Synthesis, characterization, and reactivity studies of a water-soluble bis(alkoxo)(carboxylato)- bridged diMnIII complex modeling the active site in catalase

A new diMnIII complex, Na[Mn2(5-SO3-salpentO)(μ-OAc)(μ-OMe)(H2O)]·4H2O, where 5-SO3-salpentOH = 1,5-bis(5-sulphonatosalicylidenamino)pentan-3-ol, has been prepared and characterized. ESI-mass spectrometry, paramagnetic 1H NMR, EPR and UV-visible spectroscopic studies on freshly prepared solutions of the complex in methanol and 9 : 1 methanol–water mixtures showed that the compound retains the triply bridged bis(μ-alkoxo)(μ-acetato)Mn23+ core in solution. In the 9 : 1 methanol–water mixture, slow substitution of acetate by water molecules took place, and after one month, the doubly bridged diMnIII complex, [Mn2(5-SO3-salpentO)(μ-OMe)(H2O)3]·5H2O, formed and could be characterized by X-ray diffraction analysis. In methanolic or aqueous basic media, acetate shifts from a bridging to a terminal coordination mode, affording the highly stable [Mn2(5-SO3-salpentO)(μ-OMe)(OAc)]− anion. The efficiency of the complex in disproportionating H2O2 depends on the solvent and correlates with the stability of the complex (towards metal dissociation) in each medium: basic buffer > aqueous base > water. The buffer preserves the integrity of the catalyst and the rate of O2 evolution remains essentially constant after successive additions of excess of H2O2. Turnovers as high as 3000 mol H2O2 per mol of catalyst, without significant decomposition and with an efficiency of kcat/KM = 1028 M−1 s−1, were measured for the complex in aqueous buffers of pH 11. Kinetic and spectroscopic results suggest a catalytic cycle that runs between MnIII2 and MnIV2 oxidation states, which is consistent with the low redox potential observed for the MnIII2/MnIIIMnIV couple of the catalyst in basic medium.Fil: Palopoli, Claudia Marcela. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Rosario. Instituto de Química Rosario; ArgentinaFil: Duhayon, Carine. Universite de Toulose - Le Mirail; Francia. Laboratoire de Chimie de Coordination; FranciaFil: Tuchagues, Jean Pierre. Universite de Toulose - Le Mirail; Francia. Laboratoire de Chimie de Coordination; FranciaFil: Signorella, Sandra Rosanna. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Rosario. Instituto de Química Rosario; Argentin

Tris(1,10-phenanthroline-κ2N,N′)nickel(II) bis(hexafluoridophosphate)

The asymmetric unit of the title compound, [Ni(C36H24N6)3](PF6)2, contains one and a half nickel(II) complex dications and three hexafluoridophosphate anions, one of the dications having crystallographic twofold rotational symmetry. Each NiII atom displays a distorted octahedral coordination geometry provided by the six N atoms of three bidentate 1,10-phenanthroline ligands with bite angles of 79.68 (11)–80.76 (12)°. In the crystal, C—H...F hydrogen bonds link the anions and dications into a three-dimensional supramolecular framework. Within the framework complex dications with twofold rotational symmetry are linked by weak π–π stacking interactions [centroid-to-centroid distances = 3.712 (2) Å]

Crystal structure of tetraaquabis(1,3-dimethyl-2,6-dioxo-7 H -purin-7-ido-κ N 7 )cobalt(II)

International audienceThe title complex, [Co(C7H7N4O2)2(H2O)4], comprises mononuclear molecules consisting of a CoII ion, two deprotonated theophylline ligands (systematic name: 1,3-dimethyl-7H-purine-2,6-dione) and four coordinating water molecules. The CoII atom lies on an inversion centre and has a slightly distorted octahedral coordination environment, with two N atoms of two trans-oriented theophylline ligands and the O atoms of four water molecules. An intramolecular hydrogen bond stabilizes this conformation. A three-dimensional supramolecular network structure is formed by intermolecular O-H...O and O-H...N hydrogen bonds

N -Cyclopropenio-imidazol-2-ylidene: An N-heterocyclic carbene bearing an N -cationic substituent

International audienceA cationic NHC 1+ bearing an N-bound 2,3-bis(diisopropylamino)-cyclopropenium group is reported. From an easily available dicationic imidazolium precursor, the coordination abilities and stereo-electronic properties of 1+ are evaluated by the formation of Pd(II), Rh(I) and Au(I) complexes. The cationic gold(I) complex is implemented in representative intramolecular Au(I)-catalyzed cyclizations

Bis( N -cyclopropenio)-imidazol-2-ylidene: An N -Heterocyclic Carbene Bearing Two N -Cationic Substituents

International audienceThanks to the onio-substitution strategy, tricationic imidazolium salt (1·H)(OTf)3 featuring two N-cyclopropenio substituents was readily prepared in a two-step procedure from 1H-imidazole. The influence of the two cyclopropenium moieties on the electronic properties of the related dicationic NHC 12+ was evaluated on the basis of the 1JCH, δ 77Se, and Tolman electronic parameter (TEP) values obtained, respectively, from NHC precursor (1·H)(OTf)3, NHC═Se adduct (5)(OTf)2, and NHC–Rh(CO)2 complex (7)(OTf)2, leading to the conclusion that carbene 12+ is one of the least-donating cationic NHCs reported to date. The coordinating ability of 12+ was extended to Pd(II) and Au(I) centers, providing dicationic [PdCl(allyl)(1)](OTf)2 (8)(OTf)2 and [AuCl(1)](OTf)2 (10)(OTf)2 complexes, respectively, which were fully characterized. While Pd complex (8)(OTf)2 was found to exhibit the lability of a cyclopropenium substituent upon the cleavage of a C+–N bond, Au complex (10)(OTf)2 was implemented in model Au-catalyzed intramolecular cyclization reactions, showing moderate activity

Discrete versus 1D Compounds based on Pentagonal Bipyramid Coordination Geometries: A Matter of Solubility?

International audienceA series of heterometallic compounds based on the association of trans-dicyanido Cr(III) complex [Cr(L)(CN)2]K ⋅ 2H2O and several divalent [MnII(H2Ln)Cl2] heptacoordinated complexes, where Ln stands for pentadentate ligands featuring a planar N3O2 coordination pocket and various substituents (NH2, cyclohexyl, S,S-mandelic), is described. A dinuclear compound [Cr(L)(CN)2M(H2L2)] and 1D coordination polymers of general formula [Cr(L)(CN)2M(H2Ln)]X (X=PF6− or [Cr(L)(CN)2]−) were rationally prepared by a simple adjustment of the Cr : M stoichiometry for R=NH2 or tuning the solvent mixtures to promote the crystallization of discrete complexes or chains. The crystal structures, phase purities and magnetic properties of all the compounds are reported

Bi-Compartmental Schiff-Base with Peripheral Ester Functionalization: Synthesis and Magnetic Behavior of Bi-metallic Zn-Ln Complexes (Ln = Dy, Tb, Gd)

International audienc

Structural determinations and magnetic properties of a “chiral at metal” complex and its resulting [Cu–Ln] 2 compounds

International audienceA chiral trianionic ligand possessing one amide, one imine, two phenol functions and one asymmetric carbon atom into its diamino chain reacts with CuII ions to yield anionic [LCu]− units that crystallize in a non-centrosymmetric space group as infinite 1D zig-zag chains in which a transmission of chirality to the CuII ion is effective. The distorted square planar environment of the CuII ion is large enough to induce the presence of a stereogenic CuII centre. Further reaction with LnIII ions in presence of ancillary ligands does not preserve such an arrangement but yields a tetranuclear complex made of two [LCu–Ln] units in a head-to-tail position. The tetranuclear [LCu–Ln]2 complexes made with the racemic and chiral LCu units crystallize in different space groups, so that racemization does not occur. The structural determinations confirm that a symmetry centre is present in the two structures, except for the methyl groups linked to the chiral carbon atoms, which appear as disordered in the (S-S) tetranuclear entity. Such an arrangement implies a conformation change of the diamino chain linked to the CuII ion in one [LCu–Ln] unit of the (S-S) entity, and cancels any chirality contribution of the CuII ions, as in the meso compound. Ferromagnetic Cu–Ln interactions, resulting from an alternate distribution of the CuII and LnIII ions, are the only ones to be active. Eventually the micro-Squid studies confirm that the hysteresis loops of the corresponding racemate and chiral tetranuclear [LCu–Dy]2 entities are slightly different