Interactions faibles et propriétés : vers des matériaux moléculaires multifonctionnels

La nécessité croissante des besoins énergétiques conduit à un essor des recherches sur les nouveaux matériaux en particulier dans le cadre des matériaux multifonctionnels. En effet, la coexistence de plusieurs propriétés et leur contrôle au sein d’un même composé constitue un des challenges de la chimie actuelle. Les interactions non covalentes, dites liaisons faibles (liaisons de coordination, liaisons hydrogène, interactions π, interactions électrostatiques, interactions de Van der Waals, …) ont un rôle majeur lors de la synthèse des matériaux moléculaires pour pallier aux difficultés rencontrées pour faire coexister différentes propriétés au sein d’un même matériau. La conception de nouveaux systèmes fonctionnels repose donc sur plusieurs paramètres clés : i) la nature des ions métalliques spécifiques susceptibles d’apporter les propriétés physiques souhaitées, ii) le ligand qui possède un rôle crucial car il doit organiser les ions métalliques selon la topologie désirée et transmettre efficacement les interactions d’échange entre les centres métalliques de manière contrôlée. L’assemblage préférentiel de chaque brique moléculaire par l’intermédiaire des liaisons faibles peut conduire à des édifices de dimensionnalité supérieure multifonctionnels présentant une coexistence voire une synergie entre les propriétés. Ce phénomène d’auto-assemblage tient compte de plusieurs paramètres, tels que les complémentarités stériques et d’interactions, la complexation et la sélectivité, et peut se dérouler en présence ou non d’un agent template qui favorise la formation d’un composé particulier.  A travers cette communication par affiche, différents aspects seront abordés pour les matériaux paramagnétiques, bistables et pour la séparation moléculaire. Les stratégies de synthèse et caractérisations des composés moléculaires seront détaillées pour chacun de ces systèmes, alliant des propriétés magnétiques,1 optiques,2 électrochimiques3 et de détection d’analytes.

Porous Coordination Polymers based on (bi)pyridinium Ligands

International audienc

Bipyridinium Ligands : Highly Luminescent Bismuth Complexes and Porous Coordination Polymers

National audienc

Porous Coordination Polymers (PCPs) based (bi)pyridinium ligands for gas storage and chemical sensor applications

PCPs (Porous Coordination Polymers) or MOFs (Metal Organic Frameworks) are crystalline materials whose structures consist of metal-based nodes bridged by organic linking groups. They are a well known class of porous materials which can have applications in gas storage (H2, CH4, CO2…), heterogeneous catalysis and chemical sensors.1 Up to now the main strategy to increase the absorption properties has been to introduce coordinatively unsaturated metal centres. In contrast, the incorporation of cationic organic ligands is much rarer despite a certain potential as shown by some reports.2 Our original approach consists of mixing electro-active viologen derivatives to a useful coordination function like carboxylate, which is widely used in such materials,3 to synthesize new PCPs for gas storage and molecular recognition. Those ligands are based on N-substituted-4,4’-bipyridinium monocation and N,N’-disubstituted-4,4’-bipyridinium dication carrying one or several carboxylate groups. Our synthetic strategy and new results will be described in this poster, taking the [Cd4Cl6L3](CdCl4) compound as example, with L = 4,4’-bipy-(C6H4COO)2. In addition to provide a highly stable structure upon temperature and moisture, this PCP exhibits accessible channels with a large zwitterionic surface area which allow reversible sorption properties of gas and small molecules. The obvious color shift in presence of ammonia vapors offers a high potential for chemical sensors and optical applications

Porous coordination polymers (PCPs) based on redox ligands

PCPs (Porous Coordination Polymers) or MOFs (Metal Organic Frameworks) are crystalline materials whose structures consist of metal-based nodes bridged by organic linking groups. They are a well known class of porous materials which can have applications in gas storage (H2, CH4, CO2,…), heterogeneous catalysis and chemical sensors.1 Up to now the main strategy to increase the absorption properties has been to introduce coordinatively unsaturated metal centres. In contrast, the incorporation of cationic organic ligands is much rarer despite a certain potential as shown by some reports.2 Our original approach consists of mixing electro-active viologen derivatives to a useful coordination function like carboxylate, which is widely used in such materials,3 to synthesize new PCPs for gas storage and molecular recognition. Those ligands are based on N-substituted-4,4’-bipyridinium monocation and N,N’-disubstituted-4,4’-bipyridinium dication carrying one or several carboxylate groups. Our synthetic strategy and new results will be described in this poster, taking the [Cd4Cl6L3](CdCl4) compound as example, with L = 4,4’-bipy-(C6H4COO)2. In addition to provide a highly stable structure upon temperature and moisture, this PCP exhibits accessible channels with a large zwitterionic surface area which allow reversible sorption properties of gas and small molecules. The obvious color shift in presence of ammonia vapors offers a high potential for chemical sensors and optical applications

Hightly luminescent bismuth complexes: Aggregation induced phosphorescent and polymorphism-dependent emission

The search of simple ligand based metal-organic materials exhibiting Aggregation Induced Emission (AIE) or phosphorescence (AIP) effects and strong luminescence in the solid state is of high interest. Recently, we demonstrated that bipyridine derivatives consisting of one pyridinium cycle (acting as electron acceptor) and one pyridyl (N-methyl-4,4’-bipyridinium)1 or one pyridyl-N-oxide part (N-R-N’-oxide-4,4’-bipyridinium, R= methyl, H)2 were able to bind bismuth ions, giving complexes with photochromic and average luminescent properties. In this communication, we will report the results of our investigations in the Bi(III)/L systems, where L= bipyridinium based ligands of N-oxide type (N-oxide-4,4’(2,2’)-bipirydinium (bp4mo and bp2mo) and N,N’-dioxide-4,4’-bipyridinium (bp4do)). More recently, we synthesized a 2D CP in which the bp4mo ligand acts as a bridge between two Pb2+ ions,3 but no bismuth complexes or CP based on bp4mo (bp2mo) or bp4do have been mentioned up to now. The impressive solid state Quantum Yields (QY) -up to 85% for (TBA)[BiBr4(bp4mo)]- are obtained for several materials while others are non-luminescent. The three polymorphs α- (QY= 20%), β- and γ-[BiBr3(bp2mo)2] (QY= 0) will be given as examples. These structure-property relationships are assigned to environment rigidity or interactions between ligands in the solid state. A complete study of the luminescent properties (100-300 K range, lifetime, solid state and solution measurements) combined with DFT calculations and the analysis of the crystal structures shows that the lighting phenomenon is of AIP type which is induced by complex (Figure 1)

Bipyridinium-carboxylate ligands towards photo- and thermo-chromic porous coordination polymers

Porous coordination polymers (PCP) or metal−organic frameworks (MOF) have focused attention going from synthetic strategy to applications in heterogeneous catalysis, molecular recognition and gas storage. Up to now the main strategy to increase the sorption abilities has been to introduce coordinatively unsaturated metal centres. Only few examples have been reported based on the assembly of cationic bridging ligands. Our original approach consists in combining the coordination versatility of carboxylate functions, commonly used in this field, to electro-active viologen derivatives in order to synthesize new porous coordination polymers for gas storage and redox mediators with optical and magnetic properties. The designed ligands are based on N-substituted-4,4’-bipyridinium monocation and N,N’-disubstituted-4,4’-bipyridinium dication bearing one or several carboxylate groups. In addition to act as charge-separated organic linkers, these pyridinium-carboxylate ligands will i) afford a cationic surface to enhance the interactions with guests and ii) exhibit reversible redox states involving monocationic radicals with good stability and large absorptions coefficients in the visible range. Some of our new results will be presented here and a particular attention will be dedicated to compounds that also exhibit thermo-, solvato- and photo-chromic behavior.

Bipyridinium-carboxylate ligands towards functional porous coordination polymers

Porous coordination polymers or metal−organic frameworks have focused attention going from synthetic strategy to applications in heterogeneous catalysis, molecular recognition and gas storage. Our approach consists in combining the coordination versatility of carboxylate functions to electro-active viologen derivatives (N,N’-disubstituted 4,4’-bipyridinium salts) with general formula (OOCC6H4)2(4,4’-bipy) in order to synthesized new porous coordination polymers for gas storage and redox mediators with optical and magnetic properties. In addition to act as charge-separated organic linkers, these pyridinium-carboxylate ligands will i) afford a cationic surface to enhance the interactions with guests and ii) exhibit reversible redox states involving monocationic radicals with good stability and large absorptions coefficients in the visible range

Supramolecular coordination chemistry of aromatic polyoxalamide ligands: A metallosupramolecular approach toward functional magnetic materials

The impressive potential of the metallosupramolecular approach in designing new functional magnetic materials constitutes a great scientific challenge for the chemical research community that requires an interdisciplinary collaboration. New fundamental concepts and future applications in nanoscience and nanotechnology will emerge from the study of magnetism as a supramolecular function in metallosupramolecular chemistry. Our recent work on the rich supramolecular coordination chemistry of a novel family of aromatic polyoxalamide (APOXA) ligands with first-row transition metal ions has allowed us to move one step further in the rational design of metallosupramolecular assemblies of increasing structural and magnetic complexity. Thus, we have taken advantage of the new developments of metallosupramolecular chemistry and, in particular, the molecular-programmed self-assembly methods that exploit the coordination preferences of paramagnetic metal ions and suitable designed polytopic ligands. The resulting self-assembled di- and trinuclear metallacyclic complexes with APOXA ligands, either metallacyclophanes or metallacryptands, are indeed ideal model systems for the study of the electron exchange mechanism between paramagnetic metal centers through extended π-conjugated aromatic bridges. So, the influence of different factors such as the topology and conformation of the bridging ligand or the electronic configuration and magnetic anisotropy of the metal ion have been investigated in a systematic way. These oligonuclear metallacyclic complexes can be important in the development of a new class of molecular magnetic devices, such as molecular magnetic wires (MMWs) and switches (MMSs), which are major goals in the field of molecular electronics and spintronics. On the other hand, because of their metal binding capacity through the outer carbonyl-oxygen atoms of the oxamato groups, they can further be used as ligands, referred to as metal–organic ligands (MOLs), toward either coordinatively unsaturated metal complexes or fully solvated metal ions. This well-known “complex-as-ligand” approach affords a wide variety of high-nuclearity metal–organic clusters (MOCs) and high-dimensionality metal–organic polymers (MOPs). The judicious choice of the oligonuclear MOL, ranging from mono- to di- and trinuclear species, has allowed us to control the overall structure and magnetic properties of the final oxamato-bridged multidimensional (nD, n = 0–3) MOCs and MOPs. The intercrossing between short- (nanoscopic) and long-range (macroscopic) magnetic behavior has been investigated in this unique family of oxamato-bridged metallosupramolecular magnetic materials expanding the examples of low-dimensional, single-molecule (SMMs) and single-chain (SCMs) magnets and high-dimensional, open-framework magnets (OFMs), which are brand-new targets in the field of molecular magnetism and materials science

Recommended maximum holding times for prevention of discomfort of static standing postures

The aim of the present study was threefold; (1) to analyze the influence of posture on the maximum holding time (MHT), (2) to study the possibility of classifying postures on the basis of MHT, and (3) to develop ergonomic recommendations for the MHT of categories of postures. For these purposes data concerning the MHT of 19 symmetric standing postures from 7 experimental studies from the literature were analyzed. All postures were defined by the position of the hands with respect to the feet. For each posture the mean MHT over all available data was calculated. The results show that for the 19 postures this mean MHT ranges from 2 to 35 minutes. For a given posture the variation in MHT between different studies is large. It seems that in particular the type of task (boring versus interesting) performed while maintaining the posture has a great influence on the MHT. On the basis of the mean MHT postures were classified into three classes. Comfortable postures are defined as postures that have a MHT of more than 10 minutes and are recommended not to be maintained more than 2 minutes. Moderate postures have a MHT of 5-10 minutes and are recommended to be maintained for less than 1 minute. Uncomfortable postures, having a MHT up to 5 minutes, are not acceptable. It is estimated that with theses recommendations a discomfort of more than 2 (weak discomfort) on the Borg 10-point rating scale (up to maximum discomfort) is prevented for at least 50% of the population, and a discomfort of more than 5 (strong discomfort) is prevented for at least 95% of the population. The recommended holding time valid for each class corresponds with the lowest recommended holding time of that class. Therefore the recommendations are safe for all postures. Our classification of postures corresponds well with classifications based on biomechanical and anthropometric data and is more strict than the OWAS-classification. The maximum holding time (MHT) was categorically studied to analyze its influence on postures, classify postures based on MHT and to develop ergonomic recommendations for MHT. Postures were based on the mean MHT. Comfortable postures have more than 10 minutes MHT and recommended not to be maintained for more than 2 minutes. Moderate postures have 5-10 minutes MHT and were recommended to be maintained for less than 1 minute. Uncomfortable postures with a 5-minute MHT were not accepted. These recommendations have prevented discomfort of more than 2 (weak discomfort) on the Borg 10-point rating scale for at least 50% of the population, and a discomfort of more than 5 (strong discomfort) was prevented for at least 95% of the population