Hydrogen-Bonded Host Frameworks of Cationic Metal Complexes and Anionic Disulfonate Linkers:  Effects of the Guest Molecules and the Charge of the Metal Complex

Synthesized and structurally characterized is a new series of soft host frameworks assembled by charge-assisted hydrogen bonds between a cationic metal complex (MC) and an anionic disulfonate, in this case [Co(en)₂(ox)]⁺ and 4,4‘-biphenyldisulfonate (BPDS), respectively. Four compounds with neutral guest molecules of DMF, p-nitrophenol (pnp), 4-acetylpyridine (acpy), and 4-dimethylaminopyridine (dmapy) have a general formula (MC)₂(BPDS)·n(guest) and exhibit a “brick wall” topology of their neutral pillared-layer type frameworks. A fifth compound, (H-dmapy)₂(MC)₄(BPDS)₃, forms at more acidic conditions that lead to protonation of dmapy and has a negatively charged pillared-layer framework. The layers in all five compounds are constructed of extensively hydrogen-bonded MC cations bonded both directly to each other and indirectly via the sulfonate groups and water while the organic residues of the latter serve as pillars. The structures of the layers and orientation of the pillars adjust to the specifics of the guest molecules, and as a result, the five compounds crystallize in different structures. Compared to the recently reported analogous compounds with the trication [Co(NH₃)₆]³⁺ these compounds have larger galleries between the pillars. The reason is the lower charge of [Co(en)₂(ox)]⁺ and the need for only 0.5 charge-balancing pillars per metal complex instead of 1.5 such pillars for the trication. These host−guest frameworks are analogs to the well-studied guanidinium sulfonate (GS) networks and mimic their flexibility and overall durability.