Crystal structure of 4,4′-(disulfanediyl)dipyridinium chloride triiodide

4,4′-Disulfanediyldipyridinium chloride triiodide (1) was synthesized. The structural characterization of 1 by SC-XRD analysis was supported by elemental analysis, FT–IR, and FT–Raman spectroscopic measurements.


Chemical context
The reactions of pnictogen/chalcogen donors with dihalogens X 2 or interhalogens XY (X, Y = Cl, Br, I) afford a variety of products depending on the nature of the donor, the dihalogen/ interhalogen, and the reaction conditions (Aragoni et al., 2008;Rimmer et al., 1998;Aragoni et al., 2022;Knight et al., 2012).For chalcogen donors, charge-transfer (CT) 'spoke' adducts, hypercoordinate 'T-shaped' adducts, halonium adducts, and different types of cationic oxidation products of the donors have been identified and structurally characterized (Knight et al., 2012;Saab et al., 2022).Worthy of note, diiodine CTadducts have been extensively investigated, also with a view to their application as leaching agents for toxic (Isaia et al., 2011) and precious metals (Zupanc et al., 2022) in waste from electrical and electronic equipment (WEEE).Among the pnictogen donors, many studies have focused on (poly)pyridyl derivatives.Analogous to S/Se-donors, the reactions of pyridyl donors with X 2 /XY have resulted in the formation of CTadducts featuring a linear N� � �X-Y group (Kukkonen et al., 2019;Tuikka & Haukka, 2015) and halonium derivatives with an N� � �X + � � �N moiety (X = I; Y = Cl, Br, I) (Kukkonen et al., 2019;Batsanov et al., 2005Batsanov et al., , 2006)).In addition, N-protonated pyridinium cations were obtained, whose charge can be counterbalanced by discrete halides or extended fascinating networks (Aragoni et al., 2004;Aragoni et al., 2023).Oxidation of the aromatic heterocycle to give a cationic radical species followed by solvolysis or reaction with incipient moisture has been proposed as a possible explanation for the formation of pyridinium cations (Rimmer et al., 1998;Aragoni et al., 2023).
The nature of the products isolated in the solid state is reflected in their peculiar FT-Raman response (Aragoni et al., 2004(Aragoni et al., , 2008;;Pandeeswaran et al., 2009).In particular, an elongation of the perturbed X-Y moiety with respect to the free halogen/interhalogen is found in CT-adducts, which determines a low energy shift of the relevant Raman-active stretching vibration (Aragoni et al., 2008).When polyhalide networks are formed, the stretching vibrations of the interacting synthons can be detected in the low-energy region of the FT-Raman spectrum (Aragoni et al., 2008(Aragoni et al., , 2023)).

Supramolecular features
The protonated pyridine rings of the H 2 L 02+ cation are involved in hydrogen-bonding (HB) interactions with the chloride anions (interaction a in Fig. 1; a and c in Fig. 2 and Table 1), thus forming a wavy 1-D hydrogen-bonded polymeric structure that develops perpendicular to the b-axis.In addition, each chloride interacts with a terminal iodine atom of a triiodide [I1� � �Cl1 = 3.4764 (8) A ˚; interaction b in Figs. 1  and 2 and Table 1] at a distance shorter than the sum of the relevant van der Waals radii (3.73A ˚; Bondi, 1964), so that the chloride and the triiodide could be considered to form a [I� � �I-I� � �Cl] 2-dianionic ensemble, unprecedented among the relevant polyinterhalides (Sonnenberg et al., 2020)   Ellipsoid plot of compound 1 with the numbering scheme adopted.Displacement ellipsoids are drawn at the 50% probability level.Labelled interactions are described according to Table 1.parent [I 2 Cl] À anion [for example I� � �Cl = 3.158, 3.047 A ˚in the structures with CSD codes BEQXEA (Wang et al. 1999) and BOJYIL (Pan et al. 2019), respectively] and [Cl 2 I 2 ] 2- dianions [3.070 and 3.242 A ˚in DOXDOL (Buist & Kennedy, 2014) and JUPCAA (Pan et al. 2015), respectively].These Cl� � �I interactions, shown in Fig. 2, which fall into the realm of halogen bonding (XB) interactions, generate the crystal packing along with a set of weak C-H� � �I contacts (entries dg in Table 1).

Conclusions
4,4 0 -Disulfanediyldipyridinium chloride triiodide (H 2 L 02+ )-(Cl À )(I 3 À )(1) was synthesized and characterized structurally and spectroscopically.The isolation of 1 confirms that L 0 is not susceptible to the oxidative cleavage of the S-S disulfide bond by diiodine and iodine monochloride under mild conditions, but that it can undergo protonation and template fascinating supramolecular structures, as previously observed in the case of [(HL + )(I À )•5/2I 2 ] 1.Further studies are ongoing in our laboratory to investigate the reactivity of different dipyridyldichalcogenides towards dihalogens and interhalogens and their versatility as building blocks for extended supramolecular assemblies based on �-hole interactions.

Materials and methods
All the reagents and solvents were used without further purification.Elemental analysis determinations were performed with an EA1108 CHNS-O Fisons instrument.Fourier-Transform Infrared (FT-IR) spectroscopic measurements were recorded on a Bruker IFS55 spectrometer at room temperature using a flow of dried air.Far-infrared (FIR; 500-50 cm À 1 ) spectra were recorded on polythene pellets using a Mylar beam-splitter and polythene windows (resolution 2 cm À 1 ).Middle-infrared (MIR) spectra were recorded on KBr pellets, with a KBr beam-splitter and KBr windows (resolution 2 cm À 1 ).FT-Raman spectroscopy measurements were recorded on a Bruker RFS100 spectrometer (resolution of 2 cm À 1 ), with an In-Ga-As detector operating with a Nd: YAG laser (� = 1064 nm) with a 180 � scattering geometry (excitation power 5 mW).Melting point determinations were carried out on a FALC mod.C apparatus.

Figure 2
Section of the crystal packing of compound 1 viewed along the c-axis.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 2. H atoms bonded to heteroatoms could be located from difference-Fourier maps and their positions were freely refined.Other H atoms were placed in geometrically calculated positions and were constrained to ride on their parent atom with C-H = 0.95 A ˚and with U iso (H) = 1.2U eq (C).

Special details
Geometry.All esds (except the esd in the dihedral angle between two l.s.planes) are estimated using the full covariance matrix.The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry.An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s.planes.
Fractional Geometric parameters (Å, º) � with respect to the respective C-S-S plane.The linear triiodide anion [I1-I2-I3 = 177.13(1) � ] is remarkably asymmetric with a very short I1-I2 distance [2.8180 (4) A ˚], close to the I-I distance of solid-state iodine (2.715A ˚; van Bolhuis et al. 1967), and a longer one [I2-I3 = 3.0459 (4) A ˚], in agreement to the threebody system of the I 3 À anion, showing a correlation between the two I-I distances.Accordingly, the I1-I2 and I2-I3 bond distances fall in the correlation reported by Devillanova (Aragoni et al., 2012) featured by I A -I B -I C systems, which correlates the relative elongations of the two I A -I B and I C -I D lengths with respect to the the sum of the relevant covalent radii.
deposited at the Cambridge Structural Database (CSD, version 5.45 update 1, March 2024; Groom et al., 2016).Nevertheless, the Cl� � �I distance is longer than those previously reported for the

Table 2
Experimental details.