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This round table itemized the present (batteries, antistatic coatings, food tags) and the short future applications of low dimensional materials (5 years from now: magnets, sensors, non linear optics, electrocatalysis, superconductivity), as well as the long term (10–40 years) ones, commonly grouped under the name “molecular electronics”. The advantages of low D materials were examined as well as the problems specific to each application, especially the long term ones. Finally the needs in research for the next years were examined.

The field of heteropolymetallic systems with magnetic metal centers occupies a crossing point between biology and physics. For instance the Cu(II)-Fe(III) interaction in cytochrome oxidase is of the same nature as the Cu(II)-Mn(II) interaction in a novel system which could be the first molecular ferromagnet. The mechanism of the interaction is discussed, both from a phenomenological view point using a spin Hamiltonian, and from an orbital view point. An orbital model for the isotropic interaction is presented. It is based on the concept of natural magnetic orbitals. The mechanism of the anisotropic and antisymmetric interactions is more briefly treated. The role of the Zeeman perturbation is then considered in relation with the magnetic and EPR properties of the heterobimetallic complexes. Several examples are presented to emphasize that the nature, ferro- or antiferromagnetic of the isotropic interaction is controlled by the symmetry of the magnetic orbitals. The concept of overlap density is introduced. It permits an estimation of the magnitude of the ferromagnetic stabilization in the case of orthogonality of the magnetic orbitals. The Cu(II)-Fe(III) interaction, in relation to the situation encountered in cytochrome oxidase, the Cu(II)-Ni(II) interaction and a few additional selected examples are discussed. A section deals with the case where one of the interacting ions has an orbital degeneracy. Afterwards, the heterotrinuclear complexes are studied. The important concept of regular and irregular spin state structure is developped and the Mn(II)Cu(II)Mn(II) triad is presented as a spectacular example of irregular spin state structure. A section is devoted to the ordered bimetallic chains. The theory is presented, both at a qualitative and quantitative levels and the already reported compounds of this kind are discussed. One of them may be considered as one of the first molecular ferromagnets. The last but one section concerns the systems with even more subtle spin orders. In conclusion, the vast perspectives of this area are outlined.

An approach of the exchange interaction phenomenon in polynuclear complexes grounded on the concepts of magnetic orbitals and of overlap density between these magnetic orbitals is proposed. The aim of this work is to show how these simple concepts can lead to a prevision of the variations of the JAFntiferromagnetic and the Jf ferromagnetic contributions to the J exchange parameter (J = Jaf + Jf) versus small structural changes in closely related complexes. In section 2, it is demonstrated that in binuclear complexes without direct metal-metal interaction, the exchange interaction can be studied by focusing on the overlap density between the magnetic orbitals around the bridging atoms. The section 3 deals with copper (II) dimers with the Open image in new window network; the influences of both the bridging angle θ defined as θ=2 CuXX and the dihedral angle D between the two CuXX planes are studied. The section 4 is devoted to Cu(II) — VO(II) and Cu(II)-low spin CO(II) heterobinuclear complexes in which a strict orthogonality of the magnetic orbitals is realized. The strong ferromagnetic coupling experimentally observed in CuV0(fsa)2en, CH3OH [H4(fsa)2en = N, N’-(2-hydroxy, 3-carboxy benzilidene) 1, 2-diaminoethane] is explained from the overlap density map for the appropriate model complex. A prospective study of the influence of an axial ligand coming near the Co(II) ion on the magnetic properties of Cu(II)- low spin Co(II) complexes is presented.

A convenient method for the synthesis of the previously unknown 2, 6-diformyl-4-trifluoromethylphenol is reported by a seven-stage synthesis. A methyl ether is used to protect the phenol moiety and the key-step involves a copper-mediated trifluoromethylation of a bromoanisole prepared from 4-bromophenol.

This contribution is devoted to the magnetic properties of the binuclear complexes with sulfur-containing bridging ligands. The theoretical background is presented in the first section, then the possibility to achieve a strong antiferromagnetic interaction between metal ions far away from each other through sulfur containing extended bridging ligands is discussed. The dithiooxamidato copper(II) binuclear complexes are presented as typical examples of this kind of compounds. The first results in the new field of the ordered bimetallic magnetic chains with sulfur containing bridges are mentioned. Finally, the magnetic properties of the iron-sulfur complexes are discussed.

Synthese des deux complexes CuFe[(fsa) 2 en]Cl(H 2 O) (CH 3 OH).CH 3 OH et [CuCr[(fsa) 2 en](H 2 O) 2 ]Cl.3H 2 O. Le complexe CuFe cristallise dans le groupe P2 1 /c. L'atome de cuivre possede une coordinence 5 et l'atome de fer une coordinence 6. Determination de la structure moleculaire de Cu Cr a partir de donnees IR. Interactions antiferromagnetiques pour CuFe et ferromagnetiques pour CuCr

When two paramagnetic transition metal ions are present in the same molecular entity, the magnetic properties can be totally different from the sum of the magnetic properties of each ion surrounded by its nearest neighbors. These new properties depend on the nature and the magnitude of the interaction between the metal ions through the bridging ligands. If both ions have an unpaired electron (e.g. Cu2+ ions), then the molecular state of lowest energy is either a spin singlet or a spin triplet. In the former case, the interaction is said to be antiferromagnetic, in the latter case ferromagnetic. The nature and the order of magnitude of the interaction can be engineered by judiciously choosing the interacting metal ions and the bridging and terminal ligands, and, thus, by the symmetry and the delocalization of the orbitals centered on the metal ions and occupied by the unpaired electrons (magnetic orbitals). The first success in this “molecular engineering” of bimetallic compounds was in the synthesis of a Cu2+VO2+ heterobimetallic complex in which the interaction is purely ferro-magnetic. The same strategy could be utilized for designing molecular ferromagnets, one of the major challenges in the area of molecular materials. Another striking result is the possibility of tuning the magnitude of the interaction through a given bridging network by modifying the nature of the terminal ligands, which, in some way, play the role of “adjusting screws”. By careful selection of the bridging and terminal ligands, a very large antiferro-magnetic interaction can be achieved, even if the metal ions are far away from each other. Some sulfur-containing bridges are especially suitable in this respect.

For a few years, we have participated to the efforts to design molecular systems ordering ferromagnetically. Molecular in this context means that we use the synthesis methods of the molecular chemistry -we work in solution with mild conditions of temperature and pressure- and that we attempt to build the tridimensional lattice by assembling molecular bricks in a controlable fashion. Our first step along this line has been to find a strategy leading to ferromagnetic interactions between nearest neighbor magnetic centers. This strategy is that of the orthogonality of the magnetic orbitals. When in an AB pair, the magnetic orbitals around A are all orthogonal to the magnetic orbitals around B, the interaction between A and B is purely ferromagnetic and the ground state of the pair has the highest spin multiplicity. We have synthesized several compounds of this kind involving pairs of metal ions1,2, or a metal ion and an organic radical3. This strategy to achieve a ferromagnetic interaction is very efficient in the sense that we have not found any counterexample so far. When the strict orthogonality of all the magnetic orbitals is realized, then the ground state has the highest spin multiplicity. However, the symmetry requirements allowing such an orthogonality are often difficult to obtain. A small distortion with regard to the ideal symmetry generally destroys this orthogonality, so that the interaction becomes antiferromagnetic with a stabilization of the state of lowest spin multiplicity.

In anABA symmetric and linear trinuclear system where the interaction between terminal ions is assumed to be negligible, the distribution in energy of the spin states depends on the relative values of the spinsS A andS B. If 2S A≤S B, the spin state structure is regular in the sense where the spin multiplicity varies monotonically with the energy; if 2S A>S B; it is irregular. A Cu(II)Ni(II)Cu(II) triad illustrates the former situation and a Mn(II)Cu(II)Mn(II) the latter. The concept of irregular spin state structure may be extended to the ordered bimetallic chains (AB) N withN→∞. The main theoretical ideas concerning these systems are presented as well as some typical examples. In particular, it is shown that a Cu(II)Mn(II) chain with an antiferromagnetic interaction between nearest neighbors exhibits a ferromagnetic-like behavior in the low temperature range. This corresponds to one-dimensional ferrimagnetism. Finally, it is emphasized that this concept of irregular spin state structure might lead to the first genuine molecular ferromagnets.

The structure of the title compound (I) at 19.6 K (space group P21/n, Z=4) is described by unpolarized neutron diffraction.

The first two transition metal compounds incorporating triazole−nitronyl−nitroxide radicals as ligands have been synthesized. These compounds are [Cu(4-Me-3-Nit-trz)4](ClO4)2 (1) and [Ni(4-Me-3-Nit-trz)4](ClO4)2 (2) with 4-Me-3-Nit-trz = 2-(3-[4-methyl-1,2,4-triazolyl])-4,4,5,5-tetramethylimidazoline-1-oxyl 3-oxide. Compound 1 crystallizes in the triclinic system, space group P1. The lattice parameters are a = 9.742(2) A, b = 12.214(12) A, c = 12.981(4) A, α = 67.19(4)°, β = 81.48(2)°, and γ = 79.24(4)°, with Z = 1. The structure consists of centrosymmetrical [Cu(4-Me-3-Nit-trz)4]]2+ cations and noncoordinated perchlorate anions. The Cu(II) ion is in an N4O2 elongated tetragonal environment with two oxygen atoms of two nitroxide groups occupying the apical positions. Within the lattice the cations form infinite chains with short intermolecular contacts involving the nitronyl−nitroxide moieties of two adjacents cations. The temperature dependence of the magnetic susceptibility and the field dependence of ...

A sugar-substituted ligand allowed for the synthesis of chiral Cu(II) tetranuclear aggregates which assemble via H-bonding in a 3D-network containing hydrophobic helical channels.

New iron(II) spin crossover systems with large aromatic ligands, based on 2′-pyridylmethylene 4-anilino units, have been synthesized and studied. The whole range of spin crossover behavior has been observed, starting from pure high-spin to more or less complete gradual transitions and finally to discontinuous type transitions with both small and large hysteresis. Magnetic measurements under pressure have revealed that two of the compounds exhibit pressure-induced new phases with larger hysteresis than at atmospheric pressure. For one of the compounds the formation of this new phase is irreversible and the hysteresis width is ∼100 K, as compared to 37 K before applying pressure.

The high-spin-low-spin (HS-LS) transition in iron(II) complexes was studied by the recently developed quantum chemical effective Hamiltonian method. This method uses a trial wave function which is an antisymmetrized product of the fully correlated function of d-electrons and of the Slater determinant of the ligand MOs instead of the conventional Hartree-Fock single determinant trial wave function built of the molecular orbitals spread over an entire complex. This approach allowed us to explicitly take into account the d-electron correlations, the weak covalence of the metal-ligand bonds, and the electronic structure of the ligands. The cooperativity effects in the HS-LS transition occurring in the crystals are briefly discussed and the contribution from the Coulomb forces to the intermolecular interaction responsible for the cooperativity is estimated.

Summary form only. Optically nonlinear organic materials show considerable potential for applications in optical signal processing and telecommunication. Recently, transition metal organometallic complexes have emerged. Compared to organic molecules, they offer a large variety of structures, high environmental stability, and much greater diversity of tunable electronic properties. Here, we report on the study of the first hyperpolarizability /spl beta/ of two homologous series of [M(PM-BiA)/sub 2/(NCS)/sub 2/] and [M(PM-2PEA)/sub 2/(NCS)/sub 2/] (M=Mn, Fe, Co, Ni, Zn) transition metal complexes. The influence of the /spl beta/ of the ligand and of the metal electronic configuration in octahedral geometry upon the second-order nonlinear response on passing from closed-shell to open-shell electronic structures is evidenced.

[Fe(hyetrz)3](3-nitrophenylsulfonate)2·3H2O (1·3H2O), with hyetrz = 4-(2‘-hydroxyethyl)-1,2,4-triazole, has been synthesized, and its physical properties have been investigated with several techniq...

Muon spin relaxation ( μ SR) studies were conducted on the organic ferromagnet MnCu(obbz). 1H 2 O (T c =14K), where the unpaired spins reside on d-orbitals only. The asymmetry vs. time data recorded between 5K and 65K under zero and longitudinally applied fields did not show oscillatory behaviour but indicated that the transition to the ordered state is almost complete. A fit based on a simple exponential depolarising function indicates spin fluctuations far above the Curie temperature.

The title heterobinuclear complex exhibits a very strong ferromagnetic coupling due to the orthogonality of the magnetic orbitals; it can also show the intramolecular electron transfer CoIICuII⇌ CoIIICuI.

We propose a model of the interaction between the metallic centers of a polymetallic system which permits not only the rationalization of most of the results already known, but also the design of new systems exhibiting expected properties. If we consider a copper(II) dimer, the interaction leads to two low lying states, a spin singlet and a spin triplet, separated by J . The interaction is said to be antiferromagnetic if the spin singlet is lower in energy ( J J > 0). In our model, the energy gap J is the algebraic sum of two components, J AF and J F , favoring the antiferro- and the ferromagnetic situations respectively. In some way, the sign and the magnitude of J result from the opposition between two fighters. These fighters, as the gladiators, have not the same tools. The tools of the antiferromagnetic gladiator are the overlap S between the magnetic orbitals and the energy gap Δ between the molecular orbitals built from the magnetic orbitals. The tool of the ferromagnetic gladiator is the two-electron exchange integral C between the magnetic orbitals: J = J AF + J F J AF = −2Δ S J F = −2C The concept of magnetic orbital will be specified. The antiferromagnetic gladiator is generally more efficient than his component. This is particularly true when the metallic centers are largely separated (more than ca. 4 A). We shall show how it is possible to tune the efficiency of the tools of the antiferromagnetic gladiator in a given bridging network, by playing on the nature of the terminal ligands. We shall emphasize that the interaction may be very large even when the metallic centers are far away from each other. Some new bridging ligands particularly appropriate for transmitting electronic effects over long distances will be presented. In some quite peculiar cases; it is possible to annihilate the trenchant of the tools of the antiferromagnetic gladiator, by realizing the orthogonality of the magnetic orbitals. J is then positive and the ground state is the state of highest spin multiplicity. This orthogonality can be strict or accidental. Examples corresponding to both situations will be preseted. In this respect, the extraordinary versatility of the azido bridging ligand in stabilizing either the singlet state or the triplet state in copper(II) dimers will be pointed out. In conclusion, the relevance of our work to the study of the polymetallic sites in biological systems will be discussed.

A model Hamiltonian proposed by Lines describing the magnetomechanical doupling in a magnetic dimer, is investigated. An exact solution is obtained, exhibiting variations in the nuclear geometry and vibration frequency within the different spin terms. Some theoretical and experimental implications are pointed out.

Although significant advancements have been achieved during the last years in the interpretation of the nature and the magnitude of the exchange interaction which occurs in polynuclear complexes with paramagnetic centers, a lot of problems remain to be solved in this field. For instance, in all the orbital models proposed so far to describe the exchange interaction in an A–B dimer, the J parameter of tshe phenomenological exchange Hamiltonian −J ŜA·ŜB is expressed as the sum of a negative anti-ferromagnetic contribution JAF and a positive ferromagnetic contribution JF. Whereas successful efforts have been spread out to understand how JAF varied versus small structural changes in series of similar complexes, the influence of these structural modifications on JF has never been investigated. And yet it is not doubtful that, as JAF, JF must depend on the geometry of the complex. In our lecture, we shall proposed an approach of the exchange interaction grounded on the concepts of magnetic orbitals and of overlap densities between magnetic orbitals. It is important to specify here that we do not look for proposing, after many other authors, some new mathematical considerations on the exchange but, on the contrary, to extract from the existing theory a very small number of simple and essential ideas and slow how they can lead to a prevision of the variations of JAF and JF in closely related complexes. Our results will be presented under the form of overlap density maps. In the same manner as the walker finds his way with the help of the map of the region, we wish that the experimentalists (of which we are) obtain useful informations on the complexes that it would be interesting to synthetize with the help of overlap density maps as those shown during the lecture. Such a map is schematized below for the case of a Cu(II) VO(II) heterobinuclear complex. According to the available time, we intend to approach some of the following situations:(i) planar [1] and roof-shaped [2] hydroxo-bridged copper(II) dimers; (ii) heterobinuclear complexes in which the strict orthogonality of the magnetic orbitals is realized [3]; (iii) very strong antiferromagnetic coupling between transition ions far away from each other [4]; (iv) orbital reversal in copper(II) polynuclear complexes through the action of solvent molecules [5].