Complexes formed between the quadridentate, heterocyclic molecules 6,6 '-bis-(5,6-dialkyl-1,2,4-triazin-3-yl)-2,2 '-bipyridine (BTBP) and lanthanides(III): implications for the partitioning of actinides(III) and lanthanides(III)

New hydrophobic, tetradentate nitrogen heterocyclic reagents, 6.6'-bis-(5,6-dialkyl- 1,2,4-triazin-3-yl)2,2'-bipyridines (BTBPs) have been synthesised. These reagents form complexes with lanthanides and crystal structures with 11 different lanthanides have been determined. The majority of the structures show the lanthanide to be 10-coordinate with stoichiometry [Ln(BTBP)(NO3)(3)] although Yb and Lu are 9-coordinate in complexes with stoichiometry [Ln(BTBP)(NO3)(2)(H2O)](NO3). In these complexes the BTBP ligands are tetradentate and planar with donor nitrogens mutually cis i.e. in the cis, cis, cis conformation. Crystal structures of two free molecules, namely C2-BTBP and CyMe4-BTBP have also been determined and show different conformations described as cis, trans, cis and trans, trans, trans respectively. A NMR titration between lanthanum nitrate and C5-BTBP showed that two different complexes are to be found in solution, namely [La(C5-BTBP)(2)](3+) and [La(C5-BTBP)(NO3)(3)]. The BTBPs dissolved in octanol were able to extract Am(III) and Eu(III) from 1 M nitric acid with large separation factors.

The synthesis of chiral N-heterocyclic carbene–borane and –diorganoborane complexes and their use in the asymmetric reduction of ketones

Chiral N-heterocyclic carbene–borane complexes have been synthesised, and have been shown to reduce ketones with Lewis acid promotion. Chiral N-heterocyclic carbene–borane and –diorganoborane complexes can reduce ketones with enantioselectivities up to 75% and 85% ee, respectively.

Segregated self-assembly and pillaring action of aliphatic dicarboxylic acids in the super structure of Cu-picolinate complexes

Three new supramolecular assemblies of co-crystallized metal complexes and aliphatic dicarboxylic acids, {[Cu(pic)(2)(H2O)(2)](H(2)mal)}(n) (1), {[Cu(pic)(2)(H2O)(2)](H(2)mal)(2)(H2O)(2)}(n) (2) and {[Cu(pic)(2)(MeOH)](H(2)succ)}(n) (3) {Hpic = 2-picolinic acid, H(2)mal = malonic acid and H(2)succ = succinic acid} have been synthesized and characterized by X-ray single-crystal structure determination. The crystal packings of the complexes reveal that supramolecular associations of the monomeric complex units lead to the formation of layers through hydrogen bonding. In all the complexes, the dicarboxylic acid units connect the 2-D layers to act as pillars. The interaction between water molecules and the dicarboxylic acid plays an important role in the overall supramolecular assembly. (C) 2008 Elsevier Ltd. All rights reserved.

QSAR studies of multidentate nitrogen ligands used in lanthanide and actinide extraction processes

Quantitative structure activity relationships (QSARs) have been developed to optimise the choice of nitrogen heterocyclic molecules that can be used to separate the minor actinides such as americium(III) from europium(III) in the aqueous PUREX raffinate of nuclear waste. Experimental data on distribution coefficients and separation factors (SFs) for 47 such ligands have been obtained and show SF values ranging from 0.61 to 100. The ligands were divided into a training set of 36 molecules to develop the QSAR and a test set of 11 molecules to validate the QSAR. Over 1500 molecular descriptors were calculated for each heterocycle and the Genetic Algorithm was used to select the most appropriate for use in multiple regression equations. Equations were developed fitting the separation factors to 6-8 molecular descriptors which gave r(2) values of >0.8 for the training set and values of >0.7 for the test set, thus showing good predictive quality. The descriptors used in the equations were primarily electronic and steric. These equations can be used to predict the separation factors of nitrogen heterocycles not yet synthesised and/or tested and hence obtain the most efficient ligands for lanthanide and actinide separation. (C) 2003 Elsevier B.V. All rights reserved.

Ditopic hexaazamacrocycles containing pyridine: synthesis, protonation and complexation studies

Structural studies of metal complexes of five ditopic hexaazamacrocycles containing two pyridine rings ([n] py(2)N(4) n = 18, 20, 22, 24 and 26) have been carried out. The synthesis of macrocycles [22]- to [26]- py(2)N(4) are also reported. The protonation constants of the last three compounds and the stability constants of their complexes with Ni2+, Cu2+, Zn2+, and Pb2+ were determined at 25 degreesC in 0.10 mol dm(-3) KNO3 in aqueous solution. Our results with [22] py(2)N(4) show significant differences from those described previously, while [24] py(2)N(4) has not been studied before and [ 26] py2N4 is a new compound. Mononuclear and dinuclear complexes of the divalent metal ions studied with [ 22]- to [26]- py(2)N(4) were found in solution. The stability constants for the ML complexes of the three ligands follow the Irving - Williams order: NiL2+ < CuL2+ >> ZnL2+ > PbL2+, however for the dinuclear complexes the values for Pb2+ complexes are higher than the corresponding values for the Ni2+ and the Zn2+ complexes. The X-ray single crystal structures of the supramolecular aggregates [Cu-2([20] py(2)N(4))(H2O)(4)][Cu(H2O)(6)](SO4)(3) . 3H(2)O ( 1) and [Cu-2([20] py(2)N(4))(CH3CN)(4)][Ni([20] py(2)N(4))](2)(ClO4)(8) . H2O (2), which are composed of homodinuclear [Cu-2([20] py(2)N(4)])(H2O)(4)](4+) ( 1a) and [Cu-2([20] py(2)N(4)])(CH3CN))(4)](4+) (2a), and mononuclear species, [Cu(H2O)(6)](2+) (1b) and [Ni([20] py(2)N(4))](2+) ( 2b), respectively, assembled by an extensive network of hydrogen bonds, are also reported. In both homodinuclear complexes the copper centres are located at the end of the macrocycle and display distorted square pyramidal coordination environments with the basal plane defined by three consecutive nitrogen donors and one solvent molecule, water in 1a and acetonitrile in 2a. The macrocycle adopts a concertina-type conformation leading to the formation of macrocyclic cavities with the two copper centres separated by intramolecular distances of 5.526(1) and 5.508(7) Angstrom in 1a and 2a, respectively. The mononuclear complex [Ni([20] py(2)N(4)])](2+) displays a distorted octahedral co-ordination environment with the macrocycle wrapping the metal centre in a helical shape. EPR spectroscopy of the copper complexes indicated the presence of mono- and dinuclear species.

Dioxadiaza- and trioxadiaza-macrocycles containing one dibenzofuran unit selective for cadmium

The binding properties of dioxadiaza-([17](DBF) N2O2) and trioxadiaza- ([22](DBF)N2O3), macrocyclic ligands containing a rigid dibenzofuran group ( DBF), to metal cations and structural studies of their metal complexes have been carried out. The protonation constants of these two ligands and the stability constants of their complexes with Ca2+, Ba2+, and Mn2+, Co2+, Ni2+, Cu2+, Zn2+ and Cd2+, were determined at 298.2 K in methanol-water ( 1 : 1, v/v), and at ionic strength 0.10 mol dm(-3) in KNO3. The values of the protonation constants of both ligands are similar, indicating that no cavity size effect is observed. Only mononuclear complexes of these ligands with the divalent metal ions studied were found, and their stability constants are lower than expected, especially for the complexes of the macrocycle with smaller cavity size. However, the Cd2+ complex with [ 17]( DBF) N2O2 exhibits the highest value of stability constant for the whole series of metal ions studied, indicating that this ligand reveals a remarkable selectivity for cadmium(II) in the presence of all the metal ions studied, except copper( II), indicating that this ligand reveals a remarkable selectivity for cadmium( II) in the presence of the mentioned metal ions. The crystal structures of H-2[17](DBF)N2O32+ (diprotonated form of the ligand) and of its cadmium complex were determined by X-ray diffraction. The Cd2+ ion fits exactly inside the macrocyclic cavity exhibiting coordination number eight by coordination to all the donor atoms of the ligand, and additionally to two oxygen atoms from one nitrate anion and one oxygen atom from a water molecule. The nickel( II) and copper( II) complexes with the two ligands were further studied by UV-vis-NIR and the copper( II) complexes also by EPR spectroscopic techniques in solution indicating square-pyramidal structures and suggesting that only one nitrogen and oxygen donors of the ligands are bound to the metal. However an additional weak interaction of the second nitrogen cannot be ruled out.

New dioxadiaza- and trioxadiaza-macrocycles containing one dibenzofuran unit with two amino pendant arms: synthesis, protonation and complexation studies

New dioxadiaza- and trioxadiaza-macrocycles containing one rigid dibenzofuran unit (DBF) and N-(2-aminoethyl) pendant arms were synthesized, N,N'-bis(2-aminoethyl)-[17]( DBF) N2O2 (L-1) and N,N'-bis(2-aminoethyl)-[22](DBF)N2O3 (L-2), respectively. The binding properties of both macrocycles to metal ions and structural studies of their metal complexes were carried out. The protonation constants of both compounds and the stability constants of their complexes with Co2+, Ni2+, Cu2+, Zn2+, Cd2+, and Pb2+ were determined at 298.2 K, in aqueous solutions, and at ionic strength 0.10 mol dm(-3) in KNO3. Mononuclear complexes with both ligands were formed, and dinuclear complexes were only found for L-2. The thermodynamic binding affinities of the metal complexes of L-2 are lower than those of L-1 as expected, but the Pb2+ complexes of both macrocycles exhibit close stability constant values. On the other hand, the binding affinities of Cd2+ and Pb2+ for L-1 are very high, when compared to those of Co2+, Ni2+ and Zn2+. These interesting properties were explained by the presence of the rigid DBF moiety in the backbone of the macrocycle and to the special match between the macrocyclic cavity size and the studied larger metal ions. To elucidate the adopted structures of complexes in solution, the nickel(II) and copper( II) complexes with both ligands were further studied by UV-vis-MR spectroscopy in DMSO-H2O 1 : 1 (v/v) solution. The copper(II) complexes were also studied by EPR spectroscopy in the same mixture of solvents. The crystal structure of the copper complex of L-1 was also determined. The copper(II) displays an octahedral geometry, the four nitrogen atoms forming the equatorial plane and two oxygen atoms, one from the DBF unit and the other one from the ether oxygen, in axial positions. One of the ether oxygens of the macrocycle is out of the coordination sphere. Our results led us to suggest that this geometry is also adopted by the Co2+ to Zn2+ complexes, and only the larger Cd2+ and Pb2+ manage to form complexes with the involvement of all the oxygen atoms of the macrocyclic backbone.

Photochromic dithienylethene derivatives containing Ru(II) or Os(II) metal units. Sensitized photocyclization from a triplet state

Efficient photocyclization from a low-lying triplet state is reported for a photochromic dithienylperfluorocyclopentene with Ru(bpy)(3) units attached via a phenylene linker to the thiophene rings. The ring-closure reaction in the nanosecond domain is sensitized by the metal complexes. Upon photoexcitation into the lowest Ru-to-bpy (MLCT)-M-1 state followed by intersystem crossing to emitting (MLCT)-M-3 states, photoreactive (IL)-I-3 states are populated by an efficient energy-transfer process. The involvement of these (IL)-I-3 states explains the quantum yield of the photocyclization, which is independent of the excitation wavelength but decreases strongly in the presence of dioxygen. This behavior differs substantially from the photocyclization of the nonemissive dithienylperfluorocyclopentene free ligand, which occurs from the lowest (IL)-I-1 state on a picosecond time scale and is insensitive to oxygen quenching. Cyclic voltammetric studies have also been performed to gain further insight into the energetics of the system. The very high photocyclization quantum yields, far above 0.5 in both cases, are ascribed to the strong steric repulsion between the bulky substituents on the dithienylperfluorocyclopentene bridge bearing the chelating bipyridine sites or the Ru(bpy)(3) moieties, forcing the system to adopt nearly exclusively the reactive antiparallel conformation. In contrast, replacement of both Ru(II) centers by Os(II) completely prevents the photocyclization reaction upon light excitation into the low-lying Os-to-bpy (MLCT)-M-1 state. The photoreaction can only be triggered by optical population of the higher lying (IL)-I-1 excited state of the central photochromic unit, but its yield is low due to efficient energy transfer to the luminescent lowest (MLCT)-M-3 state.

Multimetallic ruthenium(II) complexes as electrochemiluminescent labels

Two homometallic complexes containing two and three ruthenium polypyridyl units linked by amino acid lysine (Lys) and the related dipeptide (LysLys) were synthesized and their electrochemical, spectroscopic, and electrochemiluminescence (ECL) properties were investigated. The electrochemical and photophysical data indicate that the two metal complexes largely retain the electronic properties of the reference compound for the separate ruthenium moieties in the two bridged complexes, [4-carboxypropyl-4'-methyl-2,2'-bipyridine]bis(2,2'-bipyridine)ruthenium(II) complex. The ECL studies, performed in aqueous media in the presence of tri-n-propylamine as co-reactant, show that the ECL intensity increases by 30% for the dinuclear and trinuclear complexes compared to the reference. Heterogeneous ECL immunoassay studies, performed on larger dendritic complexes containing up to eight ruthenium units, demonstrate that limitations due to the slow diffusion can easily be overcome by means of nanoparticle technology. In this case, the ECL signal is proportional to the number of ruthenium units. Multimetallic systems with several ruthenium centers may, however, undergo nonspecific bonding,to streptavidin-coated particles or to antibodies, thereby increasing the background ECL intensity and lowering the sensitivity of the immunoassay.

RuII(α-diimine) or RuIII(α-diimine·–)? Structural, spectroscopic, and theoretical evidence for the stabilization of a prominent metal-to-Ligand charge- transfer excited-state configuration in the ground state

The new compounds [Ru(R-DAB)(acac)2] (R-DAB = 1,4-diorganyl- 1,4-diazabuta-1,3-diene; R = tert-butyl, 4-methoxyphenyl, 2,6-dimethylphenyl; acac– = 2,4-pentanedionate) exhibit intrachelate ring bond lengths 1.297metal-to-ligand chargetransfer (MLCT) excited states of conventional (α-diimine)- ruthenium(II) complexes and in view of other (α-diimine)- metal complexes with ambiguous oxidation-state assignments.

Mineral and geochemical characterization of a leptic aluandic soil and a thapto aluandic-ferralsol developed on trachytes in Mount Bambouto (Cameroon volcanic line)

Mineral and geochemical investigations were carried out on soil samples and fresh rock (trachytes) from two selected soil profiles (TM profile on leptic aluandic soils and TL profile on thapto aluandic-ferralsols) from Mount Bambouto to better understand geochemical processes and mineral paragenesis involved in the development of soils in this environment. In TM profile, the hydrated halloysites and goethite occur in the weathered saprolite boulders of BC horizon while dehydrated halloysite, gibbsite and goethite dominate the soils matrices of BC and A horizons. In TL profile, the dehydrated halloysites and goethite are the most abundant secondary minerals in the weathered saprolites of C and BC horizons while gibbsite, hematite and kaolinite occur in the soil matrices of BC, B and A horizons. The highest gibbsite content is in the platy nodules of B horizon. In both soil profiles, organo-metal complexes (most likely of AI and Fe) are present in the surface A horizon. Geochemically, between the fresh rock and the weathered saprolites in both soils, SiO2, K2O, CaO, Na2O and MgO contents decrease strongly while Fe2O3 and Al2O3 tend to accumulate. The molar ratio of SiO2/Al2O3 (Ki) and the sum of Ca, Mg, K and Na ions (TRB) also decreases abruptly between fresh rocks and the weathered saprolites, but increases significantly at the soil surface. The TM profile shows intense Al enrichment whereas the TL profile highlights enrichment in both AI and Fe as the weathering progresses upwards. Both soil profiles are enriched in Ni, Cu, Ba and Co and depleted in U, Th, Ta, Hf, Y, Sr, Pb, Zr and Zn relative to fresh rock. They also show a relatively low fractionation of the rare earth elements (REE: La, Nd, Sm, Eu, Tb, Yb and Lu), except for Ce which tends to be enriched in soils compared to CI chondrite. All these results give evidence of intense hydrolysis at soil deep in Mount Bambouto resulting in the formation of halloysite which progressively transforms into gibbsite and/or dehydrated halloysite. At the soil surface, the prominent pedogenetic process refers to andosolization with formation of organo-metal complexes. In TL profile, the presence of kaolinite in soil matrices BC and B horizons is consistent with ferralitization at soil deep. In conclusion, soil forming processes in Mount Bambouto are strongly influenced by local climate: (i) in the upper mountain (>2000 m), the fresh, misty and humid climate favors andosolization; whereas (ii) in the middle lands (1700-2000 m) with a relatively dry climate, both andosolization at the soil surface and ferralitization at soil deep act together. (C) 2009 Elsevier B.V. All rights reserved.

New bis(triazinyl) pyridines for selective extraction of americium(III)

New hydrophobic, tridentate nitrogen heterocyclic reagents (BATPs) such as 2,6-bis(5,5,8,8-tetramethyl-5,6,7,8-tetrahydrobenzo[1,2,4]triazin-3-yl) pyridine (1) and 2,6-bis(9,9,10,10-tetramethyl-9,10-dihydro-1,2,4-triaza-anthrane-3-yl) pyridine (2) have been studied. I is resistant to hydrolysis in 3 M nitric acid, whereas 2 is resistant to both acid hydrolysis and radiolysis. The molecules are able to give significantly enhanced separations of americium(III) from an excess of europium(III) in nitric acid. Typically, for 1 D-Am = 500 and SFAm,/Eu = 5000 compared with D-Am = 30 and SFAm /Eu = 400 with the reference molecule 2,6-bis(isopropyl[1,2,4]triazin-3-yl) pyridine (7). In order to increase the stability of 1 and 2, the labile alpha-benzylic hydrogens that are present in 7 have been replaced by alkyl groups. Three molecules of 1 are able to enclose completely the coordination sphere of the M(III) in the crystal structure of [Y(1)(3)][Y(NO3)(5)]center dot NO3 center dot 2.5H(2)O.

Influence of sulfur amino acids on the volatile and nonvolatile components of cooked salmon (Salmo salar)

Volatile and nonvolatile compounds, which could contribute to flavor, were analyzed in salmon. One hundred twenty-three volatile compounds were identified in the headspace of two different samples of cooked salmon, including lipid-derived volatiles, Maillard-derived volatiles, sulfur volatiles, Strecker aldehydes, nitrogen heterocyclic compounds, terpenes, and trimethylamine. Significant differences between samples were found for 104 of the volatiles. Although the levels of free cysteine and methionine were low in the salmon, sulfur volatiles were formed in the cooked fish, demonstrating that there were sufficient sulfur amino acids present for their formation. Notable differences in sulfur compounds between the samples suggested that small changes in sulfur amino acids could be responsible. When this hypothesis was tested, salmon heated with cysteine had increased levels of many thiophenes, thiazoles, alicyclic sulfides, and nitrogen heterocycles. With the addition of methionine, levels of dimethyl sulfides, two alicyclic sulfides, pyrazines, some unsaturated aldehydes, and alcohols and 2-furanmethanethiol increased. The largest difference found among the nonvolatile (low molecular weight water-soluble) compounds was in inosine monophosphate.

Redox-active, dinuclear sandwich compounds [Cp*Fe(μ-L)FeCp*] (L = naphthalene and anthracene)

Although there has been much interest in the chemistry of bimetallic transition metal complexes, compounds with naphthalene or anthracene as bridging ligands are still rare. In this article, we describe the synthesis of the homodinuclear iron complexes [Cp*Fe(μ-η4:η4-L)FeCp*] (1: L = C10H8, 2: L = C14H10; Cp* = η5-C5Me5). The complexes were characterized by 1H and 13C{1H} NMR, UV/Vis, and 57Fe Mössbauer spectroscopy, and their molecular structures were determined by X-ray crystallography. Both complexes are diamagnetic as a result of the strong magnetic coupling of the 17e FeI centers mediated by the polyarene bridge. An analysisof the redox behavior of 1 and 2 by cyclic voltammetry andUV/Vis spectroelectrochemistry shows that the complexes can be oxidized reversibly in two well-separated one-electron steps to the monocation [Cp*Fe(μ-L)FeCp*]+ and the dication [Cp*Fe(μ-L)FeCp*]2+. The reduction to the monoanion [Cp*Fe(μ-L)FeCp*]– was also observed.

Synthesis, characterization, crystal structure, and DNA-binding of ruthenium(II) complexes of heterocyclic nitrogen ligands resulting from a benzimidazole-based quinazoline derivative

The reaction of cis-[RuCl2(dmso)(4)] with [6-(2-pyridinyl)-5,6-dihydrobenzimidazo[1,2-c] quinazoline] (L) afforded in pure form a blue ruthenium(II) complex, [Ru(L-1)(2)] (1), where the original L changed to [2-(1H-benzoimidazol-2-yl)-phenyl]-pyridin-2-ylmethylene-amine (HL1). Treatment of RuCl3 center dot 3H(2)O with L in dry tetrahydrofuran in inert atmosphere led to a green ruthenium(II) complex, trans-[RuCl2(L-2)(2)] (2), where L was oxidized in situ to the neutral species 6-pyridin-yl-benzo[4,5]imidazo[1,2-c] quinazoline (L-2). Complex 2 was also obtained from the reaction of RuCl3 center dot 3H(2)O with L-2 in dry ethanol. Complexes 1 and 2 have been characterized by physico-chemical and spectroscopic tools, and 1 has been structurally characterized by single-crystal X-ray crystallography. The electrochemical behavior of the complexes shows the Ru(III)/Ru(II) couple at different potentials with quasi-reversible voltammograms. The interaction of these complexes with calf thymus DNA by using absorption and emission spectral studies allowed determination of the binding constant K-b and the linear Stern-Volmer quenching constant K-SV