Sponge-Like Water De-/Ad-Sorption versus Solid-State Structural Transformation and Colour-Changing Behavior of an Entangled 3D Composite Supramolecuar Architecture, [Ni4(dpe)4(btc)2(Hbtc)(H2O)9]·3H2O

Abstract

An entangled composite compound, [Ni4(dpe)4(btc)2(Hbtc)(H2O)9]·3H2O (1), where H3btc = 1,3,5-benzenetricarboxylic acid and dpe = 1,2-bis(4-pyridyl)ethane, has been synthesized and structurally characterized. Single-crystal structural determination reveals that compound 1 consists of four coordination polymers (CPs), with two two-dimensional (2D) (4,4) layered metal-organic frameworks (MOFs) of [Ni(dpe)(Hbtc)(H2O)] and [Ni(dpe)(btc)(H2O)]− anion, and two one-dimensional (1D) polymeric chains of [Ni(dpe)(btc)(H2O)3]− anion and [Ni(dpe)(H2O)4]2+ cation, respectively. The three-dimensional (3D) supramolecular architecture of 1 is constructed via the inter-penetration of inter-digited, double-layered, 2D rectangle-grid MOFs by two 1D coordination polymeric chains, and tightly entangled together via the combination of inter-CPs π–π stacking and hydrogen bonding interactions. The ad-/de-sorption isotherms of 1 for water displays a hysteresis profile with a maximum adsorption of 17.66 water molecules of per molecule unit at relative P/P0 < 0.89. The reversible de-/re-hydration processes in 1 monitored by cyclic water de-/ad-sorption TG analysis and PXRD measurements evidence a sponge-like water de-/ad-sorption property associated with a thermal-induced solid-state structural transformation. The magnetic property of 1 suggests that the ferromagnetic coupling might refer to a stronger inter-Ni(II) interaction, which could be along the btc3− or Hbtc2− ligands; the antiferromagnetic coupling corresponding to the weaker inter-Ni(II) interactions, which could be the dpe ligands for the 2D framework.