Deciphering the Structural Relationships of Five Cd-Based Metal-Organic Frameworks.

The one-pot reaction of Cd(NO3 )2 ·4H2 O and 5-(6-(hydroxymethyl)pyridin-3-yl)isophthalic acid (H2 L) in DMF/H2 O (DMF = N,N-dimethylformamide) produced a two-dimensional (2D) metal-organic framework (MOF) of [Cd(L)(H2 O)2 ] (A) bearing aqua-bridged Cd centers, accompanied by two three-dimensional (3D) MOFs [Cd(L)(DMF)0.5 ] (B) and [Cd(L)] (C). Removing the bridging aqua molecules of A by heating led to the formation of an additional 3D MOF of [Cd(L)] (D) in a single-crystal to single-crystal (SCSC) manner. The search for the preceding compound that could convert to A resulted in the isolation of a 2D MOF [Cd(L)(DMF)] (E) that readily converted to A in water, but with the loss of single crystallinity. Upon excitation at 350 nm, A, D, E, and the ligand H2 L fluoresced at 460 nm, 468 nm, 475 nm, and 411 nm, respectively. The fluorescence of A could be used for the selective detection of Fe3+ in water down to 0.58 ppm. This quenching was not affected by the presence of other common metal ions.