The functional and mechanical properties of a material are often determined by the defects in them. A thorough understanding of the relationship between the defects and the properties allows for tailoring a material’s properties into the desired combinations. Amongst the different classes of defects, experimental identification of point defects is typically difficult and indirect, usually requiring an ingenious combination of different techniques. In this context, first-principles calculations, complemented with experiments, offer insights into the formation of defects and their role in properties. This was demonstrated in this thesis through investigations on the effect of calcium vacancies on structure, vibrational and elastic properties hydroxyapatite (HAp), and oxygen vacancies on elastic properties of zinc oxide (ZnO) using first-principles calculations based on density functional theory (DFT). Our results confirm a considerable reduction in the elastic constants of HAp—the inorganic constituent of bone—due to Ca-deficiency, which was experimentally reported earlier. Elastic anisotropic behavior of stoichiometric and Ca-deficient HAp is analyzed, which will be useful in understanding the effects of crystal orientation in designing synthetic bone. Local structural stability of HAp and Ca-deficient HAp structures is assessed with full phonon dispersion studies and the specific signatures in the computed vibrational spectra for Ca deficiency in HAp can be utilized in experimental characterization of different types of defected HAp. In ZnO, formation energies of oxygen vacancies in different types of oxygen deficient structures are analyzed to ascertain their stability. Our results show considerable degradation of some of the elastic moduli due to the presence of such vacancies. Further, the charge state of the defect structure is found to influence the shear elastic constants. Evaluation of elastic anisotropy of stoichiometric and oxygen deficient ZnO indicates the significant anisotropy in elastic properties and stiff c-axis orientation. The second part of the thesis deals with developing some understanding of the pressure-induced phase transformations (PIPT) in an inorganic material, titanium nitride (TiN), and in a metal-organic framework (MOF), erbium formate crystal. PIPT, which is a common phenomenon in many materials, is of great interest in materials science as the properties of the transformation product can diverge significantly from those of the parent phase. Hence, it is important to understand the pressure induced changes so to improve the component reliability and to enhance service life of materials used in high pressure applications. TiN undergoes PIPT from NaCl to CsCl structure. On the basis of our DFT calculations, we propose a new transformation path, which shows that the stress required for this transformation is substantially lower when it is deviatoric in nature than that under hydrostatic pressure. Local stability of the structure is assessed with phonon dispersion determined at different pressures, and we find that CsCl structure of TiN is expected to distort after the transformation. Further, we provide a quantitative comparison of electronic structure of TiN in NaCl structure with that of high pressure phase with implication to electrical conduction properties. Next, we investigate the PIPT associated with bond rearrangement in erbium formate framework. Phase transition pressure is estimated and the corresponding changes in bonding characteristics are analyzed. Estimated lattice constants for both the phases agree well with the earlier experimental results. While the transformation pressure of the framework is overestimated with respect to experiment, our calculations confirm PIPT, and thus provide a theoretical evidence for the experimental finding.

No description available.

Biological systems construct varieties of self-assembled architectures with incredible elegance and precession utilizing proteins as subunits to accomplish widespread functions. Inspired by natural systems, construction of artificial model systems with such sophistication and delicacy has become an intriguing field of research over the last two decades using so-called self-assembly process. Judiciously selected complementary building units encoded with specific chemical and structural information can be self-assembled into pre-programmed abiological architectures in a manner similar to biological self-assembly. In this regard, kinetically labile metal-ligand coordination has become an efficient and powerful protocol for the construction of highly intricate structures with specific topology and functionality due to its simple design principle, high bond enthalpy, and predictable directionality. Two-component self-assembly is very widely used methodology and easy to monitor. Recently, multi-component self-assembly has come up as an alternative and effective pathway to achieve complex architectures connecting more than two components in a single step. However, formation of selective single product from multicomponents is entropically unfavorable. Only a very few 3D architectures have been known, that are obtained from a mixture of ditopic and tri- or tetratopic donors with metal acceptors with or without employing templates. Development of template-free multicomponent architectures is still in its infancy. Strong tendency of Pd(II)/Pt(II) to attain square-planar geometry around the metal center and kinetically labile nature of Pd(II)/Pd(II)-N(pyridine) bonds made them chemists’ favourite to engineer desired supramolecular coordination architectures with structural resemblance to Platonic or Archimedean solids by employing symmetrical pyridyl donors due to their predictable directionality. In case of poly-imidazole donors, free rotation of C-N bond connecting imidazole and phenyl ring allows various dispositions of the donating nitrogen with respect to the aromatic backbone, and therefore, the structural topology of the architectures, made of poly-imidazole ligands becomes much more interesting as compared to symmetrical Platonic or Archimedean solids. The physico-chemical properties of self-assembled coordination cages depend on the structures of the complexes. Presence of large internal cavity surrounded by aromatic core, provides an excellent environment for the encapsulation of varieties of guest molecule or as nano-reactors for different organic transformations. Structural investigation in terms of packing interactions, solvent molecules, intermolecular channels can sometimes determine the property of such self-assembled materials as well. Presence of acidic water as well as H-bonded 3D-networks of water molecules in molecular pockets make them potential material for proton conduction. In addition, metal-ligand coordination offers opportunity to introduce new functionality through pre-synthetic modification of the building constituents to influence the property of the supramolecular systems. Incorporation of unsaturated ethynyl functionality attached to the heavy transition metal is expected to exhibit efficient luminescence due to the facile metal to ligand charge transfer (MLCT). Hence, the final assemblies can be employed as chemosensors for electron-deficient nitroaromatics, which are the chemical signature of many of the commercially available explosives. The present investigation is focused on design and construction of discrete, nanoscopic coordination cages with unusual structural topology employing mainly imidazole-based donors with Pd(II)/Pt(II) acceptors and their applications in catalysis, chemosensing, and proton conduction. CHAPTER 1 of the thesis provides a general introduction to self-assembly focusing on the importance and advantages of metal-ligand directional bonding approach towards the construction of supramolecular architectures with various structural topologies. This chapter also includes a brief review on the applications of such coordination cages in various fields especially as ‘molecular flask’ for the observation of unique chemical phenomena and unusual reactions. Part A of CHAPTER 2 describes the synthesis of a new hollow Pd6 water soluble cage [{(tmen)Pd}6(timb)4](NO3)12 (1) via two-component self-assembly of a triimidazole donor and 90° Pd(II) acceptor [tmen = N,N,N’,N’-tetramethylethylenediamine, timb = 1,3,5-tris(1-imidazolyl)benzene]. The assembly was successfully crystallized with a hydrophilic dianionic benzoquinone derivative (formed in situ by the decomposition of DDQ) as [{(tmen)Pd}6(timb)4](NO3)10()2(H2O)18 (3), and a hydrophobic sterically demanding aromatic aldehyde as [{(tmen)Pd}6(timb)4](NO3)12{()4a}2(H2O)27 (5a) [where 2H2 = 2,3-dichloro-5,6-dihydroxycyclohexa-2,5diene-1,4-dione, 4a = 1-pyrenecarboxaldehyde,  = exohedral and  = endohedral] to confirm the hydrophobic nature of the cavity. Experiments were carried out to show that the hydrophobic confined nanospace of the cage (1) catalyses the Knoevenagel condensation of a series of different aromatic monoaldehydes with active methylene compounds in ‘green’ aqueous medium. The Knoevenagel condensation reaction is basically a dehydration reaction because water is a by-product. So the presence of water should, in principle, promote the backward reaction as per Le Chatelier’s principle. In general, these reactions with organic substrates are not performed in water. However, difficulty has been overcome using hydrophobic cavity of the cage. It has also been established that the cavity of the cage also enhances the rate of Diels-Alder reaction of 9-hydroxymethylanthracene with N-phenylmaleimide/N-cyclohexylmaleimide. Figure 1. Catalytic Knoevenagel condensation and Diels-Alder reaction using hydrophobic cavity of the cage (1) in aqueous medium. Part B of CHAPTER 2 reports unique three-component self-assembly incorporating both tri- and tetra-topic donors. Until now, a very few 3D-architectures have been known that are obtained from self-assembly of ditopic and tri- or tetratopic donors with metal acceptors. Scheme 1. Three-component self-assembly of a Pd7 cage (1) from cis-blocked Pd(II) 90° acceptor (M), tri-imidazole (timb) and tetra-imidazole (tim) donors. Self-assembled multicomponent discrete architecture composed of both tri- and tetra-topic donors is yet to be reported due to difficulty in prediction of the final structure from the mixture of ligands having multiple donor sites. The first example of self-sorted Pd7 molecular boat [{(tmen)Pd}7(timb)2(tim)2](NO3)14(H2O)20 (1) [tmen = N,N,N’,N’-tetramethylethylenediamine, timb = 1,3,5-tris(1-imidazolyl)-benzene, tim = 1,2,4,5-tetrakis(1-imidazolyl)benzene] was synthesized via three-component self-assembly of cis-(tmen)Pd(NO3)2, tetra- (tim) and tri-topic donors (timb) in a 7:2:2 ratio. The cavity of this cage was also utilized as a nanoreactor for catalytic Knoevenagel condensations of a series of aromatic aldehydes with 1,3-dimethylbarbituric acid (e) and Meldrum’s acid (f) in aqueous media. CHAPTER 3 presents the results of an investigation on how simple variation of length and coordination mode of linear donors can self-discriminate into markedly different complex architectures, from Pd8 molecular swing [{(tmen)Pd}8(tim)2(bpy)4](NO3)16 (1) or [{(tmen)Pd}8(tim)2(stt)5](NO3)6 (2) to Pd6 molecular boat [{(tmen)Pd}6(tim)2(bpe/dpe/pin/dpb)2](NO3)12, (3/4/5/6). Also by enhancing denticity [bidentate to tridentate (ptp)] as well as introducing asymmetry, they self-sort into Pd7 molecular tent [{(tmen)Pd}7(tim)2(ptp)2](NO3)14 (7) by employing it in a self-assembly of cis-(tmen)Pd(NO3)2 and tetraimidazole (tim) donor [where tmen = N,N,N’,N’-tetramethylethylenediamine, bpy = 4,4’-bipyridyl, stt = sodium terephthalate, bpe = trans-1,2-bis(4-pyridyl)ethylene, dpe = 1,2-di(pyridin-4-yl)ethane, pin = N-(pyridin-4-yl)isonicotinamide, dpb = 1,4-di(pyridin-4-yl)benzene, ptp = 6'-(pyridin-4-yl)-3,4':2',4''-terpyridine, and tim = 1,2,4,5-tetrakis(1- imidazolyl)benzene]. In these cases, control of the geometrical principles and stereo-electronic preferences of the building units allowed the formation of such intricate architectures. Some of these assemblies represent first examples of such types of structures, and their formation would not be anticipated by taking into account only the geometry of the donor and acceptor building units. In addition to their direct structural confirmation using single crystal X-ray diffraction analysis, propensity of the assemblies (1 and 3) to form inclusion complexes with large guest like C60 in solution was also demonstrated by fluorescence quenching experiment. The high KSV values for both the assemblies 1 (1.0 × 10-5 M-1) and 2 (1.6 × 10-6 M-1) with C60 indicated the propensity of these assemblies to form complexes with C60 in solution. Furthermore, inspection of crystal packing of other five complexes (2 and 4 - 7) revealed the presence of water molecules H-bonded with NO3– (O-H···O=N) and 3D H-bonded networks of water in the intermolecular pockets. Interestingly, the present complexes (2 and 4 - 7) show high conductivity across low-humidity range at ambient temperature and achieve a conductivity of ~10-3 Scm-1 at 75% relative humidity and 296 K. These supra-molecular architectures represent a new generation of discrete materials that display high proton conductivity under ambient conditions with activation energy comparable to that of Nafion. Scheme 2. Exclusive formation of Pd8 molecular swings (1 and 2), Pd6 molecular boats (3-6), and Pd7 molecular tent (7) via self-sorting. CHAPTER 4 presents self-selection by synergistic effect of morphological information and coordination ability of the ligands through specific coordination interactional algorithms within dynamic supramolecular systems involving a tetratopic Pd(II) acceptor and three different pyridine- and imidazole-based donors (La - Lc) [La = 1,3-bis((E)-2-(pyridin-3-yl)vinyl)benzene, Lb = 1,3-di(1H-imidazol-1-yl)benzene, and Lc = tris(4-(1H-imidazol-1-yl)phenyl)amine]. Three different cages, ‘paddle wheel’ cluster Pd2(La)4(NO3)4 (2a), molecular barrel Pd3(Lb)6(NO3)6 (2b) and molecular sphere Pd6(Lc)8(NO3)12 (2c) were first synthesized via two-component self-assembly of a tetratopic Pd(II) acceptor (1) and individual pyridine- and imidazole-based donors (La - Lc). When all the four components were allowed to interact in a complex reaction mixture, only one out of three cages was isolated. The inherent dynamic nature of the kinetically labile coordination bond allows constitutional adaptation through component exchange in the competition experiment involving multiple constituents to self-organize into specific combination and thereby, achieve the thermodynamically most stable assembly. The preferential binding affinity towards a particular partner was also established by transforming a non-preferred cage to a preferred cage by the interaction with the appropriate ligand and thus, this represents the first examples of two-step cage-to-cage transformation through constitutional evolution of Figure 2. Cage-to-cage transformation from non-preferred cage to preferred cage upon treatment with appropriate ligand; and Nyquist plots of the complexes (2b and 2c) under 98% RH condition and ambient temparature. dynamic systems induced by both coordination ability and geometry of the ligand. Moreover, computational study further supported the fact that coordination interaction of imidazole moiety to Pd(II) is enthalpically more preferred compared to pyridine which drives the selection process. In addition, analysis of crystal packing of both the complexes (2b and 2c) indicated the presence of strong H-bonds between NO3- and water molecules; as well as H-bonded 3D-networks of water. Interestingly, both the complexes exhibit promising proton conductivity (10-5 to ca. 10-3 S cm-1) at ambient temperature under relative humidity of ~98% with low activation energy. CHAPTER 5 covers design and synthesis of new organometallic building block 1,3,5-tris(4-trans-Pt(PEt3)2I(ethynyl)phenyl)benzene (1) incorporating Pt-ethynyl functionality and [2 + 3] self-assembly of its nitrate analogue 1,3,5-tris(4-trans-Pt(PEt3)2(ONO2)(ethynyl)phenyl)benzene (2) with “clip” type bidentate donors (L1 – L3) separately afforded three trigonal prismatic architectures (3a – 3c), respectively (Scheme 3), Scheme 3. Schematic presentation of three different donors (L1 – L3) and a new planar tritopic acceptor (2) and their [3 + 2] self-assembly into trigonal prismatic architectures (3a - 3c). [L1 = N1,N3-di(pyridin-3-yl)isophthalamide; L2 = 1,3-bis((E)-2-(pyridin-3-yl)vinyl)benzene; L3 = 1,3-bis(pyridin-3-ylethynyl)benzene]. All these prisms were characterized and their shapes/sizes are predicted through geometry optimization employing molecular mechanics universal force field (MMUFF) simulation. The extended -conjugation including the presence of Pt-ethynyl functionality make them electron rich as well as luminescent in nature. As expected, cages 3b and 3c exhibit fluorescent quenching in solution upon addition of picric acid [PA], which is a common constituent of many explosives. Interestingly, the non-responsive nature of fluorescent intensity towards other electron-deficient nitro-aromatic explosives (NAEs) makes them promising selective sensors for PA with a detection limit deep down to ppb. Complexes 3b – c represent the first examples of molecular metallocages as selective sensors for picric acid. Furthermore, solid-state quenching of fluorescent intensity of the thin film of 3b upon exposure to saturated vapor of picric acid draws special attention for infield application.

La recherche actuelle dans le domaine des nanosciences, l’assemblage supramoléculaire d’atomes métalliques et de molécules sur des surfaces ouvre la voie à des composants fonctionnels, utiles dans une multitude d’applications comme l’Optoélectronique, le magnétisme et la catalyse. Il a été démontré que dans certains cas, l’état de Spin Haut et une forte anisotropie magnétique apparaissent suite à un transfert d’électron entre ligands, surface et atome métallique. Le but de cette thèse porte sur l’auto-assemblage des 1,2,4,5-Tetracyanobenzene (TCNB) et des coordinations nanostructurelles des Fe-TCNB sur une surface d’Au(111). La formation de ces structures est conduite par les interactions non-covalentes. La spectroscopie à effet tunnel (STS) révèle que la molécule de TCNB est physisorbée sur la surface d’Au(111). Une analyse détaillée des spectres dI/dV effectués sur une monocouche de TCNB sur une surface d’Au(111) montre que la molécule de TCNB a un transfert de charge négligeable sur ce substrat avec une énergie d’adsorption de 0,5 eV par molécule. Les mesures STS révèlent un gap HOMO-LUMO de 3 eV, comme le prédit la théorie. En contrôlant les paramètres de fabrication, des composants nanostructurels avec différentes compositions chimiques ou des arrangements moléculaires ont été synthétisés. Les propriétés électroniques ont été caractérisées par une analyse spectroscopique dI/dV locale sur les centres métalliques à différentes étapes de formation des complexes Fe-(TCNB)x (x=4, 2). La déposition à très basse température forme un état intermédiaire métastable. Les données STM montrent que l’angle que forment le trièdre Fe-N-C est de 120°. La spectroscopie tunnel révèle que le Fe et la molécule de TCNB gardent leur identité spectroscopique, le Fe garde ses états de surface de la même façon que s’il avait été déposé seul sur une surface d’Au(111). Ceci indique que les molécules de TCNB sont virtuellement dans le même état électronique qu’avant la déposition du Fe. La situation change lorsque ce dépôt est effectué à température ambiante. Une augmentation de température agit sur l’interaction des composants transformant ainsi la formation en un complexe monomère de Fe(TCNB)4 avec un angle Fe-N-C de 180°. La spectroscopie STS sur ce complexe suggère fortement que la liaison de coordination est formée entre le Fe et la molécule de TCNB. Les calculs DFT soutiennent ces conclusions. Plus loin, une structure a été réalisée par la synthèse d’un réseau Fe(TCNB)2. Ce réseau a une structure carrée avec une séparation régulière entre les atomes de Fe. Les informations électroniques de la structure sont données par la molécule de FePc (où Pc représente la molécule de Phthalocyanine) pour identifier les pics de résonnance du spectre du réseau de Fe(TCNB)2. Une similitude apparait dans les spectres dI/dV effectués sur l’atome de Fe et sur les ligands dans les deux systèmes, indiquant que le Fe ressent un environnement similaire quand il est entouré de TCNB ou quand il est à l’intérieur d’une Phthalocyanine. Une analyse plus détaillée basée sur la formation des liaisons métal-ligands a été discutée. / In the bottom up approach of today’s nanoscience, the supramolecular assembly of metal atoms and molecules on surfaces is leading to functional compounds, relevant to many applications in optoelectronics, magnetism, and catalysis. It has been found that in some cases high magnetic spin states and strong magnetic anisotropy appear as a result of electron transfer between ligands, surface and metal atom. The focus of this thesis lies on the self assembling of 1,2,4,5-Tetracyanobenzene (TCNB) and Fe-TCNB coordination nanostructures on the Au(111) surface. The structural formation is directed by the non covalent interactions. Scanning tunneling spectroscopy (STS) reveal that the TCNB molecules are physisorbed on Au(111) surface. By detail analysis of the dI/dV spectra above the TCNB monolayer on the Au(111) surface, we found that the TCNB molecules on Au(111) shows a negligible charge transfer with Au(111) substrate and a small adsorption energy of 0.5 eV per TCNB molecules. STS measurement provide a HOMO-LUMO gap of 3 eV in agreement with DFT calculations. By controlling the fabrication parameters, surface coordination nanostructures with different chemical composition or molecular packing have been synthesized. The electronic properties have been characterized by the local dI/dV analysis of the metal centers at different steps of a Fe-(TCNB)x (x=4, 2) complexes formation. At low temperature deposition, first form an ordered metastable intermediate. STM data yield the bond angle between the Fe-N-C is 120°. The scanning tunneling spectroscopy reveal that Fe atoms and the TCNB molecules keep their identity while the Fe atoms localize the surface-state electrons similar to what they do on the bare Au(111) surface. This result indicates that the TCNB molecules are virtually in the same electronic state as before the Fe adsorption. The situations are different when the deposition performance at room temperature. When the temperature is changed, to room temperature, the original entities transform into the Fe(TCNB)4 monomer complexes with 180° Fe-N-C bond angles. The STS above the Fe(TCNB)4 complex strongly suggest that the coordination bond had been formed between the Fe atom and the TCNB ligands. DFT calculations support the conclusions and drawn from experimental studies and assist the interpretations of experiment. Further structural complexation is achieved by the synthesis of Fe(TCNB)2 network. The network has a square structure with a regular separation of the magnetic Fe atoms in the network. The electronic information is gathered from the spectroscopic labeling of FePc to identify some of the resonances of the Fe(TCNB)2 network. There are similar features are found in the dI/dV spectra above the Fe atoms and ligand in both system, indicating that the Fe somehow feels a similar environment from the TCNB ligands in the network and in the FePc molecules. Further analysis of this feature have been disused by means of metal-ligand bond formation.

Les bisoxazolines de symétrie C2, ligands chiraux bidentates formés par deux cycles oxazolines séparés par un atome de carbone portant deux substituants identiques, font partie de ligands le plus utilisés en chimie de coordination et en catalyse asymétrique (homogène et hétérogène). Ce travail décrit la synthèse de treize ligands polytopiques chiraux comportant des unités bisoxazolines. Ces ligands ont été par la suite utilisés, d'une part, en tant que ligands chiraux pour la construction des catalyseurs auto-supportés de Cu(II)/ ligand polytopique (catalyseurs testés par la suite dans les réactions d' α-amination de β-cétoesters énantiosélective, de desymétrisation asymétrique par benzoylation de meso-diols, de dédoublement cinétique de rac-diols et dans la nitroaldolisation du nitrobenzaldehyde ou réaction de Henry); et d'autre part, en tant que briques deconstruction dans l'autoassemblage alterné et contrôlé de polymères de coordination métalloorganiques racémiques et énantiopurs. / Chiral C2-symmetric bis(oxazolines), bidentate ligands formed by two oxazoline rings separated by a carbon atom with two identical substituents, are one of the most popular types of chiral ligands which have already been successfully used in coordination chemistry and asymmetric catalysis (heterogeneous and homogeneous). This work describes the synthesis of thirteen polytopic chiral ligands bearing bis(oxazolines) moieties which have then been used, on the one hand, as chiral ligands for the construction of selfsupported Cu(II)/ polytopic ligand catalysts which were subsequently tested in the enantioselective α-hydrazination of β-ketoesters, the asymmetric desymmetrization of meso-diols by benzoylation and the kinetic resolution of rac-diols and the nitroaldolisation reaction (Henry reaction); and on the other hand, as organic building blocks for the controlled and alternate self-assembly of racemic and enantiopur metal-organic coordination polymers.

No description available.

Ce travail théorique vise à étudier, via les méthodes Premiers Principes, les propriétés des complexes de métaux de transitions, left[Mleft(dmbpyright)_{3}right]^{n+}nCi^{-} pour un usage en batterie. Pour cette étude ab-initio, les composés mono et bi-nucléaires ont été retenus. La pertinance de notre modélisation a été validée sur les composés mononucléaires. Nous nous sommes interessé au complexes de Fe, Ru et Cu pour lesquels une validation expérimentale était possible. Notre étude a principalement consisté à faire varier les degrés de liberté que nous possédons pour optimiser le voltage et la cinétique de chargement des batteries. Pour cela, nous avons fait varier le TM = Fe, Ru, et Cu, la nature des contre-ions Ci^{-}=PF_{6}^{-}, TFSI^{-} et ClO_{4}^{-} en interaction avec le polymère lors du processus de charge, ainsi que la longeur de la chaîne alkyl qui sépare les deux monomers dans le cas des composés binucléaires. Le composé à base de Fe avec une chaîne -left(CH_{2}right)_{n=6}- a été retenu comme le meilleur candidat pour une application batterie. Le composé à base Ru montre un comportement proche de celui du Fe, quant-au complexe de Cu, il présente des changements de géométrie locale sous chargement trop importants, le rendant peu apte à conduire à une cinétique efficace. Cette étude nous a permis de déterminer que l'approximation PBE était le meilleur choix possible pour modéliser nos complexes dans les conditions de fonctionnement en batterie (dans le champ créé par les contre-ions) et que l'approximation PBE0, généralement utilisée dans la littérature, ne pouvait rendre compte de la physico-chimie de nos composés dans de telles conditions.De surcroît, nous avons dévelopé pour le complexe de Fe, un potentiel atomistique de type “Champ de forces” de manière à pouvoir aborder les aspects dynamiques impliquant de plus grandes tailles de boîte de simulation. Ici, nous modélisons une structure 3D, totalement réticulée à partir de nos monomères à base de Fe. Nous nous sommes servi de la base de donnés DFT que nous avions généré (énergies, géométries, état de spin et fréquences vibrationnelles calculées) pour ajuster les paramètres entrant dans l'écriture du modèle. La construction de la géométrie initiale du polymère 3D a nécessité l'écriture d'un code de calcul visant à produire un arrangement complétement réticulé et à assigner les charges effectives issues des calculs DFT. Ce modèle nous a permis de déterminer les coefficients de diffusion des contre-ions pour les états totalement chargé et non-chargé. Un calcul plus ambitieux vise à déterminer les chemins de diffusion des contre-ions lors d'un processus de chargement en considérant un seul centre de degré d'oxydation 3+ au centre du polymère 3D, pour lequel les centres actifs possèdent un degré d'oxidation 2+. Les contre-ions assurent la neutralité globale.Keyword: Polymer, Electrochemistry, Li-ion Battery, DFT, Force Field development, 3D structure, Atomistic modeling / Abstract Standard redox potentials for mono and bi-nuclear transition metal (TM) complexes left[Mleft(dmbpyright)_{3}right]^{n+}nCi^{-}, have been investigated using First Principles Calculation. Three metal centers are investigated: Fe, Ru, and Cu. Our modeling is validated on mono-nuclear compounds. This approach consists in determining the best small polymer (bi-nuclear) made out of these monomers for a battery application. For that, we varied the three available degrees of freedom i.e., the nature of the central TM atom (Fe, Ru, and Cu), counter-ions Ci=PF_{6}^{-}, TFSI^{-} and ClO_{4}^{-} in interaction with the polymer, and the alkyl chain -left(CH_{2}right)_{n}- of length n that connects both mono-nuclear in the bi-nuclear compound. The Iron compound with -left(CH_{2}right)_{n=6}- is found to be the best candidate. The left[Culeft(dmbpyright)_{2}right]^{n+}nCi^{-} complex shows too much structure deformation upon loading, making it less reliable for cathode material. Moreover, we studied two XC functional, PBE and PBE0 and found, for three complexes PBE approximation retains the ligand field picture whereas PBE0 functional induces an exaggerated and unexpected band dispersion by dissolving the ligand field picture expected for the octahedral environment of the TM in the studied complexes. These findings validate that hybrid functional for which it was designed to localize and cancel self-interaction error does not work for all system. More particularly, the PBE0 approximation fails to model the three complexes (Fe, Ru, and Cu) in functional conditions (in the field made by the counter-ions).Abstract Further, we have developed an atomistic potential relying on the Force Field scheme for the Iron complex in order to study the dynamical properties of this compound at larger simulation scale (3D reticulated polymerization made of our Fe complex monomers). We made an intensive use of our DFT data (energies, geometries, spin-state configurations and calculated vibrational properties) to develop the required parameters entering the model. Moreover, computational techniques (written python language) were developed specifically to create a 3D structure of transition metal complexes satisfying the condition to be fully reticulated. Bounding conditions had to be designed and a procedure aiming at fixing reliable and physical effective charges on each atom of the simulation cell (compatible with DFT results) were developed. Our first simulations have been attached to calculate the diffusion coefficients of the counter-ions in both the fully loaded and unloaded states. A more ambitious and realistic calculation aims at investigating the paths of the counter-ions when one single center starts to be loaded in an unloaded environment.Abstract Keyword: Polymer, Electrochemistry, Li-ion Battery, DFT, Force Field development, 3D structure, Atomistic modeling

Two-dimensional conjugated metal-organic frameworks (2D c-MOFs) have recently emerged for potential applications in (opto-)electronics, chemiresistive sensing, and energy storage and conversion, due to their excellent electrical conductivity, abundant active sites, and intrinsic porous structures. However, developing ultrathin 2D c-MOF nanosheets (NSs) for facile solution-processing and integration into devices remains a great challenge, mostly due to unscalable synthesis, low yield, limited lateral size and low crystallinity. Here, we report a surfactant-assisted solution synthesis toward ultrathin 2D c-MOF NSs, including HHB-Cu (HHB=hexahydroxybenzene), HHB-Ni and HHTP-Cu (HHTP=2,3,6,7,10,11-hexahydroxytriphenylene). For the first time, we achieve single-crystalline HHB-Cu(Ni) NSs featured with a thickness of 4-5 nm (~8-10 layers) and a lateral size of 0.25-0.65 μm², as well as single-crystalline HHTP-Cu NSs with a thickness of ~5.1±2.6 nm (~10 layers) and a lateral size of 0.002-0.02 μm². Benefiting from the ultrathin feature, the synthetic NSs allow fast ion diffusion and high utilization of active sites. As a proof of concept, when serving as a cathode material for Li-ion storage, HHB-Cu NSs deliver a remarkable rate capability (charge within 3 min) and long-term cycling stability (90% capacity retention after 1000 cycles), superior to the corresponding bulk materials and other reported MOF cathodes.

Metal–organic frameworks (MOFs) are emerging as an appealing class of highly tailorable electrically conducting materials with potential applications in optoelectronics. Yet, the realization of their proof-of-concept devices remains a daunting challenge, attributed to their poor electrical properties. Following the authors’ recent report on a semiconducting Fe₃(THT)₂(NH₄)₃ (THT: 2,3,6,7,10,11-triphenylenehexathiol) 2D MOF with record-high mobility and band-like charge transport, here, Fe₃(THT)₂(NH₄)₃ MOF-based photodetector operating in photoconductive mode capable of detecting a broad wavelength range from UV to NIR (400–1575 nm) is demonstrated. The narrow IR bandgap of the active layer (≈0.45 eV) constrains the performance of the photodetector at room temperature by band-to-band thermal excitation of charge carriers. At 77 K, the device performance is significantly improved; two orders of magnitude higher voltage responsivity, lower noise equivalent power, and higher specific detectivity of 7 × 10⁸ cm Hz¹/² W⁻¹ are achieved under 785 nm excitation. These figures of merit are retained over the analyzed spectral region (400–1575 nm) and are commensurate to those obtained with the first demonstrations of graphene and black phosphorus based photodetectors. This work demonstrates the feasibility of integrating conjugated MOFs as an active element into broadband photodetectors, thus bridging the gap between materials’ synthesis and technological applications.

No description available.