The crystal and molecular structures of heterocyclic compounds. I. The analysis of the crystal structure of α-phenazine

In a survey of heterocyclic compounds suited to both experimental and theoretical study of molecular dimensions, the crystallographic constants of two forms of phenazine and of four forms of acridine were measured. ~-Phenazine was chosen as the most suitable crystal structure for a detailed X-ray analysis. The intensities of 714 reflections (including 682 out of a possible total of 1024 within the limiting sphere for Cu Ks) were estimated visually. The structure problem was solved by the method of the molecular Fourier transform. Refinement was achieved in the hOl zone by Fourier methods and in the h/c0 and 0]d zones by the method of least squares. The coordinates from the two-dimensional analysis were refined by one least-squares treatment of the F(hkl) to a new set of coordinates, which corresponded to R(hkl) = O. 16. Final parameters were computed by one set'of Fo and Fc differential syntheses. The electron-density distribution in the best plane through the atomic centres was calculated by a direct Fourier method. The standard deviation a(x) of the final atomic coordinates was estimated to be 0.009 A; within the limits of error the molecule has symmetry mmm. The crystal and molecular structures of phenazine are discussed in Part II.