Redetermination of (η4-s-cis-1,3-butadiene)tricarbonyliron(0)

The crystal structure of the title compound, [Fe(C₄H₆)(CO)₃], was previously reported by Mills & Robinson [Acta Cryst. (1963), 16, 758-761]. The compound crystallizes in the centrosymmetric space goup Pnma with the complex located on a mirror plane. The redetermination of this structure at 100 K yielded almost equilibrated C—C bond lengths within the butadiene ligand according to a metal-to-ligand bonding-back-bonding mechanism. The C—C bond lengths presented herein are significantly shorter than those reported earlier. The H-atom positions that have not been reported so far were located by difference Fourier maps. The positional parameters of all H atoms and individual U _iso values were refined freely.