Abstract
Compositions (accurate to about 1%) of mixed crystals of phenazine (P) and N -oxyphenazine (NOP) were determined from their u.v. absorption spectra. Densities, habit and unit-cell dimensions were found at 20 °C for crystals containing respectively 0, 8, 52, 81 and 100 mole % NOP relative to P; and X-ray diffraction data (F obs ) were obtained for all these and also at — 90 °C for NOP. All are isostructural (NOP being pseudocentrosymmetric) in P2 1 / a with two molecules per average unit cell. Atomic coordinates, bond lengths and anisotropic temperature factors are listed, site-occupation factors for the oxygen atoms being used for the 8, 52 and 81 mole % compositions. A qualitative explanation, in terms of structure, is offered for the anisotropic thermal expansion of NOP.