The crystal packing of [M(phen)₃]I₇ (M = Mn, Fe)

Abstract

The crystallisation, crystal structures, and crystal packing of [Mn(phen)₃]I₇ and [Fe(phen)₃]I₇ are reported. The crystal lattices are isomorphous, but there are informative small differences between the two structures. The [M(phen)₃]²⁺ complexes occur as parallel (P4AE)_∞ chains, forming two parallel fourfold aryl embraces (P4AE) with adjacent cations. The polyiodide components occur between the chains, and in the (phen)₂ grooves of the complexes. The stoichiometry {I₇}^2- is comprised structurally of discrete I₃^- and half of centrosymmetric [I₈]^2- units. These [I₈]^2- units contain twofold 50:50 disorder, and are either zig-zag I₈^2-, or I₂ plus I₆^2-. Details of the disorder are different in the two crystals, reflecting the soft I...I potentials involved. The I₈^2- ion is normal, but the I₆^2- species, as a centrosymmetric pair of linear I₃^-, appears to be unprecedented. The disordered polyiodide segments are positioned in a filled aryl box motif formed by (phen)₂ grooves from complexes in adjacent (P4AE)_∞ chains. These crystal structures illustrate again the pattern of complementary orthogonality of phen ligands and polyiodide segments