A CdSO₄-Type 3D Metal–Organic Framework Showing Coordination Dynamics on Cu²⁺ Axial Sites: Vapochromic Response and Guest Sorption Selectivity

A unique 2-fold interpenetrated CdSO 4 coordination network of the formula {[Cu 2 (4-pmpmd) 2 (CH 3 OH) 4 (opd) 2 ]·2H 2 O} n [4-pmpmd = N, N ′-bis(4-pyridylmethyl)phenyldiimide; opd = o -phthalic acid] has been synthesized and characterized by IR spectra, thermogravimetric (TG) analyses, elemental analyses, and single crystal and powder X-ray diffraction methods. The metal–organic framework (MOF) exhibits reversible dehydration and rehydration in a single-crystal-to-single-crystal (SC–SC) process. Moreover, the dehydrated material, having coordinatively unsaturated Cu 2+ sites, can encapsulate CH 3 OH molecules with a color change, again in a reversible SC–SC fashion, and shows selective adsorption of CO 2 over N 2 and H 2 . This feature of obvious color variation induced by the presence of small hydroxylic molecules is highly promising for detecting hydroxylic molecules through a simple sensing mechanism. In addition, the MOF selectively interacts with hydroxylic guests and shows sorption selectivity for water, methanol, ethanol, and n -propanol over benzene guests. Notably, this compound shows complete selectivity in adsorption for n -propanol over 2-propanol owing to the effect of shape exclusion.