 reflections with I ≥ 2σ(I).The crystals consist of the complex [NH4ċ18C6]+ cations, [SiF6]2-anions and water molecules. The ammonium cation is hydrogen bonded by three of its H-atoms to the crown ether oxygen atoms with N(1) ċO separations2.923(5)–2.940(5) Å and by the fourth H-atom to the fluorine atom of thehexafluorosilicate anion, the N(1)ċF(4) distance being 2.797(6) Å.The conformation of the macrocycle and the hydrogen-bond geometry in thecomplex cation closely resemble those in related adducts between 18-crown-6and ammonium salts. All crystal components are connected via a system of hydrogen bonds into a ribbon alongthe b axis in the unit cell