Water-Driven Structural Transformation in Cobalt Trimesate Metal-Organic Frameworks

We report on the synthesis and the characterization of a novel cobalt trimesate metal-organic framework, designated as KCL-102. Powder X-ray diffraction pattern of KCL-102 is dominated by a reflection at 10.2◦ (d-spacing = 8.7 Å), while diffuse reflectance UV-Vis spectroscopy indicates that the divalent cobalt centers are in two different coordination geometries: tetrahedral and octahedral. Further, the material shows low stability in humid air, and it transforms into the well-known phase of hydrous cobalt trimesate, Co3(BTC)2·12H2O. We associated this transition with the conversion of the tetrahedral cobalt to octahedral cobalt.

Herein, we report a solvothermal process to obtain a Co-BTC MOF (KCL-102) which has a quite different powder X-ray diffraction (PXRD) pattern than the reported Co-BTCs. We investigated the stability of this novel Co-BTC after contact with air and water by using PXRD, scanning electron microscopy (SEM), thermogravimetry (TG), and diffuse ultraviolet-visible spectroscopy (DRUV-Vis). KCL-102 is not stable in moisture. Nevertheless, unlike most parts of MOFs that become amorphous upon contact with water, it undergoes a phase transformation to another crystalline phase, non-porous Co-BTC, the previously reported Co 3 (BTC) 2 ·12H 2 O [46].

Materials and Methods
All the chemicals were purchased from Sigma Aldrich and were used without any further purification. Table 1 lists three different synthesis parameters for the preparation of KCL-102. KCL-102 was synthesized using benzene-1,3,5-tricarboxylic acid (BTC) and cobalt nitrate hexahydrate in 1:2 (molar ratio). At first, BTC was dissolved in 100 mL DMF and 50 mL Millipore water mixture. The cobalt source was then added to the solution and stirred until it completely dissolved (~15 min). The solution was transferred to a 250 mL Teflon lined autoclave and kept in preheated oven at 140 • C for 1-2 h. The resulting precipitate was filtered and dried at 50 • C for 2 h, washed with DMF, and dried again at 50 • C for 2 h. PXRD patterns were recorded using a Rigaku Miniflex tabletop diffractometer equipped with a Cu X-ray tube (Kα 1 = 1.540562 Å) with fixed tube voltage of 30 kV and output current of 15 mA; it was also equipped with a graphite monochromator. The diffraction patterns were collected in Bragg Brentano geometry in the 3-70 • 2θ range with step size of 0.02 • . The simulated powder diffraction pattern of Co 3 (BTC) 2 ·12H 2 O was obtained by using the structure reported in Ref. [46] by employing the program Mercury 2020.2.0 [50]. SEM images were obtained with an FEI 400 instrument operated at 30 kV. TGA was carried out on a TAQ600 (TA Instruments) with a ramp rate of 10 • C/min from room temperature to 700 • C in nitrogen or in dry air flow using an alumina pan.
Infrared (IR) spectra were recorded on JASCO spectrometer in transmittance mode in the range of 4000 to 400 cm −1 using a deuterated triglycine sulfate detector on selfsupported pellets obtained by diluting the MOF powder in KBr. DRUV-Vis spectra were recorded on a JASCO 650 spectrometer. BaSO 4 was used as the reference standard. The spectra were acquired in air with loose powders diluted in pure BaSO 4 placed inside the standard powder cell of the instrument.

Results and Discussion
Three batches of KCL-102 were synthesized (see Table 1), and all the samples showed similar PXRD patterns (Figure 1a), indicating the good reproducibility of the synthesis. The reaction yield was not dependent on the reaction conditions used, being 35-40% in all cases. The reaction time was significantly shorter compared to the typical Co 3 (BTC) 2 ·12H 2 O synthesis (20-24 h, [46,47]). All the patterns reported in Figure 1a,b were equivalent, and they were all different from the patterns reported for other metal trimesates. The structures used for the comparison were obtained by search in articles collection databases [24,[35][36][37][38][39][40][41][42][43][44][45][46]48,[51][52][53][54] and in the Cambridge Structural Database (CCSD, [55]) using as a query in ConQuest one cobalt atom bound to one oxygen atom of a BTC linker and coordinated to two additional oxygen atoms through a single bond. The most intense reflection of the pattern was centered at 10.2 • , corresponding with a d-spacing of 8.7 Å. No variation was observed in the diffraction patterns after DMF washing (blue line, Figure 1b). orded on a JASCO 650 spectrometer. BaSO4 was used as the reference standard. The spectra were acquired in air with loose powders diluted in pure BaSO4 placed inside the standard powder cell of the instrument.

Results and Discussion
Three batches of KCL-102 were synthesized (see Table 1), and all the samples showed similar PXRD patterns (Figure 1a), indicating the good reproducibility of the synthesis. The reaction yield was not dependent on the reaction conditions used, being 35%-40% in all cases. The reaction time was significantly shorter compared to the typical Co3(BTC)2·12H2O synthesis (20-24 h, [46,47]). All the patterns reported in Figure 1a,b were equivalent, and they were all different from the patterns reported for other metal trimesates. The structures used for the comparison were obtained by search in articles collection databases [24,[35][36][37][38][39][40][41][42][43][44][45][46]48,[51][52][53][54] and in the Cambridge Structural Database (CCSD, [55]) using as a query in ConQuest one cobalt atom bound to one oxygen atom of a BTC linker and coordinated to two additional oxygen atoms through a single bond. The most intense reflection of the pattern was centered at 10.2°, corresponding with a d-spacing of 8.7 Å. No variation was observed in the diffraction patterns after DMF washing (blue line, Figure 1b).  Table 1). (b) Diffraction patterns of the assynthesized KCL-102 before and after washing with DMF.
KCL-102 is not stable in air for a prolonged time. The material dried at 50 °C and left in the air was found to undergo to a phase transformation that was completed in one week, and the resulting sample was designated as KCL-102-air following. This structural transformation was ascribable to moisture (see below), and the conversion was much  Table 1). (b) Diffraction patterns of the as-synthesized KCL-102 before and after washing with DMF.
KCL-102 is not stable in air for a prolonged time. The material dried at 50 • C and left in the air was found to undergo to a phase transformation that was completed in one week, and the resulting sample was designated as KCL-102-air following. This structural transformation was ascribable to moisture (see below), and the conversion was much faster upon contacting KCL-102 with a droplet of water and drying it in the air (KCL-102-H 2 O). A similar observation was previously noticed for MOFs in the presence of protic solvents [56]. KCL-102-air and KCL-102-H 2 O were fully equivalent from their characterization. In the following, only the results obtained for KCL-102-air are reported. The phase transformation was accompanied by a change in the color from violet (KCL-102) to pale pink (KCL-102-air and KCL-102-H 2 O). Likewise, the color change was also observed in the reaction mixture left in the air after a few days. A first attempt to measure the surface area of KCL-102 was made, thermally treating the sample in vacuum at 100 • C and 150 • C. Unfortunately, the desorption of a large amount of solvent (likely DMF) from the sample to the measurement cell hindered the isotherm collection. Future studies should be aimed at the determination of a washing procedure for the removal of DMF from the sample, e.g., using low boiling solvents.
The diffraction patterns recorded for the as-made KCL-102 (blue line) and KCL-102air (light magenta) are presented in Figure 2a. It can be seen from this figure that the two patterns were significantly different. Noteworthy, the diffraction pattern of KCL-102-air corresponded to the Co 3 (BTC) 2 ·12H 2 O pattern (see Figure 2a), a non-porous MOF reported formerly by Yaghi et al. [46] that was suggested as a catalyst for CO oxidation [47] and a promising candidate for oxygen evolution reaction [48]. The structure of Co 3 (BTC) 2 ·12H 2 O as in Ref. [46] is reported in Figure 2b. Nevertheless, some additional reflections were identified in the KCL-102-air that were not present in the Co 3 (BTC) 2 ·12H 2 O pattern at 9.3 • , 12.5 • , 23.2 • , and 23.5 • . Among them, the most intense were the reflections at 9.3 • and 12.5 • . These reflections could not be indexed as belonging to the expected products from KCL-102 decomposition (Co(OH) 2 , Co 3 O 4 , and trimesic acid) or to any other reported Co trimesates (Refs. [35][36][37][38][39][40][41][42][43][44][45][46]). Although these peaks could be related to an additional Co trimesate phase, we suggest that they were associated with the formation of mesopores due to framework collapse, as already reported for other MOFs. Unfortunately, the presence of a significant amount of DMF did not allow us to record the nitrogen isotherm for KCL-102-air or to verify this hypothesis. faster upon contacting KCL-102 with a droplet of water and drying it in the air (KCL-102-H2O). A similar observation was previously noticed for MOFs in the presence of protic solvents [56]. KCL-102-air and KCL-102-H2O were fully equivalent from their characterization. In the following, only the results obtained for KCL-102-air are reported. The phase transformation was accompanied by a change in the color from violet (KCL-102) to pale pink (KCL-102-air and KCL-102-H2O). Likewise, the color change was also observed in the reaction mixture left in the air after a few days. A first attempt to measure the surface area of KCL-102 was made, thermally treating the sample in vacuum at 100 °C and 150 °C. Unfortunately, the desorption of a large amount of solvent (likely DMF) from the sample to the measurement cell hindered the isotherm collection. Future studies should be aimed at the determination of a washing procedure for the removal of DMF from the sample, e.g., using low boiling solvents. The diffraction patterns recorded for the as-made KCL-102 (blue line) and KCL-102air (light magenta) are presented in Figure 2a. It can be seen from this figure that the two patterns were significantly different. Noteworthy, the diffraction pattern of KCL-102-air corresponded to the Co3(BTC)2·12H2O pattern (see Figure 2a), a non-porous MOF reported formerly by Yaghi et al. [46] that was suggested as a catalyst for CO oxidation [47] and a promising candidate for oxygen evolution reaction [48]. The structure of Co3(BTC)2·12H2O as in Ref. [46] is reported in Figure 2b. Nevertheless, some additional reflections were identified in the KCL-102-air that were not present in the Co3(BTC)2·12H2O pattern at 9.3°, 12.5°, 23.2°, and 23.5°. Among them, the most intense were the reflections at 9.3° and 12.5°. These reflections could not be indexed as belonging to the expected products from KCL-102 decomposition (Co(OH)2, Co3O4, and trimesic acid) or to any other reported Co trimesates (Refs. [35][36][37][38][39][40][41][42][43][44][45][46]). Although these peaks could be related to an additional Co trimesate phase, we suggest that they were associated with the formation of mesopores due to framework collapse, as already reported for other MOFs. Unfortunately, the presence of a significant amount of DMF did not allow us to record the nitrogen isotherm for KCL-102-air or to verify this hypothesis.      Figure 4, respectively. Regarding KCL-102, it was not possible to assign the different steps in the TG trace, as its chemical formula is unknown (Figure 4Error! Reference source not found.a). We were limited to observing that KCL-102 TG trace was not dependent on the reaction environment up to 350 °C (Figure 4a), with temperature corresponding to about 10% weight loss. This result indicated a significant thermal stability of KCL-102. The weight loss up to 350 °C was continuous without abrupt changes, and it was likely associated with solvent (water and DMF) and unreacted linker desorption from the MOF pores. Material decomposition started at 350 °C and 450 °C in air and nitrogen, respectively, corresponding to structural water desorption and material decomposition.
The TG traces of the hydrated cobalt trimesate, KCL-102-air, in a flow of dry air (dashed line) or nitrogen (solid line) are reported in Figure 4b. Regarding TG collected under nitrogen atmosphere, it can be seen from this figure that a substantial weight loss between 100-400 °C (~26 wt%) could be attributed to the removal of the coordinated water molecules. This result was similar to that reported by Crane et al. [38]. The plateau extended up to 450 °C, indicating the larger thermal stability of Co3(BTC)2·12H2O compared to KCL-102. The second stage weight loss (~30 wt%) evidenced in the temperature range 450-525 °C could be associated with framework collapse leading to the formation of Co(OH)2 (34.5 wt%) followed by a continuous weight loss to Co3O4 (29.8 wt%).
As expected, a similar behavior was observed for the sample heated in air (dashed line in Figure 4b), however, with the onset temperatures shifted to lower values. In this case, a plateau was reached at 420 °C, and that was maintained at least up to 700 °C. The observed weight loss (64 wt%) was close to the one expected for the formation of Co3O4.
We investigated KCL-102 using infrared (FTIR) and UV-Vis spectroscopy in order to gain some knowledge on details of KCL-102 structure. Figure 5 shows the vibration modes of KCL-102 (blue line) and KCL-102-air (pink line) in comparison with the spectra of the trimesic acid (black line) and of MIL-100(Fe), an iron trimesate [57] (brown line). MIL-100(Fe) spectrum was used a standard for the quick identification of carboxylate band and unreacted carboxylic acid groups in KCL-102 and KCL-102-air. The IR spectrum of KCL-102-air matched well with the spectrum reported by Yaghi et al. for Co3(BTC)2·12H2O [46]. In the 3600-2800 cm -1 region, the spectra of KCL-102 and KCL-102air were clearly dominated by a large band due to the solvent molecules (water and DMF), both structural and physisorbed solvent molecules. The relative intensity of these bands was larger in KCL-102-air than in KCL-102 because of the larger hydration degree of the former. IR absorption bands of the BTC linker were observed in the 1800-400 cm --1 range. For comparison, the spectra of a trimesate salt (MIL-100(Fe), brown line) and of trimesic  Figure 4, respectively. Regarding KCL-102, it was not possible to assign the different steps in the TG trace, as its chemical formula is unknown (Figure 4a). We were limited to observing that KCL-102 TG trace was not dependent on the reaction environment up to 350 • C (Figure 4a), with temperature corresponding to about 10% weight loss. This result indicated a significant thermal stability of KCL-102. The weight loss up to 350 • C was continuous without abrupt changes, and it was likely associated with solvent (water and DMF) and unreacted linker desorption from the MOF pores. Material decomposition started at 350 • C and 450 • C in air and nitrogen, respectively, corresponding to structural water desorption and material decomposition.
The TG traces of the hydrated cobalt trimesate, KCL-102-air, in a flow of dry air (dashed line) or nitrogen (solid line) are reported in Figure 4b. Regarding TG collected under nitrogen atmosphere, it can be seen from this figure that a substantial weight loss between 100-400 • C (~26 wt%) could be attributed to the removal of the coordinated water molecules. This result was similar to that reported by Crane et al. [38]. The plateau extended up to 450 • C, indicating the larger thermal stability of Co 3 (BTC) 2 ·12H 2 O compared to KCL-102. The second stage weight loss (~30 wt%) evidenced in the temperature range 450-525 • C could be associated with framework collapse leading to the formation of Co(OH) 2 (34.5 wt%) followed by a continuous weight loss to Co 3 O 4 (29.8 wt%).
As expected, a similar behavior was observed for the sample heated in air (dashed line in Figure 4b), however, with the onset temperatures shifted to lower values. In this case, a plateau was reached at 420 • C, and that was maintained at least up to 700 • C. The observed weight loss (64 wt%) was close to the one expected for the formation of Co 3 O 4 .
We investigated KCL-102 using infrared (FTIR) and UV-Vis spectroscopy in order to gain some knowledge on details of KCL-102 structure. Figure 5  and 1500-1300 cm −1 corresponded to ν asym (COO) and ν sym (COO). These bands were remarkably similar to the ones observed in the iron trimesate. No signals were observed that could be associated with unreacted carboxylic acid. The signal observed at 1681 cm −1 was likely associated with DMF [58]. The band centered at 758 cm −1 in KCL-102 spectrum was previously assigned to ν(C-H) bending mode in HKUST-1, a copper trimesate [59]. Alves et al. [60] reported the FT-IR spectra of nanoparticles of Co 3 O 4 : they observed the bands at 567 and 665 cm −1 which were related to the Co-O stretching vibrations. For Co 2 O 3 nanoparticles, the vibrational band was observed at 560 cm −1 owing to the Co-O stretching vibration mode, and 668 cm −1 was the bridging vibration of the O-Co-O bond. The higher band at 668 cm −1 was normal for Co 2+ -O vibration in a tetrahedral site, and the lower band 560 cm −1 was accredited to the Co 3+ -O vibration at the octahedral site [61]. In case of Co-BTC, at a lower wavenumber region, two vibrational modes centered at 554 and 455 cm −1 were observed. The vibrational modes corresponding to cobalt oxides falls at 554 cm −1 could be assigned to Co-O stretching vibrational modes. Co-O stretching vibrational mode at 554 cm −1 in KCL-102 was highly perturbed in KCL-102-air, hinting at the changes in coordination around Co 2+ .
Energies 2021, 14, x FOR PEER REVIEW 6 of 11 acid (black line) are also reported in Figure 5. The absorption bands in the ranges 1700-1500 cm -1 and 1500-1300 cm -1 corresponded to νasym(COO) and νsym(COO). These bands were remarkably similar to the ones observed in the iron trimesate. No signals were observed that could be associated with unreacted carboxylic acid. The signal observed at 1681 cm -1 was likely associated with DMF [58]. The band centered at 758 cm -1 in KCL-102 spectrum was previously assigned to ν(C-H) bending mode in HKUST-1, a copper trimesate [59]. Alves et al. [60] reported the FT-IR spectra of nanoparticles of Co3O4: they observed the bands at 567 and 665 cm -1 which were related to the Co-O stretching vibrations. For Co2O3 nanoparticles, the vibrational band was observed at 560 cm -1 owing to the Co-O stretching vibration mode, and 668 cm −1 was the bridging vibration of the O-Co-O bond. The higher band at 668 cm -1 was normal for Co 2+ -O vibration in a tetrahedral site, and the lower band 560 cm −1 was accredited to the Co 3+ -O vibration at the octahedral site [61].
In case of Co-BTC, at a lower wavenumber region, two vibrational modes centered at 554 and 455 cm -1 were observed. The vibrational modes corresponding to cobalt oxides falls at 554 cm -1 could be assigned to Co-O stretching vibrational modes. Co-O stretching vibrational mode at 554 cm −1 in KCL-102 was highly perturbed in KCL-102-air, hinting at the changes in coordination around Co 2+ .  Diffuse reflectance UV-vis (DR-UV-vis) provides information on the oxidation state and on the coordination of the cobalt, that is, the number of the ligands, their symmetry, and their chemical nature. Moreover, oxidation states different than 2+ cannot be excluded a priori for cobalt. As mentioned above, the phase transition caused a change in the color of the powder from violet of KCL-102 (Figure 6c) to pink of KCL-102-air (Figure 6d). A synthetized Co3(BTC)2·12H2O was a pink powder [44]. A violet color was, in general, associated with the copresence in cobalt-based materials of Co centers in both octahedral and tetrahedral coordination [32]. This was, for example, the case of UTSA-16, the spectra of which were characterized by two peaks at 527 and 566 nm due to d-d transitions in Co(II) in octahedral and tetrahedral geometry (see black line in Figure 6b and discussion in Ref. [32]). In Figure 6b (green curve), another Co(II) based MOF, ZIF-67, having all the cobalt centers in tetrahedral coordination is reported as a reference. The spectra of KCL-102 samples before and after the exposure to air confirmed the divalent state of the cobalt centers. KCL-102 spectrum (blue curve in Figure 6a) showed two bands at 520 and 578 nm that were then assigned to d-d transitions of Co(II) centers in octahedral and tetrahedral geometry in analogy to UTSA-16. KCL-102 peaks were less defined than UTSA-16, suggesting a heterogeneous nature of the two families of cobalt centers. The Co3(BTC)2·12H2O structure is known [46]. Cobalt ions in the materials were all in octahedral coordination, although of two different kinds: one coordinated with four H2O molecules and two O belonging to the same COO-group, while the other one coordinated with four H2O molecules and two O belonging to two different COO-groups (Figure 6e). Accordingly, KCL-102-air spectrum (pink spectrum in Figure 6a) was characterized by a complex broad band Diffuse reflectance UV-vis (DR-UV-vis) provides information on the oxidation state and on the coordination of the cobalt, that is, the number of the ligands, their symmetry, and their chemical nature. Moreover, oxidation states different than 2+ cannot be excluded a priori for cobalt. As mentioned above, the phase transition caused a change in the color of the powder from violet of KCL-102 (Figure 6c) to pink of KCL-102-air (Figure 6d). A synthetized Co 3 (BTC) 2 ·12H 2 O was a pink powder [44]. A violet color was, in general, associated with the copresence in cobalt-based materials of Co centers in both octahedral and tetrahedral coordination [32]. This was, for example, the case of UTSA-16, the spectra of which were characterized by two peaks at 527 and 566 nm due to d-d transitions in Co(II) in octahedral and tetrahedral geometry (see black line in Figure 6b and discussion in Ref. [32]). In Figure 6b (green curve), another Co(II) based MOF, ZIF-67, having all the cobalt centers in tetrahedral coordination is reported as a reference. The spectra of KCL-102 samples before and after the exposure to air confirmed the divalent state of the cobalt centers. KCL-102 spectrum (blue curve in Figure 6a) showed two bands at 520 and 578 nm that were then assigned to d-d transitions of Co(II) centers in octahedral and tetrahedral geometry in analogy to UTSA-16. KCL-102 peaks were less defined than UTSA-16, suggesting a heterogeneous nature of the two families of cobalt centers. The Co 3 (BTC) 2 ·12H 2 O structure is known [46]. Cobalt ions in the materials were all in octahedral coordination, although of two different kinds: one coordinated with four H 2 O molecules and two O belonging to the same COO-group, while the other one coordinated with four H 2 O molecules and two O belonging to two different COO-groups (Figure 6e). Accordingly, KCL-102-air spectrum (pink spectrum in Figure 6a) was characterized by a complex broad band centered at 540 nm. The low intensity signal at 578 nm could be associated with residual KCL-102.

Conclusions
We report here a novel cobalt trimesate, KCL-102, and we verified the high reproducibility of its synthesis protocol. KCL-102 is characterized by a large thermal stability in nitrogen and dry air (up to 350 °C), as verified by thermogravimetry. Nevertheless, KCL-102 is unstable in air, and it undergoes a slow phase transformation (for about a week) to its hydrated form, Co3(BTC)2·12H2O. This transformation is very quick in direct contact with water. Furthermore, unlike several other MOFs, KCL-102 does not become amorphous upon hydration, but it is converted to a well-known crystalline phase, Co3(BTC)2·12H2O. Various physico-chemical characterization results indicate the presence of tetrahedrally and octahedrally coordinated Co(II) in the KCL-102 framework, while in Co3(BTC)2·12H2O, only octahedrally coordinated Co(II) are present, suggesting a waterinduced phase transformation that causes the conversion of the tetrahedral Co(II) to octahedral Co(II). At this juncture, it is to be noted here that the main difference between the synthesis protocols of KCL-102 and Co3(BTC)2·12H2O is the shorter reaction time of the former, being 2 h for KCL-102 and 20-24 h for Co3(BTC)2·12H2O. The presence of cobalt centers having an oxidation state different than 2+ was excluded in this study based on the UV-Vis measurements, although these results should be confirmed also by means of other techniques such as X-ray photoelectron spectroscopy (XPS), X-ray absorption near edge spectroscopy (XANES), or superconducting quantum interference device (SQUID).
Future investigations should be aimed at the determination of the KCL-102 structure and surface area and to its testing for the several energy-related applications where cobaltbased MOFs are known to be excellent in regard to water harvesting, heat exchangers, oxygen reduction reaction (ORR), oxygen evolution reaction (OER), and CO and other oxidation reactions [54].

Conclusions
We report here a novel cobalt trimesate, KCL-102, and we verified the high reproducibility of its synthesis protocol. KCL-102 is characterized by a large thermal stability in nitrogen and dry air (up to 350 • C), as verified by thermogravimetry. Nevertheless, KCL-102 is unstable in air, and it undergoes a slow phase transformation (for about a week) to its hydrated form, Co 3 (BTC) 2 ·12H 2 O. This transformation is very quick in direct contact with water. Furthermore, unlike several other MOFs, KCL-102 does not become amorphous upon hydration, but it is converted to a well-known crystalline phase, Co 3 (BTC) 2 ·12H 2 O. Various physico-chemical characterization results indicate the presence of tetrahedrally and octahedrally coordinated Co(II) in the KCL-102 framework, while in Co 3 (BTC) 2 ·12H 2 O, only octahedrally coordinated Co(II) are present, suggesting a water-induced phase transformation that causes the conversion of the tetrahedral Co(II) to octahedral Co(II). At this juncture, it is to be noted here that the main difference between the synthesis protocols of KCL-102 and Co 3 (BTC) 2 ·12H 2 O is the shorter reaction time of the former, being 2 h for KCL-102 and 20-24 h for Co 3 (BTC) 2 ·12H 2 O. The presence of cobalt centers having an oxidation state different than 2+ was excluded in this study based on the UV-Vis measurements, although these results should be confirmed also by means of other techniques such as X-ray photoelectron spectroscopy (XPS), X-ray absorption near edge spectroscopy (XANES), or superconducting quantum interference device (SQUID).
Future investigations should be aimed at the determination of the KCL-102 structure and surface area and to its testing for the several energy-related applications where cobaltbased MOFs are known to be excellent in regard to water harvesting, heat exchangers, oxygen reduction reaction (ORR), oxygen evolution reaction (OER), and CO and other oxidation reactions [54].