Crystal structure of 2,4-di-para-methoxyphenylcyclobutadiene-1,3-quinone

The crystal structure of 2,4-di-p-methoxyphenylcyclobutadiene-1,3-quinone has been been determined using three-dimensional X-ray data collected by means of a Picker FACS-1 four-circle diffractometer. The crystal used was one of four modifications of this compound, two low density (1.38 g cm^?3) and two high density (1.54 g cm^?3) forms, obtained by us, depending on crystallization conditions. The space group isP¯1, with unit cell dimensionsa = 3.89,b = 10.80,c = 9.03 Å, α = 77.88, β = 74.12, γ = 85.15 °D _m = 1.38 g cm^?3 andZ = 1. A least-squares refinement of the positional and anisotropic thermal parameters gave a finalR-value of 6.0% for 364 reflections and 121 variables. The zwitter-ionic nature of the molecule can be seen in both the partial delocalization of the bonds in the 4-membered ring (which is square-planar) and the bonds joining thep-phenylene and 4-membered rings. The nearly planarp-phenylene rings themselves are quinone-like in structure and are parallel, but not coplanar. The columnar packing of the molecules resembles that of graphite, and observed interplanar spacing is 3.64 Å.