Cation⋅⋅⋅anion and anion⋅⋅⋅anion interactions compete in hydrogen-bonded frameworks prepared using amidinium⋅⋅⋅phosphonate hydrogen bonding

We report the synthesis of hydrogen-bonded frameworks prepared from guanidinium, bis-amidinium or tetra-amidinium cations, and diphosphonate or tetraphosphonate anions. The frameworks are assembled by both charge-assisted amidinium⋅⋅⋅phosphonate and anti-electrostatic phosphonate⋅⋅⋅phosphonate hydrogen bonds, of which the phosphonate⋅⋅⋅phosphonate interactions are notably shorter. Frameworks prepared from the tetrahedral tetraphosphonate building block contain relatively large water-filled channels, but lose crystallinity upon drying. The crystal structure of a guanidinium⋅⋅⋅diphosphonate salt has an unusual structure related to classic Ward guanidinium⋅⋅⋅sulfonate frameworks but with an additional cation/solvent layer. This material includes toluene guests, which are held strongly within the crystal lattice.