Solvents control over the degree of interpenetration in metal-organic frameworks and their high sensitivities for detecting nitrobenzene at ppm level

Solvothermal syntheses in DMF and acetonitrile afforded two novel MOFs, Zn3(L1)2(L2)·3.6 DMF·4.0 H2O (1) and Zn3(L1)2(L2) (2) [L1 = 4-[3-(4-carboxyphenoxy)-2-[(4-carboxyphenoxy)methyl]-2-methyl-propoxy]benzoate, L2 = 1,4-bis(1-imidazolyl)benzene], respectively. Single crystal X-ray analyses reveal that 1 and 2 are structurally closely related with the same building blocks and 3-dimesional 3, 8-connected tfz-d net. 1 is based on a 2-fold interpenetrating network with extra-framework DMF and water molecules located in the void space, while 2 is different in its 3-fold interpenetrating network and absence of any solvent molecules. This simple and easy strategy unprecedentedly controls the degree of interpenetration in MOFs through varying solvents. Luminescent properties of activated phase 1′ and 2 well dispersed in different solvents have also been investigated systematically, which demonstrate distinct solvent-dependent luminescent spectra with emission intensities significantly quenched toward nitrobenzene (NB). For luminescence responses of 1′ and 2 dispersed in DMF solution with gradually increased NB contents, detectable quenching effects were observed even at a very low NB concentration of 50 ppm, indicating extremely high sensitivities of 1′ and 2 towards NB.