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

Abstract

The crystal structures of (phenacetin) 2 • H I 5 (triclinic, a — 12.44 A, b — 10.67, c = 5.81, oc = 103.3°, B — 103.7, y — 87.3, P1, Z = 1) and (theobromine) 2 H 2 I 8 (triclinic, a — 14.38 A, b = 14.07, c = 7.75, = 91.2°, B = 100.8, y = 91.0, P1, Z = 2) have been solved by Patterson methods, using intensities measured by Weissenberg diffractometer with graphite-monochromated Mo Ka 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 • H I 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) A); the polyiodide layers contain zigzag chains of alternating iodine molecules and triiodide ions, with secondary bonds ( d (I...I) = 3.55 A) 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 • H 2 I 8 the organic layer consists of hydrogen-bonded theobrominium cations and the polyiodide layer of centrosymmetric S-shaped (I 4-16 ) ions, with the arrangement I - 3 •I - 2 •I - 3 •I - 3 •I - 2 •I - 3 ; there is secondary bonding between triiodide and iodine moieties within the hexadecaiodide ions. There are tertiary bonds (d/(I...I) = 3.84 A) between adjacent I 4-16 ions.