Crystal supramolecular motifs in trimorphs of [Fe(phen)3] I12

Abstract

We describe three different crystals, 1A, 1B, 1C, with the composition [Fe(phen)₃] I₁₂ (phen = 1,10-phenanthroline). They are crystallised from solutions containing [Fe(phen)₃] I₂ plus I₂, but there is not complete reproducibility in the crystallisation experiments and it appears that kinetic crystallisation is responsible for the formation of these trimorphs. The crystal packing of each is described and analysed in detail, in terms of three types of supramolecular motif: (1) multiple aryl embraces between [Fe(phen)₃]²⁺ cations; (2) [Fe(phen)₃]²⁺ ••• I_x motifs; and (3) polyiodide association. The crystallisation results indicate that the energies of these three types of motifs are closely balanced. The two main types of local [Fe(phen)₃]²⁺ ••• I_x interaction are facial with I_x chains along phen faces, and peripheral with C?H•••I interactions in the planes of the phen ligands. The three crystals appear to have different dominant motifs: 1A is controlled by a two-dimensional polyiodide network and a closely associated pair of [Fe(phen)₃]²⁺ cations in parallel fourfold aryl embrace (P4AE) motif; 1B has a cyclic polyiodide which envelops weakly interacting [Fe(phen)₃]²⁺ cations; 1C is evidently influenced by a chain of [Fe(phen)₃]²⁺ cations linked by P4AE, with I₅^? and I₇^? as the walls of the channel around the chain of cations. The expected complementary orthogonality of the phen ligand planes and the polyiodide segments is evident: an I₇^? clamp on one phen ligand occurs in 1B and 1C