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Olivier Cador

Publications and source records attributed to Olivier Cador.

9 recordsLinked to original sources
PubMed2006

Co(II)-Co(II) paddlewheel complex with a redox-active ligand derived from TTF.

A new trimethyltetrathiafulvalene (Me3TTF) derivative Me3TTF-CH=CH-py bearing a pyridyl was synthesized and coordinated to a cobalt(II) benzoate dimer, having paddlewheel core structure, leading to a complex formulated as Co2(PhCOO)4(Me3TTF-CH=CH-py)2. Single-crystal X-ray diffraction studies of the complex performed at 293 and 100 K evidenced the existence of a weak metal-metal interaction. Magnetic studies revealed an antiferromagnetic behavior, which is explained as the result of the direct exchange between metal centers.

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PubMed2005

In situ generation of carboxylate: an efficient strategy for a one-pot synthesis of homo- and heterometallic polynuclear complexes.

An efficient strategy for synthesis of a wide range of homo- and heterometallic polynuclear complexes is proposed. The synthesis protocol consists of a two-step one-pot reaction. The first step is the in situ generation of carboxylate anions via oxidation of aromatic aldehydes by metal nitrates in air. The aldehydes act as solvents and are also involved in redox processes. Solutions containing solely transition metal cations and aromatic carboxylates are obtained following this procedure. The second step is a tunable "à la carte" formation of a series of various polynuclear carboxylato complexes from solutions obtained at the former stage upon addition of different solvents. The polarity and donor properties of the solvents play a key role in determination of the nuclearities of the complexes. Hydrolytic processes can induce the formation of oxo- or hydroxo-bridges inside the polynuclear core as well. Complexes of various nuclearities are obtained: from discrete tri-, hexa-, or octanuclear units to 1D polymers. This protocol can be adapted with disconcerting simplicity to the synthesis of heterometallic species with similar molecular structures to their homometallic analogues starting from stoichiometric mixture of metal nitrates under the same reaction conditions. Detailed description of synthesis and the molecular structure of one representative complex for each series are presented in this paper. The temperature dependence of magnetic susceptibility of the heterometallic 1-D MnCo chain reveals typical behavior of a ferrimagnetic chain. The low-temperature investigations on single crystals show significant Ising type magnetic anisotropy.

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PubMed2005

Synthesis, structure, and magnetism of heterometallic carboxylate complexes [MnIII2M(II)4O2(PhCOO)10(DMF)4], M = Mn(II), Co(II), Ni(II).

Three new homo- and heterometallic hexanuclear complexes [Mn(2)M(II)(4)O(2)(PhCOO)(10)(DMF)(4)] (with M = Mn (1), Co (2) or Ni (3) and DMF = dimethylformamide) have been synthesized by redox generation of benzoate ligands from benzaldehyde in a one-pot reaction. All of the compounds are isostructural and crystallize in the I-42d space group of the tetragonal system, data for 1: a = 27.2249(8) Angstroms, c = 25.5182(5) Angstroms, R1 = 0.0681. The crystal structure contains isolated molecules. Each molecule consists of 2 x Mn(III) surrounded by four M(II) ions to form two edge-sharing OMn(2)M(2) tetrahedra giving rise to the [Mn(2)M(4)O(2)] core. The coordination sphere of each metal is completed by the bridging benzoate ligands and DMF molecules. The magnetic susceptibilities of 1-3 have been measured in the 1.8 K < T < 300 K temperature range. The magnetic susceptibilities for 1 and 2 pass through a broad maximum at low temperature which is characteristic of the diamagnetic ground state, while for 3 no maximum is detected down to 1.8 K. The magnetic data have been interpreted quantitatively for 1 and 3 on the basis of spin exchange interactions between the metallic centers (spin Hamiltonian for a pair being H(AB) = -J(AB) S(A).S(B)). Single-crystal measurements on [Mn(6)O(2)(PhCOO)(10)(CH(3)CN)(4)] (4) show that significant magnetic anisotropy develops at low temperature.

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PubMed2003

Temperature-induced solid-state valence tautomeric interconversion in two cobalt-Schiff base diquinone complexes.

The mixed-ligand complexes [Co(III)(tpy)(Cat-N-SQ)]Y and [Ni(II)(tpy)(Cat-N-BQ)]PF(6) (tpy = 2,2':6',2' '-terpyridine; Cat-N-BQ, Cat-N-SQ = mononegative and radical dinegative Schiff base diquinone ligand; Y = PF(6), BPh(4)) were prepared. Structural and spectroscopic data support the different charge distribution of the two compounds. The temperature-dependent electronic and spectral properties of solutions containing the [Co(III)(tpy)(Cat-N-SQ)](+) suggest that this compound undergoes a thermally driven valence tautomeric interconversion to [Co(II)(tpy)(Cat-N-BQ)](+) complex, the metal ion being in high-spin configuration. The comparison of the electrochemical properties of the cobalt and nickel derivatives supports the observed behavior. The same interconversion process was found to occur also in the solid state with a significant higher T(c) value than in solution. It was found that the previously reported [Co(III)(Cat-N-BQ)(Cat-N-SQ)] shows a similar behavior. The large difference between the interconversion T(c) in the solid state and in solution is suggested to come from the entropy changes associated with the modifications of vibronic interactions.

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PubMed2002

Synthetic and magnetic studies of a dodecanuclear cobalt wheel.

The synthesis, structural characterisation and preliminary magnetic studies of a Co12 wheel are reported; the magnetic investigations reveal that the electronic ground state has a spin S = 6, which corresponds to ferromagnetic interactions between the twelve Co(II) ions.

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PubMed1997

Optical Absorption Spectroscopy of the Tetranuclear Compound [Mn{Cu(oxpn)}(3)](ClO(4))(2).2H(2)O (oxpn = N,N'-Bis(3-aminopropyl)oxamide): Complementarity with Magnetic Properties.

The optical absorption spectroscopy of the tetranuclear compound [Mn{Cu(oxpn)}(3)](ClO(4))(2).2H(2)O, with oxpn standing for N,N'-bis(3-aminopropyl)oxamide, has been investigated in the 4-300 K temperature range. The central Mn(II) ion is linked to three Cu(oxpn) complex ligands, so the molecular symmetry may be defined as D(3). The spectra, in addition to a d-d transition at 19 230 cm(-)(1) due to the Cu(II) ion in square planar surroundings, exhibit narrow and intense Mn(II) spin-forbidden transitions in the 24 300-28 750 cm(-)(1) range. These transitions are activated by an exchange mechanism. The temperature dependence of the main feature corresponding to the (6)A(1) --> (4)A(1),(4)E(G) Mn(II) transition was investigated. Using a model proposed first by Tanabe and co-workers and adapted to the MnCu(3) topology, a theoretical expression for the temperature dependence of the intensity of the transition has been established and compared with the experimental data. The only parameter of this expression is the interaction parameter J between the local ground states (H = -J summation operator(i)()S(Mn)()i.S(Cu)()i), which has been found to be -33.8 cm(-)(1). The energy of the transition has been found to be shifted by 47 cm(-)(1) toward the high energies as the temperature was lowered. A theoretical expression for the energy shift of the transition has been given. It depends on both J and the interaction parameter J between the Cu(II) ions in their ground states and the Mn(II) ion in the spin flip excited state. The comparison with the experimental data has led to a negative J value of the same order of magnitude as the J value. These results have been discussed in relation with the information deduced from magnetic measurements.

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PubMed1996

New Metal Oxamates as Precursors of Low-Dimensional Heterobimetallics.

The goal of this work was to synthesize new molecular bricks which could be used as precursors of heterobimetallic low-dimensional compounds. Along this line, four compounds have been synthesized and structurally characterized, namely (NBu(4))(2)[Ni(Cl(2)opba)] (1), (NBu(4))(2)[Cu(Cl(2)opba)] (2), (NBu(4))(5)[Mn(Cl(2)opba)(DMSO)(2)](4) (3), and Cu(en)(2)[Mn(Cl(2)opba)(H(2)O)(2)](2).2DMSO (4), with Cl(2)opba = (4,5-dichloro-o-phenylene)bis(oxamato), NBu(4) = tetra-n-butylammonium, en = ethylenediamine, and DMSO = dimethyl sulfoxide. Compounds 1 and 2 are isostructural; they crystallize in the monoclinic system, space group C2/c, Z = 4, with a = 18.708(2) Å, b = 17.525(2) Å, c = 14.763(9) Å, and beta = 92.03(4) degrees for 1 and a = 18.928(2) Å, b = 17.634(2) Å, c = 14.704(9) Å, and beta = 92.38(3) degrees for 2. 3 crystallizes in the tetragonal system, space group P&fourmacr;2(1)c, Z = 2, with a = 26.295(10) Å and c = 12.342(7) Å. The structure shows a random occupation of the metal site by Mn(III) and Mn(II) ions in 3/4 and 1/4 ratios, respectively. 4 crystallizes in the triclinic system, space group P&onemacr;, Z = 1, with a = 7.066(7) Å, b = 11.844(1) Å, c = 14.292(5) Å, alpha = 105.64(2) degrees, beta = 97.67(5) degrees, and gamma = 102.13(3) degrees. The structure consists of Mn(III)Cu(II)Mn(III) trinuclear species, with Cu-O-Mn bridges involving oxygen atoms of the oxamato groups already linked to the metal atom. The magnetic properties of compounds 1-4 have been investigated and quantitatively interpreted. For 3, this magnetic investigation has been performed on a single crystal, which allows us to determine unambiguously the sign of the axial zero-field splitting parameter for the Mn(III) ion. The potentialities of these new molecular bricks have been discussed.

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