1,2-Dithiolene ligands

Coordination compounds of dianionic dithiolene (S2C2 R2) and benzene-1,2-dithiolene (bdt = (S2C6H4) and their derivatives have been studied since the 1960s by Mossbauer spectroscopy [87] and other techniques. Nevertheless, many aspects of their electronic structure remained uncertain for a long time. The five-coordinate ferric complexes with two equatorial dithiolene ligands exhibit intermediate spin and show the Mossbauer parameters = 0.25-0.38 mm s and A q = 1.6-3.2 mm s For example, [Fe° mnt)2/ y] with two mnt ligands (=S2C2(CN)2) and an... 

Dithiolene complexes [ Pd(PPh3)2 ra S2C=CCHC(0)R ] are mononuclear or homodinuclear derivatives of ferrocenyl-substituted dithiolene ligands.530 2,2-Diacetyl-1,1-ethylenedithiolato complexes of palladium can be used to prepare dinuclear PdAg and PdAu complexes 531... 

The structures and redox properties of these complexes have been extensively reviewed 170,171 of interest here is the presence of an intense NIR transition in the neutral and mono-anionic forms, but not the dianionic forms, i.e., the complexes are polyelectrochromic. The positions of the NIR absorptions are highly sensitive to the substituents on the dithiolene ligands. A large number of substituted dithiolene ligands has been prepared and used to prepare complexes of Ni, Pd, and Pt which show comparable electrochromic properties with absorption maxima at wavelengths up to ca. 1,400 nm and extinction coefficients up to ca. 40,000 dm3 mol-1 cm-1 (see refs. 170,171 for an extensive listing). 

Figure 6 Metal complexes based on 1,2-dithiolene ligands...

Dithiolene Ligands and Related Selenium and Tellurium Compounds... 

Scheme 2 Selected 1,2-dithiolene ligands and commonly used acronyms. All ligands have been drawn in their 1,2-dithiolato form...

This makes it difficult to assign clearly separated formal charges to the metal and to the ligand, which would not be meaningful as a consequence of the noninnocent nature of 1,2-dithiolene ligands.53,54 In Scheme 5, the case of neutral diamagnetic square-planar Zw(l,2-dithiolene) complexes is illustrated. 

Finally, it should be noted that tellurium can act not only as ligand donor site in 1,2-ditellurolene ligands, but can itself be bound by 1,2-dithiolene ligands, as in the case of compounds containing [Te(mnt)2]2 and [Te(dtsq)2]2 dianionic... 

We are therefore faced here with radical complexes which easily distort depending on the structural arrangement and whose SOMO is different for every crystal structure associated with a given counter-ion, a very original feature in these series. The unfolded d1 complexes can be described as Mo(IV) complexes with a spin density essentially localized on the dithiolene ligand while the more folded complexes have a stronger metal character. This variable spin density delocalization is expected to influence strongly the amplitude and dimensionality of intermolecular interactions between radical species in the solid state, as detailed below in Sect. 3. 

CpMo(S2C2Ph2)2] at 2.0275, 2.0074 and 1.9936 or from oriented single-crystal for [Cp Mo(dmit)2] at 2.027, 2.012 and 1.992, demonstrate an extensive delocalization of the unpaired electron the dithiolene ligands. The solid state properties of these series of radical complexes will be described below in detail in Sect. 3. 

---