Complexes homo- et hétéro-nucléaires de manganèse et de métaux alcalino-terreux : vers des modèles du centre de dégagement d'oxygène du photosystème II

This thesis is focused on the development and characterization of new homo- and heteronuclear complexes of manganese and alkaline-earth metals for the modelization of the Mn4CaO5 inorganic cluster of the OEC of photosystem II.New ligands incorporating a varied number of pyridine-carboxylate groups and based on the tris-(2-picolyl)amine and bis-(2-picolyl)ethylamine architectures have been synthesized. These ligands enabled the isolation of Ca2+ and Sr2+ homonuclear complexes as well as heteronuclear MnII–Ca complexes. Part of these species have been characterized (among other models) by Ca XAS spectroscopy, enabling the calibration of this technique for the study of more complex systems such as the OEC.Furthermore, a new family of MnII3M’ (M’ = Li+, Ca2+, Sr2+, Mn2+) tetranuclear complexes has been isolated, based on a trinuclear Mn2+ metallamacrocyclic architecture hosting a M’ cation in the formed cavity. These complexes exhibited an original electrochemical behavior, displaying three successive reversible redox processes in oxidation whose potentials vary depending on the metal M’. These species demonstrated an excellent stability in solution, even at the +III oxidation state of manganese. Similar homonuclear M3M (M = Fe2+, Co2+) complexes have been isolated.Finally, binuclear Mn3+ complexes bridged by oxo ligands have been isolated, as well as their Mn2+ precursors. Moreover, a mixed-valence Mn2+/Mn3+ metallamacrocyclic cluster incorporating calcium has been synthesized, revealing the first example of a manganese(II) bridged by an hydroxo ligand to Ca2+ ions.Ce mémoire de thèse est consacré au développement et à la caractérisation de nouveaux complexes homo- et hétéronucléaires de manganèse et de métaux alcalino-terreux dans le cadre de la modélisation du cluster inorganique Mn4CaO5 de l’OEC du photosystème II.De nouveaux ligands incluant un nombre variable de groupements pyridine-carboxylates basés sur les architectures tris-(2-picolyl)amine et bis-(2-picolyl)ethylamine ont été synthétisés. Ces ligands ont permis d’isoler de nouveaux complexes homonucléaires avec Ca2+ et Sr2+ et ainsi que des complexes hétéronucléaires MnII–Ca. L’analyse par spectroscopie XAS sur le calcium de certaines de ces espèces (parmi d’autres modèles) a permis de calibrer cette technique et ainsi montrer que le XAS pourrait être utilisé pour sonder le cluster naturel dans les différents états du cycle de Kok.Par la suite, une nouvelle famille de complexes tétranucléaires MnII3M’ (M’ = Li+, Ca2+, Sr2+, Mn2+) a été isolée, reposant sur une base métallomacrocyclique trinucléaire accueillant un cation M’ dans la cavité formée. Ces complexes ont révélé un comportement électrochimique original présentant trois systèmes redox successifs et réversibles dont le potentiel varie avec M’. Ces espèces ont démontré une excellente stabilité en solution, y compris à l’état d’oxydation du manganèse +III. Des complexes homonucléaires M3M (M = Fe2+, Co2+) similaires ont aussi été étudiés.Enfin, des complexes binucléaires de Mn3+ pontés par des ligands oxo ont été isolés, ainsi que leurs précurseurs de Mn2+. Par ailleurs, un exemple de cluster métallomacrocyclique à valence mixte Mn2+/Mn3+ et incorporant du calcium a été obtenu, qui représente le premier exemple d’un manganèse(II) ponté par un ligand hydroxo à deux ions Ca2+

Homo- and heteronuclear complexes of manganese and alkaline-earth metals : towards models of the oxygen-evolving center of photosystem II

Ce mémoire de thèse est consacré au développement et à la caractérisation de nouveaux complexes homo- et hétéronucléaires de manganèse et de métaux alcalino-terreux dans le cadre de la modélisation du cluster inorganique Mn4CaO5 de l’OEC du photosystème II.De nouveaux ligands incluant un nombre variable de groupements pyridine-carboxylates basés sur les architectures tris-(2-picolyl)amine et bis-(2-picolyl)ethylamine ont été synthétisés. Ces ligands ont permis d’isoler de nouveaux complexes homonucléaires avec Ca2+ et Sr2+ et ainsi que des complexes hétéronucléaires MnII–Ca. L’analyse par spectroscopie XAS sur le calcium de certaines de ces espèces (parmi d’autres modèles) a permis de calibrer cette technique et ainsi montrer que le XAS pourrait être utilisé pour sonder le cluster naturel dans les différents états du cycle de Kok.Par la suite, une nouvelle famille de complexes tétranucléaires MnII3M’ (M’ = Li+, Ca2+, Sr2+, Mn2+) a été isolée, reposant sur une base métallomacrocyclique trinucléaire accueillant un cation M’ dans la cavité formée. Ces complexes ont révélé un comportement électrochimique original présentant trois systèmes redox successifs et réversibles dont le potentiel varie avec M’. Ces espèces ont démontré une excellente stabilité en solution, y compris à l’état d’oxydation du manganèse +III. Des complexes homonucléaires M3M (M = Fe2+, Co2+) similaires ont aussi été étudiés.Enfin, des complexes binucléaires de Mn3+ pontés par des ligands oxo ont été isolés, ainsi que leurs précurseurs de Mn2+. Par ailleurs, un exemple de cluster métallomacrocyclique à valence mixte Mn2+/Mn3+ et incorporant du calcium a été obtenu, qui représente le premier exemple d’un manganèse(II) ponté par un ligand hydroxo à deux ions Ca2+.This thesis is focused on the development and characterization of new homo- and heteronuclear complexes of manganese and alkaline-earth metals for the modelization of the Mn4CaO5 inorganic cluster of the OEC of photosystem II.New ligands incorporating a varied number of pyridine-carboxylate groups and based on the tris-(2-picolyl)amine and bis-(2-picolyl)ethylamine architectures have been synthesized. These ligands enabled the isolation of Ca2+ and Sr2+ homonuclear complexes as well as heteronuclear MnII–Ca complexes. Part of these species have been characterized (among other models) by Ca XAS spectroscopy, enabling the calibration of this technique for the study of more complex systems such as the OEC.Furthermore, a new family of MnII3M’ (M’ = Li+, Ca2+, Sr2+, Mn2+) tetranuclear complexes has been isolated, based on a trinuclear Mn2+ metallamacrocyclic architecture hosting a M’ cation in the formed cavity. These complexes exhibited an original electrochemical behavior, displaying three successive reversible redox processes in oxidation whose potentials vary depending on the metal M’. These species demonstrated an excellent stability in solution, even at the +III oxidation state of manganese. Similar homonuclear M3M (M = Fe2+, Co2+) complexes have been isolated.Finally, binuclear Mn3+ complexes bridged by oxo ligands have been isolated, as well as their Mn2+ precursors. Moreover, a mixed-valence Mn2+/Mn3+ metallamacrocyclic cluster incorporating calcium has been synthesized, revealing the first example of a manganese(II) bridged by an hydroxo ligand to Ca2+ ions

Manganese-calcium/strontium heterometallic compounds and their relevance for the oxygen-evolving center of photosystem II

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Multireversible Redox Processes in a Self‐Assembled Nickel Pentanuclear Bis(Triple‐stranded Helicate): Structural and Spectroscopic Characterizations in the Ni II 5 and Ni I Ni II 4 Redox States

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Self-Assembled Heterometallic Complexes by Incorporation of Calcium or Strontium Ion into a Manganese(II) 12-Metallacrown-3 Framework Supported by a Tripodal Ligand with Pyridine-Carboxylate Motifs: Stability in Their Manganese(III) Oxidized Form

International audienceWe report on the isolation of a new family of μ-carboxylato-bridged metallocrown (MC) compounds by self-assembly of the recently isolated hexadentate tris(2-pyridylmethyl)amine ligand tpada2- incorporating two carboxylate units with metal cations. Twelve-membered MCs of manganese of the type 12-MC-3, namely [{MnII(tpada)}3(M)(H2O)n]2+ (Mn3M) (M = Mn2+ (n = 0), Ca2+ (n = 1) or Sr2+ (n = 2)), were structurally characterized. The metallamacrocycles connectivity consisting in three -[Mn-O-C-O]- repeating units is provided by one carboxylate unit of the three tpada2- ligands, while the second carboxylate coordinated a fourth cation in the central cavity of the MC, Mn2+ or an alkaline-earth metal, Ca2+ or Sr2+. The Mn3Ca and {Mn3Sr]2 join the small family of heterometallic manganese-calcium complexes and even rarer manganese-strontium complexes as models of the OEC of photosystem II (PSII). A 8-MC-4 of strontium of the molecular wheel type with four –[Sr-O] repeating unit was also isolated by self-assembly of the tpada2- ligand with Sr2+. This complex, namely [Sr(tpada)(OH2)]4 (Sr4), does not incorporate any cation in the central cavity but instead four water molecules coordinated to each Sr2+. Electrochemical investigations coupled to UV-visible absorption and EPR spectroscopies as well as electrospray mass spectrometry reveal the stability of the 12-MC-3 tetranuclear structures in solution, both in the initial oxidation state, MnII3M, as well as in the three-electrons oxidized state, MnIII3M. Indeed, the cyclic voltammogram of all these complexes exhibits three-successive reversible oxidation waves between +0.5 and +0.9 V corresponding to the successive one-electron oxidation of the Mn(II) ion into Mn(III) of the three {Mn(tpada)} units constituting the ring, which are fully maintained after bulk electrolysis

Seven Reversible Redox Processes in a Self-Assembled Cobalt Pentanuclear Bis(triple-stranded helicate): Structural, Spectroscopic, and Magnetic Characterizations in the Co I Co II 4 , Co II 5 , and Co II 3 Co III 2 Redox States

International audienceWe report on the synthesis and structural characterization of the cobalt pentanuclear helicate complex from the rigid tetradentate bis(2-pyridyl)-3,5-pyrazolate ligand bpp − , namely, [{Co II (μ-bpp) 3 } 2 Co II 3 (μ 3-OH)] 3+ (1 3+), in which a trinuclear {Co II 3 (μ 3-OH)} core is wrapped by two {Co II (μ-bpp) 3 } units. The cyclic voltammogram of 1 3+ in CH 3 CN revealed seven successive reversible one-electron waves, in the 0 and −3.0 V potential range, highlighting the remarkable stability of such architecture in several redox states. Two mixed-valent states of this complex, the two-electron-oxidized Co II 3 Co III 2 (1 5+) and the one-electron-reduced species Co I Co II 4 (1 2+), were generated by bulk electrolyses and successfully characterized by single-crystal X-ray diffraction among the eight redox levels between Co I 5 and Co II 3 Co III 2 that can be accessed under electrochemical conditions. Because of the crystallographic characterization of 1 5+ and 1 2+ , the five reduction processes located at E 1/2 values of −1.63 (1 3+/2+), −1.88 (1 2+/+), −2.14 (1 +/0), −2.40 (1 0/−), and −2.60 V (1 −/2−) versus Ag/ AgNO 3 were unambiguously assigned to the successive reduction of each of the five Co(II) ions to Co(I), starting with the three ions located in the central core followed by the two apical ions. The two other redox events at E 1/2 values of −0.21 (1 4+/3+) and −0.11 V (1 5+/4+) are assigned to the successive oxidation of the apical Co(II) ions to Co(III). The Co(I) complexes are rare, and the stabilization of a Co(I) within a trinuclear μ-hydroxo core in the reduced species, 1 2+ , 1 + , 1 0 , 1 − , and 1 2− , is probably the result of the particular structure of this complex in the presence of the two apical sites that maintain the trinuclear core through the six bridging bpp − ligands. The spectroscopic characteristics of 1 2+ , 1 3+ , and 1 5+ (ultraviolet−visible and X-band electron paramagnetic resonance) are also described as well as their magnetic properties in the solid state. ■ INTRODUCTION The self-assembly of polynuclear coordination complexes has attracted considerable attention over the past few decades. 1−3 It is now possible to direct synthesis toward structures with well-defined nuclearity and geometry by altering the ligand properties (rigidity, number and orientation of coordination sites, and nature of donor atoms) and the nature of the metal ions. 4 Among bridging ligands, heterocycles with two adjacent nitrogen donors such as pyrazolates, pyridazines, triazoles, and derivatives have been extensively used to design polynuclear complexes. Beyond their ability to maintain two metal ions in the proximity of each other, they indeed allow an electronic communication between these centers providing peculiar electronic properties and reactivities. 5−8 More particularly, the rigid tetradentate 3,5-bis(pyridyn-2-yl)-pyrazole (Hbpp) ligand 9 can form, by self-assembly with various first-row transition metal ions at high temperatures, remarkable bis(triple) helicate pentanuclear architectures of the type [{M(μ-bpp) 3 } 2 M 3 (μ 3-X)] n+ (M = Mn or Fe with X = O, and M = Ni or Zn with X = OH). 10−13 The five metal ions are arranged in a trigonal bipyramidal topology with two axial {M II (μ-bpp) 3 } units connecting a central μ 3-oxo or hydroxo trinuclear core {M 3 (μ 3-X)} through the bridging bpp − ligands. Interesting structure-specific physicochemical properties have been observed for this family of complexes, such as spin frustration for the copper complex, 11 while for the iron derivative, it has been shown that the spin states of the tw

Calcium and heterometallic manganese-calcium complexes supported by tripodal pyridine-carboxylate ligands: structural, EPR and theoretical investigations

International audienceCarboxylate-bridged Mn(II)-Ca(II) complexes are potentially relevant for mimicking the first stages of the Oxygen-Evolving Complex (OEC) assembly process. Here, we report on new homonuclear Ca(II) and heteronuclear Mn(II)-Ca(II) complexes with carboxylate-functionalized tripodal tris(2-pyridylmethyl) amine ligands, the heptadentate H(3)tpaa, previously reported, and the new hexadentate H(2)tpada, containing respectively three and two carboxylate units. The mononuclear [Ca(Htpaa)(OH2)] (Ca-1) and dinuclear [Ca(tpada)(OH2)(2)](2) (Ca-2) calcium complexes, as well as the tetranuclear [Mn(tpaa)(2)Ca(OH2)(5)(mu-OH2)(2)]-[ Mn(tpaa)](2) (Mn2Ca2 center dot 2Mn) and dinuclear [Mn(tpada) ClCa(OH2)(2.67)(MeOH)(2.33)] Cl (MnCa) heterometallic species have been structurally characterized; the syntheses of Ca1 and Mn2Ca2 center dot 2Mn being previously reported by us (Inorg. Chem., 2015, 54, 1283). The Mn(II) and Ca(II) are linked by two mu(1,1)-bridging carboxylates in MnCa, while only one mu(1,3)-carboxylate bridge connects each Ca2+ ion to each Mn(II) in Mn2Ca2. A variable number of water molecules (n = 1 to 7) are coordinated to Ca in all complexes, most of them being involved in hydrogen-bond networks, in analogy to what occurs in the photosystem II. All donor atoms of the tpaa(3-) and tpada(2-) ligands are coordinated to the Mn2+ ions, despite the unusually long distance between the Mn2+ ion and the tertiary amine imposed by the constraining nature of the ligands, as supported by theoretical calculations. Solid state EPR spectroscopy, in combination with DFT calculations, has also shown that the Ca2+ ion has an effect on the electronic parameters (zero field splitting) of the linked Mn(II) in the case of MnCa (mu(1,1)-carboxylate bridges). In Mn2Ca2 (mu(1,3)-carboxylate bridge) the Ca2+ ion induces only slight structural changes in the Mn coordination sphere

Intramolecular Electron Transfers Thwart Bistability in a Pentanuclear Iron Complex

International audienceWith the intention to investigate the redox properties of polynuclear complexes as previously reported for the pentamanganese complex [{Mn(II)(μ-bpp)3}2Mn(III)Mn(II)2(μ3-O)](3+) (2(3+)), we focused on the analogous pentairon complex that was previously isolated as all-ferrous. As Masaoka and co-workers recently published, aerobic synthesis leads to the [{Fe(II)(μ-bpp)3}2Fe(III)Fe(II)2(μ3-O)](3+) complex (1(3+)). This species exhibits in acetonitrile solution four reversible one-electron oxidation waves. Accordingly, the three oxidized species 1(4+), 1(5+), and 1(6+) with a 3Fe(II)2Fe(III), 2Fe(II)3Fe(III), and 1Fe(II)4Fe(III) composition, respectively, were generated by bulk electrolysis and isolated. Mössbauer spectroscopy allowed us to determine the spin states of all the iron ions and to unambiguously locate the sites of the successive oxidations. They all occur in the μ3-oxo core except for the 1(4+) to 1(5+) process that presents a striking electronic rearrangement, with both metals in axial position being oxidized while the core is reduced to the [Fe(III)Fe(II)2(μ3-O)](5+) oxidation level. This strongly differs from the redox behavior of the Mn5 system. The origin of this electronic switch is discussed

Ca K-Edge XAS as a Probe of Calcium Centers in Complex Systems

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