Structures of Calcium Dicarbide and Uranium Dicarbide by Neutron Diffraction

Abstract

The C–C distances of the C2 groups in calcium dicarbide and uranium dicarbide have been determined by the powder neutron diffraction method. The C–C distance in calcium dicarbide is 1.20±0.01 A, equal to the triple bond C–C distance, but not 1.4 A as reported previously. Uranium dicarbide is isostructural with calcium dicarbide and has the C–C distance of 1.34±0.01 A essentially that of a C–C double bond. The interatomic distances in calcium dicarbide, uranium dicarbide, lanthanum dicarbide, and lanthanum sesquicarbide are discussed in connection with the electronic configuration of the C2 group.