B. de Castro

Immobilisation of amine-functionalised nickel(II) Schiff base complexes onto activated carbon treated with thionyl chloride

Abstract Two Schiff base nickel complexes with amine groups, bis[o-[N-(3-aminopropyl)formimidoyl]phenolato-O,N,N′]nickel(II) and bis[4-methoxy-o-[N-(3-aminopropyl)formimidoyl]phenolato-O,N,N′]nickel(II), were anchored onto a chemically oxidised activated carbon treated with thionyl chloride. Complex anchoring was made in three consecutive steps: (i) oxidation of activated carbon with nitric acid, (ii) treatment with thionyl chloride that converts primarily the carboxylic acid carbon surface groups into acyl chloride functionalities, and (iii) reaction between the amine functionalities of the metal complexes with the carbon surface acyl chloride functionalities. The resulting carbon-based materials were characterised by elemental analysis, surface techniques (SEM and XPS), nitrogen adsorption isotherms and thermal analysis (temperature-programmed desorption and thermogravimetry). The data from all the techniques provided evidence that both nickel complexes were anchored onto the activated carbon via an amide ligation originated by the reaction between the acyl chloride carbon surface functionalities and the amine groups of both metal complexes.

Electrochemical and X-ray studies of nickel(II) Schiff base complexes derived from salicylaldehyde: Structural effects of bridge substituents on the stabilisation of the +3 oxidation state

Abstract The oxidative chemistry of three Ni(II) complexes with Schiff base ligands derived from salicylaldehyde and diamines with different steric demands, N,N′-2-methylpropane-2,3-diyl-bis(salicylideneiminate)nickel(II) (1), N,N′-1,2-cyclohexyl-1,2-dyil-bis(salicylideneiminate)nickel(II) (2) and N,N′-2,3-dimethylbutane-2,3-diyl-bis(salicylideneiminate)nickel(II) (3), was studied by cyclic voltammetry and chronoamperometry in N,N′-dimethylformamide and (CH3)2SO. The electrogenerated species were characterised by EPR spectroscopy. All three complexes exhibited metal-centred oxidised processes and the oxidised products were low-spin six-coordinate Ni(III) species (dz2 ground state) with two solvent molecules axially coordinate. Addition of pyridine resulted in the replacement of solvent molecules with no changes in the ground state. The crystal structures of compounds 1 and 3 were determined from single crystal X-ray diffraction data, and the crystal packing for any of the complexes did not show any systematic parallel orientation of any part of the molecules. X-ray structural data for the Ni(II) complexes provided a rationale for the E1/2 values obtained in the oxidation processes and for the relative energy of the low-lying excited duplets of the electrogenerated Ni(III) species.

Anchoring of a nickel(II) Schiff base complex onto activated carbon mediated by cyanuric chloride

The Schiff base nickel complex functionalised with hydroxyl groups, N,N′-ethylene-bis-(4-hydroxysalicyliminate)nickel(II), [Ni(4-HOsalen)], was anchored onto an air-oxidised activated carbon using cyanuric chloride (CC) as the linking agent. Complex anchoring was made in three consecutive steps: (i) oxidation of activated carbon with a mixture of N2 and air (with 5% O2); (ii) attachment of CC to the air-oxidised carbon surface functionalities, and (iii) reaction between the metal complex functionalised with hydroxyl groups and carbon-bound CC. The carbon-based materials were characterised by elemental analysis, surface techniques (scanning electron microscopy and X-ray photoelectron spectroscopy), X-ray diffraction, nitrogen adsorption isotherms and thermal analysis (temperature-programmed desorption and thermogravimetry). Data from all these techniques provided evidence that the nickel complex was anchored onto the air-oxidised activated carbon via CC.

Encapsulation of copper(II) complexes with pentadentate N3O2 Schiff base ligands derived from acetylacetone in NaX zeolite

Abstract Copper(II) complexes with two five co-ordinate Schiff base ligands derived from acetylacetone and which provide a N 3 O 2 co-ordination sphere, bis(acetylacetonate)-3-amino-bis(propyldiimine) and bis(acetylacetonate)-3-methylamino-bis(propyldiimine), were entrapped in the supercages of zeolite NaX by a two-step process in the liquid phase: (i) adsorption of copper(II) acetylacetonate in the supercages of the zeolite, and (ii) in situ Schiff condensation of the copper(II) precursor complex with the corresponding triamines. The new materials were characterised by several techniques: chemical analysis, morphological and surface analysis, spectroscopic methods (FTIR, UV/VIS) and electron paramagnetic resonance. Analysis of the data indicates that the Cu(II) complexes are encapsulated in the NaX zeolite supercages and exhibit structural and electronic properties that are different from those of the free complexes, which can arise from distortions caused by steric effects due to the presence of sodium cations, or from interactions with the zeolite matrix.

Zeolite-encapsulated copper (II) complexes with N3O2 Schiff bases: synthesis and characterization

Abstract Copper(II) complexes with N 3 O 2 Schiff base ligands[B: bis-(acetylacetone)-3-amino-bis(propylenediimine) = H 2 (acac) 2 trien; C: bis-(acetylacetone)-3-methylamino-bis(propylenediimine) = H 2 (acac) 2 Metrien] were encapsulated in the supercages of zeolite Y in a two-step process: (i) adsorption of copper(II) acetylacetonate in the supercage of the zeolite; (ii) in-situ Schiff base condensation of the copper(II) acetylacetonate complex with corresponding triamine. The resulting materials were purified by Soxhlet extraction. Bulk and surface chemical analysis, surface characterization (SEM, XPS), spectroscopic characterization (UV/Vis, FTIR), electron paramagnetic resonance and temperature-programmed desorption studies of the new materials provide evidence for the entrapment of Cu(II) complexes in the zeolite supercages.

Anchoring of organic molecules onto activated carbon

Abstract Three organic compounds with two different functionalities have been anchored to activated carbons, in order to assess their use either as potential coupling agents for metal complexes or as model for grafting metal complexes with the same functionalities. The selected compounds were cyanuric chloride and 5-chloro-1-phenyl-1H-tetrazole, which have chlorine atoms and 1,2-phenylenediamine with an amine group. The supports were activated carbons derived from coconut shell charcoal, which were oxidised, either with oxygen (5% in a mixture of nitrogen and air) or with concentrated nitric acid, to increase selectively the amount of surface functional groups. Additional treatment with LiAlH4 took place before anchoring chlorine containing molecules, and the anchoring of 1,2-phenylenediamine was preceded by reaction with thionyl chloride to enable formation of amide bonds with the amine. Compelling evidence for the anchoring of these compounds onto the activated carbons was provided by the characterisation of these new materials using temperature-programmed reduction, temperature-programmed desorption and X-ray photoelectron spectroscopy.

SYNTHESIS AND CHARACTERISATION OF POLYOXOTUNGSTATE COMPOUNDS WITH COMPLEX COPPER AND COBALT CATIONS

Abstract Salts of the heteropolytungstates [PW11 M(H2O)O39]5-, M=Cu, Co, Mn, with the following complex cations were prepared: [Cu(LL)2(H2O)]2+, [Cu(LL)3]2+, LL= 1,10-phenantroline (phen), 2,2′-bipyridine (bipy), [Cu(phen)2Cl]+, [Co(bipy)2(CO3)]+, and [Co(phen)3]2+, Compounds with [SiW11 M(H2O)O39]6-, M=Cu, Co, Mn, and the cations [Co(LL)2(H2O)]2+, and [Co(bipy)2(CO3)]+ were also prepared. Synthesis was carried out in aqueous or nitromethane solutions. The compounds were characterised b y elemental and thermal analysis and spectroscopic techniques. Spectroscopic properties and the thermal stability of the polyanions in these compounds could thus be compared with those of simpler salts. BET surface areas were determined. Except for salts of [Cu(bipy)3]2+, the compounds decompose on heating at temperature above 200°C, the exact temperature depending on the cation. Some are stable up to 300°C. For salts of the [Cu(LL)2(H2O)]2+ cations, more detailed thermal studies were performed, based on the infra red spectra of the decomposition products obtained at several temperatures.

EPR AND ELECTRONIC SPECTROSCOPIC STUDIES OF KEGGIN TYPE UNDECATUNGSTOPHOSPHOCUPRATE(II) AND UNDECATUNGSTOBOROCUPRATE(II)

Abstract The coordination of Cu(II) to the Keggin type anions α-undecatungstophosphocuprate(II) and α-undecatungstoborocuprate(II) was investigated in different environments by EPR and electronic spectroscopy. This study has shown that the coordination geometry around Cu(II) in the tetrabutylammonium (TBA) salts, (TBA) 4 H x [XW 11 CuO 39 ], with X=P or B, is square pyramidal, with copper bound to the five oxygen donor atoms of the polyoxometalate, whereas for the [XW 11 Cu(H 2 O)O 39 ] n − anion, on the corresponding potassium salt, a tetragonally elongated pseudo-octahedral geometry was found. For the potassium salts, in aqueous solution, six-coordinated copper is the only form found. For the TBA salts, in nonaqueous solvents, we can observe either the presence of only one form (the six-coordinated Cu(II) species, with a solvent molecule bound to copper), or of two forms: the solvent coordinated copper anions and the five-coordinated copper [XW 11 CuO 39 ] n − anions.

A new class of composite materials: Matrix auto-reinforced organic material–MARIOM

A sort of composite material can be produced from a single kind of natural organic fiber. This has been observed with bovine leather. During the formation process in a die particulated leather fibers were subjected for a period of about 6 min to a pressure of over 100 bar at a processing temperature of between 60 and 200 °C. In this way a portion of these collagenous fibers was plastically deformed and converted into continuous matrix material in which unconverted fibers act as matrix reinforcement. Round, collagenous fibers assumed an angular cross section and became the building blocks of the continuous matrix. This is clearly visible on pictures made with a scanning electron microscope. At a processing temperature of 70 °C and a pressure of 650 bar, applied for 6 min, the maximum compression strength at room temperature is found to be 185 MPa. At these processing parameters Youngs modulus is about 2.4 GPa and the bulk density is 1350 kg/m 3 . Other natural fibers, to be used as organic raw material for the production of composites, are currently under investigation.

Synthesis and structural characterization, by spectroscopic and computational methods, of two fluorescent 3-hydroxy-4-pyridinone chelators bearing sulphorhodamine B and naphthalene

Compounds MRB2 and MRB4 are part of a set of 3-hydroxy-4-pyridinone fluorescent chelators designed to be used as antimicrobial compounds. Their formulae and structures have been characterized by mass spectrometry, elemental analysis, nuclear magnetic resonance and X-ray crystallography. Identification of the most stable conformations of both compounds in an aqueous environment was achieved by molecular dynamics simulations. To the best of our knowledge, this is the first study in which: (a) a crystal structure of a rhodamine labelled 3-hydroxy-4-pyridinone chelator is reported and (b) a prediction of the range of conformations that these chelators may exhibit in solution is performed. The most frequent and energetically favoured geometries adopted by MRB2 and MRB4 have the chelating group facing the benzene and naphthalene groups of each compound, respectively. This molecular arrangement promotes the establishment of π–π interactions between both rings, which stabilize the overall conformations.