Structural Phase Transformations Induced by Guest Molecules in a Nickel-Based 2D Square Lattice Coordination Network.

Herein, we report the crystal structure and guest binding properties of a new two-dimensional (2D) square lattice () topology coordination network, , which is comprised of two linker ligands with diazene (azo) moieties, ()-1,2-di(pyridin-4-yl)diazene(azpy) and ()-5-(phenyldiazenyl)isophthallate(pdia). underwent guest-induced switching between a closed (nonporous) phase and several open (porous) phases, but unlike the clay-like layer expansion to distinct phases previously reported in switching networks, a continuum of phases was formed. In effect, exhibited elastic-like properties induced by adaptive guest binding. Single-crystal X-ray diffraction (SCXRD) studies of the phases revealed that the structural transformations were enabled by the pendant phenyldiazenyl moiety on the pdia ligand. This moiety functioned as a type of hinge to enable parallel slippage of layers and interlayer expansion for the following guests: ,-dimethylformamide, water, dichloromethane, -xylene, and ethylbenzene. The slippage angle (interplanar distances) ranged from 54.133° (4.442 Å) in the phase to 69.497° (5.492 Å) in the ethylbenzene-included phase. Insight into the accompanying phase transformations was also gained from variable temperature powder XRD studies. Dynamic water vapor sorption studies revealed a stepped isotherm with little hysteresis that was reversible for at least 100 cycles. The isotherm step occurred at ca. 50% relative humidity (RH), the optimal RH value for humidity control.