Contribution à l'élaboration de molécules paramagnétiques précurseurs d'édifices supramoléculaires à couches ouvertes : Polyradicaux à squelette Phosphore et complexes organo-métalliques.

La préparation de matériaux supramoléculaires magnétiques aux propriétés optimisées est tributaire du développement des modules moléculaires qui sont à l'origine tant de l'édifice chimique que des propriétés collectives observées. Deux types de synthons moléculaires ont été étudiés dans le cadre de cette thèse. Le premier concerne des polyradicaux aminoxyle portés par un squelette phosphoré, l'autre concerne des molécules organométalliques paramagnétiques. La synthèse, l'étude des propriétés magnétiques à l'état solide et en solution, ainsi que la détermination de la distribution de spin par MAS-RMN, RPE et DFT sur deux polyradicaux, un bi- et un tri-aminoxyle, ont permis de sonder le rôle de l'atome de phosphore dans l'interaction d'échange intramoléculaire. La seconde famille de molécules concerne des composés de Cr(III) dont la sphère de coordination comprend un ligand cyclopentadiényle ou un hydro-tris-pyrazolyl borate et des ligands cyanures ou azotures. Ces dernières ont été imaginées comme modules de construction d'édifices magnétiques finis, des clusters de spin. La démarche que nous avons suivie débute avec la conception des molécules sur la base des acquis du domaine, la mise au point d'un protocole de synthèse efficace et l'étude des caractéristiques de ces briques potentielles. Nous nous sommes également penché sur l'aptitude de ces molécules à s'associer avec un autre partenaire en un édifice supramoléculaires.The rational synthesis of magnetic supramolecular materials depends on the development of new molecular building-blocks which are behind both the chemical architecture and the collective properties exhibited by the system. Two type of molecular synthons have been studied in this work. The first concerns polyradical aminoxyl-substituted phospine derivatives; the second paramagnetic organometallic species. In order to evaluate the role played by the phosphorus atom on the intramolecular exchange interaction, two polyradicals, a bi- and a tri-aminoxyl derivative, have been prepared, their magnetic properties investigated in solid state and in solution, and the spin distribution over the molecules determined by MAS-NMR, EPR and DFT calculation. The second family of molecules considered are Cr(III) derivatives for which the coordination sphere comprises either a cyclopentanienyl or a hydro-tris-pyrazolyl borate ligand, and the bridging ligands cyanide or azide. Such molecules were envisaged as modules for the preparation of finite magnetic architectures, i.e. spin clusters

Contribution à l'élaboration de molécules paramagnétiques précurseurs d'édifices supramoléculaires à couches ouvertes: polyradicaux à squelette phosphoré et complexes organo-métalliques.

La préparation de matériaux supramoléculaires magnétiques aux propriétés optimisées est tributaire du développement des modules moléculaires qui sont à l'origine tant de l'édifice chimique que des propriétés collectives observées. Deux types de synthons moléculaires ont été étudiés dans le cadre de cette thèse. Le premier concerne des polyradicaux aminoxyle portés par un squelette phosphoré, l'autre concerne des molécules organométalliques paramagnétiques. La synthèse, l'étude des propriétés magnétiques à l'état solide et en solution, ainsi que la détermination de la distribution de spin par MAS-RMN, RPE et DFT sur deux polyradicaux, un bi- et un tri-aminoxyle, ont permis de sonder le rôle de l'atome de phosphore dans l'interaction d'échange intramoléculaire. La seconde famille de molécules concerne des composés de Cr(III) dont la sphère de coordination comprend un ligand cyclopentadiényle ou un hydro-tris-pyrazolyl borate et des ligands cyanures ou azotures. Ces dernières ont été imaginées comme modules de construction d'édifices magnétiques finis, des clusters de spin. La démarche que nous avons suivie débute avec la conception des molécules sur la base des acquis du domaine, la mise au point d'un protocole de synthèse efficace et l'étude des caractéristiques de ces briques potentielles. Nous nous sommes également penché sur l'aptitude de ces molécules à s'associer avec un autre partenaire en un édifice supramoléculaires.The rational synthesis of magnetic supramolecular materials depends on the development of new molecular building-blocks which are behind both the chemical architecture and the collective properties exhibited by the system. Two type of molecular synthons have been studied in this work. The first concerns polyradical aminoxyl-substituted phospine derivatives; the second paramagnetic organometallic species. In order to evaluate the role played by the phosphorus atom on the intramolecular exchange interaction, two polyradicals, a bi- and a tri-aminoxyl derivative, have been prepared, their magnetic properties investigated in solid state and in solution, and the spin distribution over the molecules determined by MAS-NMR, EPR and DFT calculation. The second family of molecules considered are Cr(III) derivatives for which the coordination sphere comprises either a cyclopentanienyl or a hydro-tris-pyrazolyl borate ligand, and the bridging ligands cyanide or azide. Such molecules were envisaged as modules for the preparation of finite magnetic architectures, i.e. spin clusters

Contribution à l'élaboration de molécules paramagnétiques précurseurs d'édifices supramoléculaires à couches ouvertes: polyradicaux à squelette phosphoré et complexes organo-métalliques.

The rational synthesis of magnetic supramolecular materials depends on the development of new molecular building-blocks which are behind both the chemical architecture and the collective properties exhibited by the system. Two type of molecular synthons have been studied in this work. The first concerns polyradical aminoxyl-substituted phospine derivatives; the second paramagnetic organometallic species. In order to evaluate the role played by the phosphorus atom on the intramolecular exchange interaction, two polyradicals, a bi- and a tri-aminoxyl derivative, have been prepared, their magnetic properties investigated in solid state and in solution, and the spin distribution over the molecules determined by MAS-NMR, EPR and DFT calculation. The second family of molecules considered are Cr(III) derivatives for which the coordination sphere comprises either a cyclopentanienyl or a hydro-tris-pyrazolyl borate ligand, and the bridging ligands cyanide or azide. Such molecules were envisaged as modules for the preparation of finite magnetic architectures, i.e. spin clusters.La préparation de matériaux supramoléculaires magnétiques aux propriétés optimisées est tributaire du développement des modules moléculaires qui sont à l'origine tant de l'édifice chimique que des propriétés collectives observées. Deux types de synthons moléculaires ont été étudiés dans le cadre de cette thèse. Le premier concerne des polyradicaux aminoxyle portés par un squelette phosphoré, l'autre concerne des molécules organométalliques paramagnétiques. La synthèse, l'étude des propriétés magnétiques à l'état solide et en solution, ainsi que la détermination de la distribution de spin par MAS-RMN, RPE et DFT sur deux polyradicaux, un bi- et un tri-aminoxyle, ont permis de sonder le rôle de l'atome de phosphore dans l'interaction d'échange intramoléculaire. La seconde famille de molécules concerne des composés de Cr(III) dont la sphère de coordination comprend un ligand cyclopentadiényle ou un hydro-tris-pyrazolyl borate et des ligands cyanures ou azotures. Ces dernières ont été imaginées comme modules de construction d'édifices magnétiques finis, des clusters de spin. La démarche que nous avons suivie débute avec la conception des molécules sur la base des acquis du domaine, la mise au point d'un protocole de synthèse efficace et l'étude des caractéristiques de ces briques potentielles. Nous nous sommes également penché sur l'aptitude de ces molécules à s'associer avec un autre partenaire en un édifice supramoléculaires

H2O as a chemical link for ferromagnetic interactions between aminoxyl units

A bis(radical) derivative based on a triphenylphosphane core substituted by two nitronyl nitroxide units is reported. This compound was isolated in two forms. One consists of an H2O adduct where H2O is hydrogen-bonded to the radical units, whereas the second lacks this bridging unit. Magnetic studies revealed that the presence of the H2O bridge induces ferromagnetic exchange interaction between the spin carriers

Crystallographic elucidation of purely structural, thermal and light-induced spin transitions in an iron(ii) binuclear complex

The intricate phase diagram of the binuclear iron(ii) spin-crossover complex [{Fe(3-bpp)(NCS)2}2(4,4�-bypiridine)] ·2CH3OH where 3-bpp is 2,6-bis(pyrazol-3-yl)pyridine has been investigated by variable temperature single crystal X-ray diffraction including a study into the effect of photo-irradiation. This sample is known to exhibit an incomplete spin transition at low temperature. At room temperature, in phase I, iron ions are all crystallographically equivalent, adopting the high spin state (HS). X-Ray structural investigation has revealed two phase transitions in the range (300-30 K). The first transition (T�161 K) leading to phase II is of a purely structural nature and corresponds to a break in symmetry as a result of a twist of the two rings of 4,4�-bipyridine; the two iron sites of the binuclear unit becoming crystallographically independent but remaining all HS. The second structural transition corresponds to the spin crossover, one of the two Fe(ii) ions of the binuclear complex being in the low spin state (LS) in phase III. The crystal structure shows an ordered HS-LS crystal packing where HS and LS sites are clearly identified and not randomly distributed in the metal ion sites as often observed. Moreover, light irradiation of single crystals in phase III at 30 K, leading to phase III*, induces a light-induced spin-state trapping (LIESST) effect corresponding to the full conversion of all the iron sites to HS. The crystal packing in phase III* is closer to that of phase III than to those observed in the other HS phases, I and II. This reveals an unusual differentiation between the thermal and light-induced HS states. A deeper analysis of the structural properties first demonstrates the key role of the bipyridine bridge in the peculiar preliminary pure structural transition shown by the title compound. Elsewhere, it also shows that the molecular packing is strongly dependent on the nature of the external perturbation contrary to the iron coordination sphere geometry that appears to be only dependent on the spin state. Moreover, in the HS phase II, the distortion of the iron sites that will subsequently undergo a spin crossover demonstrates some differences with the distortion of the iron sites that remain HS. The predominant role of the iron environment distortion in the spin crossover phenomenon is thus clearly evidenced. © 2010 The Royal Society of Chemistry

Experimental and Theoretical Studies on Magnetic Exchange in Silole-Bridged Diradicals.

Five bis(tert-butylnitroxide) diradicals connected by a silole [2,5-R2-3,4-diphenylsilole; R = Me3CN(®O.bul.)Z; Z = p-C6H4 (7a), p-C6H4C6H4-p (7b), 1,4-naphthalenediyl (7c), m-C6H4 (7d)] or a thiophene [2,5-R2-thiophene; R = p-Me3CN(®O.bul.)C6H4 (12)] ring as a coupler were studied. Compd. 12 crystallizes in the orthorhombic space group Pna21 with a 20.752(5), b 5.826(5), and c 34.309(5) .ANG.. X-ray crystal structure detn., electronic spectroscopy, variable-temp. EPR spectroscopy, SQUID measurements and DFT computations (UB3LYP/6-31+G*) were used to study the mol. conformations and electronic spin coupling in this series of mols. Whereas compds. 7b, 7c, and 7d are quite stable both in soln. and in the solid state, 7a and 12 undergo a partial electronic rearrangement to both a diamagnetic quinonoid form and a monoradical species owing to the fact that they correspond to the open form of a p-conjugated Kekule structure. In the solid state, magnetic measurements indicate that the diradicals are all antiferromagnetically coupled, as expected from their topol. These interactions are best reproduced by a Bieaney-Bowers model that gives values of J = -142.0 cm-1 for 7a, -1.8 cm-1 for 7b, -1.3 cm-1 for 7c, -4.2 cm-1 for 7d, and -248.0 cm-1 for 12. The temp. dependence of the EPR half-field transition in frozen CH2Cl2 solns. is consistent with singlet ground states and thermally accessible triplet states for diradicals 7b, 7c, and 7d with DET-S values of 3.48, 2.09, and 8 cm-1, resp. No evidence of a populated triplet state was found for diradicals 7a and 12. Similarities between the DET-S and J values (DET-S = -2 J) clearly show the intramol. origin of the obsd. antiferromagnetic interaction. Analyses of the data with a Karplus-Conroy-type equation enabled the authors to establish that the silole ring, as a whole, allows a more efficient magnetic coupling of the two nitroxide radicals attached to its 2,5-positions than the thiophene ring. This superiority probably originates from the non-aromaticity of the silole which thus permits a better magnetic interaction through it. DFT calcns. also support the exptl. results, indicating that the magnetic exchange pathway preferentially involves the C p system of the silole