Series of Cadmium-Organic Frameworks Based on Mixed Flexible and Rigid Ligands: Single-Crystal-to-Single-Crystal Transformations, Sorption, and Luminescence Properties.

Here, we present a series of Cd(II) coordination polymers containing two types of ligands: sterically rigid terephthalate derivatives (bdc-NO 2 2- and bdc-Br 2- ) and flexible bis(2-methylimidazolyl)propane (bmip). The combination of two types of ligands is used to obtain and characterize compounds by single crystal and powder X-ray diffraction, FT-IR, elemental analysis, and TGA. Guest exchange results in structural transformations. 2-fold interpenetrated 1 ·DMF and 2 ·DMF rapidly undergo to 4-fold interpenetrated 1 ·Et 2 O, 1 ·EtOH, and 1 ·H 2 O, or 2 ·Et 2 O, respectively. Also, changes in the coordinating numbers and length of the N , N '-donor bmip ligand were observed according to single crystal X-ray analysis. Activated guest-free compounds [Cd(bdc-NO 2 )(bmip)] ( 1 ) and [Cd(bdc-Br)(bmip)] ( 2 ) are shown to be porous with a BET surface area of 103 and 283 m 2 ·g -1 , respectively. Moreover, both compounds demonstrate gate-opening behavior of ethylene adsorption isotherms at low pressures (<1 bar) and highly selective adsorption of benzene over cyclohexane or lower alcohols. Also, both compounds demonstrate a strong dependence of the maximum of the photoluminescence emission on an excitation wavelength. As a result, the photoluminescence color changes from white to red and from blue to red through green and yellow for compounds 1 and 2 , respectively, with excitation wavelength changing from 360 to 540 nm.