3.3.1. **(lid/hq)** Systems

The asymmetric unit of **(lid)2(hq)** contains one **(lid)** molecule and half an **(hq)** molecule located at an inversion centre, leading to a 2:1 stoichiometric ratio (Figure 6a). The hydroxy groups of **(hq)** point in opposite directions, thus adopting a *trans* conformation, forming discrete intermolecular OH(phenol)···O(carbonyl) hydrogen bonds with the *<sup>D</sup>*<sup>1</sup> <sup>1</sup>(2) graph set between the OH donor **(hq)** and the carbonyl oxygen acceptor of the **(lid)**. These discrete units are further connected by centrosymmetric –C–H···π (2.968 Å) and –N–H···π (3.254 Å) interactions between **(lid)** molecules, generating a 1D chain (Figure 6b). Hydrophobic interactions involving methyl groups associate chains to build up the 3D structure.

**Figure 6.** (**a**) Asymmetric unit of **(lid)2(hq)** cocrystal. (**b**) Detailed view of the –C–H···π and –N–H···π interactions that connect discrete **(lid)2(hq)** units to form a chain structure.

The asymmetric unit of **(lidhcl)2(hq)** contains one **(lidhcl)** salt and half an **(hq)** molecule located at an inversion centre, with a 2:2:1 stoichiometric ratio considering all the components (Figure 7a). Protonation of the N1 amine group results in a change in the **(lid)** conformation, locating the amine groups in *trans* conformation. The N2 amine group and the ammonium N1 group participate in electrostatic hydrogen bonds with the chloride ion, generating a chain reinforced by C–H···O hydrogen bonds. The **(hq)** molecules connect chains via additional hydrogen bonds involving chloride ions, generating a 3D structure. The participation of chloride ions through noncovalent interactions results in a more compact crystal structure than the free base cocrystal analogue where each **(hq)** molecule is surrounded by six **(lid+)** cations, protecting the OH groups of **(hq)** from oxidation (Figure 7b).

**Figure 7.** (**a**) Asymmetric unit of **(lidhcl)2(hq)** ionic cocrystal. (**b**) Detailed view of the **(hq)** environment in the crystal structure. Blue: **(lid+)** ion, green: Cl<sup>−</sup> ion, red: **(hq)** molecule.
