The crystal and molecular structure of quaterrylene

Quaterrylene (III) is isotypic with perylene (I); it crystallizes in the monoclinic system with a = 11.25, b = 10.66, c = 19.31 $^\overset\circ{A}, \beta$ = 100.6$^\circ$, and with four molecules per unit cell and the space group P2$_1$/a. The crystal structure has been determined by two-dimensional methods. In the b-axial projection a majority of the carbon atoms are resolved, and, since the molecule lies with its greatest length almost exactly perpendicular to this axis, the lengths of the peribonds connecting the naphthalenic residues have been determined with moderate accuracy. The mean value is assessed at 1.53$\pm$0.01 $^\overset\circ{A}$, which is significantly larger than current theory predicts. Possible reasons for this difference are discussed.