Insights into water coordination associated with the Cu(II)/Cu(I) electron transfer at a biomimetic Cu centre.

International audienceThe coordination properties of the biomimetic complex [Cu(TMPA)(H2O)](CF3SO3)2 (TMPA = tris(2-pyridylmethyl)amine) have been investigated by electrochemistry combined with UV-Vis and EPR spectroscopy in different non-coordinating media including imidazolium-based room-temperature ionic liquids, for different water contents. The solid-state X-ray diffraction analysis of the complex shows that the cupric centre lies in a N4O coordination environment with a nearly perfect trigonal bipyramidal geometry (TBP), the water ligand being axially coordinated to Cu(II). In solution, the coordination geometry of the complex remains TBP in all media. Neither the triflate ion nor the anions of the ionic liquids were found to coordinate the copper centre. Cyclic voltammetry in all media shows that the decoordination of the water molecule occurs upon monoelectronic reduction of the Cu(II) complex. Back-coordination of the water ligand at the cuprous state can be detected by increasing the water content and/or decreasing the timescale of the experiment. Numerical simulations of the voltammograms allow the determination of kinetics and thermodynamics for the water association-dissociation mechanism. The resulting data suggest that (i) the binding/unbinding of water at the Cu(I) redox state is relatively slow and equilibrated in all media, and (ii) the binding of water at Cu(I) is somewhat faster in the ionic liquids than in the non-coordinating solvents, while the decoordination process is weakly sensitive to the nature of the solvents. These results suggest that ionic liquids favour water exchange without interfering with the coordination sphere of the metal centre. This makes them promising media for studying host-guest reactions with biomimetic complexes

Romantismo e objetividade: notas sobre um panorama do Rio de Janeiro

The article deals with the great Panorama of Rio de Janeiro exhibited in Paris, 1824, and its sources - a series of watercolours which have also generated succeeding engravings produced dur-ing the 1830s. Panoramas, in their early formal conventions are shown to interplay with Romanticism's and Naturphilosophie's theses and to put in motion the legacy of 11th-century paint-ing . As this geme of visual device develops, Rio's watercoulours display symptoms of a gradual dismissal of its initial ambilions, through lhe treatment of the natural site and the city. At last the invention of the daguerreotype and vai d'oiseau urban images, among other traits, signale the changes in sensibility related to the production and consumption of those circular canvasses. From 1840/50 on panoramas conceived by the will to fuse art and science and bya reflection on nature and liberty turn essentially into a mass entertainment.Romantismo e objetividade: notas sobre um panorama do Rio de Janeiro Margarelh da Silva Pereira Enfoca O grande Panorama do Rio de Janeiro, exibido em Paris em 1824, do qual se conhece a série de aquarelas que serviram de base tanto àquela ampliação quanto às sucessivas gravuras da cena que foram produzidas na década de 1830. Busca-se mostrar como os panoramas em sua formalização inicial dialogam com as teses do romantismo e da Naturphilosophie, mobilizan-do heranças da pintura seiscentista. No desenvolvimento desta forma de exibição as aquarelas do Rio apresentam sintomas do gradual afastamento das ambições iniciais através do tratamento dispensado ao sítio natural e à cidade. Por fim, a invenção do daguerreótipo, e as vistas urbanas em võo de pássaro, enlre outros, balizariam a mudança de sensibilidade na produção e na fruição dessas telas circulares. A partir de 1840/50 os panoramas engendrados pelo desejo de fusão entre arte e ciência e pela reflexão sobre a natureza e a liberdade, tornar-se-iam, sobretudo, um divertimento de massas

Conception de nouveaux hybrides moléculaires (Structures et proriétés de systèmes originaux à base de manganèse, fer ou nickel et d'entités polynitrile)

Les travaux présentés dans ce mémoire se situent dans le contexte général de la chimie de coordination des métaux de transition, à l'interface avec la chimie des matériaux moléculaires et concernent l'élaboration de nouveaux hybrides moléculaires inorganiques - organiques à basede complexes inorganiques et d'entités polynitrile. Dans la première partie, avec l'entité polynitrile (C8N5) , deux types de complexes ont pu être isolés et caractérisés (IR, RPE, RX) avec le Fe (II) et le Mn (II). Les dérivés [M(C8N5)2(H20)4] possèdent un réseau tridimensionnel assuré par de nombreuses liaisons hydrogène. Les dérivés [M(C8N5)2] présentent eux, la première coordination R3 de l'entité polynitrile (C8N5) . Celle-ci conduit à des interactions plus fortes entre les centres métalliques, dues notamment à l'action pontante de l'entité polynitrile, confirmée par des mesures de magnétisme. L'entité (C10N8)2 a permis l'obtention du nouveau composé organique bicyclique, plan et porteur de quatre groupements nitrile. Dans la seconde partie les ligands de types di-imine / pyridine, radicalaires ou non, L sont associés aux complexes métalliques. Nous avons ainsi synthétisé des précurseurs [ML(Solvant) x](BF4)2 avec le fer et le nickel, conduisant avec l'anion (C8N5) à une chaîne monodimensionnelle, dans le cas du nickel et d'un ligand non radicalaire. L'entité polynitrile joue soit le rôle de ligand pontant, soit celui de contre ion. La troisième partie correspond à une étude sur la synthèse de ligands polypyrrole et leur réactivité vis-à-vis de complexe du Sm (11) et du V(III).BREST-BU Droit-Sciences-Sports (290192103) / SudocSudocFranceF

Synthesis and crystal structure of a new salt of the complex anion [(TCNQ)3]2- [Mo2(μ2-S2)2(S 2CNMe2)4] (TCNQ)3

International audienceThe reaction of compounds [Mo2(μ2-S2)2(S 2CNR2)4] (BF4)2 (1) (a R = Me, b R = Et) with 2 equiv. of LiTCNQ in methanol results in the formation of complexes [Mo2(μ2-S2)2(S 2CNR2)4] (TCNQ)2 (2). Further reaction of 2 with TCNQ yields the derivatives [Mo2(μ2-S2)2(S 2CNR2)4] (TCNQ)3 (3). Compounds 2 and 3 were characterized fully by microanalytical, IR and electron spin resonance studies. The single crystal structure of the green product 3a ·2 CH3CN was determined by X-ray diffraction methods. The TCNQ units form centrosymmetrical trimers with a slipped conformation and an interplanar distance of 3.16 Å. In the [(TCNQ)3]2- anion, the bond lengths agree with an almost complete delocalization of the charge between three essentially identical TCNQ units. The trimers stack with an intertrimer distance of 3.56 Å. The centrosymmetrtc dinuclear cation is characterized by an Mo-Mo distance of 2.817(2) Å in agreement with a metal-metal single bond. The molybdenum atoms are bridged by two μ2-S22- ligands which present a quite normal bridge distance S-S of 2.001(2) Å. © 1998 Elsevier Science S.A. All rights reserved

Life and death of an active ethylene polymerization catalyst. Ligand involvement in catalyst activation and deactivation during the polymerization catalyzed by a vanadium di-imine complex. Isolation and characterization of two unprecedented neutral and anionic vanadium (I) alkyls.

International audienceReaction of {2,6-bis[2,6-(i-Pr)2PhNC(Me)]2(C5H3N)}VCl3·1.3(CH2Cl2) (1) with stoichiometric amount of methyl alumoxane (PMAO) in toluene resulted in the methylation of the pyridine ring ortho position affording {2,6-bis[2,6-(i-Pr)2PhNC(Me)]2(2-MeC5H3N)}VCl2·0.5 (toluene) (2). In the process the ligand became an anionic amide, one chlorine atom was eliminated by the metal center, and the vanadium coordination number decreased by one unit. This new trivalent compound is a potent ethylene polymerization precatalyst, and polymers produced by the complex activated with PMAO showed a bimodal character in the GPC. Its bimodality is tentatively explained with the existence of two catalytically active species (mono and dialkylation of the vanadium center). Further attack of a strong alkylating agent such as MeLi occurs at the pyridine ring to either remove the methyl group, or to place an additional methyl group on the ring meta position. Both processes imply two-electron reduction of the metal center and formation of the corresponding V(I) derivatives {2,6-bis[2,6-(i-Pr)2PhNC (Me)]2(C5H3N)}V(CH3)(μ-CH3)Li(Et2O)3 (3) and the ionic [{2,6-bis[2,6-(i-Pr)2PhNC(Me)]2 (2,3-Me2C5H3N)}V(CH3)2][Li(THF)2(TMEDA)2]·0.5(Et2O) (4) which were isolated in crystalline form. Crystal data are as follows. 1:  monoclinic, space group P21/n, a = 18.267(5) Å, b = 16.643(4) Å, c = 38.195(9) Å, β = 96.061(5)°, Z = 12; 2:  monoclinic, space group P21/c, a = 15.741(2) Å, b = 16.565(2) Å, c = 15.849(2) Å, β = 100.316(3)°, Z = 4; 3:  orthorhombic space group Pnma, a = 19.724(6) Å, b = 22.001(7) Å, c = 11.035(3) Å, Z = 4; 4:  monoclinic space group P21/n, a = 11.932(3) Å, b = 25.363(6) Å, c = 18.957(4) Å, β = 96.587(4)°, Z = 4

Solvent-Induced Hysteresis Loop in Anionic Spin Crossover (SCO) Isomorph Complexes

Reaction of Fe(II) with the tris-(pyridin-2-yl)ethoxymethane (py3C-OEt) tripodal ligand in the presence of the pseudohalide ancillary NCSe− (E = S, Se, BH3) ligand leads to the mononuclear complex [Fe(py3C-OEt)2][Fe(py3C-OEt)(NCSe)3]2·2CH3CN (3), which has been characterised as an isomorph of the two previously reported complexes, Fe(py3C-OEt)2][Fe(py3C-OEt)(NCE)3]2·2CH3CN, with E = S (1), BH3 (2). X-ray powder diffraction of the three complexes (1–3), associated with the previously reported single crystal structures of 1–2, revealed a monomeric isomorph structure for 3, formed by the spin crossover (SCO) anionic [Fe(py3C-OEt)(NCSe)3]− complex, associated with the low spin (LS) [Fe(py3C-OEt)2]2+ cationic complex and two solvent acetonitrile molecules. In the [Fe(py3C-OEt)2]2+ complex, the metal ion environment involves two py3C-OEt tridentate ligands, while the [Fe(py3C-OEt)(NCSe)3]− anion displays a hexacoordinated environment involving three N-donor atoms of one py3C-OEt ligand and three nitrogen atoms arising from the three (NCSe)− coligands. The magnetic studies for 3 performed in the temperature range 300-5-400 K, indicated the presence of a two-step SCO transition centred around 170 and 298 K, while when the sample was heated at 400 K until its complete desolvation, the magnetic behaviour of the high temperature transition (T1/2 = 298 K) shifted to a lower temperature until the two-step behaviour merged with a gradual one-step transition at ca. 216 K

Spin Cross-Over (SCO) Anionic Fe(II) Complexes Based on the Tripodal Ligand Tris(2-pyridyl)ethoxymethane

International audienceReactions of Fe(II) with the tripodal chelating ligand 1,1,1-tris(2-pyridyl)ethoxymethane (py 3 C-OEt) and (NCE) − co-ligands (E = S, Se, BH 3) give a series of mononuclear complexes formulated as [Fe(py 3 C-OEt) 2 ][Fe(py 3 C-OEt)(NCE) 3 ] 2 ·2CH 3 CN, with E = S (1) and BH 3 (2). These compounds are the first Fe(II) spin cross-over (SCO) complexes based on the tripodal ligand tris(2-pyridyl)ethoxymethane and on the versatile co-ligands (NCS) − and (NCBH 3) −. The crystal structure reveals discrete monomeric isomorph structures formed by a cationic [Fe(py 3 C-OEt) 2 ] 2+ complex and by two equivalent anionic [Fe(py 3 C-OEt)(NCE) 3 ] − complexes. In the cations the Fe(II) is facially coordinated by two py 3 C-OEt tripodal ligands whereas in the anion the three nitrogen atoms of the tripodal ligand are facially coordinated and the N-donor atoms of the three (NCE) − co-ligands occupy the remaining three positions to complete the distorted octahedral environment of the Fe(II) centre. The magnetic studies show the presence of gradual SCO for both complexes: A one-step transition around 205 K for 1 and a two-step transition for compound 2, centered around 245 K and 380 K

Spin crossover and high-spin state in Fe(II) anionic polymorphs based on tripodal ligands

Two new mononuclear Fe(II) polymorphs, [(C2H5)4N]2[Fe(py3C-OEt)(NCS)3]2 (1) and [(C2H5)4N][Fe(py3C-OEt)(NCS)3] (2) (py3C-OEt = tris(pyridin-2-yl)ethoxymethane), have been synthesized and characterized by single-crystal X-ray diffraction, by magnetic and photomagnetic measurements, and by detailed variable-temperature infrared spectroscopy. The molecular structure, in both complexes, is composed of the same anionic [Fe(py3C-OEt)(NCS)3]− complex (two units for 1 and one unit for 2) generated by coordination to the Fe(II) metal center of one tridentate py3C-OEt tripodal ligand and three terminal κN-SCN coligands. Magnetic studies revealed that polymorph 2 displays a high-spin (HS) state over the entire studied temperature range (300–10 K), while complex 1 exhibits an abrupt and complete spin crossover (SCO) transition at ca. 132.3 K, the structural characterizations of which, performed at 295 and 100 K, show a strong modification, resulting from the thermal evolutions of the Fe–N bond lengths and of the distortion parameters (∑ and Θ) of the FeN6 coordination sphere, in agreement with the presence of HS and low-spin (LS) states at 295 and 100 K, respectively. This thermal transition has been also confirmed by the thermal evolution of the maximum absorbance for ν(NCS) vibrational bands recorded in the temperature range 200–10 K. In 1 the signature of a metastable photoinduced HS state has been observed using photomagnetic and photoinfrared spectroscopy, leading to a similar T(LIESST) relaxation temperature (LIESST = light-induced excited spin-state trapping) of 70 K

Polypyridyl-based Cu(II) coordination polymers: Synthesis, structural and magnetic characterizations

International audienceNew Cu(II) coordination polymeric neutral chains of formula [Cu 2 (1,4-tpbd)Cl 2 L 2)] (1,4-tpbd = N,N,N'N'-tetrakis(2-pyridylmethyl)benzene-1,4-diamine, L = 1,1,3,3-tetracyano-2-ethoxypropenide (tcnoet)-(1) or 1,1,3,3-tetracyano-2-propoxypropenide (tcnopr)-(2)) have been synthesized and characterized by infrared spectroscopy, X-ray diffraction and magnetic measurements. The crystal structure determinations of 1 and 2 reveal in both cases a one-dimensional structure in which the 1,4-tpbd acts as a bis-chelating ligand and the two chloride anions as asymmetrical bridging ligands. The Cu···Cu distances through the bis-chelating 1,4-tpbd ligand (8.194(1) and 8.245(3) Å for 1 and 2 respectively) are in the range of the corresponding distances observed for parent complexes involving similar bridges; and as expected, the Cu···Cu distances through the asymmetrical ( 2-Cl) 2 bridges are significantly shorter (4.021(2) and 4.125(2) Å for 1 and 2, respectively). For both compounds, magnetic measurements exhibit a maximum in the m vs. T plot (at 50 K for 1, and at 48 K for 2), characteristic of antiferromagnetic exchange interactions occurring mainly through the tbpd organic ligand that can be very well reproduced with a S = ½ dimer model with g = 2.114, J =-41.2 cm-1 for 1 and g = 2.105 and J =-39.3 cm-1 for 2.