Francis Sécheresse

Bio: Francis Sécheresse is an academic researcher from Centre national de la recherche scientifique. The author has contributed to research in topics: Polyoxometalate & Crystal structure. The author has an hindex of 37, co-authored 128 publications receiving 3917 citations. Previous affiliations of Francis Sécheresse include Rhodia & Pierre-and-Marie-Curie University.

Iron polyoxometalate single-molecule magnets.

Abstract: Wolframate mit Eisenfullung: Zwei neue Polyoxowolframate mit paramagnetischen Eisen(III)-Ionen (siehe Struktur, W blau, Fe gelb, O rot) haben Grundzustande mit S=15/2 und S=5. Beide Verbindungen sind Einzelmolekulmagnete, und die Hexaeisen-Spezies zeigt eine starke Hysterese (siehe Diagramm) sowie Quantentunneleffekte bei tiefen Temperaturen. Elektrochemischen Untersuchungen zufolge sollten die Spezies in Losung uber einen grosen pH-Bereich bestandig sein.

A Nonanuclear Copper(II) Polyoxometalate Assembled Around a μ-1,1,1,3,3,3-Azido Ligand and Its Parent Tetranuclear Complex

Abstract: Reaction of Cu I I , [γ-SiW 1 0 O 3 6 ] 8 - , and N 3 - affords three azido polyoxotungstate complexes. Two of them have been characterized by single-crystal X-ray diffraction. Complex KNaCs 1 0 [{γ-SiW 1 0 O 3 6 Cu 2 (H 2 O)-(N 3 ) 2 } 2 ].26H 2 O (1) is obtained as crystals in few hours after addition of CsCl. This linear tetranuclear Cu I I complex consists in two [γ-SiW 1 0 O 3 6 Cu 2 -(H 2 O)(N 3 ) 2 ] 6 - units connected through two W=O bridges. When the filtrate is left to stand for one night, a new complex is obtained. From both elemental analysis and IR spectroscopy, it has been postulated that this compound could be formulated K 1 . 5 Cs 5 . . 5 [SiW 1 0 O 3 7 -Cu 2 (H 2 O) 2 (N 3 )].14H 2 O (1a), showing the loss of one azido ligand per polyoxometalate unit. Finally, when no cesium salt is added to the reaction medium, the nonanuclear complex K 1 2 Na 7 [{SiW 8 O 3 1 Cu 3 (OH)(H 2 O) 2 (N 3 )} 3 -(N 3 )].24H 2 O (2) is obtained after three days. Compound 2 crystallizes in the R3c space group and consists in three {Cu 2 } units related by a C 3 axis passing through the exceptional μ-1,1,1,3,3,3-azido bridging ligand. Each trinuclear Cu" unit is embedded in the [γ-SiW 8 O 3 1 ] 1 0 - ligand, an unprecedented tetravacant polyoxometalate, showing that partial decomposition of the [γ-SiW 1 0 O 3 6 ] 8 - precursor occurs with time in such experimental conditions. Magnetically, complex 1 behaves as two isolated {Cu 2 (μ 1 , 1 -N 3 ) 2 } pairs in which the metal centers are strongly ferromagnetically coupled (J=+224 cm - 1 , g= 2.20), the coupling through the W=O bridges being negligible. The magnetic behavior of complex 2 has also been studied. Relatively weak ferromagnetic couplings (J 1 = +1.0 cm - 1 , J 2 = +20.0 cm - 1 , g=2.17) have been found inside the {Cu 3 } units, while the intertrimeric magnetic interactions occurring through the hexadentate azido ligand have been found to be antiferromagnetic (J 3 = -5.4 cm - 1 ) and ferromagnetic (J 4 =+1.3 cm - 1 ) with respect to the end-to-end and end-on azido-bridged Cu I I pairs, respectively.

Molecular and multidimensional polyoxotungstates functionalized by {Cu(bpy)}2+ groups

Abstract: Five new materials built from polyoxotungstates and Cu(II) ions as linkers have been synthesized by hydrothermal reactions from a mixture of sodium tungstate, copper chloride and bipyridine. The value of the initial pH, the nature of the heteroelement (P or Si) and of the ligand (2,2′- and/or 4,4′-bipyridine) permit the control of the nature of the polyoxotungstate clusters and their connectivity via the copper ions, and hence the dimensionality of the framework. A single phase has been obtained with silicon as heteroelement at an initial pH of 5, namely the 2D material [SiW12O40][Cu(2,2′-bpy)2]2·10H2O (1) with saturated Keggin polyoxotungstates linked by {Cu(2,2′-bpy)2}2+ groups. With phosphorous as heteroelement and at the same initial pH, three different structures have been isolated according to the nature of the ligand. Indeed, the two 1D materials [{Cu5(2,2′-bpy)5(H2O)(HPO4)(PO4)}PW11CuO39]·6H2O (2) with 2,2′-bpy and [4,4′-Hbpy][{Cu2(2,2′-bpy)2(4,4′-bpy)2.5}PW11CuO39]·16H2O (3) with a mixture of 2,2′- and 4,4′-bpy have been characterized, and a coordination polymer with polyoxometalate guests Na3[4,4′-Hbpy]{Cu4(4,4′-bpy)8(H2O)8}[PW11CuO39(H2O)][PW10Cu2O38(H2O)2]·38H2O (4) with 4,4′-bpy has been obtained. Finally, in basic medium (pH = 10) the unprecedented molecular cluster Na2[{Cu8(2,2′-bpy)8}(PW8O31)2]·15H2O (5) has been evidenced. Magnetic studies of compound 2 revealed that the predominant interactions involve only 4 paramagnetic centers, which are interacting within pairs, among the 6 Cu(II) centers. The χMT = f(T) curve can be fitted using the dinuclear expression appropriate to the HDVV isotropic exchange Hamiltonian H = −JS1×S2, with S1 = S2 = ½ and J = −105.4 cm−1, showing strong antiferromagnetic interactions within the two Cu(II) pairs.

Hybrid porous solids: past, present, future

Abstract: This critical review will be of interest to the experts in porous solids (including catalysis), but also solid state chemists and physicists. It presents the state-of-the-art on hybrid porous solids, their advantages, their new routes of synthesis, the structural concepts useful for their ‘design’, aiming at reaching very large pores. Their dynamic properties and the possibility of predicting their structure are described. The large tunability of the pore size leads to unprecedented properties and applications. They concern adsorption of species, storage and delivery and the physical properties of the dense phases. (323 references)

Polyoxometalate clusters, nanostructures and materials: From self assembly to designer materials and devices

Abstract: Polyoxometalates represent a diverse range of molecular clusters with an almost unmatched range of physical properties and the ability to form structures that can bridge several length scales. The new building block principles that have been discovered are beginning to allow the design of complex clusters with desired properties and structures and several structural types and novel physical properties are examined. In this critical review the synthetic and design approaches to the many polyoxometalate cluster types are presented encompassing all the sub-types of polyoxometalates including, isopolyoxometalates, heteropolyoxometalates, and reduced molybdenum blue systems. As well as the fundamental structure and bonding aspects, the final section is devoted to discussing these clusters in the context of contemporary and emerging interdisciplinary interests from areas as diverse as anti-viral agents, biological ion transport models, and materials science.

Polyoxometalates: Building Blocks for Functional Nanoscale Systems

Abstract: Polyoxometalates (POMs) are a subset of metal oxides that represent a diverse range of molecular clusters with an almost unmatched range of physical properties and the ability to form dynamic structures that can range in size from the nano- to the micrometer scale Herein we present the very latest developments from synthesis to structure and function of POMs We discuss the possibilities of creating highly sophisticated functional hierarchical systems with multiple, interdependent, functionalities along with a critical analysis that allows the non-specialist to learn the salient features We propose and present a "periodic table of polyoxometalate building blocks" We also highlight some of the current issues and challenges that need to be addressed to work towards the design of functional systems based upon POM building blocks and look ahead to possible emerging application areas

Metal–organic framework composites

Abstract: Metal–organic frameworks (MOFs), also known as porous coordination polymers (PCPs), synthesized by assembling metal ions with organic ligands have recently emerged as a new class of crystalline porous materials. The amenability to design as well as fine-tunable and uniform pore structures makes them promising materials for a variety of applications. Controllable integration of MOFs and functional materials is leading to the creation of new multifunctional composites/hybrids, which exhibit new properties that are superior to those of the individual components through the collective behavior of the functional units. This is a rapidly developing interdisciplinary research area. This review provides an overview of the significant advances in the development of diverse MOF composites reported till now with special emphases on the synergistic effects and applications of the composites. The most widely used and successful strategies for composite synthesis are also presented.