Two Cd(II)-Based MOFs Constructed from Tris(3′-F-4′-carboxybiphenyl)amine: Synthesis, Crystal Structure, Luminescence Sensing towards Nitrophenols and Acetylacetone
, Yixuan Shi 1, Qiang Guo 1, Boxuan Hu 1, Leilei Li 2, Yanlan Wang 1,* and Chunlin Ma 1,*Round 1
Reviewer 1 Report
The author finds stable MOF-2 which is an excellent finding in the field although the following corrections are suggested for the improvement of the article
The title of the paper should be rewritten to reflect the content and novelty of the work.
The abstract is too much confused should be written in the concise form
Remove abbreviation from the keywords
Scheme 1 should be included in the method & material section
(Tri-carboxylic acid H3TFBA was prepared according to reported procedure via Suzuki coupling reaction). Please include detail and also provide NMR
The author claimed the stability up to 270°C but in Figure S2 I observed an 80% loss.
Figure 5 b is unclear.
Why intensity with Hacac led to an enhancing response?
Author Response
Reviewer 1:
The author finds stable MOF-2 which is an excellent finding in the field although the following corrections are suggested for the improvement of the article
- The title of the paper should be rewritten to reflect the content and novelty of the work.
Response: Thank reviewer for the meaningful advices. We have revised and adopted “Two Cd(II)-based MOFs constructed from tris(3′-F-4′-carboxybiphenyl)amine: synthesis, crystal structure, luminescence sensing towards nitrophenols and acetylacetone” as the title.
- The abstract is too much confused should be written in the concise form
Response: Thank reviewer for this meaningful comment. We have revised carefully and improved the abstract.
- Remove abbreviation from the keywords
Response: Thanks, we have removed the abbreviation from the keywords.
- Scheme 1 should be included in the method & material section
Response: Thanks for reviewer’s suggestion. We have arranged the Scheme 1 into the Section 2. Methods and Methods. And added the description “The synthesis methods of CdMOF-1 and CdMOF-2 were summarized in Scheme 1”.
- (Tri-carboxylic acid H3TFBA was prepared according to reported procedure via Suzuki coupling reaction). Please include detail and also provide NMR.
Response: Thanks for reviewer’s useful advice. We have provided the NMR and the detailed synthesis procedure of H3TFBA in Section 3. Experiments of the Supporting information.
- The author claimed the stability up to 270°C but in Figure S2 I observed an 80% loss.
Response: Sorry for our careless, we have revised this description and added more detailed analysis in the 3.2 Stability of CdMOF-1 and CdMOF-2.
- Figure 5 b is unclear.
Response: Thanks. We have revised and improved the Figure 5b.
- Why intensity with Hacac led to an enhancing response?
Response: Thank you for this meaningful comment. With the titration of acac induced an obvious enhancing effect of CdMOF-2. The possible reason could be as follows: In the structure of CdMOF-2, TFBA3- ligands with F atoms are aligned along the inner walls of the channels, and acac molecules were easily formed Hydrogen-bond with F atoms. According to references, when the excited electrons are transferred from a high-lying π*type lowest unoccupied molecular orbital (LUMO) to the conduction band (CB) of CdMOF-2, the turn-on sensing will occur.
Reviewer 2 Report
Ru and co-workers report the synthesis and luminescence properties of two new Cd(II) metal-organic frameworks. In my opinion, the work needs to be revised considerably in order to be suitable for publication in Crystals, for the following reasons:
1) According to the simulated PXRD pattern of MOF-2, the highest intensity peak should be found at an approximate 2theta angle of 4.8 degrees. However, all the provided experimental patterns of MOF-2 appear to start after approx. 7 degrees! It is important to present all related patterns (main text and SI) in a different 2theta range, otherwise the conclusions that the authors make on solvent stability and luminescence cycles are very unconvincing. My 2theta range suggestion would be 4-40 degrees, since no peaks are expected beyond these angles. This way it would also be easier to observe all details in the 10-25 2theta range, which are currently difficult to see.
2) The given 2theta range of the MOF-1 patterns is also not ideal, since it is not easy to observe all details. I would suggest to re-draw the patterns within the range of 4-35 degrees.
3) The word “calculated” for the PXRD patterns should be replaced with “experimental”, since the theoretical pattern is given as “simulated”.
4) I disagree with the authors’ conclusion that MOF-2 retains high chemical stability in all solvents; according to Figure S3, the sample clearly shows lower crystallinity in p-xylene, and also shows slightly different or additional peaks in ethanol and diethylether. The authors should revise this section or explain these results (of course, after revising the patterns in the 2theta range suggested above). The simulated pattern should also be included in this figure, to facilitate comparison.
5) The TGA results section only mentions temperature values in which the authors observe weight losses. More detailed analysis needs to be performed, indicating the corresponding chemical species in each case.
6) I would suggest to change the acronyms for both compounds. MOF-1 and MOF-2 are very generic and especially the acronym MOF-2 is probably more associated with the 1998 structure reported by Li and Yaghi.
7) The authors state that they only selected MOF-2 to perform their luminescent experiments, based on the “stability studies and solid-state photoluminescent spectra”. Since MOF-1 is also stable in solution and the emission peaks of both MOFs are at a similar wavelength, it is still unclear to me why the authors did not study the luminescent properties of MOF-1. Could the authors elaborate further on this?
8) According to references 31 and 32, the authors have generated luminescent MOFs using the same metal/ligand system but with different co-ligand. I think it would be beneficial for the current study to compare the luminescence results with the ones reported in references 31 and 32, and perhaps discuss the co-ligand effect in the resulting properties.
9) Figure 5a shows a large quenching effect for TNP, PNP and ONP. Therefore, I disagree with the authors' comment that only TNP generates luminescence quenching and "other NACs cause unapparent quenching effects". Could MOF-2 really be considered as a delicate sensor of TNP, judging from the large quenching effect that it also has for PNP and ONP? I believe this part should be revised significantly, or at least be presented in a more clear way.
10) Figure S9 or its text should be revised, to explain what the green and orange bars represent.
11) The presentation of Figure S12 should be improved. The “1-7” notations do not explain the corresponding concentrations of acac.
12) The presentation of Figure S13 should be improved. Currently, the graphs are very messy prior to in the wavelength area prior to 300 nm.
13) Other presentation issues: While the text is understandable, there are several English language mistakes which detract from the general flow. Additionally, the caption for Figure 2 contains a section (" (d) 3d topology of MOF-2") which is not presented anywhere in the paper. The main text also refers to Figure S9 for certain PXRD tests, however these are in fact presented in Figure S10.
Author Response
Reviewer 2: Ru and co-workers report the synthesis and luminescence properties of two new Cd(II) metal-organic frameworks. In my opinion, the work needs to be revised considerably in order to be suitable for publication in Crystals, for the following reasons:
- According to the simulated PXRD pattern of MOF-2, the highest intensity peak should be found at an approximate 2theta angle of 4.8 degrees. However, all the provided experimental patterns of MOF-2 appear to start after approx. 7 degrees! It is important to present all related patterns (main text and SI) in a different 2theta range, otherwise the conclusions that the authors make on solvent stability and luminescence cycles are very unconvincing. My 2theta range suggestion would be 4-40 degrees, since no peaks are expected beyond these angles. This way it would also be easier to observe all details in the 10-25 2theta range, which are currently difficult to see.
Response: We appreciate the reviewer for this meaningful comment. We have retested the PXRD of CdMOF-2 and CdMOF-2 @ analytes and adjusted the display range from 4 to 40 degrees both in main text and SI.
2) The given 2theta range of the MOF-1 patterns is also not ideal, since it is not easy to observe all details. I would suggest to re-draw the patterns within the range of 4-35 degrees.
Response: Thanks for reviewer’s comments. We have re-draw the patterns of CdMOF-1 within the range of 4-35 degrees.
3) The word “calculated” for the PXRD patterns should be replaced with “experimental”, since the theoretical pattern is given as “simulated”.
Response: Thanks for reviewer’s suggestion. We have replaced the expression of PXRD patterns “experimental” instead of “calculated”.
4) I disagree with the authors’ conclusion that MOF-2 retains high chemical stability in all solvents; according to Figure S3, the sample clearly shows lower crystallinity in p-xylene, and also shows slightly different or additional peaks in ethanol and diethylether. The authors should revise this section or explain these results (of course, after revising the patterns in the 2theta range suggested above). The simulated pattern should also be included in this figure, to facilitate comparison.
Response: We are grateful for this careful comment. We have retested the PXRD of CdMOF-2 after immersed in different solvents and displayed the patterns range from 4 to 40 degree. For comparison, we have added the simulated pattern to all corresponding PXRD graphs.
5) The TGA results section only mentions temperature values in which the authors observe weight losses. More detailed analysis needs to be performed, indicating the corresponding chemical species in each case.
Response: Thank reviewer for this valuable suggestion. We have added the more detailed analysis of TGA results in main text 3.2 Stability of CdMOF-1 and CdMOF-2. The content is as follows: For CdMOF-1, an initial weight loss of 8.61% occurring before 120 °C region was attributed to the loss of the twelve water molecules (with a calculated value of 8.95%). Coordinated four H2O and six DMF molecules lose between 120°C and 260°C (experimental, 12.58%; calculated, 15.85%), and finally the framework collapsed at 260°C. decreased smoothly and attained a minimum value at 800 °C. The TGA curves of CdMOF-2 showed the weight loss of 11.71% (calculated, 12.07%) from room temperature to 212°C, suggesting the guest three H2O and one DMF molecules were removed. The framework of CdMOF-2 begins to collapse at 265°C. The result indicated CdMOF-2 had good thermal stability. The chemical species of Cd-MOFs were calculated from the SQUEEZE results and combined with charge balance and TGA data.
6) I would suggest to change the acronyms for both compounds. MOF-1 and MOF-2 are very generic and especially the acronym MOF-2 is probably more associated with the 1998 structure reported by Li and Yaghi.
Response: Thank you for reviewer’s comment. We have changed acronyms for both compounds: CdMOF-1 and CdMOF-2.
7) The authors state that they only selected MOF-2 to perform their luminescent experiments, based on the “stability studies and solid-state photoluminescent spectra”. Since MOF-1 is also stable in solution and the emission peaks of both MOFs are at a similar wavelength, it is still unclear to me why the authors did not study the luminescent properties of MOF-1. Could the authors elaborate further on this?
Response: We appreciate the reviewer for the comment. In order to explore the luminescent properties of CdMOF-1 and CdMOF-2, we have finished the corresponding detection experiments. And the result of CdMOF-1 is not satisfactory especially in recycle stabilities and thermal stability tests. The reason of unstable framework could be possible owning to the large porosity and more coordinated H2O. For comparison, we have improved the description about luminescent sensing experiment in main text and added the corresponding experiments graphs of CdMOF-1 into supplementary information (Figure s7 and s8).
8) According to references 31 and 32, the authors have generated luminescent MOFs using the same metal/ligand system but with different co-ligand. I think it would be beneficial for the current study to compare the luminescence results with the ones reported in references 31 and 32, and perhaps discuss the co-ligand effect in the resulting properties.
Response: Thank you for this meaningful suggestion. This suggestion will guide us to systematically study the structure-properties relationship of Luminescence MOFs. In recent work, we use same multi-carboxylic acids-H3TFBA, Cd(II) ions and different co-ligands such as bipy this work, bpe reference 32 and bibp reference 31, they show various structures, show similar luminescence properties in solid-state, but different in chemical and thermal stabilities. So, different sensing analytes experiments were carried out. According to the results, we can speculate that the fluorescence sensing performance is mainly due to the main ligand of H3TFBA. In our future work, we will explore the relationship between co-ligand and luminescence properties systematically.
(4,4’-bipy = 4,4'-bipyridine; bpe = trans-1,2-bis(4-pyridyl)ethene; bibp = 4,4'-Di(1H-imidazol-1-yl)-1,1'-biphenyl).
9) Figure 5a shows a large quenching effect for TNP, PNP and ONP. Therefore, I disagree with the authors' comment that only TNP generates luminescence quenching and "other NACs cause unapparent quenching effects". Could MOF-2 really be considered as a delicate sensor of TNP, judging from the large quenching effect that it also has for PNP and ONP? I believe this part should be revised significantly, or at least be presented in a more clear way.
Response: We appreciate the reviewer for this constructive comment. Figure 5a shows larger quenching effect for nitrophenols (such as TNP, ONP and PNP) than other NACs. In this work, we selected the most obvious analytes (TNP and PNP) to carry out the corresponding fluorescence detection experiments. And the corresponding description have been improved and added in the 3.4 Sensing of nitrobenzene explosives.
10) Figure S9 or its text should be revised, to explain what the green and orange bars represent.
Response: Thank you for this meaningful suggestion, we have revised the Figure S9 and the explained what the colors represent.
11) The presentation of Figure S12 should be improved. The “1-7” notations do not explain the corresponding concentrations of acac.
Response: Thank reviewer for this comment. We have improved the Figure S12 and explained the corresponding concentrations of acac.
12) The presentation of Figure S13 should be improved. Currently, the graphs are very messy prior to in the wavelength area prior to 300 nm.
Response: We appreciate the reviewer for the comment. We have improved the Figure S13.
13) Other presentation issues: While the text is understandable, there are several English language mistakes which detract from the general flow. Additionally, the caption for Figure 2 contains a section (" (d) 3d topology of MOF-2") which is not presented anywhere in the paper. The main text also refers to Figure S9 for certain PXRD tests, however these are in fact presented in Figure S10.
Response: Thank you for your help to improve the quality of our manuscript. We have revised the caption of Figure 2 and revised the main text Figure S10 instead of Figure S9.
Round 2
Reviewer 1 Report
The manuscript is now looking appropriate
Reviewer 2 Report
I would like to thank the authors for making a great effort to address observations and concerns. I feel the revised manuscript is much improved and suitable for publication in Crystals.
