Di­chloro­[N,N,N′,N′-tetrakis(2-pyridyl­methyl)­benzene-1,4-di­amine]­iron(II)

In the title complex, [FeCl₂(C₃₀H₂₈N₆)], the Fe atom is five-coordinated by two terminal chloride ligands and one end of the bis-tridentate ligand. The complexes display intermolecular C—H⃛π, π-stacking and C—H⃛X (X = N, Cl) interactions.     

Strongly etale extensions and weak henseliziations

Abstract

Since the circulation, in 1974, of the first draft of “The construction D + XD _S [X], J. Algebra 53 (1978), 423–439” a number of variations of this construction have appeared. Some of these are: The generalized D + M construction, the A + (X)B[X] construction, with X a single variable or a set of variables, and the D + I construction (with I not necessarily prime). These constructions have proved their worth not only in providing numerous examples and counter examples in commutative ring theory, but also in providing statements that often turn out to be forerunners of results on general pullbacks. The aim of this paper will be to discuss these constructions and the remarkable uses they have been put to. I will concentrate more on the A + XB[X] construction, its basic properties and examples arising from it.     

Protein immobilization capacity and covalent binding coverage of pulsed plasma polymer surfaces

Three carbon surfaces were deposited using pulsed plasma enhanced chemical vapour deposition method: a low and a high nitrogen-containing plasma polymer surfaces and a diamond-like carbon surface. The surfaces were analysed using both X-ray photoelectron spectroscopy (XPS) technique and the enzyme-linked immunosorbent assay (ELISA) method combining with sodium dodecyl sulphate (SDS) cleaning to investigate the capacity and covalent binding of the immobilized proteins. A good correlation was found on quantification of remaining protein after SDS cleaning using the ELISA method and the XPS technique. All surfaces had similar initial capacity of protein attachment but with large different resistance to SDS cleaning. The analysis showed that the high nitrogen-containing plasma polymer was the best biocompatible material due to its highest resistance to SDS cleaning, i.e. with the highest quantity (∼80%) of proteins bound covalently.     

Definability in Substructure Orderings,II: Finite Ordered Sets

Let \({{\uppercase {\mathcal{p}}}} \) be the ordered set of isomorphism types of finite ordered sets (posets), where the ordering is by embeddability. We study first-order definability in this ordered set. We prove among other things that for every finite poset P, the set \(\{p,p^{\partial}\}\) is definable, where p and \(p^{\partial}\) are the isomorphism types of P and its dual poset. We prove that the only non-identity automorphism of \({{\uppercase {\mathcal{p}}}}\) is the duality map. Then we apply these results to investigate definability in the closely related lattice of universal classes of posets. We prove that this lattice has only one non-identity automorphism, the duality map; that the set of finitely generated and also the set of finitely axiomatizable universal classes are definable subsets of the lattice; and that for each member K of either of these two definable subsets, \(\{K,K^{\partial}\}\) is a definable subset of the lattice. Next, making fuller use of the techniques developed to establish these results, we go on to show that every isomorphism-invariant relation between finite posets that is definable in a certain strongly enriched second-order language \(\textup{\emph L}_2\) is, after factoring by isomorphism, first-order definable up to duality in the ordered set \({{\uppercase {\mathcal{p}}}}\). The language \(\textup{\emph L}_2\) has different types of quantifiable variables that range, respectively, over finite posets, their elements and order-relation, and over arbitrary subsets of posets, functions between two posets, subsets of products of finitely many posets (heteregenous relations), and can make reference to order relations between elements, the application of a function to an element, and the membership of a tuple of elements in a relation.     

DFT study of paramagnetic adducts of tris-(8-hydroxyquinoline)aluminum (III)

Radicals formed by the addition of hydrogen (H) or muonium (Mu) to tris(8-hydroxyquinoline)aluminum(III) (Alq(3)) have been studied using density functional theory (DFT) calculations. Drew et al. (Phys. Rev. Lett. 2008, 100, 116601) studied Alq(3) using the longitudinal field muon spin relaxation technique and assumed the formation of muoniated radicals and rapid intermolecular electron hopping with a rate of (1.4 ± 0.2) × 10(12) s(-1). In this work, the results of DFT calculations on Alq(3), the H/Mu adducts of Alq(3), and the corresponding anions and cations are reported. The energy required to transfer an electron to or from the H/Mu adducts of Alq(3) is prohibitively large, ranging from 4.09 to 5.68 eV, which suggests that the unpaired electron does not hop onto neighboring molecules and that there is no long-range diffusion of the unpaired electron. The hyperfine coupling constants for the muoniated radicals were calculated and used to predict avoided level crossing resonance fields, which will allow experimenters to confirm that the unpaired electron is localized in close proximity to the muon.     

Self-assembled monolayer of a peroxo-bridged dinuclear cobalt(III) complex on Au(111)

Densely packed Self-Assembled Monolayers (SAMs) of a peroxide-bridged dicobalt complex, [Co2(O2)(bpbp)(O2CCH2CH2S)]2+, 3, (bpbp- = 2,6-bis((N,N-bis-(2-picolyl)amino)-methyl)-4-tert-butylphenolato) have been prepared on atomically planar Au(111) surfaces. Surface voltammetric and interfacial capacitance data, along with electrochemical scanning tunnelling microscopy (in situ STM) imaging, support the formation of a densely packed adlayer of 3 attached via a gold-thiolate bond. In solution, the disulfide linked precursor for 3 reversibly binds dioxygen with high affinity. Electrochemical measurements show that the redox potential of the O22-/O2*- couple of the monolayer of 3 is cathodically shifted by nearly 500 mV compared to the precursor in solution. This is attributed to the close proximity of the O2 binding site to the gold surface. Since the redox potential of the O22-/O2*- couple reflects tentatively the binding affinity of O2 to the deoxygenated CoII2 binding site, the potential of the O22-/O2*- couple of the SAM of 3 suggests a much higher affinity towards O2 compared to the solution precursor.     

Controlled formation and topologies of thiophenolate-based macrocycles: rings, cylinders and bowls

The Schiff-base condensations of 1,3-diaminopropane with a protected thiophenol dialdehyde in the presence of Ni(2+), Pd(2+) or Zn(2+) can be controlled to yield either mononuclear acyclic, or 2 + 2 and 4 + 4 macrocyclic complexes by the choice of both metal cation and counteranion. The Ni(2+) complex of the 2 + 2 macrocycle contains two square-planar nickel ions and shows an arrangement similar to one observed previously: the mu-S atoms of the thiophenolate groups are pyramidal and lie on the same side of the plane defined by the four N atoms of the macrocycle to give a V-shaped molecule. By contrast, the Zn(2+) complex of the 2 + 2 macrocycle undergoes oligomerization to yield a bowl-shaped hexanuclear complex that includes a mu(3)-carbonate anion. Essential for this topology is the presence of three mu(3)-S-thiophenolato groups that link the three macrocyclic units to form a Zn(3)S(3) ring that seals the bottom part of the bowl. In this arrangement, one of the pyramidal mu(3)-S atoms in each dinuclear Zn(2+) complex is inverted relative to the arrangement observed for the dinickel complexes. Molecular modelling suggests that inversion about the mu-S atoms of the 2 + 2 macrocyclic complexes is readily accessible at room temperature and that the contrasting arrangements observed for the Ni(2+) and Zn(2+) complexes are those energetically most favourable for the respective metal ions. Rare 4 + 4 macrocyclic complexes are isolated as neutral dinuclear complexes for Ni(2+) and Pd(2+) and as a tetranuclear complex cation for Zn(2+). The topologies of these systems contrast significantly: those with two square-planar Ni(2+) or Pd(2+) ions form extended rings, while that with Zn(2+) forms a sulfur-lined cylinder which hosts acetonitrile molecules in the crystalline state. Reaction conditions can also be optimised to produce 2 + 1 acyclic ligands as their mononuclear Ni(2+) and Pd(2+) complexes, providing potentially useful building blocks for production of more complicated macrocyclic and supramolecular systems.     

Phosphine dissociation and diffusion on Si(001) observed at the atomic scale

A detailed atomic-resolution scanning tunneling microscopy (STM) and density functional theory study of the adsorption, dissociation, and surface diffusion of phosphine (PH(3)) on Si(001) is presented. Adsorbate coverages from approximately 0.01 monolayer to saturation are investigated, and adsorption is performed at room temperature and 120 K. It is shown that PH(3) dissociates upon adsorption to Si(001) at room temperature to produce both PH(2) + H and PH + 2H. These appear in atomic-resolution STM images as features asymmetric-about and centered-upon the dimer rows, respectively. The ratio of PH(2) to PH is a function of both dose rate and temperature, and the dissociation of PH(2) to PH occurs on a time scale of minutes at room temperature. Time-resolved in situ STM observations of these adsorbates show the surface diffusion of PH(2) adsorbates (mediated by its lone pair electrons) and the dissociation of PH(2) to PH. The surface diffusion of PH(2) results in the formation of hemihydride dimers on low-dosed Si(001) surfaces and the ordering of PH molecules along dimer rows at saturation coverages. The observations presented here have important implications for the fabrication of atomic-scale P dopant structures in Si, and the methodology is applicable to other emerging areas of nanotechnology, such as molecular electronics, where unambiguous molecular identification using STM is necessary.     

Conformational analysis: crystallographic,NMR, and molecular mechanics studies of flexible sulfonic esters

Two novel X-ray structures of the sulfonic ester derivatives 2-(6-iodo-1,3-benzodioxol-5-yl)ethyl 4-nitrobenzenesulfonate, 3, and 2-(6-iodo-1,3-benzodioxol-5-yl)ethyl 4-methylbenzenesulfonate, 4, have been obtained in a study aimed at analyzing the structures and conformations of sulfonic ester derivatives that are routinely used in alkaloid syntheses. The crystal structure of 4 is highly unusual, containing four independent molecules that belong to two distinct conformational types: (1) a hairpin conformation (stabilized mainly by intramolecular pi-stacking) and (2) a stepped conformation (stabilized mainly by intermolecular pi-stacking). Compound 3, on the other hand, crystallizes exclusively as the hairpin conformer. New MM+ force field parameters for sulfonic esters have been developed using the X-ray data, empirical rules, and DFT calculations to estimate the bond dipole parameters. Grid searches of conformational space for 3 and 4 using MM methods show that there are several gas-phase conformations within 5 kcal/mol of the global minimum and that the lowest energy conformations (by approximately 4.6 kcal/mol) are of the hairpin type. Analysis of the MM conformational energies suggests that the dominant intramolecular interaction stabilizing the hairpin conformations of 3 and 4 is van der Waals attraction. Moreover, the lattice energies for packing the hairpin conformations of 3 and 4 are approximately 4 kcal/mol more favorable than for the stepped conformations. Various intermolecular interactions contribute to the complexity of the observed crystal structures of 3 and 4, including electrostatic attraction between O and I atoms in neighboring molecules. Langevin dynamics (LD) simulations at several temperatures (6.0 ns, friction coefficient = 2.5 ps(-1)) indicate that the conformational exchange rates are approximately 10(10)-10(11) s(-1) over the temperature range 213-400 K, accounting for the temperature-independent (1)H NMR spectra of 3 and 4.