Effect of ligand constraints on the geometry of two sulfur-bridged binuclear iron (II) complexes. Structures of bis. mu. -N, N'-dimethyl-N, N'-bis (. beta. -mercaptoethyl) ethylenediamine-diiron (II) and bis. mu. -N, N'-dimethyl-N, N'-bis (. beta. -mercaptoethyl) -1, 3-propanediamine-diiron (II) | Synapse