Metalloceniums

Metallocenium Salts of Transition Metal Bisdichalcogenate Anions Structure and Magnetic Properties... 

Keywords Crystal structures, Magnetic properties, Metallocenium salts, Metal-bisdithiolenes... 

This review concerns the materials made from the combination as charge transfer salts of the above-mentioned metallocenium cations with transition metal bisdithiolene anions, expanding and updating a previous review [34]. Most of the materials studied so far are decamethylmetallocenium based salts, but other compounds based on different metallocenium derivatives have also been reported and will be also referred. 

Fig. 2 (a) Basic structural mixed chain motifs of the metallocenium based salts of metal bisdichalcogenate anions, (b) Variations of the type IV chain motif... 

Table 1 Cation and anion S values basic structural motives Weiss constants transition temperatures, magnetic ordering critical fields of the salts based on metallocenium and on metal bisdichalcogenate complexes ... 

Besides the decamethylmetallocenium salts, in the compounds based on other metallocenium derivatives, mixed linear chain arrangements were only observed in the case of the salts [Fe(C5Me4SCMe3)2][M(mnt)2], M = Ni and Pt, which present type I structural motives. 

In this section the salts based on metallocenium cations and metal bisdichalcogenate anions will be reviewed according to the previously referred structural classification. After referring to the general characteristics of the crystal structures the supramolec-ular features will be correlated with the magnetic properties. 

Table 2 Cation and anion S values Weiss constants of the metallocenium salts of metal bisdichalcogenate complexes based on segregate chains of anions...

The compounds [Fe(C5Me4SCMe3)2][M(mnt)2] (M = Ni, Pt) are the only cases of salts based on metallocenium derivatives and on [M(mnt)2 complexes where the crystal structure is based in parallel arrangements of the type I chain motif [49]. In the chains the [Pt(mnt)2]- units are considerably tilted in relation to the chain direction, and short interatomic D+A- intrachain contacts were observed, involving one C from the Cp and a S atom from the anion, with a C-S distance of the order of dtf/. Relatively short interchain interionic distances were observed, where the closest corresponds to a S... C, involving one S atom from the anion and a C atom from a Me group of the cation, exceeding dw by 10%. 

In the salts based on segregated stacks of metallocenium-based cations with [M(mnt)2)] (M = Ni, Pd and Pt) anions, the anionic stacks are isolated from each other by the cations in a few compounds these stacks are regular (at high temperatures) but in most cases the [M(mnt)2)] units form dimers. The magnetic behavior of these compounds is dominated by the AF interactions between the anion units. 

The study of salts based on metallocenium cations and transition metal bisdichal-cogenide anions was started almost 20 years ago and it experienced a renewed interest in the last few years, allowing a large number of compounds to be characterized. These studies, as summarized in this review, enabled it to be clearly... 

Abstract Metal complexes including the dmit2- (1,3-dithio-2-thione-4,5-dithiolato) ligand are the only class of metal bis-dithiolenes to give rise to superconductive molecular materials. This chapter first focuses on the description of these superconductive phases. Further sections describe the association of M(dmit)2 moieties with three types of magnetic molecules, i.e., metalloceniums, radical cations, and spin crossover complexes. 

Keywords M(dmit)2, Metal bis(dithiolene), Metallocenium, Radical cations, Spin crossover, Magnetic properties, Superconductor... 

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