3.3.3. **(lid/pyr)** Systems

The **(lid)2(pyr)** is an ionic cocrystal and crystallises in the triclinic P-1 space group. Its asymmetric unit contains one **(lid+)** molecule, one **(pyr-)** anion, and one **(pyr)** neutral molecule in a stoichiometric ratio 1:1:1 (Figure 11a). Protonation of the tertiary amine in **(lid)** imposes a change in its molecular conformation, pointing both amine protons in opposite directions with –N–C–C–N– torsion angles of −157.97◦ for **(lid)2(pyr)** in comparison with −11.27◦ and 6.41◦ for **(lid)2(hq)** and **(lid)2(res)**, respectively. The **(pyr)** molecules adopt the anti-conformation [22]. This conformation is energetically the least stable. However, considering the packing arrangement in **(lid)2(pyr)**, the anti-conformation ensures that each hydroxyl group of the pyrogallol moiety participates in hydrogen bonding interactions. In the crystal, **(pyr)** molecules are connected to three **(pyr-)** anions through H-bonding interactions generating chains running along the a axis. The **(lid+)** molecules intercalate between two adjacent **(pyr***−***)** anions through N–H···O(hydroxyl) and O–H···O(carbonyl) H-bonding and C–H interactions (Figure 11b). In the crystal, C–H···π interactions connect these supramolecular chains to form the 3D structure.

**Figure 11.** (**a**) Asymmetric unit of **(lid)2(pyr)** ionic cocrystal. (**b**) Fragment of the supramolecular chain running along the a axis. Green: **(lid+)** cations, red: **(pyr***−***)** anions, blue: **(pyr)** molecules.

The **(lidhcl)2(pyr)** is also an ionic cocrystal and crystallises in the monoclinic P21/c space group. Its asymmetric unit contains two **(lid+)** two chloride ions and one **(pyr)** molecule in a stoichiometric ratio 2:2:1 (Figure 12a). As observed in the free base ionic cocrystal, **(pyr)** adopts an anti-conformation where each hydroxyl group forms a hydrogen bond interaction with the corresponding chloride ion. In the crystal, Cl1A and Cl1B ions are H-bonded to four molecules, two **(pyr)** and two **(lid+),** and three molecules, one **(pyr)** and two **(lid+)** ions, respectively. This arrangement leads to efficient packing, shielding pairs of **(pyr)** molecules that are surrounded with **(lid+)** and Cl<sup>−</sup> ions, thus protecting the coformer from oxidation (Figure 12b).

**Figure 12.** (**a**) Asymmetric unit of **(lidhcl)2(pyr)** ionic cocrystal. (**b**) Detailed view of the environment of a pair of **(pyr)** molecules in the crystal structure. Red: **(lid+)** cations, blue: **(pyr)** molecules, green: Cl− ions.
