The Role of Acidity in the Synthesis of Novel Uranyl Selenate and Selenite Compounds and Their Structures
Fabrice Dal Bo
Round 1
Reviewer 1 Report
Submitted manuscript is reporting about crystal structures of four new compounds with hexavalent uranium and selenium. It is suitable for Crystals but only after major revision. The manuscript of the article gives the impression of being written in a hurry.
- Subscripts and superscripts are omitted everywhere. Italics is omitted in space group symbols. “Under acidic conditions” is repeated in about every second sentence. Regroup the sentences and summarize. Add also R1 values obtained for each structure.
- The main idea of the manuscript coming from the title suggests the discussion of the acidic environments for the formation of uranyl compounds with selenium. It is an interesting topis not covered yet in scientific literature. Authors should take into account and consider in the manuscript three recently published papers pertinent to the main theme of the manuscript (“…the ability for acid to drive novel 89 structure and topology formation….”):
- https://www.degruyter.com/document/doi/10.1515/zkri-2020-0078/html
- https://www.degruyter.com/document/doi/10.1515/ract-2018-3050/html
- https://www.mdpi.com/2305-7084/5/1/5
Compare selenium based systems with chromate and sulfate systems.
The big part of the introduction is devoted to the non centrosymmetric uranyl compounds. It is good to cite many papers devoted to ferroelectric and non centrosymmetric materials done by chinese groups recently. However, authors do not provide any other properties except of crystal structures in their manuscript! Therefore, such references are just a tribute to fashion. This part should be shorten. Also a lot is devoted to iodates. Note, two of four new compounds contain Se6+ and not Se4+. Crystal chemistry of selenium and iodine bear considerable differences. This part must be also shorten to become concise.
- Once again, synthesis part should be reorganized. Too many repetitions in the text of this part. Although the semantic part is not great.
- Single-crystal X-ray diffraction. Flack parameters and Sheldrick criteria in the table are obligatory for all non-centrosymmetric structures. Which groups were also considered during the structure solution? Were hydrogen atoms located in the last two structures? Add to the text.
- Add complete bond-valence tables for each compound to the text of the manuscript.
- Rb4[(UO2)4(SeO4)6] = Rb2[(UO2)2(SeO4)3] Unit-cell parameters for your structure are doubled comparing to the previously reported uranyl chromate with identical structural topology - https://onlinelibrary.wiley.com/doi/abs/10.1002/zaac.201300219
Add the discussion about the unit-cell metrics. One of the oxygen atoms in a selenate group is disordered in your case!
- Evaporation method is the most common for the synthesis of uranyl compounds with oxyanions. Most of the selenates and selenites were obtained by this method. Acidity obviously changes during the evaporation of aqueous solution. What is the novelty of your method? How did you control the pH during synthesis? “…particularly those that that may possess salient SHG properties. ….” - remove.
- Author contributions are not given
- Reference list should be formatted according to the journal rules.
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Reviewer 2 Report
I believe that after the elimination of six comments that are indicated in the review, the manuscript can be accepted for publication.
Comments for author File: Comments.pdf
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Reviewer 3 Report
I have read with interest the present manuscript. The content is interesting for the researchers working on the crystal-chemistry of uranyl compounds. I think the manuscript would benefit of a bit more detailed discussion. I have listed here below a few comments that I hope will be helpful to the authors to improve their manuscript.
Experimental part: please provide more details about the synthetic products such as the color and size of the crystals and the yields of the synthesis.
The structural comparison provided for the compound Rb4[(UO2)4(SeO4)6] is not correct. Firstly, please check the formula at lines 172 and 177. I assume you are referring to [C2H5N]3[H5O2][(UO2)2(SeO4)3(H2O)2]2(H2O)5 (Compound IV in Gurzhiy et al. 2015). In the compound [C2H5N]3[H5O2][(UO2)2(SeO4)3(H2O)2]2(H2O)5 the UO7 bipyramids are sharing four equatorial ligands to SeO4 tetrahedra, while in Rb4[(UO2)4(SeO4)6] the five equatorial ligands are shared with SeO4 tetrahedra. All the compounds reported by Gurzhiy et al. (2015) are topologically dissimilar to Rb4[(UO2)4(SeO4)6]. Also, note that in Rb4[(UO2)4(SeO4)6] the Se(1)O4 tetrahedra is connected to four UO7 polyhedra, while the Se(2)O4 tetrahedra is connected to three UO7 polyhedra. That is an interesting structural feature to discuss, as it may be promoted by the corrugation of the sheets. When it comes to the description of sheet topology I would recommend to use the nodal representation as explained by Krivovichev (2004, Crystallography Reviews, 10, 182-232). Please have a look to the review of Lussier et al. (The Canadian Mineralogist, 2016, 54, 177–283), and especially to the compounds with the {5.3.5.3}{5.3.5.4} topology (Table 5, page 200). For instance, Rb4[(UO2)4(SeO4)6] may be isostructural with Cs2[(UO2)2(CrO4)3] described by Siidra et al. (Z. Anorg. Allg. Chem., 2013, 639, 2302–2306).
The structure of the compound Rb2[UO2(SeO4)2(H2O)3] is based on a uranyl-selenate chain topologically similar to the uranyl-sulfate chains occurring in the minerals bobcookite (Mineralogical Magazine, 2015, 79, 695–714) and svornostite (Journal of Geosciences, 2015, 60, 113–121). I think a stronger emphasis on the comparison with mineral structures should be developed when similar structural features are observed.
Line 314: It would have been interesting to follow the work of Gurzhiy et al. and to calculate the complexity parameters of your compounds.
At the line 317 you are comparing the structure of Rb4[(UO2)4(SeO4)6] to that of marthozite, although these two structures are completely different. As you have mentioned previously in the text, Rb2[(UO2)3(SeO3)2O2] is structurally related to marthozite, but this compound is triclinic and thus the discussion around the symmetry-complexity relationship is not in agreement.
Line 347, as I have already mentioned previously Rb4[(UO2)4(SeO4)6] is not topologically identical to [C2H5N]3[H5O2][(UO2)2(SeO4)3(H2O)2]2(H2O)5.
Additional minor comments:
Abstract: Carefully check the formula and space group notations.
Line 38: To my knowledge W5+-bearing compounds are extremely rare at the opposite of W6+-bearing ones.
Line 114: The reacting agents used to synthetize Rb2[UO2(SeO4)2(H2O)3] are really like those used for Rb4[(UO2)4(SeO4)6]. Is that correct?
Line 205: What could the reason for the reduction of Se6+ from the starting reagents to Se4+? The synthesis process is following roughly the same route than for Rb4[(UO2)4(Se6+O4)6] and Rb2[UO2(Se6+O4)2(H2O)3].
Line 207: It should be written Rb2[(UO2)3(SeO3)2O2] instead of Rb4[(UO2)4(SeO4)6].
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Round 2
Reviewer 1 Report
Authors took into account most of the recommendations. Several things to be corrected before it can be accepted:
1. - The salient effect solution acidity has upon controlling structure formation in uranyl systems has also been recently observed in uranyl chromates and chromate-nitrates [19,20]. - Reference number 19 in this case should be
Nazarchuk E.V., Ikhalaynen Yu.A., Charkin D.O., Siidra O.I., Petrov V.G., Kalmykov S.N., Borisov A.S. Effect of solution acidity on the structure of amino acid-bearing uranyl compounds. Acta. 2019. Vol. 107. N 4. P. 311–325.
This reference does not exist and should be inserted,
Reference 20 is correct.
2. - Indeed, the same sheet corrugation is observed in Cs2[(UO2)2(CrO4)3] and [pyH]2[(UO2)2(SO4)3] which respectively form tetragonal (SG P4̅21m) and orthorhombic (SG C2221) structures [19,21].
The reference citing Cs2[(UO2)2(CrO4)3] should be
- Siidra, O.I.; Nazarchuk, E.V.; Kayukov, R.A.; Bubnova, R.S.; Krivovichev, S.V. CrVI→ CrV Transition in Uranyl Chromium Compounds: Synthesis and High‐temperature X‐ray Diffraction Study of Cs2 [(UO2) 2 (CrO4) 3]. Z. Anorg. Allg. Chem. 2013, 639, 2302-2306.
It is already present in the reference list. Just renumber after the insertion of Nazarchuk E.V. et al. 2019.
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Reviewer 2 Report
All the above remarks 1-6 were corrected by the authors. I believe that the revised manuscript can be accepted for publication. True, in the new version of the manuscript (v2) an error remains (the repetition of the word "structures" (line 368, v1), which I mentioned in remark 6 as "etc". Unfortunately, the authors did not notice it.
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Reviewer 3 Report
Dear authors,
All the comments have been addressed accordingly and I think that the manuscript is now suitable for publication.
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