# Metal-Organic Frameworks Characterization via Inverse Pulse Gas Chromatography
## 3 Applications of IGC for the Characterization of MOFs
### Hkuet-1  
HKUST-1 (HKUST = Hong Kong University of Science and Technology), known also as MOF-199, was reported initially by [PERSON] et al. [80]. This MOF entails copper(II)-dimer forming paddle-wheel SBUs, which form coordination bonds with four carboxylate groups from the organic linker trimesic acid (benzene-1,3,5-tricarboxylate (BTC)), and has the formula Cu\({}_{3}\)(BTC)\({}_{2}\cdot\)xH\({}_{2}\)O. The three-dimensional extension of these paddle-wheel units forms a three-dimensional structure with an underlying **tbo** topology (Figure 3). This MOF has a relatively high surface area in the range of 1500-2100 m\({}^{2}\) g\({}^{-1}\). \begin{table}
\begin{tabular}{c c c c c c c c c c} \hline \hline  
\begin{table}
\begin{tabular}{c c c c c c c c c c} \hline \hline  
\begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline  
Some research groups have identified this MOF as having three different types of cages with pore diameters of 4-4.7 A, 10-10.3 A, and 11-12.1 A [81, 82]. The large- and medium-sized pores are directly interconnected in an alternating manner, while the small 4-4.7 A pores are situated at the vertexes of the large- and medium-sized pores and are directly interconnected with the large pores only. Other authors have identified this MOF structures with only two types of pores: large 9-12 A pores connected by 7-8.3 A windows, and small 5 A pores accessible by 3.5 A windows [80, 83, 84]. In the hydrated HKUST-1 structure, a water molecule is coordinated at the axial position of the paddlewheel unit and can be removed upon an activation process, without any change in MOF crystallinity or loss of porosity. An unoccupied coordination site at the Cu\({}^{2+}\) atoms is called a coordinatively unsaturated site (CUS) and can be accessed by other probe molecules [82]. One metal ion coordination site is unsaturated and therefore open to Lewis basic molecules [80, 85]. HKUST-1 possesses Lewis acidic centers from the copper(II)-SBUs, and Lewis basic centers from \(\pi\) electron-rich benzene rings in the BTC molecule. The Fe-BTC MOF is analogous in structure to HKUST-1 and is synthesized as a porous solid, however, in a gel-like form (surface area is about 1300-1600 m\({}^{2}\) g\({}^{-1}\)) [86]. Fe-BTC MOF, unlike HKUST-1, has not been thoroughly explored or studied because its structure is not highly crystalline that may cause distortion of its pore geometry. Its morphological properties were studied in comparison to MIL-100 (Fe) (MIL = Material of Institute Lavoisier) [87], and Fe-BTC MOF has been found to encompass 21.2% of Fe\({}^{3+}\) as a nodal metal and the BTC linker in a distorted form of MIL-100(Fe) MOF [87, 88]. While its composition is similar to that of MIL-100 (Fe), with respect to many applications, Fe-BTC MOF cannot be compared directly with MIL-100 (Fe). HKUST-1 and Fe-BTC MOF were commercialized under the commercial names Basolite C300 and F300, respectively. [PERSON] et al. [49] demonstrated a possible use of HKUST-1 MOF for adsorptive separation based on shape selectivity. They found that linear alkanes were adsorbed preferably over methyl-branched alkanes. The high adsorption enthalpy and low Henry constants of  
Figure 3: Crystal structure of the desolvated HKUST-1 (Cu\({}_{3}\)(BTC)\({}_{2}\)) MOF. The blue polyhedra represent the Cu paddlewheel SBU structure. (red: oxygen, and black: carbon). the branched alkanes relative to those of their linear isomers suggested shape selectivity, as the Henry constants decreased with branching degree. Shape-based discrimination was used to examine the logarithm of the vapor pressure versus the logarithm of the Henry constant plot (Figure 4). A linear relationship with 2-methyl-branched alkanes on this trend line was observed for linear alkanes, although not all alkanes branched like 3-methyl- and dimethyl- alkanes behaved similarly.