The structure of the title compound (hereinafter called PALDIM) has been determined by a 3-dimensional X-ray crystallographic analysis. The space group is orthorhombic, P212121, and cell parameters are a= 5·468, b= 20·442, c= 13·088 Å. X-ray intensity data were measured on a computer-controlled diffractometer with Cu radiation. Least-squares structure refinement used anisotropic temperature factors for C and N and isotropic terms for H. The final R factor was 0·021. An electron density difference map showed evidence for solid state disorder in terms of two half-hydrogen atoms positioned in the N⋯N region. A single, symmetrical H location also could be ruled out from X-ray photoelectron spectroscopic data. Bond lengths and angles in the N⋯HN regions of PALDIM and 1-methylamino-7-methylimino-1,3,5-cycloheptatriene indicate that the intramolecular H bond should be stronger in PALDIM, despite the fact that the PALDIM N⋯N distance is 0·28 Å longer than that in the cycloheptatriene. This conclusion is confirmed by IR data. © 1974.