The Crystal and Molecular Structures of Overcrowded Halogenated Compounds VII. 1:10‐Dichloro‐3:8‐Dimethyl4:7‐Phenanthroline

Abstract

Abstract1,10‐dichloro‐3,8‐dimethyl‐4,7‐phenanthroline crystallizes in the triclinic system with a = 7.651(3), b = 7.792(3), c = 12.301(3)Å, α = 108.48(6), β = 82.74(2), γ = 116.53(4)° space group magnified image, Dm = 1.479 g cm−3, Dc = 1.480(5) g cm−3 for two formula units per cell. The intensities of about 2000 reflections were measured by semi‐automatic Weissenberg diffractometer and supplemented by precession diffractometer measurements. The crystal structure was solved by the SEARCH method (Rabinovich and Schmidt, Nature, 211: 1391 (1968)) and refined by full‐matrix least squares methods, using anisotropic temperature factors for non‐hydrogen atoms. The final R‐factor was 0.067 and the “goodness of fit” 0.94. The molecule has an approximate two‐fold axis of symmetry and is appreciably distorted from planarity, the two chlorines being displaced by +1.12Å and −1.15Å from the mean molecular plane; the non‐bonded ClCl distance is 3.082(3)Å. Bond lengths are close to standard values but there are appreciable distortions in bond angles, torsion angles and fold angles. There is hexagonal close packing of stacks of molecules, with van der Waals binding between stacks. Anti‐parallelism of adjacent molecules in a stack suggests that dipole‐dipole forces are important in the intrastack binding. Comparison of the present molecular structure with that of 2,7‐dibromo‐4,5‐bis‐(2‐pyridyl)phenanthrene‐3,6‐diol (Smith and Barrett, Acta Crystallogr., B27: 419 (1971)) shows that the present molecule is the more highly overcrowded.