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.
Keywords: coordination polymer; magnetic property; metal-organic framework; photoluminescence; structural transformation; supramolecular architecture.