Charge - Transfer Complexes of Metal Dithiolenes XXIV: Ion Pairs of the Tetrakis(dimethylamino)ethene Dication with Dithiolene Metalate Dianions

The dication of tetrakis(dimethylamino)ethene (TDAE2+) forms ion pair complexes with [M(mnt)2]2~, mnt2= maleonitrile-2,3-dithiolate, M(II) = Ni, Pd, Pt, and Zn. According to X-ray analysis the structure of {TDAE2+[Pt(mnt)2]2~ } consists of a chain-like arrangement of planar dianions and twisted (71°) dications. Shortest interionic contacts are 11 pm longer than the corresponding van der Waals radii. In the UV-VIS diffuse reflectance spectra of the complexes with a d8 central metal there is no unambiguous evidence for the presence of an ion pair CT band. This band is observed, however, at 450 nm when the d 10 metal Zn(II) is present. Application of the Hush-Marcus model affords a reorganization energy of 110 kJ / mol for electron transfer from [Zn(mnt)2]2to TDAE2+. This value is 40 kJ / mol higher than the one reported for the analogous complex wherein TDAE2+ is replaced by a 2,2'-bipyridinium acceptor of similar reduction potential.