The crystal structure of 8.1 2-diethyl-2.3.7.13.17.18-hexamethylcorrole has been elucidated by X-ray crystallographic analysis and the geometry of the macrocyclic ring system has been found to be not strictly planar. The distortions are probably caused by short N-N contacts brought on by the direct C(l)-C(19) link. The ' ruffling ' of the pyrrole rings is similar to that found in some substituted porphyrins, although individual ring geometries have been altered by the inner crowding. Crystallographic evidence suggests that the three inner hydrogen atoms are statistically distributed among the four nitrogen atoms. Packing is in the ' parallel disc ' mode and is specific for the molecular distortion.Laboratory, South Parks Road, Oxford DURING attempts at synthesis of the vitamin B,, corrin nucleus and assessments of the feasibility of various biosynthetic pathways for the porphyrins and corrins, Johnson and Kay2-* described the synthesis of a new macrocyclic system, corrole. This system, lacking a C (2O)meso-carbon bridge, appeared to have a corrin-type skeleton with 10 double bonds, involving porphyrin-like conjugation. The structure of Johnson's original compound (I), C,,H,,N4, 2,3,7,13,17,18-hexamethyl-8,12diethyl corrole has been elucidated by X-ray crystallographic analysis which confirms the organic synthetic conclusions. light petroleum (b.p. 40-60@) on chloroforni-corrole. The two forms were characterized as monoclinic ( P 2 J c ) with 2 = 4, a = 4-71, b = 38.15, G = 13.57 A, Q = 94-85', and orthorhombic (Pbca) with 2 = 8, a = 8.98, b = 36-96, and G = 14.57 A. Neither form contained solvent of crystal-lization. Because they were much larger, the orthorhombic crystals were used for data collection. Approximately 3000 independent reflections were measured using a computer-controlled four-circle diffractometer with nickelfiltered Cu-K, radiation. Lorentz, polarization and semiempirical absorption corrections 5 3 6 were then applied. The structure was solved with an automated centrosymmetric symbolic addition procedure on the Oxford KDF 9 computer. Refinement was performed using first isotropic and then anisotropic least-squares procedures, large-block 4
