Syntheses, structures and photoluminescent properties of a series of metal–organic frameworks based on a flexible tetracarboxylic acid and different bis(imidazole) ligands

Abstract

A series of new metal–organic frameworks (MOFs), namely, [Co₂(L)(H₂O)₃]·5H₂O (1), [Co(L)_0.5(biim-4)]·H₂O (2), [Co(L)_0.5(biim-5)]·H₂O (3), [Co(L)_0.5(biim-6)]·1.5H₂O (4), [Co₂(L)(BIE)_1.5]·H₂O (5), [Co₂(L)(bbip)₂]·3H₂O (6), [Ni(L)_0.5(biim-4)_1.5] (7), [Ni₂(L)(biim-6)₂]·2H₂O (8), [Zn(L)_0.5(biim-4)]·H₂O (9), [Zn(L)_0.5(biim-5)]·H₂O (10), [Zn(L)_0.5(biim-6)]·H₂O (11), [Zn₂(L)(BIE)] (12), and [Zn(L)_0.5(bbip)_0.5]·0.5H₂O (13), where biim-4 = 1,1′-(1,4-butanediyl)bis(imidazole), biim-5 = 1,1′-(1,5-pentanedidyl)bis(imidazole), biim-6 = 1,1′-(1,6-hexanedidyl)bis(imidazole), BIE = 1,1′-(2,2′-oxybis(ethane-2,1-diyl))bis(1H-imidazole), bbip = 1,1′-(1,4-butanediyl)bis(imidazole-2-phenyl), and H₄L = 5,5′-(ethane-1,2-diyl)-bis(oxy)diisophthalic acid, have been synthesized under hydrothermal conditions. Their structures have been determined by single-crystal X-ray diffraction analyses and further characterized by infrared spectra (IR), elemental analyses, powder X-ray diffraction (PXRD) and thermogravimetric (TG) analyses. Compound 1 features a 3D 2-fold interpenetrating diamond framework. Compounds 2–4 and 9–11 are isostructural and display 3D 3-fold interpenetrating frameworks with (6⁴·8²)(6⁶) topologies. Compound 5 exhibits a 3D (4,6)-connected (6⁴·7²)(4·6⁵)(4²·6⁴·7⁵·8⁴) topology. Compounds 6 and 7 are 3D 2-fold interpenetrating frameworks with (6⁶)₂(6⁴·8²) and (4²·6⁴)(4³·6⁷) topologies, respectively. Compound 8 shows a 2D double-layer structure. Compound 12 possesses a 3D framework with (4,6)-connected (3·4²·5²·6)(3²·4²·5²·6⁴·7⁴·8)₂ topology. Compound 13 has a 3D 2-fold interpenetrating framework with (4⁴·6²)(4⁴·6¹⁰·8) topology. The luminescent properties of 9–13 have also been investigated in detail.