Association of copper(II) isonicotinamide moieties via different anionic bridging ligands: Two paths of ferromagnetic interaction in the azide coordination compound

Three isonicotinamide (isn) copper(II) complexes with different bridging ligands, azide, thiocyanate and sulfate, have been prepared. The molecular structure of [Cu₂(μ-1,1-N₃)₂(μ-1,3-N₃)₂(isn)₂]_n (1) is composed of binuclear species, Cu₂(μ-1,1-N₃)₂(isn)₂, inter-connected by additional four azide bridges in the end-to-end mode (1,3). This gives a CuN₄N square-pyramidal coordination sphere around each copper(II) ion. A trans mononuclear octahedral coordination sphere CuN₄S₂ is present in [Cu(μ-N,S-NCS)₂(isn)₂]_n (2), with thiocyanato ligands serving as bridges between the adjacent Cu(isn)₂ moieties. The third anionic ligand, i.e. sulfate, in {[Cu(μ-O,O’-SO₄)(H₂O)(isn)₂]·2H₂O}_n (3) completes the CuO₂N₂O square-pyramidal coordination sphere, and thus enables bridging between the mononuclear Cu(H₂O)(isn)₂ moieties. The ligands that bridge the principal building blocks, i.e. binuclear in 1 and mononuclear in 2 and 3, connect the axial ligands with the equatorial positions of the copper(II) coordination spheres in all three cases. A ferromagnetic interaction FM is found for 1, while 2 and 3 are paramagnetic. Therefore, the key structural difference between 1 on one hand, and 2 and 3 on the other, is found in the anionic ligand, serving in 1 also as the intra-binuclear bridge, showing the main path (J₁) for the FM interaction. Additionally, the inter-binuclear pathway in 1 gives another contribution (J₂) to the whole FM interaction seen herein (J₁ = 18.5 cm^–1, J₂ = 4.9 cm^–1).     

Supramolecular Architecture via Self-Complementary Amide Hydrogen Bonding in [Ag(pia)<Subscript>2</Subscript>](NO<Subscript>3</Subscript>)·H<Subscript>2</Subscript>O: Synthesis,Thermal and Structural Studies

Abstract  

The synthesis, thermal and spectral characterization and crystal structure of silver(I) complex with picolinamide, [Ag(C₆H₆N₂O)₂](NO₃)·H₂O, are reported. The silver(I) atom is chelated by two picolinamide (pia) ligands in approximately square planar geometry. The distortion within the coordination environment is mainly imposed by formation of the chelate rings, but it is also observed in two longer (Ag–O) and two shorter (Ag–N) bond lengths. The compound crystallizes in the triclinic space group P[`1]P\bar{1} with a = 7.1265(2) ?, b = 8.9157(4) ?, c = 12.9527(4) ?, α = 83.934(3)°, β = 86.094(2)°, γ = 67.023(3)° and Z = 2. Cationic complexes are linked through amide–amide hydrogen bonds of ‘head-to-head’ R ₂²(8) motif leading to infinite chains, while nitrate anions and H₂O molecules act only as a cross-link between such four symmetry related cationic chains via hydrogen bonds forming 2D supramolecular double sheets. Therefore, the ‘head-to-head’ amide interactions in [Ag(C₆H₆N₂O)₂](NO₃)·H₂O are robust enough to accommodate the usually disruptive NO₃ ⁻ anion and H₂O molecule and could be regarded as a tool for controlling the assembly of this silver complex.     

Gevrey properties of the asymptotic critical wave speed in a family of scalar reaction–diffusion equations

We consider front propagation in a family of scalar reaction–diffusion equations in the asymptotic limit where the polynomial degree of the potential function tends to infinity. We investigate the Gevrey properties of the corresponding critical propagation speed, proving that the formal series expansion for that speed is Gevrey-1 with respect to the inverse of the degree. Moreover, we discuss the question of optimal truncation. Finally, we present a reliable numerical algorithm for evaluating the coefficients in the expansion with arbitrary precision and to any desired order, and we illustrate that algorithm by calculating explicitly the first ten coefficients. Our analysis builds on results obtained previously in [F. Dumortier, N. Popovi?, T.J. Kaper, The asymptotic critical wave speed in a family of scalar reaction–diffusion equations, J. Math. Anal. Appl. 326 (2) (2007) 1007–1023], and makes use of the blow-up technique in combination with geometric singular perturbation theory and complex analysis, while the numerical evaluation of the coefficients in the expansion for the critical speed is based on rigorous interval arithmetic.     

NIR photoresponse in the mixed phthalocyanine films

The structure, optical and conducting properties of thin vacuum deposited films of erbium bisphthalocyanine (Pc₂Er) and its mixtures with metal-free phthalocyanine (H₂Pc) have been studied with particular reference to the near infrared (NIR). It has been found that, in spite of intense optical absorbance over the UV/Vis/NIR domain, pure Pc₂Er films are weakly photoconductive. However, in the mixed Pc₂Er/H₂Pc films the photocurrent signal was detected in the NIR range of 1200–1500 nm, which is associated with optical activity of Pc₂Er molecules. An erratum to this article is available at .     

Mass spectrometric and quantum chemical studies of the thermodynamics and bonding of neutral and ionized LnCl, LnCl2, and LnCl3 species (Ln = Ce, Lu)

The mass spectral patterns of CeCl3(g) and LuCl3(g) and appearance energies for the identified ions were measured using a Nier-type mass spectrometer coupled with a Knudsen cell. The molecular ion CeCl3+ was found to be considerably less stable in comparison to LuCl3+. Partial pressures and sublimation enthalpies of LnCl3(s) to monomeric LnCl3(g) and dimeric Ln2Cl6(g) species were obtained in the ranges of 882-1028 (Ln = Ce) and 850-1004 K (Ln = Lu). The contribution of dimeric Ce2Cl6(g) species to equilibrium vapors of CeCl3(s) is considerably smaller than the Lu2Cl6(g) contribution in LuCl3(s) vapors. The measurements were supplemented by quantum chemical ab initio studies of structures, energetics, and vibrational frequencies of neutral and singly ionized LnCl, LnCl2, and LnCl3 species (Ln = Ce, Lu). The theoretical appearance energies of different ions, calculated from the energies of the gaseous species, are in good agreement with experimental data. The fragmentation energies of LnCl, LnCl2, and LnCl3 were also computed and compared with the mass spectral patterns of respective vapor species. The Mulliken and natural bond orbital electron population methods were applied for the systematic analysis of the bonding scheme in molecules and cations.     

A geometric approach to bistable front propagation in scalar reaction–diffusion equations with cut-off

‘Cut-offs’ were introduced to model front propagation in reaction–diffusion systems in which the reaction is effectively deactivated at points where the concentration lies below some threshold. In this article, we investigate the effects of a cut-off on fronts propagating into metastable states in a class of bistable scalar equations. We apply the method of geometric desingularization from dynamical systems theory to calculate explicitly the change in front propagation speed that is induced by the cut-off. We prove that the asymptotics of this correction scales with fractional powers of the cut-off parameter, and we identify the source of these exponents, thus explaining the structure of the resulting expansion. In particular, we show geometrically that the speed of bistable fronts increases in the presence of a cut-off, in agreement with results obtained previously via a variational principle. We first discuss the classical Nagumo equation as a prototypical example of bistable front propagation. Then, we present corresponding results for the (equivalent) cut-off Schlögl equation. Finally, we extend our analysis to a general family of reaction–diffusion equations that support bistable fronts, and we show that knowledge of an explicit front solution to the associated problem without cut-off is necessary for the correction induced by the cut-off to be computable in closed form.     

Analysis of Tea for Metals by Flame and Graphite Furnace Atomic Absorption Spectrometry with Multivariate Analysis

The concentrations of iron, zinc, manganese, copper, chromium, nickel, lead, arsenic, and cadmium were determined using flame and graphite furnace atomic absorption spectrometry in nine herbal tea samples. Hawthorn, yarrow, elderflower, and bearberry are herbal teas for which the metal content has been rarely determined. The concentration of cadmium in St John’s wort exceeded the maximum permissible limit of 0.3?mg/kg. The metals were also determined in aqueous extracts following 5, 10, and 20?min of boiling and using different preparations, including acidification with lemon juice. The influence of these factors on metal release was demonstrated using multivariate analyses by redundancy analysis and principal component analysis. The metal release was not considerably affected by the boiling time, while the acidity of the medium was generally positively correlated. For the infusions, arsenic was detected only in acidified mint tea. The extraction efficiencies of metals were determined and classified as highly, moderately, and poorly extractable, with chromium showing largest variations.