Copper(II) Complexes of 3,4,5‐Trisubstituted Pyrazolates: In Situ Formation of Pyrazole Rings from Different Carbon Centers

The synthesis and characterization of two pyrazolate‐bridged dicopper(II) complexes, [Cu₂(L¹)₂(H₂O)₂](ClO₄)₂ ( 1 , HL¹=3,5‐dipyridyl‐4‐(2‐keto‐pyridyl)pyrazole) and [Cu₂(L²)₂(H₂O)₂](ClO₄)₂ ( 2 , HL²=3,5‐dipyridyl‐4‐benzoylpyrazole), are discussed. These copper(II) complexes are formed from the reactions between pyridine‐2‐aldehyde, 2‐acetylpyridine (for compound 1 ) or acetophenone (for compound 2 ), and hydrazine hydrate with copper(II) perchlorate hydrate under ambient conditions. The single‐crystal X‐ray structure of compound 1? 2 H₂O establishes the formation of a pyrazole ring from three different carbon centers through C? C bond‐forming reactions, mediated by copper(II) ions. The free pyrazoles (HL¹ and HL²) are isolated from their corresponding copper(II) complexes and are characterized by using various analytical and spectroscopic techniques. A mechanism for the pyrazole‐ring synthesis that proceeds through C? C bond‐forming reactions is proposed and supported by theoretical calculations.     

Computational study of tautomerism and aromaticity in mono‐ and dithio‐substituted tropolone

Keto‐enol tautomerism in mono‐ and dithio‐substituted analogs of tropolone was investigated using electronic structure computations. Seven structural isomers of C₇H₆OS and four of C₇H₆S₂ were optimized fully in gas phase at HF and B3LYP theoretical levels in combination with the 6‐311++g** basis set, as well as with the CBS‐QB3 and G3 methods. To examine the effects of an aqueous solvent on tautomeric equilibrium constants, each species was optimized in water using the self‐consistent reaction field polarizable continuum model at HF/6‐311++g** and B3LYP/6‐311++g** model chemistries. In both phases it was found that the enol forms were significantly more stable with respect to electronic energy and Gibbs free energy compared to the keto isomers, and outnumbered the keto species by several orders of magnitude. This was understood on the basis of elementary Hückel theory and the 4n + 2 rule, and supported by nucleus independent chemical shifts computations of NMR chemical shifts in these seven membered cyclic systems. © 2012 Wiley Periodicals, Inc.     

The controlled flocculation of submicron emulsion particles. I. A three-step synthetic route to supermicron polymer particles

The basic features of a three-step experimental process to produce supermicron polymer particles are described. First, a submicron emulsifier-free latex is prepared by a well-known technique. Second, the latex is aggregated by destabilizing with cetyl pyridinium chloride under constant stirring conditions, to yield roughly spherical clusters of 6-12 μ diameter. Third, the aggregates are stabilized with poly(vinyl alcohol) and internally coalesced by heating at or above the glass transition temperature. The final product particles have relatively smooth surfaces. Results are qualitatively interpreted in terms of a dynamic equilibrium where the aggregate size is determined by a balance between attractive interparticle potentials and stirring shear forces. Bimodal aggregate size distributions suggest the aggregate break-up mechanism may involve the erosion of individual latex particles and small fragments from the surface of aggregates. © 1996 John Wiley & Sons, Inc.     

Fragmentation pathways of 2,3‐dimethyl‐2,3‐dinitrobutane cations in the gas phase

2,3‐Dimethyl‐2,3‐dinitrobutane (DMNB) is an explosive taggant added to plastic explosives during manufacture making them more susceptible to vapour‐phase detection systems. In this study, the formation and detection of gas‐phase [M+H]⁺, [M+Li]⁺, [M+NH₄]⁺ and [M+Na]⁺ adducts of DMNB was achieved using electrospray ionisation on a triple quadrupole mass spectrometer. The [M+H]⁺ ion abundance was found to have a strong dependence on ion source temperature, decreasing markedly at source temperatures above 50°C. In contrast, the [M+Na]⁺ ion demonstrated increasing ion abundance at source temperatures up to 105°C. The relative susceptibility of DMNB adduct ions toward dissociation was investigated by collision‐induced dissociation. Probable structures of product ions and mechanisms for unimolecular dissociation have been inferred based on fragmentation patterns from tandem mass (MS/MS) spectra of source‐formed ions of normal and isotopically labelled DMNB, and quantum chemical calculations. Both thermal and collisional activation studies suggest that the [M+Na]⁺ adduct ions are significantly more stable toward dissociation than their protonated analogues and, as a consequence, the former provide attractive targets for detection by contemporary rapid screening methods such as desorption electrospray ionisation mass spectrometry. Copyright © 2009 Commonwealth of Australia. Published by John Wiley & Sons, Ltd.     

Hexanuclear copper(II) cage with {Cu3O···H···OCu3} core supported by a dicompartmental oxime ligand with m-xylyl spacer: synthesis, molecular structure and magnetic studies

A new dicompartmental dioxime ligand (H(2)L) with m-xylyl spacer between the donor sites has been synthesised by Schiff-base condensation of α,α'-diamino-m-xylene and diacetyl monooxime. The ligand reacts with copper(ii) salts giving rise to hexanuclear tricationic copper(II) cage complexes [Cu(II)(6)(μ(3)-O···H···O-μ(3))L(3)(H(2)O)(6)]X(3) (X = BF(4), 1a; X = ClO(4), 1b). The complexes have been characterised by different analytical and spectroscopic techniques and confirmed the hexanuclear structure even in solution. Single crystal X-ray diffraction studies of both the complexes revealed a very similar core structure with three dicompartmental ligands supporting two triangular Cu(3)O cores that share a proton, located on their common threefold axis and involved in a strong hydrogen bond interaction (O···O distance of 2.517(2) ?). Two Cu(3)O units do not superimpose but are staggered and disposed with the formation of a helicate structure. However both the enantiomers are present in the centrosymmetric space group. The facing Cu(3)-planes in 1a are separated at a distance of 3.476 ?. The temperature dependence of the magnetic behaviour of the hexanuclear complex 1a clearly indicates an overall antiferromagnetic exchange interaction between the spin carriers in the cage having two Cu(3)O subunits and leaves a single unpaired electron in each triangular unit. The unpaired electrons in the two Cu(3)O units interact antiferromagnetically through hydrogen bonding giving rise to an overall singlet-spin ground state.     

Controlled hydrothermal growth of ZnO nanostructures by sequestering the Zn metal ions with the chelating agent EDTA

In the present work, a controlled growth of ZnO nanostructures by manipulating Zn metal ion concentration by the chelating action of ethylene diaminetetra acetic acid in hydrothermal method is studied. EDTA produces metal–chelate complex by the formation of bidentate ligand with Zn²⁺ in the solution and diminishes the reactivity of Zn metal cations. Concentration of EDTA in the mother solution was varied in different ranges like 3, 5 and 10 mM while retaining the zinc metal salt and the NaOH concentration the same. Three different morphologies of wurtzite structured ZnO nanostructures such as nanorods-bunch, separate/discrete uniformly sized hexagonal nanorods and tapered flower petals like shapes are achieved by 3, 5 and 10 mM strengths of EDTA, respectively. The medium concentration 5 mM of EDTA is found to have moderate control over producing ZnO nanostructures of uniform diameter and a high aspect (length to diameter) ratio. An array of vertically aligned free standing ZnO nanorods with uniform spacing is successfully achieved by the addition of 5 mM of EDTA in the mother solution and the same is studied for its fluorescence property at an excitation of 325 nm and it has exhibited a characteristic UV emission of ZnO around 383 nm.