Synthesis, Structural Features, and Hydrogen Adsorption Properties of Three New Flexible Sulfur-Containing Metal–Organic Frameworks

Abstract

Three novel flexible sulfur-containing MOF materials named Co-URJC-5, Cu-URJC-6 and Zn-URJC-7, based on the 5,5′-thiodiisophthalic acid linker have been synthesized through solvothermal methods and characterized by different physicochemical techniques. Hydrogen adsorption analysis at room temperature reveals that these compounds display a gate-opening type adsorption mechanism at low pressures, attributed to the flexible nature of the H4TBTC ligand. This behavior is even more noticeable for Cu-URJC-6, since the layer arrangement by π–π stacking interactions between the aromatic layers could contribute to the flexibility of the structure. These results can be considered as a representative example to elucidate how MOF structures are built using flexible ligands and more significantly as a promising route for designing materials with selective gas sorption properties.

Understanding the Mechanism of Amorphization for Co‐URJC‐5

“…Recently, we have reported the interesting H 2 uptake gate‐opening behavior of a Co(II)‐based MOF as known Co‐URJC‐5 (URJC=Universidad Rey Juan Carlos), which is formed by 5–5'‐thiodiisophthalic acid as a ligand and a saturated single octahedral cobalt(II) cluster with two pyridine molecules in axial positions (Figure S1) [17] . Due to the flexible performance and the lack of OMS we decided to investigate the SO 2 adsorption properties of this material.…”

“…Co‐URJC‐5 was obtained via a solvothermal reaction of Co(NO 3 ) 2 ⋅ 6H 2 O with 5–5'‐thiodiisophthalic acid (H 4 TBTC: Scheme 1) according to a reported procedure [17] . A pink crystalline solid was obtained and characterized by X‐ray diffraction and N 2 adsorption which afforded a BET surface area of 233 m 2 g −1 .…”

“…Once the coordination geometry changes, the crystallinity collapses probably due to the loss of weak interactions generated by pyridine. In fact, Fonseca et al [17] . showed that a reversible transformation process from crystal to amorphous (SCA) depends on the amorphous state and, more importantly, preserves the short‐range environment (coordination geometry) of the pristine state.…”

Factors Affecting Hydrogen Adsorption in Metal–Organic Frameworks: A Short Review

“…The hydrogen adsorption analysis of three flexible sulfur-containing MOF materials named M-URJC-n (M = Co, Cu, Zn) based on the 5,5′-thiodiisophthalic acid linker (H 4 TBTC) showed that these compounds display a gate-opening type adsorption mechanism at low pressures, attributed to the flexible nature of the ligand [ 113 ]. The hydrogen adsorption capacities of the compounds were not high, with levels of 2.81, 2.21, and 1.99 wt%, for Co–, Cu–, and Zn modification, respectively, at 77 K and up to 18 bar, and 0.12, 0.14, and 0.13 wt%, at 298 K and 170 bar, due to the presence of flexible ligands.…”

“…These compounds showed an interesting gate-opening type adsorption mechanism. Considering the flexibility and the dynamic nature of the new structures, these compounds are candidates for applications such as hydrogen selective adsorption and gas separation processes, including hydrogen purification in precombustion mixtures of H 2 /CO 2 [ 113 ].…”