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

Abstract

Herein, we report the crystal structure and guest binding properties of a new two-dimensional (2D) square lattice (sql) topology coordination network, sql-(azpy)(pdia)-Ni, which is comprised of two linker ligands with diazene (azo) moieties, (E)-1,2-di(pyridin-4-yl)diazene(azpy) and (E)-5-(phenyldiazenyl)isophthallate(pdia). sql-(azpy)(pdia)-Ni underwent guest-induced switching between a closed (nonporous) β phase and several open (porous) α phases, but unlike the clay-like layer expansion to distinct phases previously reported in switching sql networks, a continuum of phases was formed. In effect, sql-(azpy)(pdia)-Ni exhibited elastic-like properties induced by adaptive guest binding. Single-crystal X-ray diffraction (SCXRD) studies of the α phases revealed that the structural transformations were enabled by the pendant phenyldiazenyl moiety on the pdia2– ligand. This moiety functioned as a type of hinge to enable parallel slippage of layers and interlayer expansion for the following guests: N,N-dimethylformamide, water, dichloromethane, para-xylene, and ethylbenzene. The slippage angle (interplanar distances) ranged from 54.133° (4.442 Å) in the β 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.

The Chemistry of Metal Organic Framework Materials

“…More recently, MOF glasses, a disordered form of MOFs, are finding niche applications. This virtual collection catalogues recent MOF advances featured in Chemistry of Materials from 2022 to 2023, − with an accompanying editorial by Laura Gagliardi and Omar Yaghi that outlines three critical future directions for MOFs …”

Water vapour and gas induced phase transformations in an 8-fold interpenetrated diamondoid metal–organic framework

“…The study of rigid MOFs that exhibit pore-filling at low relative humidity, RH, as alternatives to conventional desiccants such as zeolites and silica gel, is of growing interest in the context of AWH, 32–35 as exemplified by Al-fumarate, 36 MIL-160, 37 MOF-303 31 and CAU-10-H. 38 FMOMs, which are less studied than rigid MOFs, exhibit a different mechanism, water vapour induced structural transformation(s), e.g. JUK-8, 39 [Cu(HQS)(TMBP)], 40 Zn(3-tba) 2 (H 2 O) 2, 41 sql-(azpy)(pdia)-Ni 42 and DUT-98. 26 Regardless of the AWH mechanism, key performance parameters include the need for an S-shaped isotherm with an inflection at low RH, negligible hysteresis, low regeneration temperature and hydrolytic/mechanical stability to extended recycling.…”

The Effect of Pendent Groups upon Flexibility in Coordination Networks with Square Lattice Topology

“…Such isotherms can exhibit enhanced working capacities compared with the type I (Langmuir) sorption isotherms typically displayed by rigid materials. Therefore, FMOFs are of potential utility in gas storage − or separation − and water sorption. , …”

“…Whereas >118000 entries have been archived in the metal–organic framework (MOF) subset of the Cambridge Structural Database (CSD), the number of reported FMOFs is much smaller. , Nevertheless, that FMOFs can exhibit strong performance for gas/vapor storage or separation makes elucidation of crystal engineering principles for the design of FMOFs a topical area of investigation. The mechanism of flexibility in FMOFs tends to belong to one or more of the following three categories: , ligand contortion (e.g., bending, twisting, and/or rotation); ,− structural changes in the metal node or molecular building block (MBB) coordination environment (e.g., deformation, isomerism, or changes in coordination number); ,,− relative motions of individual nets (such as interpenetrated or layered net sliding or expansion). ,, There also exist examples of light-modulated adsorbents with photoactive linkers. − …”

“…Regulated by interlayer H-bonds, slippage between adjacent sql layers was enabled by the contortion of the pendent ligand (E)-5-(phenyldiazenyl)isophthalic acid (H 2 pdia). 18 Here, we present a new crystal engineering strategy to establish control over expansion between sql layers, varying the bulk and length of pendent groups in a family of isophthalic acid linkers. The prototypal structure of this family of networks, [Zn(nipa)(bphy)] n , 1, was previously reported by Chen's group and is comprised of Zn 2+ nodes, 5-nitroisophthalic acid (H 2 nipa) and 1,2-bis(pyridin-4-yl)hydrazine (bphy).…”