Some structural systematics in metal carbonyl cluster chemistry

The recently developed electron-counting rules for condensed polyhedral metal carbonyl clusters have been utilised to develop a systematic approach for enumerating the structural alternatives for metal cluster compounds which are isoelectronic. The more usual cluster degradation and aggregation processes are represented in a matrix form which relates the change in electron count to the number of new bonds formed (or broken). The matrices for cluster degradation and aggregation are represented in a complementary fashion so that the search for isoelectronic clusters greatly simplified. The utility of the approach is illustrated by reference to some recent examples from metal carbonyl cluster chemistry.     

The effect of terminal chain modifications on the mesomorphic properties of 4,4′-disubstituted diphenyldiacetylenes

The typical sidewalls produced in the fabrication of protrusion electrodes are proposed to create a low voltage (4.5 V_rms) and high transmittance (93%) blue-phase liquid crystal display (BP-LCD). The tilted electrodes produce a strong horizontal electrical field that reduces the operating voltage considerably. The common problem of the ‘dead zones’ is solved by reflecting the light onto the electrodes. In order to estimate the phase retardation of the reflected light, a ray tracing simulation program for anisotropic mediums has been developed. The proposed device is more competitive than vertical field switching based BP-LCD and also, has the advantages of protruded in-plane-switching structures. These facts make this technology a potential candidate for the next generation of BP-LCDs.     

Cyclic (ALN)n Compounds as Precursors to Aluminum Nitride: Synthesis and Structure of [(CH3)2AlNH2]3 and the Planar Species [(t-C4H9)2AlNH2]3

Abstract

The crystal and molecular structures of the title compounds, [(CH₃)₂AlNH₂]₃ 1 and [(t-C₄H₉)₂AlNH₂]₃ 2, have been determined in connection with their investigation as possible precursors to aluminum nitride. Both compounds have an (AlN)₃ ring-structure with distorted tetrahedral geometries for the ring Al and N atoms. The distortion from tetrahedral geometry is most pronounced for the N atoms where the endocyclic Al-N-Al bond angles average 125.3 for 1 and 134.2 for 2. The (AlN)₃ ring in 1 is in a skew-boat conformation with no unusual intra- or intermolecular contacts. Compound 2 on the other hand exhibits an unprecedented planar (AlN)₃ ring as required by a crystallographic three-fold symmetry axis. The effects of the Al and N substituents on the (AlN)₃ ring size and conformation, as well as on the endocyclic Al-N-Al bond angles, are discussed in the context of the structural results obtained for these and other (AlN)_n ring compounds.     

Mixed-Ligand Complex Formation Equilibria of Vanadium(III) with 2,2′-Bipyridine and the Amino Acids Glycine, Proline, α-Alanine and β-Alanine Studied in 3.0 mol?dm?3 KCl at 25 °C

We studied speciation of the mixed-ligand complex formation equilibria of vanadium(III) with both 2,2??-bipyridine (Bipy) and the amino acids glycine (HGly), proline (HPro), ??-alanine (H??Ala), and ??-alanine (H??Ala) by means of electromotive forces measurements emf(H) using 3.0?mol?dm^?3 KCl as the ionic medium at 25 °C. The experimental data were analyzed by means of the computational least-squares program LETAGROP, taking into account the hydrolysis of the vanadium(III) cation, the respective stability constants of the binary complexes, and the acid/base reactions of the ligands which were kept fixed during the analysis. In all four amino acid systems studied we observed the complexes [V₂O(Bipy)(B)]³⁺, [V₂O(Bipy)₂(B)₂]²⁺, [V(OH)(Bipy)(B)₂] and [V(OH)₂(Bipy)(B)], where B represents the deprotonated form of the amino acids studied in this work. The respective stability constants were determined and the species distribution diagrams as a function of pH are briefly discussed.     

Comparison of solid-phase extraction methods for the determination of azaspiracids in shellfish by liquid chromatography-electrospray mass spectrometry

Azaspiracids have been identified as the cause of a new toxic syndrome called azaspiracid poisoning (AZP) that has led to incidents of human intoxications throughout Europe following the consumption of mussels. Although five AZP toxins have been structurally elucidated to-date, azaspiracid (AZA1), 8-methylazaspiracid (AZA2) and 22-demethylazaspiracid (AZA3) are the predominant toxins. Separation of the three main AZP toxins was achieved using reversed-phase liquid chromatography (LC) and coupled to an electrospray ionisation source of an ion-trap mass spectrometer. Five reversed-phase (C18) and three diol solid-phase extraction (SPE) cartridges were compared for their efficacy in the cleanup of shellfish matrix. The comparison was based on the optimum recoveries of AZA1, AZA2 and AZA3 from extracts of mussel tissues. LC-electrospray MS3 analysis was used to quantify the AZP toxins in wash and eluate fractions in the SPE studies. Good recovery and reproducibility data were obtained for one diol SPE cartridge and two C18 SPE cartridge types.     

Templating and selection in the formation of macrocycles containing [[P(micro-NtBu)(2)](micro-NH)](n) frameworks: observation of halide ion coordination

Amination of [ClP(micro-NtBu)](2) (1) using NH(3) in THF gives the cyclophospha(III)zane dimer [H(2)NP(micro-NtBu)](2) (2), in good yield. (31)P NMR spectroscopic studies of the reaction of 1 with 2 in THF/Et(3)N show that almost quantitative formation of the cyclic tetramer [[P(micro-NtBu)](2)(micro-NH)](4) (3) occurs. The remarkable selectivity of this reaction can (in part) be attributed to pre-organisation of 1 and 2, which prefer cis arrangements in the solid state and solution. The macrocycle 3 can be isolated in yields of 58-67 % using various reaction scales. The isolation of the major by-product of the reaction (ca. 0.5-1 % of samples of 3), the pentameric, host-guest complex [[P(micro-NtBu)(2)](2)(micro-NH)](5)(HCl).2 THF] (4.2 THF), gives a strong indication of the mechanism involved. In situ (31)P NMR spectroscopic studies support a stepwise condensation mechanism in which Cl(-) ions play an important role in templating and selection of 3 and 4. Amplification of the pentameric arrangement occurs in the presence of excess LiX (X=Cl, Br, I). In addition, the cyclisation reaction is solvent- and anion-dependent. The X-ray structures of 2 and 4.2 THF are reported.     

Solution and solid-state structure of the anion [Ag(2)[closo-CB(11)H(12)](4)](2-)

Addition of the carbene 1,3-dimesitylimidazol-2-ylidene (IMes) to a toluene solution of Ag[closo-CB(11)H(12)] results in the formation of the complex [(IMes)(2)Ag](2)[Ag(2)[closo-CB(11)H(12)](4)], the anionic component of which contains two silver(I) centers bridged by two carboranes in addition to one terminally bound carborane on each metal, in the solid-state. Comparison of the observed (11)B[(1)H] NMR chemical shifts of [(IMes)(2)Ag](2)[Ag(2)[closo-CB(11)H(12)](4)] or Ag[closo-CB(11)H(12)] with [NBu(4)][closo-CB(11)H(12)] in CD(2)Cl(2) demonstrates that the silver ion interacts significantly with the cage in solution. Theoretical investigations using the ab initio/GIAO/NMR method of [closo-CB(11)H(12)](-) and Na[closo-CB(11)H(12)] as model geometries for the silver salts support experimental evidence for these Ag...[BH] interactions in solution.     

One‐Step Multicomponent Self‐Assembly of a First‐Generation Sierpiński Triangle: From Fractal Design to Chemical Reality

A novel terpyridine‐based architecture that mimics a first‐generation Sierpiński triangle has been synthesized by multicomponent assembly and features tpy? Cd^II? tpy connectivity (tpy=terpyridine). The key terpyridine ligands were synthesized by the Suzuki cross‐coupling reaction. Mixing two different terpyridine‐based ligands and Cd^II in a precise stoichiometric ratio (1:1:3) produced the desired fractal architecture in near‐quantitative yield. Characterization was accomplished by NMR spectroscopy, mass spectrometry, and transmission electron microscopy.     

Allyl ether of aralkyl phenolic resin with low melt viscosity and its Alder‐ene blends with bismaleimide: synthesis,curing, and laminate properties

This paper outlines the synthesis and characterization of O‐allyl aralkyl phenolic (O‐allyl Xylok, OAX) resins having low melt viscosity and its Alder‐ene blends with 2, 2′‐bis 4‐[(4′‐maleimido phenoxy) phenyl] propane. The blends manifested a three‐stage curing pattern that converged to a two‐stage pattern on enhancing the maleimide content. The polymerization kinetics of typical allyl and maleimide rich resin systems showed apparent activation energy increasing and pre‐exponential factor decreasing from ene to the Diels–Alder step. Increased allyl content improved mechanical and impact properties of the composites at ambient temperature, although it diminished the retention of interlaminar shear strength at elevated temperature. Increased maleimide content of the resin was conducive for the higher rigidity for the composite and its retention at elevated temperature. A substantial increase in T_g (from 153°C to 280°C) and thermal stability was observed with an increase in maleimide content. High allyl content resulted in improved mechanical properties thanks to better resin–reinforcement interaction as revealed from morphological analysis. Copyright © 2014 John Wiley & Sons, Ltd.     

Interfacial electronic structure of vanadyl naphthalocyanine on highly ordered pyrolytic graphite

We present a core and valence region spectroscopic analysis of the interfacial electronic structure of thin films of vanadyl naphthalocyanine (VONc) deposited onto highly oriented pyrolytic graphite (HOPG). X-ray photoelectron spectroscopy indicates the predominantly ionic character of the vanadyl metal center coordinated by the heterocycle and affords the bandgap in the thin VONc films. Valence band photoelectron spectroscopy points to the existence of three different adsorption geometries of VONc on the HOPG surface. The distribution of the different geometries can be systematically influenced in a simple post-deposition processing step, with an immediate effect on the interfacial electronic environment. We find spectroscopic evidence in the valence levels that VONc grows on HOPG most likely in a 2D-gas fashion rather than by nucleation and growth of islands. These data allow us to predict accurately the interface dipole in the case of a broad class of dipolar organic semiconductors, based simply on molecular dipole moment, polarizability and molecular diameter. This ability provides an important step towards rational optimization of energy level alignment in organic electronics.