Syntheses, structures, and photoluminescent properties of a series of metal–organic frameworks constructed by 5,5′-bis(1H-imidazol-1-yl)-2,2′-bithiophene and various carboxylate ligands

Abstract

A series of new metal–organic frameworks (MOFs), namely, {[Co(BIBP)(hfipbb)]}_n (1), {[Co(BIBP)(Hbtc)]}_n (2), {[Zn(BIBP)(5-OH-bdc)]}_n (3), {[Cd(BIBP)(bdc)]}_n (4), {[Zn₂(BIBP)_0.5(hfipbb)₂]·H₂O}_n (5), {[Zn₄(BIBP)₄(bdc)₄]}_n (6), {[Zn(BIBP)(DL-ca)]·H₂O}_n (7), (BIBP = 5,5′-bis(1H-imidazol-1-yl)-2,2′-bithiophene, H₂hfipbb = 4,4′-(hexafluoroisopropylidene)bis(benzoic acid), H₃btc = 1,3,5-benzenetricarboxylic acid, H₂bdc = isophthalic acid, 5-OH-H₂bdc = 5-hydroxyisophthalic acid, D-H₂ca = D-camphor acid), have been hydrothermally synthesized. These compounds were structurally characterized by IR spectroscopy, elemental analysis and X-ray single-crystal diffraction. Compound 1 exhibits a 2D → 3D framework with an unusual parallel polycatenation of corrugated 2D (4,4) nets. Compounds 2–4 are structurally similar and display 2D layer structures, in which 2 and 3 extend into 3D supramolecular frameworks through interlayer O–H⋯O hydrogen-bonding interactions. Compound 5 displays a 3D 2-fold interpenetrating framework with a rare {4⁴·6⁶} sqp topology, containing an interesting ⋯LRLR⋯ double helical layer structure. Compound 6 is a 2D network with {4⁴·6²}-sql topology and further extends via C–H⋯O hydrogen bonds into the 3D supramolecular framework. Compound 7 possesses a rare 3D non-interpenetrated cds-type framework with the Schläfli symbol {6⁵·8}. Thermal stabilities for 1–7 and photoluminescence properties of the compounds 3–7 have been examined in the solid state at room temperature. Furthermore, solid-state UV–vis spectroscopy experiments show that compounds 1–7 exhibit optical band gaps which are characteristic for optical semiconductors, with band gaps of 2.41, 2.44, 2.48, 2.46, 2.83, 2.68, and 2.72 eV, respectively.