Solvent-Induced Structural Dynamics in Noninterpenetrating Porous Coordination Polymeric Networks

Abstract

Three novel soft porous coordination polymer (PCP) or metal–organic framework (MOF) compounds have been synthesized with a new rigid ligand <i>N</i>-(4-pyridyl)-1,4,5,8-naphathalenetetracarboxymonoimide (PNMI) by partial hydrolysis of <i>N,N′</i>-di-(4-pyridyl)-1,4,5,8-naphthalenete-tracarboxydiimide (DPNI) during solvothermal reactions with Zn­(II), Cd­(II), and Mn­(II) salts, and they are [Zn­(PNMI)]·2DMA (<b>1</b>·2DMA, <b>1a</b>), [Cd­(PNMI)]·0.5DMA·5H₂O (<b>2</b>·0.5DMA·5H₂O), and [Mn­(PNMI)]·0.75DMF (<b>3</b>·0.75DMF). The structure of <b>1</b> is based on paddle-wheel secondary building unit (SBU) with a 3,6-connected <b>rtl</b> net topology, whereas <b>2</b> and <b>3</b> are isotypical but the M­(O₂C–C)₂ fragments aggregate in one-dimension and the overall connectivity is the same <b>rtl</b> net topology. All these three MOFs have one-dimensional rhombic channels filled with guest molecules. The guest molecules in <b>1a</b> can be exchanged with EtOH in a single-crystal to single-crystal (SCSC) manner to <b>1</b>·1.25EtOH·0.375H₂O (<b>1b</b>). Further, the guest molecules in <b>1b</b> can be replaced with ethylene glycol, triethylene glycol and allyl alcohol without destroying its single crystal nature. These guest exchanges are accompanied by reduction in volume of the unit cell up to 16%, as well as the void volume up to 33.1%. Similarly, triethylene glycol (TEGly) selectively exchanges EtOH in a mixture of the above solvents, which might be the result of correct fit of the hydrogen-bonded TEGly dimer in the channel of <b>1</b>. While activated <b>1</b> and <b>3</b> exhibit no uptake of N₂ and H₂ at 1 bar and 77 K and very low uptake of CO₂ gas at 1 bar and 196 K, activated <b>2</b> shows selective CO₂ uptake, 278 cm²·g^–1, over N₂ and H₂ at 1 bar and 196 K, which corresponds to 5.87 molecules of CO₂ per formula unit of <b>2</b>