Stereochemistry of [M(bidentate ligand)₂(unidentate ligand)]. Crystal structure of iodobis(pyrrolidinyldithiocarbamato)iron(III)-iodine (2/1)

The crystal structure of a complex analysing as FeL₂I₂, L = pyrrolidinyldithiocarbamate, has been determined at 295(1) K by X-ray diffraction and refined to a residual of 0.046 for 1 422 'observed' reflections. Crystals are monoclinic, P2₁/c, a = 6.735(4), b = 18.28(2), c = 15.11(1) Å, β = 96.71(5)°, and Z = 4. The substance has been shown to be a molecular complex, [Fel{S₂CN(CH₂)₄}₂]·0.5 I₂, the iodine molecule being located on a crystal-lographic centre of symmetry. The bond lengths are as expected [Fe-I 2.652(3), Fe-S 2.271(4)-2.305(5) Å]; for the iodine molecule, I-I is 2.779(3) Å. The latter has a contact at 3.516(3) Å to the complexed iodine atom. The stereochemistry of the five-co-ordinate complex is a square pyramid with the iodine atom in the apical site, distorted towards a square pyramid with the iodine atom in a basal site. This distortion is discussed in terms of repulsion theory.