Synthesis, Structure, and Luminescence of a Molecular Europium Tetracyanoplatinate Incorporating 4,5-Diazafluoren-9-One
Round 1
Reviewer 1 Report
The manuscript details the synthesis, structure, and luminescence of a europium/plantinum complex as a co-crystal with a fluorenone derivative.
The work is well presented and has been conducted to a good standard, I can see no issues with scientific aspects of the results. The results are an incremental step from previous works, but suitable for publication in Crystals. My only significant comment is that the article lacks any conclusions at the end, which would help to give the paper some final context. Also, I assume that figure 1 is the asymmetric unit, but it would help if this is explicitly mentioned.
Author Response
Responses to Reviewer 1.
Reviewer 1 Recommendation: “The manuscript details the synthesis, structure, and luminescence of a europium/plantinum complex as a co-crystal with a fluorenone derivative.
The work is well presented and has been conducted to a good standard, I can see no issues with scientific aspects of the results. The results are an incremental step from previous works, but suitable for publication in Crystals.”
Author Response: I thank this reviewer for the time to review our manuscript and for the recommendation regarding the fit of this manuscript in this special issue of Crystals.
Reviewer Comment: “My only significant comment is that the article lacks any conclusions at the end, which would help to give the paper some final context.”
Author Response: The Instructions for Authors for this journal says the following regarding a Conclusion section. “This section is not mandatory but can be added to the manuscript if the discussion is unusually long or complex.” I did not feel that the manuscript was unusually long nor overly complex so I had omitted a Conclusion section from the original submission. However, I have added a short Conclusion section to the manuscript at the request of this reviewer.
Reviewer Comment: “Also, I assume that figure 1 is the asymmetric unit, but it would help if this is explicitly mentioned.”
Author Response: I reworded the Figure 1 caption to add that this figure does represent the asymmetric unit of the structure.
Reviewer 2 Report
Lanthanide complexes containing chromophoric ligands are being actively studied due to their promising luminescent properties. Linking these fragments by various building blocks, including metalloligands, is considered as the favorable way for fine-tuning target performances. For example, the scientific group of Jagiellonian University has recently successfully applied tetracyanidometallates of PtII and PdII as metalloligands for the design of lanthanide luminescent thermometers.
The manuscript under review is in line with these topical studies, as is aimed at expanding a number of compounds that combine lanthanides, square planar cyanometallates, and aromatic nitrogen-containing heterocyclic systems. The current work continues the research of the group of authors, reflected in References [31-34], where 2,2'-bipyridine, 1,10-phenanthroline, or 2,2':6',2”-terpyridine was introduced as chromophore ligands. The synthesis, structure and luminescent properties (room temperature) of the new complex [Eu2(Pt(CN)4)3(H2O)12]·4dafone·6H2O are presented here (dafone = 4,5-diazafluoren-9-one, C11H6N2O).
At the moment, the amount of the presented material does not allow considering this manuscript as an Article, and the scientific novelty and significance do not seem to be as outstanding as the Communication in Crystals requires. Thus, it is required to add material to the manuscript, for example, expanding the Discussion in detail, or adding another related complex for comparison. In addition, a number of negative points must be overcome. These points and possible topics for Discussion part are presented below.
1) The most significant drawback of the work is the lack of information confirming the chemical and phase purity of the obtained sample. Without this, it is impossible to accept the luminescence data. Since IR spectroscopy data are insufficient, the author is strongly advised to add data of analytical methods (elemental analysis, NMR, etc.) and powder XRD.
2) The quality of the structural data cannot currently be verified, since cif-file not provided. It is also desirable to submit a checkcif file.
3) The stoichiometry of the reaction mixture (the molar ratio of the reactants, lines 67-69) differs significantly from the stoichiometry of the resulting complex. Which reagent was used to calculate the yield? How was the product separated from the excess of reagents? Why was this stoichiometry of the reaction mixture applied for the synthesis? Will the yield increase if it is adjusted to match the stoichiometry of the complex? What product will be obtained if the europium/cyanometallate ratio is changed from 1:1 to 1:2, 2:1, etc.? These studies are important from the point of view of coordination and preparative chemistry, since will show the lability of the system or its absence.
4) There is not enough discussion why dafone is not coordinated to the europium metal center, for example, as a bidentate ligand, but only contacts through hydrogen bonds. In fact, in the author's previous works, all related nitrogen-donor chromophores coordinated directly to the lanthanides. Could this fact be related to the use of THF as a solvent in the current work, instead of DMF or DMSO used earlier? Perhaps the same synthesis should be carried out in DMF?
Moreover, Ref. [30] and similar can give an idea of how characteristic dafone coordination is to the lanthanides and europium in particular. These points are also interesting from the point of view of coordination chemistry.
5) The geometric characteristics of hydrogen bonds should also be added.
6) It is important not only to provide primary data on emission in a solid, but also to compare these results with the most structurally similar complexes. One such example would be the object from Ref. 35, named "reminiscent" from the structure of the dimer core (lines 114-115). If possible, discuss what changes when the chromophoric part is not coordinated to the metal center, but is connected to it indirectly. This will make it possible to supplement the basis for directed control of the luminescence of such systems.
If this is a completely new structural type of europium complexes, then the differences in luminescence should be clearly indicated in comparison with typical europium complexes with coordinated chromophoric ligands.
Author Response
Responses to Reviewer 2
Reviewer Recommendation: “At the moment, the amount of the presented material does not allow considering this manuscript as an Article, and the scientific novelty and significance do not seem to be as outstanding as the Communication in Crystals requires. Thus, it is required to add material to the manuscript, for example, expanding the Discussion in detail, or adding another related complex for comparison.”
Author Response: I disagree with this recommendation. I feel that the content of this manuscript is suitable for publication in this Special Issue of Crystals, focusing on material characterization with the use of single crystal XRD.
Reviewer Comment: “1) The most significant drawback of the work is the lack of information confirming the chemical and phase purity of the obtained sample. Without this, it is impossible to accept the luminescence data. Since IR spectroscopy data are insufficient, the author is strongly advised to add data of analytical methods (elemental analysis, NMR, etc.) and powder XRD.”
Author Response: I fully understand and appreciate this comment by the author regarding the phase purity of the samples used for the photoluminescence studies, since purity is a major concern in PL experiments. For this reason, all samples used for the PL experiments were hand-selected, diffraction quality single crystals that were individually screened by single-crystal X-ray diffraction to confirm phase purity. Section 2.3 of the manuscript originally stated “All of the spectroscopic experiments are conducted on neat crystalline samples, screened for phase purity, and held in sealed quartz capillary tubes.” However, this sentence has been modified to add some additional details regarding the steps taken to ensure the quality of the samples.
Reviewer Comment: “2) The quality of the structural data cannot currently be verified, since cif-file not provided. It is also desirable to submit a checkcif file.”
Author Response: The cif file was deposited with the Cambridge Database prior to manuscript submission and the deposition number included in the manuscript. In the revised submission I have included a copy of the cif file and checkcif report to be included as supplementary materials.
Reviewer Comment: “3) The stoichiometry of the reaction mixture (the molar ratio of the reactants, lines 67-69) differs significantly from the stoichiometry of the resulting complex. Which reagent was used to calculate the yield? How was the product separated from the excess of reagents? Why was this stoichiometry of the reaction mixture applied for the synthesis? Will the yield increase if it is adjusted to match the stoichiometry of the complex? What product will be obtained if the europium/cyanometallate ratio is changed from 1:1 to 1:2, 2:1, etc.? These studies are important from the point of view of coordination and preparative chemistry, since will show the lability of the system or its absence.”
Author Response: The limiting reagent for the reaction, dafone, was used to calculate the yield. The product was separated by decantation from the mother liquor containing the excess reagents. The stoichiometry used for the synthesis results in a very good yield of 87% as reported in the synthesis section. Based on our experience, this is a very good yield so we did not feel the need to commit large amount of time nor resources in attempts to improve the yield. That said, we have not attempted reactions using all of the stoichiometries mentioned by the reviewer so we cannot answer these questions.
Reviewer Comment: “4) There is not enough discussion why dafone is not coordinated to the europium metal center, for example, as a bidentate ligand, but only contacts through hydrogen bonds. In fact, in the author's previous works, all related nitrogen-donor chromophores coordinated directly to the lanthanides. Could this fact be related to the use of THF as a solvent in the current work, instead of DMF or DMSO used earlier? Perhaps the same synthesis should be carried out in DMF?”
Author Response: We chose to prepare dafone in THF for this reaction because of its enhanced solubility. The reactions that the author proposes are interesting, but we have not attempted those and therefore cannot comment on them. They would be interesting future areas of study.
Reviewer Comment: “5) The geometric characteristics of hydrogen bonds should also be added.”
Author Response: We have added a new table, Table 2, containing the hydrogen bond information as this reviewer requested. Because of this addition, Table 2 and Table 3 from the original manuscript have been renamed as Table 3 and Table 4 in the revised manuscript.
Reviewer Comment: “6) It is important not only to provide primary data on emission in a solid, but also to compare these results with the most structurally similar complexes. One such example would be the object from Ref. 35, named "reminiscent" from the structure of the dimer core (lines 114-115). If possible, discuss what changes when the chromophoric part is not coordinated to the metal center, but is connected to it indirectly. This will make it possible to supplement the basis for directed control of the luminescence of such systems. If this is a completely new structural type of europium complexes, then the differences in luminescence should be clearly indicated in comparison with typical europium complexes with coordinated chromophoric ligands.”
Author Response: I would like to make note that this manuscript was submitted to a special issue of Crystals. From the journal website: “In this Special Issue on the topic of “Characterization and Study of Compounds by Single Crystal X-ray Diffraction”, we want to highlight the importance of this technique in scientific research, alone or in combination with other analytical methods. All contributions involving SCXRD are welcome,…” The focus of this manuscript is on the structural studies conducted by the use of single crystal X-ray diffraction and not on the photoluminescence. For that reason, I feel that an in-depth review of and comparison between the photoluminescence of related compounds is beyond the scope of this article.
Round 2
Reviewer 2 Report
The author's responses allowed to positively resolve only the issues related to the quality and presentation of a crystal-structure data. Unfortunately, the rest of my previous comments were ignored. The author appealed to the fact that the manuscript was submitted to a Special Issue focusing on single-crystal XRD studies. However, the requirements of the SI did not indicate that single-crystal XRD analysis should be the only research method used here. Thus, in my opinion, belonging to the SI should not reduce the quality of the rest of the data provided in the article.
Therefore, I continue to insist on the following adjustments to the submitted material, which will not require extra effort from the author.
1) The purity of the substance must be resolved in order to provide luminescence data. Moreover, without confirming the purity of the substance, one cannot even simply talk about "successful synthesis" and "yield of the product." Thus, without adding additional data from analytical methods (elemental analysis, NMR, etc.), the author should remove the word "synthesis" from the text of the manuscript and the title. Then there will be no chemical aspect of the work. In summary, the proof of purity is a prerequisite for proving a successful synthesis for a respected scientific journal.
2) Moreover, powder XRD data is also required to prove the identity of the investigated single-crystal and the obtained sample, whose yield was 71%.
3) Despite the author's response that he tried to clarify the issue of selecting crystals for luminescence research, no relevant changes were found in the new version of the manuscript. In addition, there is the question of the expediency of manual selection (Pasteur's method) of crystals, if we consider the possible further use of the studied complex.
4) Since the author positions both “structure” and “synthesis” in the title of the article, it is necessary to link these stages. This means that it is necessary to add a brief discussion of what synthesis conditions led to the fact that dafone is not coordinated to the metal center. Before that, it is necessary to briefly indicate to what extent the coordination of dafone is typical for europium (or analogues) in general (previous comment 4).
5) Since the author also positions "luminescence" in the title of the article, it is necessary to analyze these provided data. The entire responsibility for this step should not be shifted to the reader. Of course, no one demands from the author a complete review of the luminescence of all europium complexes. However, a simple comparison with the closest analogues should be added (previous comment 6).
Author Response
Response to Reviewer #2
Reviewer Comment: “The author's responses allowed to positively resolve only the issues related to the quality and presentation of a crystal-structure data. Unfortunately, the rest of my previous comments were ignored.”
Author Response: This statement is completely false. I did not ignore any of the comments of the reviewer. I considered and responded to all of the reviewer’s comments (labeled 1-6 in the original review). However, with only five days provided to submit a revised article, it is completely impossible for me to perform the large number of additional experiments that the reviewer asked me to complete (PXRD, NMR, elemental analysis, multiple additional synthesis experiments, etc.). Therefore the only choice I had was to make changes where I could, in that timeframe.
Reviewer Comment: “The author appealed to the fact that the manuscript was submitted to a Special Issue focusing on single-crystal XRD studies. However, the requirements of the SI did not indicate that single-crystal XRD analysis should be the only research method used here. Thus, in my opinion, belonging to the SI should not reduce the quality of the rest of the data provided in the article.”
Author Response: The author has misinterpreted my response regarding this topic. I made the point that the call for papers mentioned that SCXRD alone was the sole requirement and that papers COULD be based just on this topic. I never said that papers SHOULD only contain SCXRD. Obviously, by including synthesis, luminescence, and IR in my submitted article I was following the ideal that SCXRD used in combination with other techniques is preferred. Since the SCXRD is the linking feature for the SI, it was given highest priority in the article and the other techniques were included in an ancillary role. I agree completely that the quality of data should not be reduced, but the quantity of data can certainly be reduced.
Reviewer Comment: “Therefore, I continue to insist on the following adjustments to the submitted material, which will not require extra effort from the author.”
Author Response: I am extremely puzzled by this statement from the reviewer. He states that in order to make all of the adjustments that he requests “…will not require extra effort from the author.” However, he goes on to insist on elemental analysis, PXRD, numerous syntheses, and a rewrite of the luminescence section to add more comparisons/detail. There is definitely a large effort (and cost) associated with these additional experiments. Therefore, I am not sure how to properly respond to this comment.
Reviewer Comment: Five specific comments on the same topics as in the first review.
Author Response: I carefully considered all of these specific comments and replied in kind in my previous review. I would point out that the reviewer states a much lower yield (71% stated) in his comment. In section 2.1 of the manuscript I clearly mention the yield as 87%. The last sentence in Section 2.3 contains the relevant changes made to the manuscript between the original and revised versions, regarding the purity of the luminescence samples.
Author Response File: 
Author Response.docx
