Rational synthesis, crystal structure, and sensing and adsorption properties of luminescent metal–organic frameworks

Abstract

Five novel Cd(II) metal–organic frameworks (Cd-MOFs), namely [Cd₆(L)₄(1,3-bit)₂(H₂O)₄]_n (1), [Cd(HL)(4,4′-bbibp)]_n (2), [Cd₃(L)₂(1,4-bimb)₂(H₂O)₂]_n (3), [Cd(HL)(4,4′-bidpe)]_n (4) and [Cd₃(L)₂(1,1′-bbi)(H₂O)₄]_n (5) (flexible H₃L = 5-(2-carboxylphenoxy)isophthalic acid, rigid 1,3-bit = 1,3-bis(l-imidazoly)toluene, rigid 4,4′-bbibp = 4,4′-bis(benzoimidazo-1-ly)biphenyl, semi-flexible 1,4-bimb = 1,4-bis(imidazol-l-ylmethyl)benzene, semi-flexible 4,4′-bidpe = 4,4′-bis(imidazolyl)diphenyl ether, and flexible 1,1′-bbi = 1,1′-(1,4-butanediyl)bis(imidazole)) were synthesized employing a rational design approach under solvothermal conditions and further characterized by elemental analysis, IR spectra, thermogravimetric (TG) analysis, powder X-ray diffraction (PXRD), and single-crystal X-ray diffraction. Diversity architectural topologies have been generated by adjusting the N-donor ligands. They exhibit varied structures: 1 displays an unprecedented 6-nodal (3,3,4,4,8,8)-c 3D topology framework with the point Schläfli symbol of (3·4·5)₂(3²·4²·5²·6⁶·7⁸·8⁷·9)(3²·6³·7)(4·6⁴·8)(4¹⁰·6¹¹·8⁷)(4³)₂; 2 shows a 2-fold interpenetrating 4-connected cds topology with the point Schläfli symbol of (6⁵·8); 3 exhibits an unprecedented 2-nodal (3,8)-c 3D topology network with the point Schläfli symbol of (4²·5)₂(4⁴·5⁶·6¹⁰·7⁵·8²·9); 4 shows a 4-connected sql topology with the point Schläfli symbol of (4⁴·6²); 5 displays a tfz-d topology 2-nodal (3,8)-c 3D network with the point Schläfli symbol of (4³)₂(4⁶·6¹⁸·8⁴). The luminescence studies reveal that MOFs 1–5 display highly sensitive and selective fluorescence sensing towards Fe³⁺ cations, CrO₄²⁻ anions and molecular acetone. Meanwhile, the targeted dye adsorption properties of MOFs 1–5 are investigated.