STRUCTURAL ASPECTS OF [2.2 HETEROPHANES .1. MOLECULAR-STRUCTURE OF [2.2](2,6) PYRIDINOPHANE

The crystal and molecular structure of the title compound has been determined from three-dimensional X-ray diffractometer data. Crystals are orthorhombic with a = 13.49(8), b = 7.525(7), c = 11.24(8) Å, space group Pbca. The structure was solved by direct methods and refined by least squares techniques to R 0.047 for 616 independent reflections. The crystals are built up by discrete centrosymmetric molecules approaching C2h symmetry. The pyridine rings are distorted towards an asymmetric boat conformation and are so arranged as to get a stepped geometry (N ⋯ N 2.54, inter-ring distance 2.22 Å). A significant stretching of the C-C bond length of the ethylene bridges, in a gauche conformation (63°), is observed (1.581 Å). The geometrical features are compared with those of free pyridine and other [2.2]phanes.