The crystal structure of 2-2'-dichlorobenzidine (Cl.C₆H₃.NH₂)₂

Standard single crystal methods show that the unit cell of 2-2'-dichlorobenzidine is orthorhombic, with a, b, c translations 7.51, 15.20, 10.40 A. respectively; the cell contains four molecules and has space group Pnca. The atomic co-ordinates are deduced from two-dimensional Fourier syntheses of electron density projected on (100) and (001). The structure is racemic, the molecules showing a tendency to adopt the cis-configuration; steric hindrance, however, necessitates an angle of 72° between the planes of the two rings. The diphenyl link is 1.53 A. and the C-C bonds are alternately long and short with mean values 1.45 and 1.30 A. respectively.