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

An entangled composite compound, [Ni(4)(dpe)(4)(btc)(2)(Hbtc)(H(2)O)(9)]·3H(2)O (1), where H(3)btc = 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)(H(2)O)] and [Ni(dpe)(btc)(H(2)O)](−) anion, and two one-dimensional (1D) polymeric chains of [Ni(dpe)(btc)(H(2)O)(3)](−) anion and [Ni(dpe)(H(2)O)(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/P(0) < 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 btc(3−) or Hbtc(2−) ligands; the antiferromagnetic coupling corresponding to the weaker inter-Ni(II) interactions, which could be the dpe ligands for the 2D framework.