Assembly of two Zinc(II)-squarate coordination polymers with noncovalent and covalent bonds derived from flexible ligands, 1,2-bis(4-pyridyl)ethane (dpe)

Two metal-organic frameworks (MOFs) based on Zn(II)-squarate bridges associated with non-covalent and covalent bonds of dpe ligands, [Zn(dpe)(C4O4)(H2O)(2)](n) (1), and {[Zn(Hdpe)(C4O4)(0.5)(H2O)(3)][Zn(C4O4)(2)(H2O)(2)]}(n) (2) (C4O42-(squarate) dianion of 3,4-ihydroxycyclobut- 3-ene-1,2-dione (H2C4O4); dpe 1,2-bis(4-pyridyl) ethane), have been synthesized and characterized by spectroscopic analysis and single-crystal X-ray diffraction studies. Compound 1 is a two-dimensional (2D) metal-organic framework (MOF), being constructed via the crosslinkage of one-dimensional (1D) [Zn(mu(1,3)-squarate)] chains and 1D sinusoidal-like [Zn(gauche-dpe)] chains. Compound 2 is a 2D tri-layered composite network composed of one cationic polythreading [Zn(Hdpe)(C4O4)(0.5)(H2O)(3)](2+) MOF and two anionic [Zn(C4O4)(2)(H2O)(2)](2-)MOFs with the penetration of the monoprotonated anti-form Hdpe(+) ligands dangling above and below the 2D Zn(II)(mu(1,2,3,4)-squarate) layer of cationic [Zn(Hdpe)(C4O4)(0.5)(H2O)(3)](2+) MOF into the windows of two 2D Zn(II)-(mu(1,3)-squarate) layers of anionic [Zn(C4O4)(2)(H2O)(2)](2-) OFs. Both of their 2D MOFs in compounds 1 and 2 are then extended to 3D supramolecular architectures via the intermolecular hydrogen bonding interaction among the squarate, protonated dpe ligands and water molecules.