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

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), {[Zn-2(BIBP)(0.5)(hfipbb)(2)]center dot H2O}(n) (5), {[Zn-4(BIBP)(4)(bdc)(4)]}(n) (6), {[Zn(BIBP)(DL-ca)]center dot H2O} n (7), (BIBP = 5,5'-bis(1H-imidazol-1-yl)-2,2'-bithiophene, H(2)hfipbb = 4,4'-(hexafluoroisopropylidene)bis(benzoic acid), H(3)btc = 1,3,5-benzenetricarboxylic acid, H(2)bdc = isophthalic acid, 5-OH-H(2)bdc = 5-hydroxyisophthalic acid, D-H(2)ca = 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 center dot center dot center dot O hydrogen-bonding interactions. Compound 5 displays a 3D 2-fold interpenetrating framework with a rare {4(4)center dot 6(6)} sqp topology, containing an interesting center dot center dot center dot LRLR center dot center dot center dot double helical layer structure. Compound 6 is a 2D network with {4(4)center dot 6(2)}-sql topology and further extends via C-H center dot center dot center dot O hydrogen bonds into the 3D supramolecular framework. Compound 7 possesses a rare 3D non-interpenetrated cds-type framework with the Schlafli symbol {6(5)center dot 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.