In this study, two new organic–inorganic hybrid materials (C9H8NO)2[MCl4] (M = Hg, Co) were synthesized and isolated via the slow evaporation of an aqueous solution at room temperature, and they were characterized based on elemental, single crystal X-ray diffraction (XRD), powder XRD, thermal, spectroscopic (infrared (IR) and Raman), and magnetic studies. XRD showed that the crystal structures of both materials comprised infinite zigzag zero-dimensional chains of 8-hydroxyquinolinium cations and slightly distorted tetrahedral anions [MCl4]2– (where M = Hg or Co). The crystal packing was governed by N-H⋯Cl, O-H⋯Cl, N-H⋯O, and C-H⋯Cl hydrogen bonds and offset π–π stacking interactions to build a three-dimensional network. Thermogravimetry and differential scanning calorimetry analyses indicated the presence of a phase transition and a single loss of mass. Furthermore, the room temperature IR and Raman spectra were used to obtain further insights into the compounds. Magnetic investigation demonstrated that the second compound exhibited an antiferromagnetic exchange combined with perfect magnetic reversibility.