Das Methylviologen-Radikalkation. Synthese, Kristallstruktur und ab initio-Rechnungen von N,N′-Dimethyl-4,4′ -bipyridinium-chlorid-dihydrat / The Methylviologen Radical Cation. Synthesis, Crystal Structure and ab initio Calculations of N,N′ -Dimethyl-4,4′ -bipyridinium Chloride Dihydrate

The title compound has been prepared by the reduction of N,N′-dimethyl-4,4′-bipyridinium dichloride with dilithium tritelluride in dimethylformamide solution. It forms deep blue crystal needles, which were characterized by a crystal structure determination. Space group Pna 21,Z = 8,3450 observed unique reflections, R = 0.045. Lattice dimensions at -70°C: a =1707.6(8), b = 2323.9(11), c = 664.6(3) pm. The N,N′-dimethyl-4,4′-bipyridinium radical cations are planar and form ion pairs in the lattice. The chloride ions together with the water molecules form an infinite network of hydrogen bridges along the crystallographic a-axis. The structural parameters of the radical cation are in excellent agreement with ab initio calculations.