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]−, 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-μ1,1-azido-bis­[(2-{1-[2-(isopropyl­amino)ethyl­imino]eth­yl}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,N′,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 Cu⋯Cu separation is 3.2365 (3) Å. A pair of intra­molecular N—H⋯O hydrogen bonds helps to establish the mol­ecular 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 complex‐as‐ligand 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 building‐blocks, associated to a control of the metal ions chirality and stoichiometry, allowed us to obtain coordination polymers with predictable dimensionality. For the synthesis of single‐chain 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 molecule‐based 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 post‐synthetic 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]6− (1 a), [CoIIIW12O40]5− (2 a), [SiCoII(H2O)W11O39]6− (3 a), and [SiCoIII(H2O)W11O39]5− (4 a), 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 1 a and 3 a are considered to result from metal-to-polyoxometalate charge transfer (MPCT) from CoII to W, while the longer-lived excited state of 1 a is tentatively assigned to a localized intermediate MPCT state. The excited state formed by the tetrahedral cobalt(II) centered heteropolyanion (1 a) is far longer-lived (τ=420 ps in H2O; τ=1700 ps in MeCN) than that of 3 a (τ=1.3 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 2 a (τ=4.4 ps) and 4 a (τ=6.3 ps) and assigned solely to OCoIII charge transfer. The dramatically extended lifetime for 1 a versus 3 a 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 W atom, a phenomenon not noted previously in POMs

Synthèse de polyoxométallates possédant des propriétés en magnétisme moléculaire ou en conduction ionique (synthèse spécifique pour l'obtention de systèmes 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 synthèse 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 synthèse 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 avère 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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