Reaction of N,N'-dimethylimidazolidine-2-selone (4) with TCNQ. Characterisation and X-ray crystal structure of the mixed-valence compound 4.(TCNQ)(1.167)

The reaction of 1,3-dimethyl-2-imidazolidineselone (I) with TCNQ affords lustrous dark crystals with elemental anal. corresponding to the formula I·(TCNQ)1.167. X-Ray crystal structure detn. shows that this compd. is formed by discrete [I2]2+ dications, in which two oxidized imidazolidine mols. are bonded through an -Se-Se- bridge [2.5187(7) Å]. These dications interact on one side with a third disordered mol. of I (occupancy factor 0.5) via Se···Se soft interactions of 2.715(4) and 2.899(4) Å to give almost linear -Se-Se···Se- arrangements [Se(2)-Se(1)···Se(3), 177.64(6)° and Se(2)-Se(1)···Se(3a), 167.89(5)°]. The unit cell contains six imidazolidine mols. bearing a total of four pos. charges, balanced by four neg. charges distributed on seven TCNQ mols., stacked in two dimers and a trimer. Structural data suggest that the neg. charges are unevenly distributed on the TCNQ mols. Single crystal IR spectra also suggest the presence of at least three differently charged TCNQ's, and in addn. indicate a room temp. optical gap of ∼0.3 eV, placing this compd. among wide bandgap semiconductors (σ = 3.45 × 10-3 S cm-1). Cyclic voltammetry of I is discussed in comparison with those of previously studied 2-imidazolineselone derivs. [i.e., 1,3-dihydro-1,3-dimethyl-2H-imidazole-2-selone, 1,1'-methylenebis[1,3-dihydro-3-methyl-2H-imidazole-2-selone], 1,1'-(1,2-ethanediyl)bis[1,3-dihydro-3-methyl-2H-imidazole-2-selone]], and shows that for this donor the achievement of a mixed valence compd. with TCNQ is possible in MeCN.