Synthesis of Conductors and Superconductors Based on Metal Bis-Dithiolene Complexes

2 Synthesis of Conductors and Superconductors Based on Metal Bis-Dithiolene Complexes 

Metal bis-dithiolene complexes exhibiting conducting or superconducting properties can be neutral or in a fractional oxidation state. In FOSCs, the associated cation is of the closed-shell type, while in DA compounds, the metal bis-dithiolene is an acceptor and the donor is an open-shell cation. As already mentioned in Section 4.2.2.3, the most encountered 

FOSCs can be obtained by further chemical oxidation of the corresponding C[M(dmit)2] precursor complex. However, in many cases direct aerial oxidation, or oxidation with an oxidising agent such as iodine or bromine, is not well controlled and a mixture of partially oxidised species with different stoichiometries is obtained an example is given by the bromine oxidation of [Bu4N][Ni(dmit)2]. Moreover, direct chemical oxidation mostly yields poor quality crystals. As any molecular conductors are insoluble in common solvents, it is not possible to recrystallise them. Therefore, in order to isolate good quality crystals, convenient for structural and physical studies, specific crystal growth techniques have to be used. 

The electrochemical method is the most widely used technique to grow FOSC crystals. The technique also appHes to grow crystals of DA compounds. The so-called electrocrystalUsation of molecule-based materials has been reviewed elsewhere. 

Except for the family of neutral extended TTF-dithiolene complexes, the conducting properties of DA compounds or FOSCs originate from the partial oxidation state of the constitutive molecules or building blocks. Two synthetic routes allow this feature to be realised (i) electrochemical oxidation of the complex, that is, change in its oxidation state, and 

---