Synthesis, structural characterization and thermal stability of a 2D layered Cd(II) coordination polymer constructed from squarate (C₄O₄²⁻) and 2,2’-<em>bis</em>(2-pyridyl)ethylene (2,2’-bpe) ligands

Abstract

A mixed-ligands Cd(II) coordination polymer, [Cd(2,2’-bpe)(C4O4)(H2O)2] (1) (2,2’-bpe = 1,2-bis(2-pyridyl)ethylene; C4O42− = dianion of squaric acid), has been synthesized and structurally characterized by single-crystal X-ray diffraction method. The coordination environment of Cd(II) ions in compound 1 is six-coordinate bonded to four oxygen atoms from two μ1,3-squarate (C4O42−) and two water molecules, and two nitrogen atoms from two 2,2’-bpe ligands. The squarate and 2,2’-bpe both act as bridging ligands with bis-monodentate coordination modes, connecting the Cd(II) ions to form a two-dimensional (2D) layered metal-organic framework (MOF). Adjacent 2D layers are then arranged in an ABAB parallel non-interpenetrating manner to construct its three dimensional (3D) supramolecular network. Intra- and inter-layers hydrogen bonding interactions between the C4O42− and water molecules in 1 provide an extra-stabilization energy on the construction of its 3D supramolecular network. The thermal stability of 1 is studied and discussed in details by TG analysis and in-situ PXRD measurement.

Keywords

• coordination polymer
• metal-organic framework
• hydrogen bond
• squarate
• Cd(II)