Formation of extended polyiodides at large cation templates

By studying the structures of (μ-1,4,10,13-tetrathia-7,16-diazacyclooctadecane)bis[iodidopalladium(II)] diiodide penta(diiodine), [Pd₂I₂(C₁₂H₂₆N₂S₄)](I)₂·5I₂ or [Pd₂I₂([18]aneN₂S₄)](I)₂·(I₂)₅, and 4,7,13,16,21,24-hexaoxa-1,10-diazoniabicyclo[8.8.8]hexacosane triiodide iodide hemipenta(diiodine) dichloromethane monosolvate, C₁₈H₃₈N₂O₆²⁺·I₃^-·I^-·2.5I₂·CH₂Cl₂ or [H₂([2.2.2]cryptand)](I₃)(I)(I₂)_2.5·CH₂Cl₂, we confirm the structural variety of extended polyiodides achievable upon changing the shape, charge and dimensions of the cation template, by altering the synthetic strategy adopted and/or the experimental conditions. Although it is still often difficult to characterize discrete [I_2m+n]^n- polyiodides higher than I₃^- on the basis of structural parameters, such as I-I bond distances, FT-Raman spectroscopy appears to identify them as aggregates of I₂, I^- and (symmetric or slightly asymmetric) I₃^- building blocks linked by I...I interactions of varying strengths. However, because FT-Raman spectroscopy carries no information about the topological features of extended polyiodides, the two techniques should therefore be applied in combination to enhance the analysis of this kind of compounds.