Amidinium⋯phosphonate charge assisted hydrogen-bonded organic frameworks: influence of diverse intermolecular interactions

The synthesis of charge assisted amidinium⋯phosphonate hydrogen-bonded organic frameworks (HOFs) is reported. Two tectons, with either a biphenyl or naphthalene diimide backbone, were combined with bis-amidinium salts to afford HOF1 and HOF2, respectively. Whereas HOF1 formed rapidly, typically within two days of mixing, HOF2 proved more challenging to synthesise. Interestingly, the presence of sunlight facilitated the rapid formation of HOF2 within a few hours. Although crystals of tectons 1H₄ or 2Et₄ exhibited densely packed structures, combination of the corresponding phosphonate bases with bis-amidinium cations, through amidinium⋯phosphonate interactions, gave open framework materials. The HOFs formed through this approach exhibited notable stability limitations, including a propensity for phase transformations or structural collapse upon solvent removal.