Approche structurale du phénomène de transition de Spin par diffraction des rayons X sous contraintes (T, P, hv)

The spin transition phenomenon corresponds to the spin state modification of a transition metal ion under an external perturbation (T, P, B, hv). Some iron (II) complexes, for example, can change from the paramagnetic spin state (S = 2) to the diamagnetic low spin state (S = 0). Before thinking to potential industrial applications, it is necessary to understand and control the differences of magnetic behaviour of such compounds. To this aim, the molecular science group of the ICMCB is studying, for a few years, mononuclear iron (II) complexes, which present very distinct spin transition magnetic features. In this thesis, the structural parameters which govern the behaviour differences from one complex to the other are identified. Moreover, direct correlations between the magnetic features and the structural properties of the [FeLn(NCS)2] series of complexes are pointed out. In addition, for the first time, the crystal structures of theses complexes in metastable high spin states obtained by thermal trapping or by light irradiation at very low temperature have been determined.The spin transition phenomenon corresponds to the spin state modification of a transition metal ion under an external perturbation (T, P, B, hv). Some iron (II) complexes, for example, can change from the paramagnetic spin state (S = 2) to the diamagnetic low spin state (S = 0). Before thinking to potential industrial applications, it is necessary to understand and control the differences of magnetic behaviour of such compounds. To this aim, the molecular science group of the ICMCB is studying, for a few years, mononuclear iron (II) complexes, which present very distinct spin transition magnetic features. In this thesis, the structural parameters which govern the behaviour differences from one complex to the other are identified. Moreover, direct correlations between the magnetic features and the structural properties of the [FeLn(NCS)2] series of complexes are pointed out. In addition, for the first time, the crystal structures of theses complexes in metastable high spin states obtained by thermal trapping or by light irradiation at very low temperature have been determined

Evidence for microstructure-dependent hysteresis in SCO molecular ceramics prepared by Cool-SPS

In recent decades, the development of new molecular materials with spin transition has aroused a growing interest from scientists in the field of information and communication technologies [1]. These compounds have the capacity to change their electronic state under the effect of an external disturbance such as temperature, pressure, or light irradiation, with important consequences on their structural, magnetic, or optical properties making them attractive for potential applications in the field of sensors, memories, molecular motors, or smart pigments. If the relations between the properties of these compounds and the crystalline structures are well established [2], the effects related to their microstructure were recently highlighted [3] and are still being discussed. Recently, the efficiency of Cool-SPS for the sintering of fragile materials at low temperature was established [4] Cool-SPS allowed the first molecular ceramics to be obtained at ICMCB [5]. Current work aims to develop new molecular ceramics from functional materials such as spin-transition complexes, to extend their diversity and to establish relationships between the microstructures obtained, their physical properties, and their switching behaviors. The compound [Fe(Htrz)2(trz)](BF4) was chosen as starting material because the switching of the Fe2+ ion between a diamagnetic low spin state (LS, S=0), and a paramagnetic high spin state, (HS, S=2) is carried out with a large thermal hysteresis (~ 40K) above the room temperature [6]. Moreover, the importance of the microstructure on this compound is known [7], and recent work has shown a clear evolution on this scale following several cycles or heat treatments [8]. In this work, first molecular ceramics from SCO materials have been developed by Cool-SPS, the optimal sintering conditions will be discussed, the influence of the sintering parameters (temperature, pressure, etc.) on the structural and morphological properties will be studied, and the correlation between microstructure and hysteresis loop after sintering will be highlighted (Figure 1). The future work, within the framework of this thesis, aims to pay attention to a further characterization of the ceramics elaborated in order to investigate the influence of the sintering conditions on the physical properties of the powders and to study in detail the relationship between the microstructural properties and the physical properties. SPS treatment conditions will be optimized to obtain denser ceramics while controlling their microstructure. Please click Additional Files below to see the full abstract

Comprehensive determination of the solid state stability of bethanechol chloride active pharmaceutical ingredient using combined analytical tools

International audienceThe use of an integrative analytical approach allowed us to establish the intrinsic solid state stability of bethanechol chloride (BC), an active pharmaceutical ingredient used in the treatment of urinary retention. First, the crystal structure of the monoclinic form has been described using single crystal X-ray diffraction studies. Second, thermal analyses revealed that the compound degrades upon melting, with an apparent melting temperature estimated to be 231 °C. No transition from the monoclinic to the orthorhombic form has been observed, suggesting that the monoclinic form is the stable one. Third, the two-step melting–decomposition process has been elucidated by liquid chromatography and thermogravimetry coupled to mass spectrometry. The first step corresponds to the sample liquefaction, which consists of the gradual dissolution of bethanechol chloride in its liquid degradant, i.e. betamethylcholine chloride. This step is in agreement with Bawn kinetics and the activation energy of the reaction has been estimated at 35.5 kcal mol−1. The second step occurs with accelerated degradation in the melt. Elucidation of secondary decomposition pathways evidenced autocatalytic properties conferred by the formation of both isocyanic acid and methyl chloride. Finally, dynamic water vapor sorption analysis showed a substantial hygroscopicity of the drug substance. A deliquescent point has been determined at 56% relative humidity at 25 °C

Cool-SPS: Pulling down the temperature, pushing up the reactivity

The use of materials, especially in the field of electronics, but also for catalysis, health (…), requires the control of their shaping (dense or porous materials, spherical or anisotropic particles…). This objective is frequently reached through the preparation of ceramics by conventional, high temperature sintering. Spark Plasma Sintering (SPS) is a particularly efficient densification method, initially dedicated to refractory materials, that is now extremely versatile and allows for the elaboration of nanostructured and/or transparent ceramics, among many other applications. Please click Additional Files below to see the full abstract

Synthesis and biological evaluation of novel substituted pyrrolo[1,2-a]quinoxaline derivatives as inhibitors of the human protein kinase CK2

Herein we describe the synthesis and properties of substituted phenylaminopyrrolo[1,2-a]quinoxaline-carboxylic acid derivatives as a novel class of potent inhibitors of the human protein kinase CK2. A set of 15 compounds was designed and synthesized using convenient and straightforward synthesis protocols. The compounds were tested for inhibition of human protein kinase CK2, which is a potential drug target for many diseases including inflammatory disorders and cancer. New inhibitors with IC50 in the micro- and sub-micromolar range were identified. The most promising compound, the 4-[(3-chlorophenyl)amino]pyrrolo[1,2-a]quinoxaline-3-carboxylic acid 1c inhibited human CK2 with an IC50 of 49 nM. Our findings indicate that pyrrolo[1,2-a]quinoxalines are a promising starting scaffold for further development and optimization of human protein kinase CK2 inhibitorsFil: Guillon, Jean. Universite de Bordeaux; Francia;Fil: Le Borgne, Marc. Université de Lyon; Francia;Fil: Rimbault, Charlotte. Universite de Bordeaux; Francia;Fil: Moreau, Stéphane. Universite de Bordeaux; Francia;Fil: Savrimoutou, Solène. Universite de Bordeaux; Francia;Fil: Pinaud, Noël. Universite de Bordeaux; Francia;Fil: Baratin, Sophie. Universite de Bordeaux; Francia;Fil: Marchivie, Mathieu. Universite de Bordeaux; Francia;Fil: Roche, Séverine. Universite de Bordeaux; Francia;Fil: Bollacke, Andre. Institut für Pharmazeutische und Medizinische Chemie. Westfälische Wilhelms-Universität Münster; Alemania;Fil: Pecci, Adali. Consejo Nacional de Invest.cientif.y Tecnicas. Oficina de Coordinacion Administrativa Ciudad Universitaria. Instituto de Fisiol., Biol.molecular y Neurociencias; Argentina;Fil: Alvarez, Lautaro Damian. Consejo Nacional de Invest.cientif.y Tecnicas. Oficina de Coordinacion Administrativa Ciudad Universitaria. Unid.microanal.y Met.fisicos En Quim.org.(i); Universidad de Buenos Aires. Facultad de Cs.exactas y Naturales. Departamento de Quimica Organica;Fil: Desplat, Vanessa. Universite de Bordeaux; Francia;Fil: Joachim, Jose. Institut für Pharmazeutische und Medizinische Chemie. Westfälische Wilhelms-Universität Münster; Alemania

Spin crossover molecular ceramics by Cool-SPS: consequences on switching features beyond the sole microstructural effect

The sintering of spin crossover material using Spark Plasma Sintering at low temperature (Cool-SPS) lead to a new way of shaping such compounds into functional molecular ceramics. These ceramics reach a high relative density of 95%, what may address several issues for using spin crossover materials into barocaloric devices. Starting from the reference complex [Fe(Htrz)2(trz)]BF4, we first investigated the magnetic, structural, microstructural properties as well as the fatigability behavior of the starting powder using multiple magnetic measurements, X-ray diffraction and calorimetry to compare them to the elaborated ceramics. The best conditions of pressure and temperature during the SPS process to obtain reproductible molecular ceramics with high relative density where found to be between 250 and 300 °C, and 300 and 400 MPa. The same complete set of characterizations made on a molecular ceramic of 95% of relative density reveal that crystal structure as well as the abrupt hysteretic SCO of [Fe(Htrz)2(trz)]BF4 are perfectly conserved after sintering. However, ceramic presents a faster stabilization of their microstructural and magnetic properties upon cycling and a higher cooperativity at the macroscopic level was observed compared to the starting powder

Photoinduced HS state in the first spin-crossover chain containing a cyanocarbanion as bridging ligand

A new polymeric approach, based on cyanocarbanion ligands, for the design of spin crossover (SCO) compounds led us to the compound [Fe(abpt)2(tcpd)] (1) (tcpd^2 = (C[C(CN)2|3)^2 , abpt = 4-amino-3,5-bis(pyridin-2-yl)-1,2,4-triazole) which has been characterised as the first SCO molecular chain involving a cyanocarbanion as bridging ligand.Gomez Garcia, Carlos Jose, [email protected]

Structures and Spin States of Crystalline [Fe(NCS)2L2] and [FeL3]2+ Complexes (L = an Annelated 1,10-Phenanthroline Derivative)

The phase behaviour and spin states of [Fe(NCS)2(dpq)2] (1; dpq = dipyrido[3,2-f:2′,3′-h]quinoxaline), [Fe(NCS)2(dppz)2] (2; dppz = dipyrido[3,2-a:2′3′-c]phenazine) and [Fe(NCS)2(dppn)2] (3; dppn = dipyrido[3,2-a:2′3′-c]benzophenazine) have been investigated. Solvent-free 1 and 2 are isostructural and low-spin in the crystalline state, in contrast to previously published 2·py (py = pyridine) which exhibits a hysteretic spin-crossover (SCO) transition near 140 K. The inactivity of 1 and 2 towards SCO may relate to their more crowded intermolecular lattice environment, particularly two very short intermolecular anion⋯π contacts involving the NCS− ligands. Two solvate phases of 1 are also described, including 1·2py which undergoes gradual SCO with T½ca. 188 K. Bulk samples of 2 and 3 are predominantly low-spin and isostructural with the crystals of 2 by powder diffraction, but bulk samples of 1 contain an extra phase that exhibits hysteretic SCO, but was not crystallographically characterised. Crystal structures of low-spin [Fe(dppz)3][ClO4]2 (4) and a solvate of [Fe(dppn)3][BF4]2 (5) are also described, which are the first homoleptic complexes of these ligands to be crystallographically characterised

Theoretical investigation of the electronic structure of Fe(II) complexes at spin-state transitions

The electronic structure relevant to low spin (LS)high spin (HS) transitions in Fe(II) coordination compounds with a FeN6 core are studied. The selected [Fe(tz)6]2+(1) (tz=1H-tetrazole), [Fe(bipy)3]2+(2) (bipy=2,2’-bipyridine) and [Fe(terpy)2]2+ (3) (terpy=2,2’:6’,2’’-terpyridine) complexes have been actively studied experimentally, and with their respective mono-, bi-, and tridentate ligands, they constitute a comprehensive set for theoretical case studies. The methods in this work include density functional theory (DFT), time-dependent DFT (TD-DFT) and multiconfigurational second order perturbation theory (CASPT2). We determine the structural parameters as well as the energy splitting of the LS-HS states (ΔEHL) applying the above methods, and comparing their performance. We also determine the potential energy curves representing the ground and low-energy excited singlet, triplet, and quintet d6 states along the mode(s) that connect the LS and HS states. The results indicate that while DFT is well suited for the prediction of structural parameters, an accurate multiconfigurational approach is essential for the quantitative determination of ΔEHL. In addition, a good qualitative agreement is found between the TD-DFT and CASPT2 potential energy curves. Although the TD-DFT results might differ in some respect (in our case, we found a discrepancy at the triplet states), our results suggest that this approach, with due care, is very promising as an alternative for the very expensive CASPT2 method. Finally, the two dimensional (2D) potential energy surfaces above the plane spanned by the two relevant configuration coordinates in [Fe(terpy)2]2+ were computed both at the DFT and CASPT2 levels. These 2D surfaces indicate that the singlet-triplet and triplet-quintet states are separated along different coordinates, i.e. different vibration modes. Our results confirm that in contrast to the case of complexes with mono- and bidentate ligands, the singlet-quintet transitions in [Fe(terpy)2]2+ cannot be described using a single configuration coordinate

A probe of steric ligand substituent effects on the spin crossover of Fe(II) complexes

Identifying and quantifying the individual factors affecting the temperature and properties of the spin crossover in transition metal complexes is a challenging task, because many variables are involved. While the most decisive factor is the crystal field imparted by ligands around the active metal center, some less common actors are intramolecular steric repulsions or non-covalent interactions. A series of three Fe(II) complexes of 1,3bpp derivatives of (2-(pyrazol-1-yl)-6-(1H-pyrazol-3-yl)pyridine) have been prepared and characterized crystallographically to probe these effects: [Fe(1,3bpp)2](ClO4)2 (1), [Fe(met1,3bpp)2](ClO4)2 (2) and [Fe(dimet1,3bpp)2](ClO4)2 (3). The ligands exhibit none, one or two methyl substituents on the pyrazol-1-yl heterocycle. These groups exert a dramatic effect on the SCO temperature in the solid state, and, most significantly, in solution (with TSCO (3) > TSCO (1) > TSCO (2)). Extensive DFT calculations have unveiled the origin of these effects which lie in the intramolecular non-covalent or steric interactions rather than resulting from crystal field effects.The authors thank the Generalitat de Catalunya for the prize ICREA Academia 2008 and 2013, and acknowledge the ERC for the Starting Grant StG-2010-258060 (GA), MINECO for grants MAT2014-53961-R (OR), MAT2015-70868-ERC (OR), CTQ2012-32247 (GA) and CTQ2015-68370-P (GA, CBM, RD), LabEx-Chemistry of Complex Systems for the post-doctoral grant ANR-10LABX-0026CSC (SV), the regional High-Performance Computing (HPC) center in Strasbourg for computational resources (SV) and the Avempace II Erasmus Mundus Action 2program for a PhD scholarship (MD). This research used resources of the Advanced Light Source, which is a DOE Office of Science User Facility under contract no. DE-AC02-05CH11231.Peer reviewe