Bimetallic Molecular-Based Magnetic Materials

Abstract

Among all the molecules and molecular assemblies relevant to molecular magnetism [1], those containing two (or possibly more) kinds of metal ions have played a particularly important role. Two reasons, at least, justify this situation. First, the diversity of the situations which can be encountered concerning the interaction between two spin carriers A and B within a molecular unit is much greater when A and B are different. For instance, the strict orthogonality of the magnetic orbitals leading to the stabilization of the molecular state of highest spin multiplicity is much easier to achieve in heterobimetallic than in homobimetallic species [2]. Secondly, with several kinds of magnetic centers, it is possible to design molecular lattices showing quite peculiar spin topologies. It is in particular the case of ferrimagnetic lattices.The first review article devoted to the magnetism of heteropolymetallic systems appeared in 1987 [3]. Since, this field has developed tremendously, in particular in relation with the synthesis of molecular-based magnets. This short review will be organized around the central theme of bimetallic magnets. The next section reviews some key concepts in molecular magnetism, such as spin delocalization and polarization, and then treats of the interaction between two spin carriers. Each subsequent section, from III to VII, is devoted to one type of bridge which have already allowed to design molecular-based magnets. To date, these bridges are : oxamato, oxamido, oxalato, dithiooxalato, oximato,

Effect of hydrostatic pressure on the crystal structure of sodium oxalate: X-ray diffraction study and ab initio simulations

“…Cations can occupy different positions within the framework formed by oxalate anions, so that their coordination polyhedra are different. Both "oxalate oxygen --metal cation" and "metal cation --metal cation" interactions account for the coordination of cations by oxalate ions "chosen" by a particular crystal structure [1][2][3][4][5].…”

“…In general, in their crystalline forms oxalate-ions are usually considered as structure-forming units, defining the crystal packing (the framework) and the positions of other species, in particular of metal cations [1][2][3]. The variety of crystal structures arises because the sequence of alternating close packed layers formed by oxalate anions can differ: mono-layer (AAA), double-layer (ABAB), triple layer (ABCABC), etc.…”

Two-Dimensional Nitroxide-Based Molecular Magnetic Materials

“…In contrast, the metal-radical approach [9,10] exploits the direct coordination of a ligand atom of high spin density to the [1] 4 , a molecule containing triply bridging methyl groups (hexacoordinate carbon), [5] a single-crystal study of polymeric [Mg{CH(SiMe 3 ) 2 } 2 ], a compound containing intermolecular methyl interactions of the type Si ± CH 3´´´M g, [6] and a single-crystal study of tetrameric [LiBMe 4 ], a compound with two different kinds of B ± CH 3´´´L i bridges. [7] [ [18] The principal distances and angles in 1 are similar to those reported earlier in the X-ray study.…”

“…These ferrimagnetic structures are assembled with polydentate bridging ligands such as oxalato, oxamato, oxamido, oximato, and dithiooxalato groups. [5] The use of these ligands has been fruitful, and several structures of high dimensionality have been reported. These include a few three-dimensional structures in which control over the chirality of the coordination sphere of the metal was achieved.…”

Green function study of a mixed spin‐2 and spin‐5/2 Heisenberg ferrimagnetic system on a honeycomb lattice

“…A number of intensive experimental works in the area have been carried out and the magnetic properties -that is, the molecular magnetism -has become an important focus of scientific interest [1][2][3][4][5]. Among these materials, many bimetallic molecule-based magnetic materials have exhibited ferrimagnetic properties, and these ferrimagnets in which two kinds of magnetic atoms regularly alternate antiferromagnetically to form two-dimensional honeycomb layered lattices seem to be rather well interpreted by the use of the mixed spin model [6]. In a ferrimagnetic material, there is the possibility of the existence of a compensation temperature: a temperature where the resultant magnetization vanishes below the critical temperature because of the different temperature dependence of the sublattice magnetizations [7].…”