Contrasting crystal supramolecularity for [Fe(phen)3]I8 and [Mn(phen)3]I8: complementary orthogonality and complementary helicity

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Abstract
The crystallisation, crystal structures, and analyses of crystal supramolecularity for [Fe(phen)3]I8 and [Mn(phen)3]I8 are reported. Crystalline [Fe(phen)3]I8 contains the first example of one-dimensionally extended sixfold aryl embraces (6AE) between [M(phen)3]2+ complexes. The interchain domains contain twisted I8 2– ions, which are translated along the axis of the domain to form polyiodide helices. Sections of the polyiodide helix slot into the grooves between the phen ligands in each [Fe(phen)3]2+ complex: these grooves are canted in helical fashion in each complex, even though the extended 6AE chain is not helical, and there is good local registry and geometrical complementarity between the polyiodide helices and the cation chains. The polyiodide helices are buttressed further by concerted C–H⋯I interactions. The crystal approaches trigonal symmetry. In contrast, crystalline [Mn(phen)3] (I3)(I5) contains neither 6AE nor the parallel fourfold aryl embraces (P4AE) characteristic of [M(phen)3]z complexes, but does display a relatively rare instance of a homo-chiral P4AE. The association of [Mn(phen)3]2+ complexes and the I3 – and I5 – ions is effective and close, and manifests well the complementary orthogonality of [M(phen)3]z complexes and polyiodides. There are two formula units in the asymmetric unit of [Mn(phen)3](I3)(I5), and the high-spin [Mn(phen)3]2+ cations are distorted from the octahedral stereochemistry of low-spin [Fe(phen)3]2+. The issues of whether these two structures could be regarded as substitutional polymorphs, and which is the more stable, and whether each could crystallise with the structure of the other, are discussed.

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