162 research outputs found
Solvothermal Synthesis of Oxamate-Based Helicate: Temperature Dependence of the Hydrogen Bond Structuring in the Solid
International audienceSolvothermal synthesis has been successfully tested as a new synthetic method towards the formation of oxamate-based coordination compounds. The reaction of 1,3-benzenedioxamic acid (H4mpba) with divalent metal ions has afforded the dinuclear compounds TBA2[Co2(H2mpba)3].2DMF.5H2O (1a), (HNEt3)2[Co2(H2mpba)3].6DMF.5H2O (1b), TBA2[Ni2(H2mpba)3].2DMF.2.5H2O (2) and (HNEt3)2[Co2(H2mpba)3] (3). Although the 3:2 ligand to metal ratio is known for the (mpba) 4-ligand under bench conditions these complexes are the first examples of oxamate-based helicate. Furthermore, crystalographic studies show a temperature-dependent hydrogen bond structuring that leads to racemic or chiral hexagonal 3D networks
A cyanide and hydroxo-bridged nanocage: a new generation of coordination clusters
International audienceCombining serendipitously-formed hydroxo-clusters, [CoII3(OH)(piv)4(L)]+ (where L = MeCN or Hpiv), with assembling cyanide building block, [FeIII(Tp)(CN)3]â, has led to an unprecedented architecture where polymetallic cobalt clusters and blocked tris-cyanide iron complexes define the apexes of a unique magnetic cubic nanocage
Di-ÎŒ1,1-azido-bisÂ[(2-{1-[2-(isopropylÂamino)ethylÂimino]ethÂyl}phenolato)copper(II)]
In the centrosymmetric binuclear title complex, [Cu2(C13H19N2O)2(N3)2], the CuII atom adopts an elongated CuON4 square-based pyramidal coordination geometry, arising from the N,NâČ,O-tridentate ligand and two bridging end-on azide anions. The O atom is in the basal plane, one of the azide N atoms is in the apical site and the CuâŻCu separation is 3.2365â
(3)â
Ă
. A pair of intraÂmolecular NâHâŻO hydrogen bonds helps to establish the molÂecular conformation
Combining Cyanometalates and Coordination Clusters: An Alternative Synthetic Route toward Original Molecular Materials
International audienceWith the discovery of molecules or molecule-based compounds that can display blocked magnetization, magnetic ordering or switchable magnetic bistability, the research efforts devoted to molecular magnetic materials have considerably increased over the past two decades, fully exploiting the advantages of the bottom-up approach. 1-4 This research field focuses on promising properties for potential technological applications such as information storage, quantum computing and spintronics at the molecular scale, but it also provides fundamental insights into original quantum phenomena. 5,6 Coordination chemists have developed efficient synthetic tools for the preparation of interesting magnetic systems
Design of Magnetic Coordination Polymers Built from Polyoxalamide Ligands: A Thirty Year Story
International audienceThe aim of this review is to pay tribute to the legacy of O. Kahn. Kahn's credo was to synthesize magnetic compounds with predictable structure and magnetic properties. This is illustrated herein with results obtained by Kahn's group during his Orsay period thirty years ago, but also on the basis of our recent results on the synthesis of coordination polymers with oxamate ligands. The first part of this review is devoted to a short description of the necessary knowledge in physics and theoretical chemistry that Kahn and his group have used to select oxamate ligands, the complexâasâligand strategy and the synthesis of heterobimetallic systems. Then, we describe the strategies we have later used to obtain the desired target compounds. The use of complexes as buildingâblocks, associated to a control of the metal ions chirality and stoichiometry, allowed us to obtain coordination polymers with predictable dimensionality. For the synthesis of singleâchain magnets (SCMs) we show that the ligand chemical flexibility makes the isolation of the chains in the solid and the occurence of slow magnetic relaxation possible. For 1D and 2D moleculeâbased magnets (MBMs), the magnetic ordering strongly depends on the interchain or interplane interactions, which are difficult to control. Again the flexibility of the oxamate ligands allowed their strengthening in the solid sate, yielding MBMs with critical temperatures up to 30 K. We will also present our results on 3D coordination polymers, particularly on the porous magnets displaying large octagonal channels. This family of porous MBMs possess outstanding chemical properties, such as postâsynthetic transformation in the solid state. Finally, we will also show that oxamate ligands allows the design of multifunctional materials, as in the case of the first chiral SCM. Overall, the results presented in this review show the impressive potential the oxamate ligands have for the design of coordination polymers
Extending Metal-to-Polyoxometalate Charge Transfer Lifetimes: The Effect of Heterometal Location
In an effort to develop robust molecular sensitizers for solar fuel production, the electronic structure and photodynamics of transition-metal-substituted polyoxometalates (POMs), a novel class of compound in this context, was examined. Experimental and computational techniques including femtosecond (fs) transient absorption spectroscopy have been used to study the cobalt-containing Keggin POMs, [CoIIW12O40]6â (1âa), [CoIIIW12O40]5â (2âa), [SiCoII(H2O)W11O39]6â (3âa), and [SiCoIII(H2O)W11O39]5â (4âa), finding the longest lived charge transfer excited state so far observed in a POM and elucidating the electronic structures and excited-state dynamics of these compounds at an unprecedented level. All species exhibit a bi-exponential decay in which early dynamic processes with time constants in the fs domain yield longer lived excited states which decay with time constants in the ps to ns domain. The initially formed states of 1âa and 3âa are considered to result from metal-to-polyoxometalate charge transfer (MPCT) from CoII to W, while the longer-lived excited state of 1âa is tentatively assigned to a localized intermediate MPCT state. The excited state formed by the tetrahedral cobalt(II) centered heteropolyanion (1âa) is far longer-lived (Ï=420â
ps in H2O; Ï=1700â
ps in MeCN) than that of 3âa (Ï=1.3â
ps), in which the single CoII atom is located in a pseudo-octahedral addendum site. Short-lived states are observed for the two CoIII-containing heteropolyanions 2âa (Ï=4.4â
ps) and 4âa (Ï=6.3â
ps) and assigned solely to OCoIII charge transfer. The dramatically extended lifetime for 1âa versus 3âa is ascribed to a structural change permitted by the coordinatively flexible central site, weak orbital overlap of the central Co with the polytungstate framework, and putative transient valence trapping of the excited electron on a single Wâ
atom, a phenomenon not noted previously in POMs
SynthÚse de polyoxométallates possédant des propriétés en magnétisme moléculaire ou en conduction ionique (synthÚse spécifique pour l'obtention de systÚmes étendus)
L utilisation de l anion de Keggin trivacant [SiW9O34]10- a permis la complexation de clusters originaux tetra et octanucléaire de cobalt(II) sur lesquels sont greffés des ligands acétate, azoture ou carbonate. L emploi de l anion divacant [SiW10O36]8- a conduit à l obtention de composés sandwich incluant des clusters trinucléaires de cobalt(II) dont les propriétés magnétiques ont été étudiées.Par voie hydrothermale, plus de dix composés polyoxotungstiques hybrides et multidimensionnels ont été isolés. Ces derniers sont obtenus à partir de [WO4]2- en présence de cuivre(II) ou de vanadium(IV) et d amines linéaire ou cyclique. L introduction de phosphate ou de silicate ainsi que la variation du pH de synthÚse ont conduit à une grande diversité des phases caractérisées, comme par exemple des clusters phosphométalliques à base d ions cuivre(II) ou vanadium (IV/V) qui ont été étudiés en magnetisme ou encore une phase tridimensionnelle à base d isopolyoxotungstates.Enfin, l étude de la réactivité du cation [MoV2O4(H2O)6]2+ en présence du ligand [O3PCH2PO3]4- et de différents ligands inorganiques polydentes a permis la synthÚse de roues hexa et octanucléaires obtenues sous la forme de sels d ammonium, de sodium ou de lithium. Cette étude a révélé l influence des contre-cations sur la topologie des polyoxomolybdates isolés et les différents sels alcalins purs ou mixtes ont été étudiés en solution par RMN du 31P et sous forme solide en conduction ionique. Il s avÚre que les sels mixtes se comportent comme de bons conducteurs protoniquesThe reactivity of lacunary silicotungstate [SiW9O34]10- together with cobalt(II) has allowed the synthesis of unprecedented tetra and octanuclear cobalt-based clusters bearing acetate, azide or carbonate ligands. The divacant anion [SiW10O36]8- has lead to sandwich type polyoxometalates incorporating trinuclear cobalt(II) clusters. Magnetic measurements on these clusters reveal a ferromagnetic behaviour.More than ten multidimensional hybrid polyoxotungstates have been successfully synthesized by hydrothermal reaction starting from [WO4]2-, copper(II) or vanadium(IV) and polyamines. Addition of phosphate or silicate and tuning of the medium pH have yielded various structures like copper(II) or vanadium(IV/V)-based phosphometallic clusters which have been studied in magnetism. Also, this method has allowed the characterization of the first three-dimensional hybrid isopolyoxotungstate.Finally, the [MoV2O4(H2O)6]2+ cation reacts with [O3PCH2PO3]4- ligand and some inorganic templating ligands to yield hexa and octanuclear anionic wheels isolated as ammonium, sodium or lithium salts. This study has shown that the anionic structure is strictly correlated to the nature of the counter-cation. The different salts have been studied in solution by 31P NMR and in the solid state by ionic conduction measurements.VERSAILLES-BU Sciences et IUT (786462101) / SudocSudocFranceF
Design of silica-coated microcapsules for bioencapsulation.
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Hydrothermal syntheses and characterizations of 0D to 3D polyoxotungstates linked by copper ions
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