Yves Journaux

Coordination chemistry of N,N′-bis(coordinating group substituted)oxamides: a rational design of nuclearity tailored polynuclear complexes

Abstract The coordinating properties of N , N ′-bis(coordinating group substituted)oxamides have been thoroughly investigated both in aqueous solution and in the solid state. The easy cis – trans isomerization equilibria that they exhibit together with the great variety of N , N ′-substituents which can be used to play on the overall charge, complexing ability and polarity, make them very suitable ligands in designing homo- and heterometallic species. The knowledge of their complex formation in aqueous solution by potentiometry and using the hydrogen ion concentration as a probe, allowed us to settle the basis of a rational design of oxamidate-containing polynuclear species whose nuclearity can be easily tuned. Concerning their electronic properties, the strong basicity of the deprotonated amide–nitrogen atoms stabilizes high oxidation states of late first-row transition metal ions. Finally, one of the most appealing aspects of this type of ligands is the remarkable efficiency they exhibit to mediate strong antiferromagnetic interactions between paramagnetic centres when acting as bridges but in order to maintain the present work within a rational length, we have omitted this last point which deserves a further review.

Synthesis, Structural Characterisation, and Monte Carlo Simulation of the Magnetic Properties of the 3D-Stacked Honeycomb Csn[{Mn(N3)3}n] and the Irregular Double Chain [{N(C2H5)4}n][{Mn2(N3)5(H2O)}n]

Two new polymeric manganese-azido systems with formula Cs(n)-[[Mn(N3)3]n] (1) and [[N(C2H5)4]n][[Mn2-(N3)5(H2O)]n] (2) were synthesised and structurally characterised. Compound 1 crystallises in the P2(1)/n group and consists of a three-dimensional system with end-to-end and end-on azido bridges with the caesium atoms in the holes of the net. Magnetically, compound 1 is a rare case of a three-dimensional network with alternate ferro-antiferromagnetic interactions. Compound 2 crystallises in the P1 group and consists of double chains of manganese atoms bridged by end-on and, the exceptional, (mu-1,1,1)-azido bridges. Magnetically, compound 2 shows net ferromagnetic behaviour. Exact fit of the magnetic data was performed for the two compounds by means of Monte Carlo simulations based on the Metropolis algorithm on sets of 10 x 10 x 10 (1) and 1 x 1 x 320 (2) S = 5/2 classical spin centres.

Natural or orthogonalized magnetic orbitals: Two alternative ways to describe the exchange interaction

Abstract The two approaches defined in the title, NMO and OMO, are compared and their advantages discussed. In the OMO approach, the stabilization of the spin singlet arising apparently from the ground configuration-charge-transfer configuration coupling is in fact a black box which implicitly contains a first-order contribution independent of the energy gap between the two configurations.

Highly Selective Chemical Sensing in a Luminescent Nanoporous Magnet

Among the wide variety of properties of interest that a given material can exhibit, luminescence is attracting an increasing attention due to its potential application in optical devices for lighting equipment and optical storage, [ 1a − c] optical switching, [ 1d ,e] and sensing. [ 1f − i ] At this respect, many scientists, working in the multidisciplinary fi eld of the materials science, have directed their efforts to the obtention of luminescent materials with potential sensing applications. For instance, sensitive and selective detection of gas and vapor phase analytes can result specially interesting because of the variety of applications that can be found in many different fi elds. A key principle concerning the luminescent chemosensors [ 2 ] is that they must be able to detect differences between small molecules, [ 2 , 3 ] and sequentially implement a recognition– transduction protocol. [ 2b ] In this sense, the remarkable shape selectivity of a class of highly porous materials, the so-called metal-organic frameworks (MOFs) [ 4 ] which have already shown applications in different fi elds (gas storage and separation, molecular recognition and catalysis, molecular electronics and spintronics, molecular photonics, etc) [ 4–6 ] has converted them in excellent candidates for the fabrication of chemical sensors. [ 2 , 3 ] The key point responsible for the high potential success of MOFs as chemo-sensors is the exceptional tunability of their structures and properties.

Trinuclear magnetic clusters based on cyanide metal complexes: synthesis, crystal structures, and magnetic properties of four new [MnII2MIII] complexes (M = Cr, Fe, Co)

Four new cyano-bridged [MnIIMIIIMnII] heterotrinuclear complexes (MIII = Cr, Fe, Co) have been synthesized and crystallographically characterized: {[(H2O)L1Mn–NC–Cr(CN)4–CN–MnL1(H2O)]}3[Cr(CN)6]·10H2O 1, [(H2O)L2Mn–NC–M(CN)4–CN–MnL2(NCS)]·2H2O 2, [(H2O)L2Mn–NC–Fe(CN)4–CN–MnL2(H2O)](NCS)·1.5H2O 3, and [(H2O)L2Mn–NC–Co(CN)4–CN–MnL2(H2O)](NCS)·1.5H2O 4 (L1 = 2,13-dimethyl-3,6,9,12,18-pentaazabicyclo[12.3.1]octadeca-1(18),2,12,14,16-pentaene, L2 = 2,13-dimethyl-6,9-dioxa-3,12,18-triazabicyclo[12.3.1]octadeca-1(18),2,12,14,16-pentaene). The crystal structure of 1 consists of independent [MnCrMn] monocations whose charges are counterbalanced by [Cr(CN)6]3− anions. The crystal structure of 2 consists of neutral heterotrinuclear [MnCrMn] species, with the isothiocyanato ion coordinated to one of the manganese atoms. Compounds 3 and 4 are isomorphous. Their crystal structure consists of centrosymmetric [MnMMn] entities, uncoordinated NCS− ions, and solvent molecules. The magnetic properties of the four complexes have been investigated. Compounds 1 and 2 are new examples of systems with an irregular spin state structure, exhibiting the characteristic minimum on the the χMTversusT curves. The exchange interaction between the chromium(III) and the manganese(II) ions is antiferromagnetic (1: J = −9.8 cm−1; 2: J = −6.52 cm−1). For compound 3, the exchange interaction between manganese(II) and iron(III) was found to be ferromagnetic.

Alcohol Oxidation by Dioxygen and Aldehydes Catalysed by Square-Planar Cobalt(III) Complexes of Disubstituted Oxamides and Related Ligands

The square-planar cobalt(III) complexes of o-phenylenebis(N′-methyloxamidate) (Me2opba) and related oxamate (Meopba) and bis(oxamate) (opba) ligands catalyse the selective oxidation, by dioxygen and pivalaldehyde, of a wide range of secondary alcohols to the corresponding ketones, in good yields and under mild conditions in acetonitrile at room temperature. Thus, the oxidation of the series of α-alkylbenzyl alcohols PhCH(OH)R (R = Me, Et, iPr, tBu) results in the exclusive formation of ketones as a product of C−H bond cleavage, and no C−C bond cleavage products are observed in any case. The modulation of catalytic activity by ligand substituents among this series of cobalt catalysts highlights the role of oxocobalt(IV) species as the putative intermediates in these aerobic alcohol oxidation reactions. Relative reactivities for the oxidation of 1-phenylethanol increase in the order Me2opba < Meopba < opba, which correlates with the oxidising power of the postulated CoIV=O intermediate. In contrast, competitive reaction studies on the oxidation of the series of para-substituted 1-phenylethanol derivatives XPhCH(OH)CH3 (X = H, OMe, Br, CF3, NO2) show little variation in relative rate (kX/kH) with the para substituent and no correlation with Hammett σ parameters. Overall, these results are more in line with a mechanism involving concerted hydride transfer in the oxidation of alcohols by high-valent oxocobalt species (rather than a hydrogen atom transfer or an electron transfer mechanism).

Ferromagnetic Coupling by Spin Polarization in a Trinuclear Copper(II) Metallacyclophane with a Triangular Cage-Like Structure

A series of trinuclear copper(II) complexes of general formula A(6)[Cu(3)L(2)] x nH(2)O [L = benzene-1,3,5-tris(oxamate); A = Li(+) (n = 8), 1a; Na(+) (n = 11.5), 1b; and K(+) (n = 8.5), 1c] have been synthesized, and they have been structurally and magnetically characterized. X-ray diffraction on single crystals of 1c shows the presence of three square-planar copper(II)-bis(oxamato) moieties which are connected by a double benzene-1,3,5-triyl skeleton to give a unique metallacyclophane-type triangular cage. The copper basal planes are virtually orthogonal to the two benzene rings, which adopt an almost perfect face-to-face alignment. Complexes 1a-c exhibit a quartet (S = 3/2) ground spin state resulting from the moderate ferromagnetic coupling (J values in the range of +7.3 to +16.5 cm(-1)) between the three Cu(II) ions across the two benzene-1,3,5-tris(amidate) bridges [H = -J(S(1) x S(2) + S(2) x S(3) + S(3) x S(1)) with S(1) = S(2) = S(3) = S(Cu) = 1/2]. Density functional theory calculations on the S = 3/2 Cu(II)(3) ground spin state of 1c support the occurrence of a spin polarization mechanism for the propagation of the exchange interaction, as evidenced by the sign alternation of the spin density in the 1,3,5-substituted benzene spacers.

Aerobic epoxidation of olefins catalysed by square-planar nickel(II) complexes of bis-N,N′-disubstituted oxamides and related ligands

The new square-planar nickel(II) complexes of o-phenylenebis(N′-methyloxamidate) and related ligands catalyse the aerobic epoxidation of olefins with co-oxidation of pivalaldehyde; the modulation of catalytic activity by substituents along this series of metal complexes points out the role of high-valent nicke(IV)-oxo species as the putative intermediate in these oxygen atom transfer reactions.

Topological ferrimagnetic behavior of one new chain with the new AF/F/F'/F'/F alternating sequence

An azido-bridged chain with formula [Mn(Menic)(N3)2]n, where Menic is methylnicotinate, was prepared and studied from the magnetic point-of-view. This compound crystallizes in the monoclinic system, space group P21/a, with a = 15.556(2), b = 16.831(2), c = 17.595(2) A, β = 110.80(1)° and Z = 10. The structure consist of a one-dimensional system in which each manganese atom is bridged by two azido ligands in a trans arrangement. Along the chain there are four double end-on azido bridges followed by one double end-to-end azido bridge. This unusual kind of alternation leads to a new one-dimensional magnetic behavior, which has been studied by means of susceptibility and single crystal ESR measurements. The magnetic response has been reproduced by Monte Carlo simulations and exact laws following the classical approach. The characteristic signature of the magnetic behavior has allowed us to determine the three different magnetic coupling constants present in this system. These results have been analyzed in the framework of a theoretical and experimental magneto-structural correlation.

Supramolecular Assembly with Calix[6]arene and Copper Ions − Formation of a Novel Tetranuclear Core Exhibiting Unusual Redox Properties and Catecholase Activity

The supramolecular biomimetic chemistry based on calix[6]arene N-ligands has been further explored. A tris(imidazole)CuI complex was treated with 1 mol-equiv. of cuprous ion under dioxygen to produce a tetranuclear cupric species. X-ray structural determination of this novel Cu4 complex revealed that the self-inclusion of an imidazolyl coordinating arm into the hydrophobic calixarene cavity provides the base of coordination for a {ClImCu(OH)2CuIm2}2 assembly. The Cu4 core is maintained in solution and is stable even in a coordinating solvent such as acetonitrile. Magnetic susceptibility measurements evidenced a strong antiferromagnetic coupling in each Cu(OH)2Cu subunit with J = −408 cm−1. The complex displayed catecholase activity in the presence of 3,5-di-tert-butylcatechol behaving as a four-electron hole with, however, a sluggish CuI4 ⇄ CuII4 regeneration through O2 autooxidation. Finally, electrochemical studies revealed two oxidative reversible processes that successively gave rise to a {CuIICuIII}{CuII2} and a {CuIICuIII}2 mixed-valence species that could be characterized by UV/Vis and EPR spectroscopy. The overall structure and behavior of this tetranuclear complex is reminiscent of multicopper enzymes. (© Wiley-VCH Verlag GmbH, 69451 Weinheim, Germany, 2002)