Crystal Structure of New Zinc-Hydroxy-Sulfate-Hydrate Zn₄(OH)₆SO₄·2–2.25H₂O

Dear Reviewer, thank you very much for taking the time to review this manuscript. With your efforts, the quality of our manuscript is improved.

Comments 1: The submitted manuscript presents very interesting scientific problematics related to formation and crystal structures of zinc hydroxy sulfate hydrates and could bring interesting new data and informations for crystallography. Unfortunately, the chosen approach and research methods are inappropriate. For unambiguous phase identification, we need to obtain really high-quality PXRD data (not use conditions 0.02 degree two theta with 1.5 second per step, but at least 0.01 degree and time 8-10 seconds), reliable determination of the chemical composition of the investigated phase (not EDS but WDS data), including water content (quantitatively, for example, using thermogravimmetric analyse or CHN analyzer) and especially good data from X-ray single crystal study. Results with R = 19.18% would be acceptable for a rare mineral species where only a minimal amount of imperfectly crystallized material is available but not for synthetically prepared phase. Only after obtaining such data can follow a discussion and comparison with otherwise hydrated analogues. All considerations of the structural model in the manuscript (lines 88-205) are completely unnecessary.

Response 1: Thank you for remarks. According to your advice, we recorded new powder XRD patterns and composed new Figure. We added DTA-TG-MS data.

Regarding the single crystal diffraction data, of course you are correct. We have tried in our known various ways of synthesis to obtain well-shaped crystals. Relatively large crystals were obtained only by the method described in the manuscript. As can be seen from the data presented, the crystals retain the general original shape and size but are delaminated. This suggests that they either crystallized without much mass transfer and/or are the product of dehydration processes. Both cases are a prerequisite for the manifestation of inhomogeneity and disorder. Unfortunately, all attempts to specify this disorder have failed. We would be grateful if a crystallographer with better skills would review the experimental data and be able to refine the structure with better indicators. In this regard, we will send the experimental data if desired.

Attempts to solve the structure on the basis of single-crystal diffraction data alone were unsuccessful. Therefore, based on the data from the other used methods and our knowledge, we derived the theoretical model and presented its description in the manuscript.

Comments 2:  

Furthermore, it is necessary to mention the pointless presentation of bechererite as hemihydrate, without mentioning that it is a mineral with a completely different composition (Zn7Cu(OH)13[(SiO(OH)3(SO4)]) and also with substantial content of Si and Cu.

Response 2: We are grateful for the reviewer's comments. We checked the text and made corrections.

Comments 3:  

line 54 - missing number for reference (Stanimirova et al., 2018); 

line 137 - reference " Bear and coauthors [3]" is incorrect number 3 is Stanimirova et al. 2018;

line 242 phrase "P-3 triclinic symmetry." is incorrect P-3 is trigonal space group.

Response 3: Agree. We checked the text and made corrections.

Response to Reviewer 2 Comments

Dear Reviewer, thank you very much for taking the time to review this manuscript. With your efforts, the quality of our manuscript is improved.

Comments 1: I would also like to note that sometimes there are many detailes that complicate reading. For example, in the IR section authors can simply focuse on "new phase" spectra in comparison to other similar phases (in this context info on hemihydrate could be shortened or avoided, like lines 180-188). The same about deduced phase. Shortening of the text would make reading easier, but I leave this choice to authors.

Response 1: Thank you for recommendation. We checked the text and made corrections.

Response to Reviewer 3 Comments

Dear Reviewer, thank you very much for taking the time to review this manuscript. With your efforts, the quality of our manuscript is improved.

Comments 1: The work is very good, with clear and well-presented results. There are just a few details to fix:

Line 12 - put the numbers as subscripts in the formula OK

38 – put the minus sign of NO3 superscript

39 – Center, Diffraction, and Data with capital letters

101 – larger

130 – put 2 as a subscript

178, 187, 190, 226, 293 – put 4 as a subscript.

In all formulas put SO4 in parentheses

227 – hydrogen ions, not hydrogens

Table 4 – Cell, not sell

242 – trigonal, not triclinic

247 – namuwite with lowercase initial

259 – put a hyphen between Zn and 4

260 – put a hyphen between Zn and 3

In some places, the formula is given as 2-2.5 H2O and in others as 2-2.25 H2O, without justification

Response 1: Thank you for your remarks. We checked the text and made corrections.

Response to Reviewer 4 Comments

Dear Reviewer, thank you very much for taking the time to review this manuscript.

Comments 1: The crystal data is poor, and the reliable factors R indexes are very large, implying the crystal structure of the title compound is not convincing.

Response 1: Thank you for your remarks.

We have tried in our known various ways of synthesis to obtain well-shaped crystals. Relatively large crystals were obtained only by the method described in the manuscript. As can be seen from the data presented, the crystals retain the general original shape and size but are delaminated. This suggests that they either crystallized without much mass transfer and/or are the product of dehydration processes. Both cases are a prerequisite for the manifestation of inhomogeneity and disorder. Unfortunately, all attempts to specify this disorder have failed. We would be grateful if a crystallographer with better skills would review the experimental data and be able to refine the structure with better indicators. In this regard, we will send the experimental data if desired.

.

Dear Reviewer, thank you very much for taking the time to review this manuscript again.

Comments 1: Formal errors have also been corrected. Only at line 183 delete space between P and -3.

Response 1: Thank you noticed this. We made corrections.

Dear Reviewer, thank you very much for taking the time to review this manuscript.

Comments 1: Due to the poor crystal data, the crystallographic parameters such as atomic sites are not reliable, especially for the crystal water content determination from the single crystal data. I suggest the authors have solved this problem, then they can submit this paper. Crystal data can be solved by other technique such as Electronic Diffraction.

Response 1: Thank you for your remark and recommendation.

The quality of the experimental data (crystal data) is determined by various parameters such as completeness (99%), I/ɕI (9.1), number of data/number of parameters (1482/92), Rint (8.86%), etc. The values of these parameters for our experiment are given in brackets. These values are acceptable and indicate a good quality of the experiment.

The reliability of the atomic coordinates is in turn confirmed by the acceptable values of the displacement parameters, as well as by the fact that there is a convergence in the refinement of the structure model. We agree with the reviewer that in our case the number of water molecules is not reliable because there is a possibility of adding other atoms from the (Fo – Fc) electron density map. But in our opinion, these extra electron density is related to the disordered structure of the studied samples.

We agree with the reviewer's comment that electron diffraction methods are a good alternative. However, our material contains loosely bound water molecules in the interlayer space (water is released in the range from room temperature to 190oC). In this case, when the electron microscope system is evacuated, these water molecules will leave the structure and this will affect the structural parameters.