Showing papers in "New Journal of Chemistry in 2002"

Crystal faces of rutile and anatase TiO2 particles and their roles in photocatalytic reactions

Abstract: A titanium dioxide powder consisting of 1 μm size rutile and anatase particles was obtained, on which developed crystal faces were observed by a scanning electron microscope. From electron diffraction analyses, it was found that the rutile particles exposed {011} and {110} crystal faces, and the anatase particles exposed {001} and {011} faces. This powder showed high activity for some photocatalytic reactions, including oxidation of water. After photocatalytic oxidation of water on the powder using hexachloroplatinate(IV) ions as the electron acceptors, Pt deposits were observed mostly on the rutile particles, especially on the {110} face. When 2-propanol was added to the solution, Pt was deposited on both the anatase and rutile particles. Using the thus prepared Pt-deposited TiO2 powder, Pb2+ ions were photocatalytically oxidized into PbO2. After this reaction, PbO2 deposits were seen on the {011} face of the rutile particles. On the anatase particles, PbO2 deposits were observed in a larger amount on the {001} face than on the {011} face. These results indicate that the crystal faces help in the separation of electrons and holes, and that this effect is stronger for the rutile particles than for the anatase particles.

Tri-s-triazine derivatives. Part I. From trichloro-tri-s-triazine to graphitic C3N4 structures

Abstract: The first detailed structural characterisation of a functionalised tri-s-triazine derivative, trichloro-tri-s-triazine, is reported, which is a promising starting material for numerous compounds including graphitic C3N4 phases. DFT calculations show that a C3N4 structure based on tri-s-triazine should exist and that it is ∼30 kJ mol−1 more stable than the previously reported C3N4 phase of lowest energy.

High efficiency single dopant white electrophosphorescent light emitting diodes

Abstract: Efficient white electrophosphorescence has been achieved with a single emissive dopant. The dopant in these white organic light emitting diodes (WOLEDs) emits simultaneously from monomer and aggregate states, leading to a broad spectrum and high quality white emission. The dopant molecules are based on a series of platinum(II) [2-(4,6-difluorophenyl)pyridinato-N,C2′] β-diketonates. All of the dopant complexes described herein have identical photophysics in dilute solution with structured blue monomer emission (λmax = 468, 500, 540 nm). A broad orange aggregate emission (λmax ≈ 580 nm) is also observed, when doped into OLED host materials. The intensity of the orange band increases relative to the blue monomer emission, as the doping level is increased. The ratio of monomer to aggregate emission can be controlled by the doping concentration, the degree of steric bulk on the dopant and by the choice of the host material. A doping concentration for which the monomer and excimer bands are approximately equal gives an emission spectrum closest to standard white illumination sources. WOLEDs have been fabricated with doped CBP and mCP luminescent layers (CBP = N,N′-dicarbazolyl-4,4′-biphenyl, mCP = N,N′-dicarbazolyl-3,5-benzene). The best efficiencies and color stabilities were achieved when an electron/exciton blocking layer (EBL) is inserted into the structure, between the hole transporting layer and doped CBP or mCP layer. The material used for an EBL in these devices was fac-tris(1-phenylpyrazolato-N,C2′)iridium(III). The EBL material effectively prevents electrons and excitons from passing through the emissive layer into the hole transporting NPD layer. CBP based devices gave a peak external quantum efficiency of 3.3 ± 0.3% (7.3 ± 0.7 lm W−1) at 1 cd m−2, and 2.3 ± 0.2% (5.2 ± 0.3 lm W−1) at 500 cd m−2. mCP based devices gave a peak external quantum efficiency of 6.4% (12.2 lm W−1, 17.0 cd A−1), CIE coordinates of 0.36, 0.44 and a CRI of 67 at 1 cd m−2 (CIE = Commission Internationale de l'Eclairage, CRI = color rendering index). The efficiency of the mCP based device drops to 4.3 ± 0.5% (8.1 ± 0.6 lm W−1, 11.3 cd A−1) at 500 cd m−2, however, the CIE coordinates and CRI remain unchanged.

Continuous symmetry maps and shape classification. The case of six-coordinated metal compounds

Abstract: A continuous symmetry study of the structures of transition metal six-vertex polyhedra is presented, considering both molecular models and experimental structural data. The concept of symmetry map is introduced, consisting of a scatterplot of the symmetry measures relative to two alternative ideal polyhedra. In the case of hexacoordinated complexes, we take as reference shapes the octahedron and the equilateral trigonal prism and study different distortions from these two extremes, including the Bailar twist that interconverts one into another. Such a symmetry map allows us to establish trends in the structural chemistry of the coordination sphere of hexacoordinated transition metal atoms, including the effects of several factors, such as the electron configuration or the presence of bidentate, terdentate or encapsulating ligands. Also introduced is the concept of a symmetry constant, which identifies a distortive route that preserves the minimum distance to two reference symmetries. A wide variety of model distortions are analyzed, and the models are tested against experimental structural data of a wide variety of six-coordinated complexes.

Effects of calcination temperature on the photocatalytic activity and photo-induced super-hydrophilicity of mesoporous TiO2 thin films

Abstract: Mesoporous TiO2 nanometer thin films were prepared on fused quartz by the dip-coating sol–gel method from a system containing a triblock copolymer as a template (or pore-forming agent), and then calcined at different temperatures. These films were characterized by X-ray diffraction, atomic force microscopy, X-ray photoelectron spectroscopy, BET surface area and UV-visible spectrophotometry. The photocatalytic activity and photo-induced super-hydrophilicity of the films were evaluated by the photocatalytic degradation of acetone and water contact angle measurement in air, respectively. It was found that the thin films calcined at 700 °C not only show the highest photocatalytic activity, but also possess the greatest light-induced hydrophilicity and the slowest conversion rate from the hydrophilic to a hydrophobic state. The former is attributed to the fact that the films calcined at 700 °C are composed of anatase and rutile, which is beneficial in enhancing the transfer of photo-generated electrons from the anatase to the rutile phase, reducing the electron–hole combination rate in anatase and enhancing its activity. The high light-induced hydrophilicity and slow hydrophilic to hydrophobic conversion rate are due to the synergetic effect of good photocatalytic activity, sufficient surface hydroxyl content and a degree of surface roughness. Because of their high specific surface areas and mesoporous structures, the photocatalytic activity of mesoporous TiO2 thin films is higher than that of conventional TiO2 thin films.

New perylenes for dye sensitization of TiO2

Abstract: We describe a new generation of perylene photosensitizers based upon N-(2,5-di-tert-butylphenyl)perylene-3,4-dicarboximide. The new sensitizers have more favorable energetics for electron injection into TiO2 and better light absorption properties for solar conversion than previous sensitizers based upon perylene tetracarboxylic acid dianhydride. Syntheses, absorption properties, and electrochemical potentials for the new perylenes are reported. We compare the solar conversion efficiencies of the dyes in the dye sensitized solar cell (DSSC) and discuss trends in terms of energetics and structural differences that may affect the injection and recombination processes. These are the highest efficiencies yet reported for perylene sensitizers in the DSSC.

Arene–perfluoroarene interactions in crystal engineering 8: structures of 1∶1 complexes of hexafluorobenzene with fused-ring polyaromatic hydrocarbons

Abstract: A series of 1∶1 complexes of hexafluorobenzene (HFB) with naphthalene, anthracene, phenanthrene, pyrene and triphenylene were prepared and their X-ray crystal structures determined at low temperatures. Each structure contains infinite mixed stacks of alternating nearly-parallel molecules of HFB and arene, which display various ‘slip’ distortions and form different 3-dimensional motifs. The naphthalene, anthracene and pyrene complexes show polymorphism. Crystal packing of HFB complexes is compared with that of corresponding octafluoronaphthalene complexes. Ab initio DFT calculations on the infinite lattices give lattice parameters and ‘slip’ parameters in close agreement with the experimental crystal structures, while showing that intermolecular cohesion is predominantly of electrostatic, rather than van der Waals, origin.

ZnO nanowires fabricated by a convenient route

Abstract: A convenient microemulsion-mediated hydrothermal process was employed to synthesize ZnO nanowires, which exhibited a strong ultraviolet emission and a relatively weak defect emission. X-Ray diffraction, scanning electron microscopy, transmission electron microscopy and fluorescence spectroscopy were used to characterize the as-prepared ZnO nanowires.

Synthesis and near-infrared luminescence of 3d-4f bi-metallic Schiff base complexes

Abstract: The reaction of the zinc(II) Schiff base complex ZnL [H2L=N,N′-bis(3-methoxysalicylidene)ethylene-1,2-diamine] with one equivalent of Ln(NO3)3·xH2O (Ln=Nd, Ho, Er or Yb) gives the neutral 3d-4f bi-metallic Schiff base complexes [Zn(NO3)(μ-L)Ln(NO3)2(H2O)], which in solution exhibit emission corresponding to the Ln(III) ions (Ln=Nd, Er and Yb) in the near-infrared region.

Rapid synthesis of mesoporous TiO2 with high photocatalytic activity by ultrasound-induced agglomeration

Abstract: Three-dimensional and thermally stable mesoporous TiO2 was synthesized without the use of any surfactants via treatment with high intensity ultrasound irradiation for a short period of time. Monodispersed TiO2 sol particles were formed initially by ultrasound-assisted hydrolysis of acetic acid-modified titanium isopropoxide. Then, the mesoporous spherical or globular particles, which have a narrow pore size distribution, were produced by controlled condensation and agglomeration of these sol nanoparticles under high intensity ultrasound irradiation. The mesoporous TiO2 was characterized by XRD, TEM, nitrogen adsorption, TGA/DTA and FTIR. Low-angle XRD and TEM show the mesoporous TiO2 has a wormhole-like structure and a lack of long-range order. Nitrogen adsorption results indicate that the mesoporous TiO2 retains mesoporosity with a narrow pore size distribution and high surface area to at least 673 K. The thermal stability of mesoporous TiO2 is attributed to its thick inorganic walls, consisting of TiO2 nanoparticles. TGA study shows that this synthetic method is environmentally friendly. The photocatalytic activity of mesoporous TiO2 for the oxidation of acetone in air was measured. As-prepared mesoporous TiO2 has negligible activity due to its amorphous structure. Calcined mesoporous TiO2 shows better activity than commercial photocatalyst P25. The reasons for the high activity of mesoporous TiO2 are discussed.

First ring-opening metathesis polymerization in an ionic liquid. Efficient recycling of a catalyst generated from a cationic ruthenium allenylidene complex

Abstract: Ring-opening metathesis polymerization (ROMP) of norbornene was carried out in a biphasic medium consisting of the ionic liquid [bdmim][PF6] and toluene with a cationic ruthenium allenylidene precatalyst. The ionic liquid contained the ruthenium allenylidene complex and toluene dissolved the formed polymer. Both the catalyst and the ionic liquid were reused several times and led to very good polymer yields.

Hydrothermal synthesis and structural studies of novel 2-D lanthanide coordination polymers with phthalic acid

Abstract: This paper presents four lanthanide coordination polymers, [Ln2(BDC)3(H2O)]n (Ln = La, 1; Ln = Eu, 2; Ln = Tb, 3; BDC = 1,2-benzenedicarboxylate) and [Yb4(BDC)6(H2O)2]n (4) prepared by the hydrothermal technique. They are all 2-D infinite structures with BDC anions connecting adjacent metal ions. In complex 1, La(III) ions are eight- and nine-coordinated, and all La(III) ions are coplanar in the 2-D structure. In complexes 2 and 3, Eu(III) and Tb(III) ions are also eight- and nine-coordinated, but they are distributed in a wave-like 2-D network. In complex 4, the Yb(III) ions have four different coordination numbers (6, 7, 8 and 9), which are rarely found in one lanthanide complex. Both the coordination numbers and the arrangement of Ln atoms in these coordination polymers show the lanthanide contraction. In the four complexes, all the oxygen atoms of BDC take part in coordination with Ln(III) ions, adopting tetra-, penta- and hexadentate coordination modes for the phthalate anions. The luminescent properties of complex 2 have been investigated and the results for the explanation of the chemical environment of the Eu(III) ion are consistent with the X-ray analysis.

Heterogeneously catalyzed liquid-phase oxidation of alkanes and alcohols with molecular oxygen

Abstract: RuCl3 successfully reacts with the lacunary silicotungustate in organic medium, giving a Ru3+-substituted silicotungstate that can act as a heterogeneous catalyst for the oxidation of a wide range of alkanes and alcohols using 1 atm of molecular oxygen as the sole oxidant.

Cobalt bis(dicarbollide) ions with covalently bonded CMPO groups as selective extraction agents for lanthanide and actinide cations from highly acidic nuclear waste solutions

Abstract: A new series of boron substituted cobalt bis(dicarbollide)(1−) ion (1) derivatives of the general formula [(8-CMPO-(CH2-CH2O)2-1,2-C2B9H10)(1′,2′-C2B9H11)-3,3′-Co]− (CMPO = Ph2P(O)-CH2C(O)NR, R = C4H9 (3b), -C12H25 (4b), -CH2-C6H5 (5b)) was prepared by ring cleavage of the 8-dioxane-cobalt bis(dicarbollide) (2) bi-polar compound by the respective primary amines and by subsequent reaction of the resulting amino derivatives (3a–5a) with the nitrophenyl ester of diphenylphosphorylacetic acid. The compounds were synthesized with the aim to develop a new class of more efficient extraction agents for liquid–liquid extraction of polyvalent cations, i.e. lanthanides and actinides, from high-level activity nuclear waste. All compounds were characterized by a combination of 11B NMR, 1H high field NMR, Mass Spectrometry with Electrospray and MALDI TOF ionisation, HPLC and other techniques. The molecular structure of the supramolecular Ln3+ complex of the anion 5b was determined by single crystal X-ray diffraction analysis. Crystallographic results proved that the Ln(III) atom is bonded to three functionalised cobalt bis(dicarbollide) anions in a charge compensated complex. The cation is tightly coordinated by six oxygen atoms of the CMPO terminal groups (two of each ligand) and by three water molecules completing the metal coordination number to 9. Atoms occupying the primary coordination sphere form a tri-capped trigonal prismatic arrangement. Very high liquid–liquid extraction efficiency of all anionic species was observed. Moreover, less polar toluene can be applied as an auxiliary solvent replacing the less environmentally friendly nitro- and chlorinated solvents used in the current dicarbollide liquid–liquid extraction process. The extraction coefficients are sufficiently high for possible technological applications.

Efficient heterogeneous oxidation of organosilanes to silanols catalysed by a hydroxyapatite-bound Ru complex in the presence of water and molecular oxygen

Abstract: RuHAP is a highly selective and reusable catalyst for the oxidation of a wide variety of organosilanes to the corresponding silanols in the presence of water and molecular oxygen.

Novel heterogeneous PET fluorescent sensors selective for transition metal ions or protons: polymers regularly labelled with naphthalimide

Abstract: 4-(N,N-Dimethylaminoethylene)amino-N-allyl-1,8-naphthalimide has been synthesized as a new polymerizable dye in monomeric form, and can increase its fluorescence intensity in the presence of protons or metal cations. Two intensely yellow–green fluorescent co-polymers of the dye with methyl methacrylate (MMA) and styrene (ST) have been obtained. These polymeric fluorophores, which could be used as heterogeneous photoinduced electron transfer (PET) fluorescent sensors, show different fluorescence behaviour in the presence of protons and Cu2+ ions, depending on the structures of their main polymer chains. The fluorescence of poly(MMA–co-dye) is not sensitive towards H+ ions, but it is to Cu2+ ions. That of poly(ST–co-dye) is sensitive to the presence of both H+ and Cu2+ ions, the signal increasing and decreasing, respectively.

Topological isomerism in the formation of a novel three-dimensional metal-organic polycatenane

Abstract: The self-assembly of cadmium nitrate with sodium dicyanamide and 1,3-bis(4′-pyridyl)propane generates a kinetic 1D isomer and a thermodynamic 2D isomer, which presents an unusual pattern of 3D supramolecular entanglement.

Synthesis and characterization of novel nickel(II) complexes bearing N,P ligands and their catalytic activity in ethylene oligomerization

Abstract: The novel chloro(1-naphthyl)[8-(diphenylphosphino)quinoline]nickel(II) (1), chloro(1-naphthyl)[2-methyl-8-(diphenylphosphino)quinoline]nickel(II) (2), and [2-methyl-8-(diphenylphosphino)quinoline]nickel(II) dichloride (3) complexes were synthesized in satisfactory yield and fully characterized. The structures of complexes 1 and 3 were determined by single crystal X-ray analysis, which indicated that complex 1 exists in a square planar configuration, while complex 3 is dimeric square pyramidal. In the presence of MAO cocatalyst, complexes 1–3 displayed good catalytic activities for ethylene oligomerization in toluene, up to 2.45 × 105 g ethylene (mol Ni·h·atm)−1 by complex 3.

Synthesis, crystal structures and magnetic properties of 1D polymeric [MnIII(salen)N3] and [MnIII(salen)Ag(CN)2] complexes

Abstract: The syntheses, crystal structures and variable temperature (5–300 K) magnetic susceptibility measurements of two salen complexes of manganese(III) [where H2salen = N,N′-bis(salicylidene)-1,2-diaminoethane] having azido and dicyano argentate(I) as bridging ligands are reported. Both complexes belong to one-dimensional systems in which the azido functions as μ-(1,3) and Ag(CN)2− as ⋯NC– Ag–CN⋯ bridging ligands. The azido-bridged compound is antiferromagnetic with an intrachain interaction constant J = −4.52(4) cm−1 (Weng model) or J = −5.19(8) cm−1 (Fisher model), and it is a candidate to observe the Haldane gap in a S = 2 system. The silver cyanide bridged complex shows single ion behaviour of the Mn(III) ion, perhaps in combination with a very weak antiferromagnetic interaction.

Interesting proton behaviour in molecular structures. Variable temperature neutron diffraction and ab initio study of acetylsalicylic acid: characterising librational motions and comparing protons in different hydrogen bonding potentials

Abstract: Variable temperature single crystal neutron diffraction has been used to examine the behaviour of protons in the structure of acetylsalicylic acid (Aspirin). The neutron diffraction study, at seven temperatures between 20 and 300 K, has allowed a full description of the molecular structure and the intermolecular interactions in the material and their variation with temperature. In particular the variable temperature studies have allowed the full description of the apparent torsional motions of the terminal methyl group, which exhibit characteristic substantial zero-point motion. The extracted values for the barrier height for the cosine potential governing this motion are found to be in good agreement with that found from ab initio calculations and are compared with those found in a range of other materials. Our previously postulated empirical method for correcting bond lengths in such a case is once again found to have some validity. The data also yield a full description of the various hydrogen bonds present, notably the direct observation of likely anharmonicity in the potential governing the hydrogen bond in the carboxylic acid dimer motif. The availability of data at various temperatures is found to be important in identifying this effect, and in discriminating between alternative explanations of the observed structural parameters. The direct images of protons in various hydrogen bonding potentials, calculated from the neutron data, are also found to be valuable in this context.

Synthesis and structure of a one-dimensional cobalt(II) coordination polymer with 1,3-bis(1,2,4-triazol-1-yl)propane

Abstract: A novel 1D-coordination polymeric Co(II) complex [Co(btp)2(NCS)2]n [1, btp = 1,3-bis(1,2,4-triazol-1-yl)propane] was synthesized and characterized. The coordination geometry of the cobalt ions is distorted octahedral, with the equatorial plane formed by the four nitrogen atoms of the four triazole groups and the axial sites occupied by two terminal trans thiocyanato ligands. The Co(II) ions are linked by the btp ligands, building up coordination polymers of infinite 1D-neutral chains.

Ferromagnetic coupling in the malonato-bridged copper(II) chains [Cu(Im)2(mal)]n and [Cu(2-MeIm)2(mal)]n(H2mal=malonic acid, Im=imidazole and 2-MeIm=2-methylimidazole)

Abstract: Two new malonato-bridged copper(II) complexes of formula [Cu(Im)2(mal)]n (1) and [Cu(2-MeIm)2(mal)]n (2) (Im=imidazole, 2-MeIm=2-methylimidazole and mal=malonate dianion) have been prepared and their structures solved by X-ray diffraction methods. The [Cu(Im)2(mal)] and [Cu(2-MeIm)2(mal)] neutral entities act as monodentate ligands towards the adjacent copper(II) units through one of the two carboxylate groups, the OCO bridge exhibiting an anti-anti conformation. The environment of each copper atom in 1 and 2 is distorted square pyramidal: two carboxylate oxygen atoms from a bidentate malonate and two nitrogen atoms from two imidazole (1) or 2-methylimidazole (2) ligands form the equatorial plane whereas the apical position is occupied by a carboxylate oxygen from the malonate group of the neighbouring complex unit. The intrachain copper-copper separation is 6.036(2) (1) and 6.099(2) A (2). The magnetic properties of 1 and 2 have been investigated in the temperature range 1.9–290 K. Overall, ferromagnetic behaviour is observed in both cases and the intrachain magnetic coupling (J) between the copper(II) ions through the carboxylato group is found to be 1.64 (1) and 0.39 cm−1 (2) (the Hamiltonian being H=−JΣiSi·Si+1).

On the determination of the molecular static first hyperpolarisability: how reliable are literature data?

Abstract: The shortcomings of the two-level model in extrapolating the molecular static first hyperpolarisability, β0, are discussed in the context of literature data. However, except for some spurious β0 data, in many other cases, the reported β0 values can be considered reasonably reliable due to a balancing of effects.

Efficient panchromatic sensitization of nanocrystalline TiO2 films by β-diketonato ruthenium polypyridyl complexes

Abstract: The β-diketonato Ru(II)-polypyridyl complexes, Ru(4,4′,4″-tricarboxy-2,2′:6′,2″-terpyridine)(1,1,1-trifluoropentane-2,4-dionato)(NCS) and Ru(4,4′,4″-tricarboxy-2,2′:6′,2″-terpyridine)(1,1,1-trifluoroeicosane-2,4-dionato)(NCS), when anchored to nanocrystalline TiO2 films, achieve very efficient panchromatic sensitization over the whole visible range extending into the near IR region, yielding 70% incident photon to current conversion efficiencies (IPCE). The presence of long hydrocarbon substituents on the β-diketonato ligand helps to prevent surface aggregation of the sensitizer.

Organically-modified mesoporous silica spheres with MCM-41 architecture

Abstract: New hybrid inorganic–organic materials displaying both an ordered mesoporous structure and spherical morphology have been synthesised by co-condensation of tetraethoxysilane and organoalkoxysilanes in water–ethanol solution containing ammonia in the presence of surfactant as templating agent.

Syntheses, characterisation and photophysical studies of novel biological labelling reagents derived from luminescent iridium(III) terpyridine complexes

Abstract: A series of new luminescent iridium(III) terpyridine complexes functionalised with an isothiocyanate group, [Ir(tpy-R)(tpy-C6H4-NCS-p)](PF6)3 [R = H (1), C6H5 (2), C6H4-CH3-p (3), C6H4-Cl-p (4)] has been synthesised, characterised and their photophysical properties studied; the X-ray crystal structure of one of the intermediate complexes, [Ir(tpy-C6H4-Cl-p)(CF3SO3)3] (4b), has also been determined; complex 1 has been used as a luminescent label for proteins.

Pathways for decomposition of THF by organolithiums: the role of HMPA

Abstract: The decomposition of THF by organolithiums in the presence of HMPA gives lithium but-3-en-1-oxide by a reverse 5-endo-trig ring opening.

Preparation and nonlinear optical properties of ultrathin composite films containing both a polyoxometalate anion and a binuclear phthalocyanine

Abstract: An ultrathin composite film containing both polyoxometalate anion [PMo12O40]3− (PMo12) and a planar binuclear phthalocyanine, bi-CoPc, has been prepared by the electrostatic layer-by-layer self-assembly method. UV-vis measurements revealed regular film growth with each four-layer {PMo12/bi-CoPc/PSS/PAH} adsorption. The film structure was characterized by small-angle X-ray reflectivity measurements, X-ray photoelectron spectra, and AFM images. The nanothick film shows a third-order nonlinear optical response of χ(3) = 4.21 × 10−12 esu. Experimental investigations also indicate that the combination of polyoxometalate anions [PMo12O40]3− with the phthalocyanine bi-CoPc in multilayer films can enhance the third-order NLO susceptibility and modify the third-order NLO absorption of bi-CoPc.

Oxidations by the “hydrogen peroxide–manganese(IV) complex–carboxylic acid” system.

Abstract: Whereas the dinuclear manganese(IV) complex [LMn(O)3MnL](PF6)2 (1a, L = 1,4,7-trimethyl-1,4,7-triazacyclononane) does not react with H2O2 in acetonitrile solution containing cyclohexane, acetic acid added to this mixture in small amounts induces the catalytic decomposition of hydrogen peroxide to O2 and H2O (catalase activity) and the transformation of cyclohexane to cyclohexyl hydroperoxide (oxygenase activity). Addition to the acetic acid containing solution only 2 equivalents (relative to the Mn catalyst) of a base enhances the catalase activity and suppresses the oxygenase activity. The proposed mechanism includes the formation of dinuclear dihydroperoxy derivatives of manganese, which can be transformed under the action of acetic acid to OMn(V)–Mn(IV)–OOH species. The latter can abstract a hydrogen atom from an alkane. The interaction of the so-formed R˙ radical with Mn(IV)–OOH can give the alkyl hydroperoxide, ROOH, which is the main primary product of the oxidation process.

An unusual alternating ferro- and antiferromagnetic 1D hydrogen-bonded μ2-1,3-azide-bridged copper(II) complex: a dominant ferromagnetic coupling

Abstract: A single-crystal structure analysis of [Cu2(bben)2(N3)4]n (1) [bben1,2-bis(benzylamino)ethane] revealed that the complex consists of double asymmetric μ2-1,3-azide-bridged dimeric copper(II) moieties; each copper(II) coordinates with one bben, one terminal azido, and the two bridging azido ligands. The Cu–N3–Cu torsion angle has a very large value of 47.5°. The dimeric units are assembled into 1D chains through N(bben)–H⋯N (azido) hydrogen bonds. The intra- and the interdimeric Cu⋯Cu distances in the chain are 5.281(2) and 3.662(2) A, respectively. Magnetic measurements on 1 have revealed the existence of a dominant ferromagnetic interaction with exchange coupling parameters of JF = 16.8 cm−1, and JAF = −3.6 cm−1, using an alternating ferro- and antiferromagnetic chain model for S = 1/2 local spins. The ferro- and antiferromagnetic interactions are ascribed to the μ2-1,3-azide bridges and the hydrogen bonds, respectively; the former interactions are rationalized by the large Cu–N3–Cu torsion angles.