Reversible solid-state structural transformation of a 1D-2D coordination polymer by thermal De/rehydration processes.

A new coordination polymer, [Zn(HBTC)(BPE)0.5(H2O)]n·nH2O (1) with an extended 1D ladderlike metal-organic framework (MOF) has been synthesized and structural characterized by single-crystal X-ray diffraction method. Structural determination reveals that, in compound 1, the Zn(II) ion is four-coordinated in a distorted tetrahedral geometry, bonded to one nitrogen atom from one BPE ligand, and three oxygen atoms from two monodentate carboxylate groups of two HBTC(2-) ligands and one coordinated water molecule. The HBTC(2-) acts as a bridging ligand with a bis-monodentate coordination mode, connecting the Zn(II) ions to form a one-dimensional (1D) [Zn(HBTC)] chain. Two 1D chains are then interlinked via the connectivity between the Zn(II) ions and anti-BPE liagnds to complete the 1D ladderlike MOF. Adjacent 1D Ladders are further extended to a 2D hydrogen-bonded layered network through the intermolecular O-H · · · O hydrogen bond between the carboxylic group and carboxylate group of interladder HBTC(2-) ligand. Adjacent 2D layers are then packed orderly in an ABAB-type array via the intermolecular interactions of combined π-π interaction and O-H · · · O hydrogen bonds to form a 3D supramolecular architecture exhibiting 1D channels intercalated with guest water molecules. The reversible solid-state structural transformation between crystalline 1 with 1D ladderlike framework and its dehydrated powder 2, [Zn(HBTC)(BPE)0.5]n, with 2D framework via the displacement of coordinated water molecule to HBTC(2-) ligand, by thermal de/rehydrated processes has been verified by PXRD measurements. The emission of 1 and 2 is ascribed to a ligand-based transition.