Reversible single-crystal-to-single-crystal transformation driven by adsorption/desorption of water over organic solvents and thermal stimulation

Two new isomorphous complexes [M(OBPT)₂]·0.6H₂O (M = Co, (1), M = Ni, (2), HOBPT = 4,6-bis(4-pyridyl)-1,3,5-triazin-2-ol) have been synthesized under hydrothermal conditions and characterized by single-crystal X-ray diffraction. Each ligand bridges two metal ions and each metal ion links to four ligands, resulting in a (4,4) 2D framework with rhombic cavities. Furthermore, the uncoordinated pyridine rings are further linked to each other via forming hydrogen bonding with the lattice water molecules into 3D three-fold interpenetrated, hydrogen-bonded networks. Interestingly, they are high stable up to 450 °C and exhibit reversible single crystal to single crystal transformation triggered by thermal treatment involving dehydration and rehydration processes. Moreover, they selectively adsorb/desorb water molecules over organic solvents much depending on the strength of hydrogen bonding between water molecule and solvent.