Combined X-ray and neutron study of 1,1,2,2-ethanetetracarbonitrile, C6H2N4, at 158 K

Msub(r)=130.11. X-ray: monoclinic, P21/n, a=7.367(1), b=5.705(1), c=7.780(1) A, β=95.02(1)0, V=325.8 A3, Z=2, Dsub(x)=1.327 g cm-3, T=158 K, Mo Kα, lambda=0.7107 A, μ=0.99 cm-1, F(000)=132. In order to explain the lengthening observed in the central bond of a number of symmetrically substituted ethanes, an analysis of the charge density of the title compound has been undertaken. The structure was redetermined at 158 K from neutron and X-ray diffraction data and refined to Rsub(w)=1.4 and 2.8% respectively. X-N and X-X deformation maps show a weak density in the region of the central bond. A least-squares refinement including atomic charges was performed on the X-ray data and indicates two negatively charged C atoms at the ends of the central bond. (Auth.)