Source of material 4-Aminopyridine(0.16 g; 1.7mmol) wasdissolved in 10 ml concentrated hydroiodicacid yielding abrown mixture. This mixture was heated to 90°C and then slowly cooled to room temperature. Within afew days orange needles grew from this solution. Elemental analysis ([C 5 [4,5]. For the quantitative analysis of iodine alternatively aluminium was used as the reducing agent. The Ramanspectrum (BrukerMULTIRAM spectrometer (Nd:YAG-Laser at 1064 nm; RT-InGaAs-detector; back scattering geometry))s hows twov erys trongb ands at 154a nd 105cm -1 which can be assigned to the triiodide anion [6]. Experimental detailsAll investigated crystals suffer from the samen on-merohedral twinning (180°about (1, 0, -0.03) in the reciprocal space and 180°about [1 00]inthe direct space). An image of the h0l layer (constructed from the raw diffraction data [1]) of the reciprocal lattice of the title structure is shown in the upper figure. The increasing offset of the reflections of the second, smaller component (direction a 2 *) towards higher diffraction angles can be clearly seen. The data collection for this study was undertaken using acrystal with arelatively large ratio of the twin components (0.93 :0.07).Inaddition there is an orientational disorder (ratio 3:1)ofone of the four crystallographically independent cations (For clarity not shown in the figure; see tables). All hydrogen atomswere included in the final stages of the refinement using riding models. The U iso values of the hydrogen atomsa re set to plausible values in respect to the U eq values of the atomsthey are attached to. Thel argestd ifference electron density peaks (< 2e/Å 3 )are locatedneariodineatompositions.

Source of material 3-Aminopyridine(0.16 g; 1.7mmol) wasdissolved in 10 ml concentrated hydroiodicacid yielding abrown mixture. This mixture was heated to 90°C and then slowly cooled to room temperature. Within 3-4 days orange needles grew from this solution. Elemental analysis (C 5 H 12 N 2 I 6 O 2 ): Calcd., %: C, 6.72; H, 1.35; N, 3.13; I, 85.21. Found, %: C, 6.83; H, 1.28; N, 3.19; I, 85.02. For details on theelemental analytical methods used, see general procedures giveninthe literature [3,4]. For the quantitative analysis of iodine alternatively aluminium was used as the reducing agent. The Raman spectrum (BrukerM ULTIRAMs pectrometer (Nd:YAG-Laser at 1064 nm; RT-InGaAs-detector; backscatteringgeometry))shows twostrongbands at 140and 115cm -1 indicating aslightly asymmetric triiodide anion [5]. Experimental detailsOne of the water molecules (O2/O2a) is disordered over two sites close to the mirror plane (ratio: 1/1; for clarity only one of the two half occupied positions is shown in the figure). Positional coordinates of hydrogen atomsi nvolved in hydrogen bonds were refined using distance restraints. U iso values for all hydrogen atoms were settoplausible values.The Flackparameter of 0.01(2)was determined using 1624 quotients [(I+)- DiscussionBecause of their biological activity there is ageneral interest in aminopyridines [7]. Especially the monoprotonated cations are known to inactivate K + channels reversibly [8]. Polyiodides are defined as extended ionic structures that fulfill the general formula I (2m+n) n-(n =1-4, m =integer).They are formally built from I -,I 3 -and I 2 units and show astrong tendency to concatenate to extended motifs by halogen halogen interactions [9, 10].Moreover there is afocus on diaminium and pyridinium iodides and corresponding polyiodides, as they have asignificant influence on the redox chemistry in dye-sensitized solar cells [11, 12].In the recent past, several groups have synthesized new polyiodides using stick-shaped cations whose lengths andshapes fit with the structures of the polyiodide anions [13][14][15][16].I np articular, the semi-flexible a,w-diazaniumalkane dicationsh aves uccessfully been used for the synthesis of aseries of new polyiodide salts [4,[17][18][19][20]. Nitrogen based heterocyclic cations are also known to template the synthesis of new polyiodides [21][22][23].This contribution is part of our ongoing interest in the structural chemistry of iodide and polyiodide containing compounds. The asymmetric unit of the title structure is composed of one half of adication, and one half water molecule (O1) both lying on amirror plane; asecond water molecule (O2) appears disordered over two positions near to amirror plane and one triodide anion is located in ageneral position (see figure; ellipsoidsare drawn at the 70 %proba-bility level). All moieties are connected by N-H×××I, O-H×××Iand N-H×××Oh ydrogen bonds whose parameters are in accord with those reported in the literature [24]. Hydrogen bonded subunits are composed of one dication, two anions and two w...

The asymmetric unit of the title compound, C5H7N2 +.I3 −, consists of one 2-amino­pyridin-1-ium cation (apyH+) and one triiodide anion, both located in general postions. The apyH+ cation is planar within the experimental uncertainties. The short N—C distance [1.328 (5) Å] of the exocyclic NH2 group is typical for the imino-form of protonated 2-amino­pyridines. Consequently, the bond lengths within the six-membered ring vary significantly. The geometric parameters of the triiodide anion are in the typical range, with bond lengths of 2.8966 (3) and 2.9389 (3) Å and a bond angle of 176.02 (1)°. In the crystal, N—H ⋯ I hydrogen bonds connect adjacent ions into screwed chains along the b-axis direction. These chains are twisted pairwise into rectangular rods. The pyridinium moieties of neighbouring rods are arranged parallel to each other with a plane-to-plane distance of 3.423 (5) Å.