Dimers and chains of {3d-4f} single molecule magnets constructed from heterobimetallic tectons

A tetranuclear complex and a 1-D coordination polymer with a ladder-like topology have been obtained by connecting [Ni(II)Dy(III)] nodes with dicarboxylato ligands: [Ni?(valpn)?Dy?(III)(pdca)?(NO?)(H?O)?](NO?)·4H?O 1, and (∞)1[Ni?(H?O)?(valpn)?Dy?(tfa)?]·4CH?CN 2 (valpn2? = the dianion of the Schiff base resulting from reacting o-vanillin with 1,3-propanediamine; pdca2? = the dianion of 2,6-pyridinedicarboxylic acid; tfa2? = the dianion of the terephthalic acid). The magnetic measurements show a ferromagnetic interaction between Ni(II) and Dy(III), and that both compounds behave like SMM with strong tunnelling. The barrier of 2 (17.4 K) is higher than that of 1 (13.6 K).     

Thermogravimetry of metal chelates of 1,1,1-trifluoropentane-2,4-dione in a flow of helium and helium containing ligand vapor

Thermogravimetry of 22 metal chelates of 1,1,1-trifluoropentane-2,4-dione, H(tfa) in a flow of helium and helium containing H(tfa) vapor is described. Samples were placed in an inserted tube in the inlet port of a gas chromatograph and heated stepwise. The presence of H(tfa) vapor in the helium flow was very effective in suppressing thermal dissociation of hydrated tfa chelates, which decomposed in a helium flow but could be completely vaporized, after dehydration, in a flow of helium containing H(tfa) vapor. The relationship between the volatility and the structure of the tfa chelates is discussed. Results obtained by the proposed method and with a conventional thermobalance are compared.     

X-ray structure and temperature dependent luminescent properties of two bimetallic europium complexes

The structural, luminescent and temperature dependent luminescent properties of two homodinuclear europium complexes bridged by 2,2′-bipyrimidine (bpm) are reported. β-Diketonate ligands 4,4,4-trifluoro-1-(2-furyl)-1,3-butanedione (tfa) and 4,4,4-trifluoro-1-(2-thienyl)-1,3-butanedione (tta) are used as capping ligands resulting in complexes of the form [Eu(tfa)₃]₂bpm (1) and [Eu(tta)₃]₂bpm (2). All Eu^III ions are eight coordinate with six O atoms from the β-diketones and two N atoms from the polyazine bridging ligand. Excitation of the β-diketonate ligands tfa or tta at ca. 340 nm in toluene solutions results in the characteristic Eu^III emission in the visible region of the spectrum. The emission intensity and lifetime associated with the Eu^III centers decrease as the temperature of the solution is increased. Lifetime measurements are fit to a monoexponential while the temperature dependent lifetime data is fit to an Arrhenius-type equation. Evaluation of the data in comparison to data obtained from the monometallic Eu^III analogs reveal very similar photoluminescent properties. This suggests little electronic communication between Eu^III ions via the polyazine bpm bridging ligand.     

Determination of chromium(III) in water by solid-phase microextraction with a polyimide-coated fiber and gas chromatography-flame photometric detection

A method for the determination of trace Cr(III) in aqueous solution by solid-phase microextraction (SPME) coupled with gas chromatography (GC)-flame photometric detection (FPD) was developed. Aqueous Cr(III) was first converted to the volatile chromium trifluoroacetylacetonate (Cr(tfa)3) by derivatization with 1,1,1-trifluoroacetylacetone (Htfa), followed by SPME extraction using a polyimide-coated silica fiber. The distribution constants (K) of derivatized cis- and trans-Cr(tfa)3 between the polyimide phase and aqueous phase were 2012 and 2214, respectively. The two Cr(tfa)3 isomers extracted can be efficiently separated by a DB-210 GC column within 9 min. Selective detection of Cr was performed by a FPD equipped with a 385-nm long-pass filter. Linearity (r> 0.99) over the concentration range 5-300 ng ml(-1) Cr was obtained and the limit of detection was 2 ng ml(-1) Cr. The relative standard deviation was 7% at 10 ng ml(-1) Cr (n = 5). Applicability of this method to water analysis was tested by analyzing the chromium content in a reference standard water sample and an industrial effluent.     

EUROPIUM(III) AND TERBIUM(III) β-DIKETONATE ADDUCTS WITH 2,6-DIMETHYLMORPHOLINE: SYNTHESIS,CHARACTERIZATION AND EMISSION SPECTRA

Abstract

Complexes with composition Ln₂(β-diketonate)₆ (dmm) (Ln = Eu, Tb; dmm = 2,6-dimethyl-morpholine; β-diketonate = 4,4,4-trifluoro-l-(2-thienyl)-l,3-butanodionate (tta); 4,4,4-tri-fluoro-1-phenyl-1,3-butanodionate (tfpb) and l,l,l-trifluoro-l,4-pentanedionate (tfa)) have been synthesized. The adducts were characterized by microanalyses, IR spectra and emission spectra at room temperature and at 77K. The spectra of europium complexes indicate the oligomeric at least dimeric, nature of the compounds, since the bands are broad. The number of peaks in all cases was interpreted as C_3V symmetry around the central ion.     

Strategic design and synthesis of osmium(II) complexes bearing a single pyridyl azolate pi-chromophore: achieving high-efficiency blue phosphorescence by localized excitation

We present the strategic design and synthesis of Os(II) complexes bearing a single pyridyl azolate pi-chromophore with an aim to attain high efficiency blue phosphorescence by way of localized transition. It turns out that our proposal of localized excitation seems to work well upon anchoring a single pi-chromophore on the Os(II) complexes such that the control of MLCT versus pipi* (or even LLCT) transitions is more straightforward. Among the titled complexes, [Os(CO)3(tfa)(fppz)] (1) and [Os(CO)3(tfa)(fbtz)] (5) (tfa=trifluoroacetate, (fppz)H=3-(trifluoromethyl)-5-(2-pyridyl)pyrazole, and (fbtz)H=3-(trifluoromethyl)-5-(4-tert-butyl-2-pyridyl)-1,2,4-triazole) give the anticipated blue phosphorescence with efficiencies of 0.26 (lambdamax=460 nm) and 0.27 (lambdamax=450 nm), respectively. For their halide analogues [Os(CO)3(X)(fppz)] (2, X=Cl; 3, X=Br; 4, X=I) and phosphine-substituted isomeric derivatives [Os(tfa)(fppz)(PPh2Me)2(CO)] (6-8), the localization of the excitation energy seems to populate at certain vibrational modes with weak bonding strength and hence an associated shallow potential energy surface to induce a facile radiationless transition. Furthermore, their ancillary ligands play an important role in fine-tuning not only the energy gap but also the emission intensity, i.e., in manifesting the radiationless transition pathways. Our results clearly show that there is always a tradeoff upon varying the parameters in an aim to optimize the hue and efficiency of phosphorescence toward blue.     

Microwave-assisted derivatization and single-drop microextraction for gas chromatographic determination of chromium(III) in water

A rapid and efficient sample preparation method combining microwave-assisted derivatization (MAD) and single-drop microextraction (SDME) for the gas chromatographic (GC) determination of trace Cr(III) in water was developed. Aqueous Cr(III) was first converted to the volatile chromium trifluoroacetylacetonate (Cr(tfa)3) by reaction with 1,1,1-trifluoroacetylacetone (Htfa) under the irradiation of microwave. Derivatization of Cr(III) at ng ml(-1) level could be completed in less than 1 min. The formed Cr(tfa)3 was then extracted into a small droplet (2 microl) of toluene suspended at the tip of a microsyringe needle. The optimal extraction time was 30 min. The solvent drop was directly injected into a GC equipped with a flame photometric detector (FPD) for analysis. The two Cr(tfa)3 isomers extracted could be efficiently separated in 2 min. Linearity (r>0.99) over the concentration range 2-300 ng ml(-1) Cr was obtained and the limit of detection was 0.5 ng ml(-1) Cr. The relative standard deviation was 7.8% at 20 ng ml(-1) Cr (n=5). Applicability of this method to water analysis was examined by analyzing the chromium content in a reference standard water sample and an industrial effluent.     

A New CoII Complex as a Bulge-Specific Probe for DNA

Bulge cleavage of two or three bases occurs when a DNA substrate is specifically cleaved oxidatively by [Co^II(tfa)₂(happ)] (see picture). Hydrogen peroxide is necessary for the activation of this octahedral complex, which suggests that hydroxyl radicals are the reactive species. The complex has no significant reactivity towards the corresponding sequence in a single-stranded DNA region, and it exhibits only a low affinity towards double-stranded DNA. happ=macrocyclic ligand based on 1,10-phenanthroline, tfa=trifluoroacetate.     

Regioselective oxidative coupling reactions of 3-substituted thiophenes with arylboronic acids

Under optimized conditions, 3-substituted thiophenes (EWG = COOEt, PO(OEt)(2)) undergo a facile and regioselective oxidative coupling reaction at carbon atom C4. The reactions were performed with various aryl boronic acids as nucleophiles in the presence of silver oxide (2.0 equiv), cesium trifluoroacetate (tfa) (1.0 equiv), benzoquinone (BQ) (0.5 equiv), and catalytic amounts of Pd(tfa)(2) (10 mol %) employing trifluoroacetic acid (TFA) as the solvent.     

Synthesis of coumarin-nucleoside conjugates via Huisgen 1,3-dipolar cycloaddition

An efficient synthesis of fluorescent coumarin-nucleoside conjugates via Cu(I) catalysed Huisgen 1,3-dipolar cycloaddition is described. Starting from azidonucleosides and coumarin derivatives, products are obtained in good yields. The fluorescent properties of the newly prepared coumarin-nucleoside conjugates are determined.     

How molecular oxygen binds to bis[trifluoroacetylacetonato(-1)]cobalt(II)--ab initio and density functional theory studies

Cobalt(II) diketonate complexes, such as bis[trifluoroacetylacetonato(-1)]cobalt(II) [Co(tfa)(2)], catalyze the aerobic oxidation of alkenols into functionalized tetrahydrofurans. To gain insight into activation of triplet dioxygen by Co(tfa)(2) in a protic solvent, as used in oxidation catalysis, the electronic structure of aquabis[trifluoroacetylacetonato(-1)]cobalt(II)--Co(tfa)(2)(H(2)O)--and the derived dioxygen adduct were characterized using ab initio (CASSCF, NEVPT2) and density functional theory (BP86, TPSSh, B3LYP) methods. The ground state of Co(tfa)(2)(H(2)O) is a high-spin, quartet state. As dioxygen approaches the cobalt atom, the quartet state couples with a triplet dioxygen molecule and forms a sextet, a quartet, and a doublet spin state with the high-spin state being the lowest in energy. At the equilibrium Co-O(2) distance of 1.9 ?, Co(tfa)(2)(H(2)O)(O(2)) has a doublet superoxo Co(III) ground state with the unpaired electron residing on the oxygen moiety, in a nearly unchanged O(2)π* orbital.     

Trans-, cis-isomers of (1,1,1-trifluoro-2,4-pentandionato)Pt(II): Volatility, structure and crystal lattice energy

Trans-and cis-complexes of platinum(II) with trifluoroacetylacetone (Pt(tfa)₂) have been prepared and studied. The synthesis and the separation technique for the isomers are described. Temperature dependencies of saturated vapor pressure measured with a spoon gauge are reported for the cis-Pt(tfa)₂ and trans-Pt(tfa)₂ complexes. The isomers show a significant difference in volatility. The structural study of Pt(tfa)₂ isomers has been performed. Molecular packings in the crystal of each isomer are considered on the base of structural data. The calculation of van der Waals energy of the crystal lattice of cis-Pt(tfa)₂ and trans-Pt(tfa)₂ was made by the atom-atom potential technique, their values being compared with experimental ΔH _T ⁰ values of sublimation for the complexes.     

Acid catalysed reactions between diols and vinyl-ethers in basic solvents towards a selective protection of polyols by 2,3-dihydro-4H-pyran

Acid catalysed synthesis of THP ethers of 1,3-butanediol takes place much more selectively and in high yields if DMSO is used as solvent, instead in CHCl₃, even with mild acid catalysts, rearranged 1,3-dioxans are obtained.     

A novel palladium(0) catalysed tandem 1,3-allyl shift and Heck arylation

On treatment with Pd(PPh₃)₄ allyl vinyl ether (1) undergoes a Pd(0) catalysed 1,3 oxygen to carbon allyl shift to afford -allyl ketone (2). In the presence of both Pd(PPh₃)₄ and base the allyl vinyl ether undergoes a Pd(0) catalysed tandem 1,3 allyl shift and intramolecular Heck arylation to give the spiro indane (3). Mechanistic investigations suggest that the 1,3-allyl shift proceeds via a π-allyl palladium intermediate.     

Influence of Ag(I) and Li(I) Catalysts for 1,3-Dipolar Cycloaddition Reactions of Azomethine Ylides. Reversal of the Stereochemistry

The 1,3-dipolar cycloadditions of ester stabilised azomethin ylides to aryl-nitro olefines catalysed by Li(I) gave products of different stereoselectivity than those arising from processes catalysed by Ag (I). The cycloadditions involve the stereospecific generation of dipoles. The formation of products with reverse stereochemistry when using different metal salt catalysts is caused by the differences in endo and exo approaches of nitro-ethylene compounds.     

Tetrahedral intermediates 3: The kinetics and mechanism of the breakdown of some hemiorthoesters

The kinetics of the breakdown of hemiorthoesters generated from dialkoxyalkyl acetates or ketene acetals have been investigated. The following compounds were studied: dimethyl hemiorthoformate (1b), diethyl hemiorthoformate (2b), 2-hydroxy-1,3-dioxolane (3b), 2-hydroxy-4,4,5,5-tetramethyl-1, 3-dioxolane, (4b), 2-hydroxy-2-methyl-1,3-dioxolane (5b),and 2-hydroxy-2,4,4,5,5-pentamethyl-1,3-dioxolane (6b).The whole series was studied in aqueous acetonitrile (c_H2O= 8.33 M); 4b, 5b, and 6b were studied in aqueous acetonitrile (c_H2O = 2.22 M) and 4b and 6b in water. Complete pc_H-rate or pH-rate profiles were obtained for each reaction. The mechanisms of the hydronium-ion, hydroxide-ion and “water” catalysed reactions are discussed and compared to those for the breakdown of hemiacetals and the hydrolysis of orthoesters.     

Enantioselective cycloadditions of 2-alkenoylpyridine-N-oxides catalysed by a bis(oxazoline)/Cu(II) complex: structure of the reactive intermediate

Diels–Alder and 1,3‐dipolar cycloadditions involving (E)‐3‐aryl‐1‐(pyridin‐2‐yl‐N‐oxide)prop‐2‐en‐1‐ones as the 2π components are efficiently catalysed by bis(oxazoline)–Cu^II complexes. The cycloadducts are obtained in quantitative yields with up to 98 % ee; absolute configurations were determined by X‐ray analysis. The structure of the reactive complex, determined by X‐ray analysis, is fully consistent with the stereochemical outcome of the catalysed process (approach of the diene or nitrone to the less hindered face of the coordinated pyridine‐N‐oxide derivative).     

Structure and properties of a heterocomplex compound based on lead(II) hexafluoroacetyl acetonate and copper(II) trifluoroacetyl acetonate Cu(tfa)2·Pb(hfa)2

The crystals of a heterobimetallic complex based on lead(II) hexafluoroacetyl acetonate and copper(II) trifluoroacetyl acetonate were investigated by X-ray diffraction. Crystal data for Cu(tfa)₂·Pb(hfa)₂: a = 9.3991(4) Å, b = 11.7816(5) Å, c = 13.9736(5) Å, α = 88.311(2)°, β = 89.972(1)°, γ = 76.326(1)°, space group P-1, Z = 2, d _calc = 2.190 g/cm³. The basic structural motif for the complexes is coordination polymer in the form of chains of alternating complex molecules. The Cu(tfa)₂ molecules have a trans configuration. The results of a DTA-TG analysis of the compound are given.     

Facile Synthesis of 1,3-Diaryl-propanones Through Heck Reaction

1,3-diaryl propanones (1a-6a) and 1,3-diaryl-2-carbomethoxy-propanones (1b-6b) have been synthesized through facile palladium catalysed arylation of Baylis- Hillman adducts.     

Enhancement effect of 3,5-dichlorophenol on the solvent extraction of copper(II) and zinc(II) with acetylacetone and trifluoroacetylacetone

The effect of 3,5-dichlorophenol (DCP) on the extraction of Cu(II) and Zn(II) with acetylacetone (Hacac) and trifluoroacetylacetone (Htfa) in heptane and carbon tetrachloride has been investigated. DCP enhances these chelate extractions; the largest effect is observed on the extraction of Cu(II) with Hacac, which is much larger than the corresponding synergistic effect seen with neutral electron donors such as trioctylphosphine oxide. By analysing the various equilibria involved, the enhanced extraction has been ascribed to the formation of association complexes of the bis(beta-diketonato) chelates (MA(2)) with DCP as MA(2).nDCP (n = 1 for A = tfa and n = 2 for A = acac) in the organic phase, and the association constants have been determined. The association constants increase in the following order of ligand and metal(II): tfa < acac and Zn(II) < Cu(II). These orders are exactly opposite those observed in the adduct formation of the chelates with neutral electron donors.