Novel oligonuclear ZnII4, ZnII8 and ZnII2NiII2 complexes with bis(benzoylacetone)-1,3-diiminopropan-2-ol

Reactions of bis(benzoylacetone)-1,3-diiminopropan-2-ol (abbreviated as H₃L) with zinc salts in the presence of triethylamine afforded the compounds [Zn₄(HL)₄]·4CH₃CN (1·4CH₃CN) and [Zn₈L₄(OH)₄]·2CH₃CN (2·2CH₃CN). Further reaction of 1 with Ni(CH₃COO)₂·4H₂O gave the heteronuclear species [Zn₂Ni₂(L)₂(CH₃O)₂(CH₃OH)₂] (3). The crystal structures of 1·4CH₃CN, 2·2CH₃CN and 3 were determined by the X-ray diffraction method.     

Kinetics of the catalytic esterification of castor oil with lauric acid using <Emphasis Type="Italic">n</Emphasis>-butyl benzene as a water entrainer

The esterification of castor oil with lauric acid was investigated using tetra n-butyl titanate (TBT), SnCl₂·2H₂O (stannous chloride), CoCl₂·6H₂O (cobalt chloride), and (CH₃COO)₂Zn·2H₂O (zinc acetate dihydrate) as catalysts. Effects of catalyst concentration and reaction temperature on the progress of the reaction were investigated. TBT was the best catalyst for the esterification of castor oil with lauric acid at temperatures lower than 200°C. The reaction was first order with respect to each reactant. The activation energy for the esterification reaction of castor oil with lauric acid using TBT was 26.69 kcal/mol. The rate constants obtained for the esterification of castor oil with decanoic, lauric, palmitic, and stearic acids were nearly the same (15.80, 15.44, 15.06, and 14.67 mL mol⁻¹ min⁻¹), as were the rate constants obtained for the reaction of castor oil and hydrogenated castor oil.     

Novel Copper(II) Complexes of <Emphasis Type="Italic">N</Emphasis>-Phenylanthranilic Acid Containing Ethanol and Hydroxo Ligands

The complexes, tetra-μ-[2-(phenylamino)benzoato](O,O′)-bis[(ethanol)copper(II)] (1) and di-μ-[2-(phenylamino)benzoato](O,O′)-bis[(hydroxo)copper(II)] (2), were synthesized by the reaction of N-phenylanthranilic acid and CuCl₂·2H₂O in an ethanol water mixture. In complex 1, each Cu(II) atom, which is in a slightly distorted square pyramidal environment, is coordinated equatorially by four N-phenylanthranilate O-atoms and axially by the ethanol O-atoms. In complex 2, [Cu₂(C₆H₅NHC₆H₄COO)₂(OH)₂], each Cu(II) atom, which is in tetrahedral environment, is coordinated by two N-phenylanthranilate O-atoms and hydroxo ligands. The crystal structure (monoclinic, P21/c space group) of complex 1 comprises a dinuclear [Cu₂(C₆H₅NHC₆H₄COO)₄(CH₃CH₂OH)₂] species and the dimer is located on a crystallographic inversion centre. The Cu(II) ions, 2.591(2) Å apart, are bridged by the carboxylate groups of four N-phenylanthranilate ligands. The complex molecules show three-dimensional supramolecular networks by O–H···O, C–H···O and C–H···π interactions.     

Influence of Electrostatic Interactions on Complexes with Short O···O Hydrogen Bonds in Basic Salts of Pyridine Betaines and Acid Salts of ω-Phenyloalkanocarboxylic Acids

The isostructural complexes [C₅H₅N⁺(CH₂)_nCOO]₂HX and [C₆H₅(CH₂)_nCOO]₂HK (n = 1–4), which differ in their counterions and charge on the ring, were synthesized, and their powder FT-IR spectra analyzed. All complexes containing a charged pyridine ring are of Hadži type iii, characterized by an intense broad (continuum) absorption below 1600 cm⁻¹ typical of a short-strong hydrogen bond (SSHB) with a delocalized proton and a single vC=O band. The positively charged nitrogen atoms interact electrostatically with the X⁻ ion and, additionally, with one of the oxygen atoms of the carboxylic group, producing a more or less symmetric environment of the H-bonded proton, and stabilizing the SSHB. The broad absorption of [C₆H₅CH₂COO]₂HK is very similar to that of other pyridine complexes. Upon addition of methylene groups the broad absorption moves to higher wavenumbers, the O···O distance is elongated, and the H-bonded proton becomes more localized. In the spectrum of [C₆H₅(CH₂)₄COO]₂HK the vC=O and v_asCOO bands were found at 1704 and 1641 cm⁻¹, respectively, which shows that the H-bonded proton is asymmetrically located. The observed variation of absorption with the number of CH₂ groups reflects changes of contacts between the K⁺ ion and COO⁻ groups.     

A hybrid density functional theory study of the low-temperature dimethyl ether combustion pathways. I: Chain-propagation

Dimethyl ether (DME) has been proposed to be a promising alternative to conventional diesel fuel because of its favorable compression ignition property (high cetane number) and its soot-free combustion. A radical chain mechanism for hydrocarbon autoignition has been proposed for DME at low temperatures. In this mechanism, the chain initiation step consists of DME undergoing hydrogen abstraction by a highly reactive species (typically ·OH). The CH₃O·H₂ created in the initiation step then combines with O₂; the subsequent CH₃OCH₂OO· radical is involved in a Lindemann-type mechanism, which can lead to the production of formaldehyde (CH₂ = O) and ·OH. This concludes the chain-propagating step: the one ·OH produced then sustains the chain-reaction by creating another CH₃O·H₂. A relatively stable intermediate (·CH₂OCH₂OOH), formed via isomerization of CH₃OCH₂OO· in the chain-propagation step, can combine with a second O₂ to produce a radical (·OOCH₂OCH₂OOH) that can potentially decompose into two ·OH radical (and other products). This path leads to chain-branching and an exponential increase in the rate of DME oxidation. We have used spin-polarized density functional theory with the Becke-3-parameter Lee—Parr—Yang exchange-correlation functional to calculate the structures and energies of key reactants, intermediates, and products involved in (and competing with) the chain-propagating and chain-branching steps of low-temperature DME oxidation. In this article, Part I, we consider only the chain-propagation mechanism and its competing mechanisms for DME combustion. Here, we show that only certain conformers can undergo the isomerization to ·CH₂OCH₂OOH. A new transition state has been discovered for the disproportionation reaction ·CH₂OCH₂OOH → 2CH₂O + ·OH in the chain-propagating step of DME autoignition that is much lower than previous barriers. The key to making this decomposition pathway facile is initial cleavage of the O—O rather than the C—O bond. This renders all transition states along the chain-propagation potential energy surface below the CH₃O·H₂ + O₂ reactants. In contrast with the more well-studied CH₃·H₂ (ethyl radical) + O₂ system, the H-transfer isomerization of CH₃OCH₂OO· to ·CH₂OCH₂OOH in low-temperature DME oxidation has a much lower activation energy. This is most likely due to the larger ring strain of the analogous transition state in ethane oxidation, which is a five-membered ring opposed to a six-membered ring in dimethyl ether oxidation. Thus low-temperature ethane oxidation is much less likely to form the ·ROOH (where R is a generic group) radicals necessary for chain-branching, which leads to autoignition. Three competing reactions are considered: CH₃O·H₂ → CH₂O + ·CH₃; ·CH₂OCH₂OOH → 1,3-dioxetane + ·OH; and ·CH₂OCH₂OOH → ethylene oxide + HOO·. The reaction barriers of all these competing paths are much higher in energy (7–10 kcal/mol) than the reactants CH₃O·H₂ + O₂ and, therefore, are unlikely low-temperature paths. Interestingly, an analysis of the highest occupied molecular orbital along the CH₃O·H₂ decomposition path shows that electronically excited (¹A₂ or ³A₂) CH₂O can form; this can also be shown for ·CH₂OCH₂OOH, which forms two formaldehyde molecules. This may explain the luminosity of DME's low-temperature flames.     

Doppler-Resolved Laser Probing of Photon-Initiated Bimolecular Collisions O(1D) + CH4 → OH(v,N) + CH3

The stereodynamics of the reaction O(¹D) + CH₄ → OH(v ≤ 4,N) + CH₃ at collision energies of ˜ 40 kJ mol⁻¹, has been probed via Doppler-resolved, polarized laser-induced fluorescence spectroscopy. Velocity-aligned, reagent O(¹D) atoms were generated under bulb conditions via polarized laser photodissociation of N₂O. Analysis of the Doppler profiles of nascent OH(v,N) fragments has allowed both scalar and vectorial product correlations to be determined, including differential scattering cross sections and rotational alignments. These imply the operation of a ‘delayed’ collision mechanism, dominated by the deeply attractive potential energy surface associated with the insertion to form CH₃OH; the intermediacy of a long-lived complex is excluded, however. Rotational angular momentum in the recoiling OH fragments is preferentially aligned perpendicular to, and azimuthally distributed about, their recoil velocity. The rotational excitation is thereby attributed to bending motion in the C···O···H plane during the reagent collisions. The scalar product pair correlations establish a near-zero translational exoergicity and anticorrelated internal energy distributions in the two reaction products.     

Salen Type Sandwich Triple-Decker Tri- and Di-nuclear Lanthanide Complexes

Four N,N′-bis(salicylidene)-1,2-(phenylene-ediamine) (H₂L) trinuclear lanthanide complexes, namely, [Ln₃L₃(CH₃OH)₂(NO₃)₃]·(CH₂Cl₂)·(CH₃OH)·(H₂O)₂ [Ln = Tb (1), Ho (2), Er (3) and Lu (4)], have been isolated by the reactions of H₂L and Ln(NO₃)₃·6H₂O. And one N,N′-bis(salicylidene)-1,2-(phenylene-ediamine) dinuclear neodymium complex [Nd₂L₃(CH₃OH)] (5) has been harvested from the reaction of H₂L with Nd(OAc)₃·4H₂O. X-ray crystallographic analysis reveals that complexes 1?4 are of triple-decker trinuclear sandwich structure, while complex 5 is of a triple-decker dinuclear sandwich structure, expanding upon the recent reports of the multinuclear pure lanthanide complexes.     

Solvent Control Over Structural Diversity of Two Copper (II) Complexes Based on Polyaromatic Acid Ligand

Abstract  

A new bipod polyaromatic acid ligand H₂bcm (H₂bcm = {2, 4-bis [(2′-carboxyphenoxy) methyl]-1,3,5-trimethylbenzene}) is prepared and its two novel binuclear coordination compounds, [Cu₂(bcm)₂(CH₃OH)₂]·2CH₃OH (1) and [Cu₂(bcm)₂(CH₃CH₂OH)₂]·2CH₃CH₂OH (2), have been synthesized with copper acetate and H₂bcm ligand in methanol solvent and ethanol solvent respectively, and characterized by the element analysis, IR, TGA and single crystal X-ray diffraction. The results of structural analysis indicate that 1 crystallizes in the triclinic system with space group P1, while 2 crystallizes in the monoclinic system with space group P2₁ /c. Furthermore, 1 adopts μ ₂ -COO⁻ and syn–syn coordination mode with Cu (II)···Cu (II) separation of 2.5868(11) ? and forms 1D zigzag chain structure by O···O interactions. The coordination of 2 is similar to that of 1 except that ethanol molecules are coordinated instead of methanol molecules with Cu (II)···Cu (II) separation of 2.5973(13) ?. Two-dimensional network structures of 1 and 2 are formed through π–π interactions.     

Reduction of lean NOx by ethanol over Ag/Al2O3 catalysts in the presence of H2O and SO2

The reduction of lean NOx using ethanol in simulated diesel engine exhaust was carried out over Ag/Al₂O₃ catalysts in the presence of H₂O and SO₂. The Ag/Al₂O₃ catalysts are highly active for the reduction of lean NOx by ethanol but the reaction is accompanied by side reactions to form CH₃CHO, CO along with small amounts of hydrocarbons (C₃H₆, C₂H₄, C₂H₂ and CH₄) and nitrogen compounds such as NH₃ and N₂O. The presence of H₂O enhances the NOx reduction while SO₂ suppresses the reduction. The presence of SO₂ along with H₂O suppresses the formation of acetaldehyde and NH₃. By infrared spectroscopy, it was revealed that the reactivity of NCO species formed in the course of the reaction was greatly enhanced in the presence of H₂O. The NCO species readily reacts with NO in the presence of O₂ and H₂O at room temperature, being converted to N₂ and CO₂ (CO). Addition of SO₂ suppresses the formation of NCO species and lowers the reactivity of the NCO species. However, the reduction of NOx is still kept at high conversion levels in the presence of H₂O and SO₂ over the present catalysts. About 80% of NOx in the simulated diesel engine exhaust was removed at 743 K. This revised version was published online in July 2006 with corrections to the Cover Date.     

Three new polyoxometalate-based hybrids prepared from choline chloride/urea deep eutectic mixture at room temperature

Three new polyoxometalate-based hybrids {[(CH₃)₃N(CH₂)₂OH]₂(H₃O)}[Na₂(H₂O)₆][IMo₆O₂₄]·H₂O 1 , {Na₂[(CH₃)₃N(CH₂)₂OH]₄}[Al(OH)₆Mo₆O₁₈]₂·8NH₂CONH₂·4H₂O 2 and {Na₆(H₂O)₁₈[(CH₃)₃N(CH₂)₂OH]₂(CON₂H₅)₂}[NaMo₇O₂₄]₂·4NH₂CONH₂·H₂O 3 were successfully synthesized in the choline chloride/urea deep eutectic mixture at room temperature. Reactant quantities of water presents in the nonaqueous eutectic mixture solvent may influence the structure of the products. The three compounds are fully characterized by elemental analyses, IR, UV–vis, TG analyses, power X-ray diffraction and single-crystal X-ray diffraction. The photocatalytic properties of 1 and 2 are investigated.     

Solvothermal synthesis,structure and photoluminescent properties of europium complex based on fluorene derivatives

A novel coordination polymer, {[Eu₂(L)₃(CH₃OH)(H₂O)]·(CH₃OH)(H₂O)}_n (1), has been synthesized by solvothermal reaction of Eu(NO₃)₃·6H₂O and 9,9-diethylfluorene-2,7-dicarboxylic acid in a mixture solution of CH₃OH and H₂O. Single crystal X-ray structural analysis reveals that complex 1 crystallizes in an orthorhombic, space group P2(1)2(1)2(1), holding the unusual (2,3,8)-connected 3D topological network. Thermogravimetric analysis shows remarkable thermal stability of the structural framework of compound 1, the photoluminescence properties are also discussed.     

Metallopolymer Films Exhibiting Three-Color Electrochromism in the UV/Vis and Near-IR Region: Remarkable Utility of Trimetallic Clusters Bearing Thienyl Pendants and Their Mixed-Valent Charge Transfer Transitions

Novel oxo-centered, acetate-bridged trinuclear ruthenium clusters functionalized with two pyridine ligands with thienyl substituents, [Ru₃O(CH₃COO)₆(CO)(L1)₂] (1) and [Ru₃O(CH₃COO)₆(CO)(L2)₂] (2), where L1 = 4-(2-thienyl)pyridine and L2 = 4-(2,2′-bithienyl)pyridine, have been synthesized and characterized. The molecular structure of 2 has been determined by single-crystal X-ray diffraction. One-electron oxidation of 2 with silver(I) cation has led to the isolation of a CO-dissociated product, [Ru₃O(CH₃COO)₆(H₂O)(L2)₂]PF₆ (3·PF ₆ ), and subsequent reaction with 4-dimethylaminopyridine (dmap) gave [Ru₃O(CH₃COO)₆(dmap)(L2)₂]PF₆ (4·PF ₆ ). Linear metallopolymers containing the {Ru₃O(CH₃COO)₆} groups have been deposited onto indium-tin oxide surface via oxidative electropolymerization of 2, 3·PF ₆ , and 4·PF ₆ . These metallopolymer thin films exhibit three-color electrochromism in the UV/Vis and near-IR region associated with the Ru₃ ^II,III,III, Ru₃ ^III,III,III, and Ru₃ ^III,III,IV oxidation states.     

Oxidative coupling of methane over alkali metal oxide promoted La2O3/BaCO3 catalysts

The oxidative coupling of methane (OCM) over various alkali metal oxide promoted La₂O₃/BaCO₃ catalysts and the effects of Na₂O content on the performance of Na₂O–La₂O₃/BaCO₃ catalysts have been studied. It was found that Na₂O promoted La₂O₃/BaCO₃ catalysts had the advantages of high CH₄ conversion, C₂ selectivity and C₂H₄/C₂H₆ ratio. Na₂O might affect the properties of the catalysts through electronic and geometric effects. The highest C₂ yield (19·0–20·6%) was obtained with Na₂O–9 wt% La₂O₃/BaCO₃ catalysts of 1·0–3·0% Na₂O. The effects of reaction conditions on OCM over 3 wt% Na₂O–9 wt% La₂O₃/BaCO₃ catalysts have also been investigated. The catalysts were characterized by BET, TPD and XRD. TPD studies on 3 wt% Na₂O–9 wt% La₂O₃/BaCO₃ catalysts demonstrated that CO₂, CH₄ and O₂ could be adsorbed strongly on the catalyst. This might be related to the activation of CH₄ and the formation and regeneration of active oxygen species.     

Syntheses,structures and properties of four inorganic–organic hybrid heteropolymolybdates functionalized by chiral serine ligands

Four new inorganic–organic hybrid polyoxomolybdates K₂[Se^IVMo₆O₂₁(L-O₂CCHNH₃ CH₂OH)₃]·6H₂O (1) and K₂[Se^IVMo₆O₂₁(D-O₂CCHNH₃CH₂OH)₃]·6H₂O (2), K₂[Te^IVMo₆O₂₁(D-O₂ CCHNH₃CH₂OH)₃]·6H₂O (3) and K₂[Te^IVMo₆O₂₁(L-O₂CCHNH₃CH₂OH)₃]·6H₂O (4) have been synthesized by a simple one-pot reaction of NaMoO₄·2H₂O, Na₂SeO₃/K₂TeO₃, KCl and corresponding chiral serine ligands in the aqueous medium and further characterized by single-crystal X-ray diffraction, elemental analyses, IR spectra, thermogravimetric (TG) analyses, electrospray ionization mass spectrometry (ESI-MS) and circular dichroism (CD) spectra. 1–4 are the representative chiral heteropolymolybdates featuring that a common {Se/TeMo₆} fragment is made up of a six-membered MoO₆ octahedral ring functionalized by three serine ligands. TG analyses reveal that 1–4 undergo a two-step weight loss in the temperature range of 25–850 °C.     

Solvent control on the structural versatility and properties of manganese(II) complexes surrounded by the flexible hinge-like ligand

Four different types of polynuclear manganese(II) compounds with bhnq^2? bridges were obtained from the reaction of Mn(CH₃COO)₂·4H₂O with the flexible hinge-like ligand H₂bhnq (H₂bhnq = 2,2′-bi(3-hydroxy-1,4-naphthoquinone)) by controlling the reaction solvent: [Mn₃(bhnq)₃(H₂O)₂]·10.5H₂O (1), [Mn₂(bhnq)₂(DMSO)₄]·2DMSO·CHCl₃ (2), {[Mn(bhnq)(H₂O)₂]·2H₂O}_n (3), and {[Mn(bhnq)(DMF)₂]}_n (4). All complexes are neutral with the same Mn/bhnq 1:1 formulation ratio. Compounds 1 and 2 are discrete systems, while compounds 3 and 4 are one-dimensional ones. All compounds were characterized by X-ray diffraction and show different coordination modes for the bhnq^2? ligand.     

A novel two-dimensional network self-assembled by the narrowest ladder cations [Cu(CH3COO)(bpe)(H2O)]nn+ containing the Cu2(μ-O)2 cores and the dimeric anions [Cu2(nta)2(bpe)]2− through hydrogen-bonding interaction

A novel complex [Cu(CH₃COO)(bpe)(H₂O)]_n·n/2[Cu₂(nta)₂(bpe)] ·6nH₂O) (bpe=trans-1,2-bis(4-pyridyl)ethylene) was synthesized and characterized. The molecule structure shows that it is composed of the ladder-like double chain cations [Cu(CH₃COO)(bpe)(H₂O)]_nⁿ⁺ and the dimeric anions [Cu₂(nta)₂(bpe)]²⁻. Through bridging oxygen atom of the acetate, the Cu₂ (μ-O)₂ core is formed. The ladder-like chain cation is the narrowest ladder [3.422(3) Å]. Two-dimensional undulating network is constructed by the cations and the dimeric anions through hydrogen-bonding interactions.     

New dinuclear cobalt (ΙΙ, ΙΙΙ) and tetranuclear manganese (ΙΙΙ) complexes assembled by a polydentate Schiff-base ligand: synthesis,structure and magnetic properties

The reactions of 2-(((2-hydroxy-3-methoxyphenyl)methylene)amino)-2-(hydroxymethyl)-1,3-propanediol (H₄L) and Mn(ClO₄)₂·6H₂O or Co(SCN)₂·3H₂O in the presence of triethylamine in methanol led to the formation of two new complexes [Mn^ΙΙΙ₄(HL)₂(H₂L)₂(CH₃OH)₄]·4CH₃OH·(ClO₄)₂ (1) and [Co^ΙΙCo^ΙΙΙ(H₂L)₂(CH₃OH)(SCN)]·1.5CH₃OH·1.5H₂O (2), respectively. According to structural data and magnetic properties tetranuclear complex 1 contains four homo-valence manganese (ΙΙΙ) atoms, while in the binuclear complex 2 composed of hetero-valence bi- and trivalent cobalt (ΙΙ, ΙΙΙ) atoms. Weak antiferromagnetic exchange interactions between neighboring manganese ions in 1 have place. χ_MT for 2 was fitted using a model of isolated cobalt (ΙΙ) ion with zero-field splitting parameters and the study confirms its mixed valence Co^ΙΙ/Co^ΙΙΙ nature. No slow magnetic relaxation effects were observed for both complexes in the absence of an applied dc magnetic field.     

Two new carboxylate–oxygen bridged trinuclear M(II) (MMn and Co) compounds with zwitterionic dicarboxylate ligands: crystal structures and magnetism

Two new Mn(II) and Co(II) coordination polymers with azide and zwitterionic dicarboxylate ligands L¹ and L² (L¹ = [4-((1-carboxylatobenzyl)pyridimium-3-yl) benzoic acid] chloride, L² = [1,1′-bis(4-carboxylatobenzyl)-4,4′-bipyridinium] dichloride) were synthesized and structurally and magnetically characterized. They are formulated as [Mn₃(L¹)₄(N₃)(CH₃CH₂OH)(H₂O)]ClO₄·4H₂O (1) and [Co₃(L²)₄(N₃)₂(H₂O)₂]·4NO₃ (2). Compound 1 contains two different linear trinuclear [Mn₃(COO)₈(CH₃CH₂OH)₂]^2 − and [Mn₃(COO)₆(H₂O)₂(N₃)₂]^2 − units built from the mixed bridges of (μ-COO)₂(μ₂-O_carboxylate). The trinuclear units are alternately linked into 1D chains by L¹. Compound 2 contains linear trinuclear [Co₃(N₃)₂(COO)₄(H₂O)₂] units built from the mixed bridges (μ-COO)₂(μ-H₂O). Magnetic studies demonstrated that the mixed triple bridges are antiferromagnetic in compounds 1 and 2.     

Single‐Pot Ethane Carboxylation Catalyzed by New Oxorhenium(V) Complexes with N,O Ligands

The oxorhenium(V) chelates [ReOCl(N,O‐L)(PPh₃)] [N,O‐L=(OCH₂CH₂)N(CH₂CH₂OH)(CH₂COO) ( 2 ), (OCH₂CH₂)N(CH₂COO)(CH₂COOCH₃) ( 3 )] and [ReOCl₂(N,O‐L)(PPh₃)] [N,O‐L=C₅H₄N(COO‐2) ( 4 ) C₅H₃N(COOCH₃‐2)(COO‐6) ( 5 )] have been prepared by reaction of [ReOCl₃(PPh₃)₂] ( 1 ), in refluxing methanol, with N,N‐bis(2‐hydroxyethyl)glycine [bicine; N(CH₂CH₂OH)₂(CH₂COOH)], N‐(2‐hydroxyethyl)iminodiacetic acid [N(CH₂CH₂OH)(CH₂COOH)₂], picolinic acid [NC₅H₄(COOH‐2)] or 2,6‐pyridinedicarboxylic acid [NC₅H₃(COOH‐2,6)₂], respectively, with ligand esterification in the cases of 3 and 5 . All these complexes have been characterized by IR and multinuclear NMR spectroscopy, FAB⁺‐MS, elemental and X‐ray diffraction structural analyses. They act as catalysts, in a single‐pot process, for the carboxylation of ethane by CO, in the presence of potassium peroxodisulfate K₂S₂O₈, in trifluoroacetic acid (TFA), to give propionic and acetic acids, in a remarkable yield (up to ca. 30%) and under relatively mild conditions, with some advantages over the industrial processes. The picolinate complex 4 provides the most active catalyst and the carboxylation also occurs, although much less efficiently, by the TFA solvent in the absence of CO. The selectivity can be controlled by the ethane and CO pressures, propionic acid being the dominant product for pressures about ca. 7 and 4 atm, respectively (catalyst 4 ), whereas lower pressures lead mainly to acetic acid in lower yields. These reactions constitute an unprecedented use of Re complexes as catalysts in alkane functionalization.     

Tetranuclear Eu(III)-Co(II) complex of an N4O4 macrocycle

The reaction of an Eu(III) complex of the protonated form of the macrocyclic Schiff base derived from 1,3-diamino-2-hydroxypropane and 2,6-diformylphenol, [Eu(H₄L)Cl₃], with three equivalents of base results in a mononuclear complex of the triply deprotonated form of the ligand, [Eu(HL)]. The photophysical properties of the [Eu(HL)] complex are discussed on the basis of emission and excitation spectra, as well as of the emission decay times. The [Eu(HL)] complex in a reaction with cobalt(II) chloride gives a heterometallic Eu(III)-Co(II) macrocyclic complex, [EuCo(HL)(CH₃OH)₂Cl]₂Cl₂·4CH₃OH. In the presence of base and an excess of cobalt(II) chloride the starting [Eu(H₄L)Cl₃] complex is converted to a dinuclear Co(II) complex, [Co₂(H₂L)Cl₂(CH₃OH)₂]·1.5CH₃OH.