The crystal structures of the polyiodide salts (phenacetin) ₂ HI ₅ and (theobromine) ₂ H ₂ I ₈

The crystal structures of (phenacetin)$_{2}\cdot $HI$_{5}$ (triclinic, a = 12.44 angstrom, b = 10.67, c = 5.81, $\alpha $ = 103.3 degrees, $\beta $ = 103.7, $\gamma $ = 87.3, P$\overline{1}$, Z = 1) and (theobromine)$_{2}\cdot $H$_{2}$I$_{8}$ (triclinic, a = 14.38 angstrom, b = 14.07, c = 7.75, $\alpha $ = 91.2 degrees, $\beta $ = 100.8, $\gamma $ = 91.0, P$\overline{1}$, Z = 2) have been solved by Patterson methods, using intensities measured by Weissenberg diffractometer with graphite-monochromated Mo K$\alpha $ radiation (2815 and 2827 intensities, R = 8.3% and 11.1% respectively). Both structures are polyiodide salts, with alternating cationic (organic) and anionic (polyiodide) layers. In (phenacetin)$_{2}\cdot $HI$_{5}$ the organic layers consist of hydrogen-bonded phenacetin 'dimers', with the proton bridging the oxygens of the carbonyl bonds in a short hydrogen bond (d(O...O) = 2.46 (2) angstrom); the polyiodide layers contain zigzag chains of alternating iodine molecules and triiodide ions, with secondary bonds (d(I...I) = 3.55 angstrom) between these moieties. There is only van der Waals bonding between parallel chains. This substance, bis-(phenacetin)hydrogen iodine triiodide, is a type A basic salt. In (theobromine)$_{2}\cdot $H$_{2}$I$_{8}$ the organic layer consists of hydrogen-bonded theobrominium cations and the polyiodide layer of centrosymmetric S-shaped (I$_{16}^{4-}$) ions, with the arrangement I$_{3}^{-}\cdot $I$_{2}\cdot $I$_{3}^{-}\cdot $I$_{3}^{-}\cdot $I$_{2}\cdot $I$_{3}^{-}$; there is secondary bonding between triiodide and iodine moieties within the hexadecaiodide ions. There are tertiary bonds (d(I...I) = 3.84 angstrom) between adjacent I$_{16}^{4-}$ ions.