Solvent-Induced Controllable Supramolecular Isomerism: Phase Transformation, CO2 Adsorption, and Fluorescence Sensing toward CrO42-, Cr2O72-, MnO4-, and Fe3+

摘要

Complexes {[Zn(bpdc)(Cz-3,6-bpy)]center dot DMF center dot H2O}(n) (1 alpha-DMF, H(2)bpdc = biphenyl-4,4'-dicarboxylic acid, Cz-3,6-bpy = 3,6-bis(pyridine-4-yl)9H-carbazole, DMF = N,N'-dimethylformamide) and {[Zn(bpdc)(Cz-3,6-bpy)]center dot 2DMAc center dot H2O} n (1 beta-DMAc, DMAc = N,N'-dimethylacetamide) as a couple of solvent-induced supramolecular isomers were hydro(solvo)thermally synthesized using DMF/H2O and DMAc-only as reaction media, respectively. Complexes 1 alpha-MF and 1 beta-DMAc adopt very similar wavy sql sheet structures but present great differences in the 3-fold interweaving 2D similar to 2D nets, which result in free voids of 17.6 and 33.4%, respectively. Desolvated 1 beta has about 2 times the free voids compared to that of desolvated 1 alpha; however, the former displays a CO2 uptake of 87.9 cm(3) g(-1) STP at 195 K and P/P-0 = 1 which is only slight larger than that (73.7 cm(3) g(-1) STP) of the latter under the same conditions. This is mainly interpreted by activation-and adsorption-induced framework distortion that caused partial transformation of crystal phase from 1 beta to 1 alpha and thus reduced free voids. The isosteric heat of CO2 adsorption (Qst) at zero loading is 29.8 kJ mol(-1) for desolvated 1 alpha and 30.6 kJ mol(-)1 for desolvated 1 beta. On the other hand, results from XRPD, IR, and TGA measurements imply that 1 alpha-DMF and 1 beta-DMAc are highly stable in several different solvents, with the exception of 1 alpha-DMF in DMAc, which experienced complete transformation to convert to 1 beta-DMAc and 1 beta-MAc in acetone and methanol, which would respectively completely and partially transform to the crystal phase of 1 alpha-DMF. Remarkably, 1 alpha-DMF and 1 beta-DMAc display intense blue and cyan fluorescence emissions, respectively, promising them to be multifunctional sensing platforms in sensitive detection of CrO42-, Cr2O72-, MnO4-, and Fe3+ with high selectivity and a fairly low limit of detection through perceptible fluorescence quenching effect. The possible sensing mechanisms were also investigated.