Two diverse 3D 6-connected Cd(II)/Co(II) MOFs based on binuclear clusters as fluorescence sensors for detection of Fe³⁺, Cr₂O₇²⁻ and nitrobenzene

Two novel three-dimensional (3D) Cd(II)/Co(II) metal-organic frameworks (MOFs), [Cd₂(seb)₂(bbmb)(H₂O)₂]_n (1) and {[Co₂(seb)₂(bbmb)₂(H₂O)]·0·5H₂O}_n (2), were synthesized under hydrothermal conditions based on sebacic acid (H₂seb) and 4,4′-Bis(benzimidazol-1-ylmethyl) biphenyl (bbmb) ligands. Their crystal structures were structurally characterized by single-crystal X-ray diffraction. MOFs 1 and 2 both show a 3D framework based on binuclear Cd₂ or Co₂ clusters, respectively. In 1, the Cd₂ clusters are linked by seb^2- into a 2D corrugated layer. These layers are further connected by bbmb to generate a 3D structure with 6-connected (4⁴·6¹⁰·8) mab topology. In 2, the Co₂ clusters form a 1D chain through the bbmb ligands, the chains are linked by seb²⁻ into a 3D framework with 6-connected (4⁸·5⁴·6³) bsn topology. Fluorescence sensing experiments show that 1 and 2 have good ability for detection of Fe³⁺, Cr₂O₇²⁻ and nitrobenzene (NB) with low detection limits as 5.83μM, 1.36μM and 2.70 × 10⁻⁷M for 1 and 6.19μM, 1.40μM and 2.90 × 10⁻⁷M for 2, respectively. Furthermore, the sensing mechanism was also investigated in detail by various detection means and theoretical calculations.