1,2-Dicyanoethylene-1,2-dithiolate ligand

Transition metal complexes (1) of 1,2-dicyanoethylene-1,2-dithiol (maleonitrile), mnt, have received special study since this ligand can stabilize transition metals in a variety of oxidation states and the high electron affinity of the terminal cyanide groups aids the delocalization of charge within the complex, thus reducing potential coulombic repulsions. 

Indium(III) complexes of dianionic sulfur ligands are mostly those derived from toluene-3,4-dithiolate (TDT ), l,2-dicyanoethylene-l,2-dithiolate (MNT ), 1,2-ethanedithiol (EDT ), or l,l-dicyanoethylene-2,2-dithiolate (i-MNT ). Various adducts (e.g., four-coordinate [In(MNT)2], five-coordinate [XIn( -MNT)2] (X = C1, Br, or I), or six-coordinate [In( -MNT)3] ) have been reported. " ... 

The two best characterized examples are (Ph4P)3[Os(mnt)3] (mnt = cis-l,2-dicyanoethylene-l,2-dithiolate), made from [OsBr ] " and the sodium salt of the ligand with Na2S204 Os(tdt)j (tdt = toluene-3,4-dithiol), a black material made from the hand and [OsBr ] in base, and (Me4N)[Os(tdt)3] for which a similar reaction is used but sodium dithionite is used as reducing agent. The ESR spectrum of [Os(mnt)3] has been measured and also IR and electronic spectra on the tdt complexes. Cyclic voltammetric studies on Os(tdt)3 show that the redox system in equation (10) exists. ... 

The polarographic reduction of a number of InL complexes (L = toluene-3,4-dithiolate) [InL2D] (D = phen, bipy, etc.), InLl" (L= l,2-dicyanoethylene-l,2-dithiolate), etc., in non-aqueous solution demonstrated a series of reversible one-electron changes corresponding formally to In ->In In - In°, in contrast to the In - In° reduction observed in aqueous solution. As noted above (Section 25.2.3.3), the formal oxidation states are assigned to the metal on the assumption that the ligand itself is not reduced, and this remains to be confirmed experimentally. 

MLCT metal-to-ligand charge transfer mn " = l,l-dicyanoethylene-2,2-dithiolate mtc" = di-n-propylmonothiocarbamate = methyl viologen Np = I-naphthyl... 

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