Magnetochemistry: advances in theory and experimentation

Polynuclear NiII and MnII azido bridging complexes. Structural trends and magnetic behavior

Zero-field splitting in metal complexes

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.

Magnetism of the heteropolymetallic systems

The isostructural, chiral molecular magnetic materials with the formula [MxM'(2-x)(ca)2(1,4-dimb)]n [H2ca = D-(+)-camphoric acid, 1,4-dimb = 1,4-di-(1-imidazolyl-methyl)-benzene, M = Ni(II), M' = CoII, 0 < or = x < or = 2] consist of ca-bridged (4,4) layers with [M2(O2CR)4] as secondary building units that are pillared by the 1,4-dimb ligands into a unique 3D framework. The high-spin octahedral symmetry and the proportions of the mixed-metal ions were characterized by UV-vis spectroscopy. The compounds exhibit the onset of antiferromagnetic ordering at 7.5 approximately 23 K, as well as weak ferromagnetism, spin-flop, and glassy behavior that result from the randomness of the mixed-metal pairs, magnetic anisotropy of the metallic cations, and antisymmetric exchange. The composites should be regarded as molecular alloys of the pure Ni(II) and Co(II) compounds. The magnetic behavior of the solid solutions shows unambiguously that the organic bridges, bond angles, and bond distances greatly influence the effective interactions and bring about cooperative magnetic behavior in the chiral 3D frameworks.

Chiral Magnetic Metal-Organic Frameworks of Dimetal Subunits: Magnetism Tuning by Mixed-Metal Compositions of the Solid Solutions

Magnetic exchange in transition metal complexes. IX. Dimeric nickel(II)-ethylenediamine complexes

Magnetic exchange in transition metal complexes. IV. Linear trimeric bis(acetylacetonato)nickel(II)

Parallel spin coupling via a three-atom covalent bridge in di-.mu.-thiocyanato-tetrakis(ethylenediamine)dinickel(II) iodide

Ferromagnetic Ni–Ni interactions in trimeric bis(acetylacetonato)nickel(II)

Magnetischer austausch in uebergangsmetallkomplexen 5. mitt. ferromagnetische spinkopplung von tetrakis-(my(3)-methoxo-pentandion-(2,4)-ato-methanol-nickel(ii))

A. P. Ginsberg

Papers

Magnetic exchange in transition metal complexes. IX. Dimeric nickel(II)-ethylenediamine complexes

Magnetic exchange in transition metal complexes. IV. Linear trimeric bis(acetylacetonato)nickel(II)

Parallel spin coupling via a three-atom covalent bridge in di-.mu.-thiocyanato-tetrakis(ethylenediamine)dinickel(II) iodide

Ferromagnetic Ni–Ni interactions in trimeric bis(acetylacetonato)nickel(II)

Magnetischer austausch in uebergangsmetallkomplexen 5. mitt. ferromagnetische spinkopplung von tetrakis-(my(3)-methoxo-pentandion-(2,4)-ato-methanol-nickel(ii))