Four dual-functional luminescent Zn(ii)-MOFs based on 1,2,4,5-benzenetetracarboxylic acid with pyridylbenzimidazole ligands for detection of iron(iii) ions and acetylacetone

Abstract

Four new Zn(II) metal–organic frameworks (MOFs): {[Zn(L1)(BTEC)_0.5]·3.1H₂O}_n (1), {[Zn(L2)_0.5(BTEC)_0.5]·1.5H₂O}_n (2), {[Zn₂(L3)(BTEC)(H₂O)]·H₂O}_n (3), and {[Zn₂(L4)(BTEC)]·H₂O}_n (4) were constructed by selecting N-containing linkers with the Zn(II)/H₄BTEC system (H₄BTEC = 1,2,4,5-benzenetetracarboxylic acid, L1 = 1,4-bis(1-(pyridin-4-ylmethyl)-1H-benzo[d]imidazol-2-yl)cyclohexane, L2 = 1,4-bis(1-(pyridin-4-ylmethyl)-1H-benzo[d]imidazol-2-yl)butane, L3 = 1,5-bis(1-(pyridin-4-ylmethyl)-1H-benzo[d]imidazol-2-yl)pentane, L4 = 1,4-bis(1-(pyridin-4-ylmethyl)-1H-benzo[d]imidazol-2-yl)methyl)benzene). Structural analyses indicate that 1 exhibits a (3,4)-connected 2D 3,4L13 sheet. 2 manifests a rare (4,4,4)-connected 2D 4,4,4L10 layer. 3 displays an unprecedented (3,3,4,4,4)-connected 3D network based on the point symbol {4·8²}₂{4²·6·8³}₂{4²·6}₂{4²·8²·10²}{8⁴·12²} and 4 presents an unusual 4,4,4,6,6T3 3D network with a 5-node (4,4,4,6,6)-connected network. The structural variety of these Zn(II) MOFs demonstrates that different N-containing ligands can induce the BTEC⁴⁻ linkers exhibiting various coordination modes, exerting a great influence on the final MOF frameworks. Further, MOFs 1–4 are favorable dual-functional fluorescent sensors for the detection of Fe³⁺/acetylacetone with high sensitivity and selectivity. To our knowledge, this is the first report of fluorescent MOFs based on L1–L4 ligands for the detection of Fe³⁺ and acac in the naked eye range.