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Peer-Review Record

Cocrystals of 2-Aminopyrimidine with Boric Acid—Crystal Engineering of a Novel Nonlinear Optically (NLO) Active Crystal

Crystals 2019, 9(8), 403; https://doi.org/10.3390/cryst9080403
Reviewer 1: Anonymous
Reviewer 2: Anonymous
Reviewer 3: Anonymous
Crystals 2019, 9(8), 403; https://doi.org/10.3390/cryst9080403
Received: 16 July 2019 / Revised: 29 July 2019 / Accepted: 31 July 2019 / Published: 3 August 2019

Round 1

Reviewer 1 Report

Němec and coworkers describe two cocrystals of 2-aminopyrimidine and boric acid. The cocrystals differ in their hydrogen-bonding patterns, and the solids are characterized by IR and Raman spectroscopy. The 3/2 cocrystal was studied for second harmonic generation behavior. Overall, the manuscript is appropriate for the Journal, but I recommend that the authors address the following points before publication.

1. The cif files and cif check files were not supplied by the authors. These should be uploaded so all reviewers can quickly evaluate the quality of the X-ray data.

2. Values for the experimental powder data are provided in a table in the SI. However, since the powder sample is used for the SHG experiments, a single plot that includes experimental data and calculated data should be supplied to ensure the bulk powder correlates with simulated pattern.

3. On page 10, first paragraph, the authors state, “This interaction is not present in the crystal structure of (2-AMP)3(H3BO3)2 where such bands are much less pronounced (see Figure 7).” It is unclear exactly which bands the authors are referring to. Both spectra show bands in the 1400 region, which is labeled as the BOH band.

4. In the introduction and conclusion, the authors mention efforts to synthesize neutral cocrystals involving 2-aminopyrimidine. Have the pKa values of the components been compared? These values can aid in determining if a salt or cocrystal is expected (see Cruz Cabeza, CrystEngComm 2012, 14, 6362-6365).

Author Response

We would like to thank reviewer for all comments and suggestions. Corrections made in manuscript and Supplementary Materials are highlighted with yellow colour.

 

Comment 1: The cif files and cif check files were not supplied by the authors. These should be uploaded so all reviewers can quickly evaluate the quality of the X-ray data.

Reply: Accepted, CIF files and CheckCIF files were uploaded.

 

Comment 2: Values for the experimental powder data are provided in a table in the SI. However, since the powder sample is used for the SHG experiments, a single plot that includes experimental data and calculated data should be supplied to ensure the bulk powder correlates with simulated pattern.

Reply: Accepted, we have added Figure S2 (Supplementary Materials) presenting comparison of recorded powder diffraction pattern with theoretical diffraction pattern calculated from single-crystal X-ray diffraction data. Moreover, we have also added Figure S1 (Supplementary Materials) presenting comparison of powder diffraction patterns of (2-AMP)3(H3BO3)2, 2-AMP(H3BO3)2, boric acid and 2-aminopyrimidine.

 

Comment 3:  On page 10, first paragraph, the authors state, “This interaction is not present in the crystal structure of (2-AMP)3(H3BO3)2 where such bands are much less pronounced (see Figure 7).” It is unclear exactly which bands the authors are referring to. Both spectra show bands in the 1400 region, which is labeled as the BOH band.

Reply: Accepted, we have modified text on pages 8 and 10 and we have also added Figure S1 (Supplementary Materials) explaining observed differences related to IR spectra. Generally, we can conclude that the presence of O-H…O hydrogen bonding interconnecting boric acid molecules in 2-AMP(H3BO3)2 leads to similar shapes (i.e. broadening and increase of intensity) of IR bands known from pure crystalline boric acid.   

 

Comment 4:   In the introduction and conclusion, the authors mention efforts to synthesize neutral cocrystals involving 2-aminopyrimidine. Have the pKa values of the components been compared? These values can aid in determining if a salt or cocrystal is expected (see Cruz Cabeza, CrystEngComm 2012, 14, 6362-6365). 

Reply: Accepted, we have modified text on page 13 (chapter Conclusions) according this comment.   


Reviewer 2 Report

The reviewed manuscript presents X-ray studies, IR and Raman spectra comparison with results of DFT quantum-chemistry periodic computations and analysis of optical properties of two novel 2-aminopyrimidine boric acid cocrystals of potential NLO activity.

I have read this manuscript with great interest. In my opinion it is an excellent, well organized paper. The presentation of the objectives, the experimental part and the conclusions are adequate. The obtained results are not only clearly ad convincingly described but also properly illustrated. Summarizing, the presented material represents a significant new and I recommend its publication without any changes.


Author Response

No response is necessary.

Reviewer 3 Report

Ivan Němec and coworkers reported preparation of two type of cocrystals based on hydrogen-bonded components of 2-aminopyrimidine and boric acid.
The two crystals were structurally determined by single crystal X-ray diffraction, characterized by powder X-ray diffraction and vibrational spectroscopy.
SHG activity of non-centrosymmetric (2-AMP)3(H3BO3)2 was also examined.
The characterization was well done and the results were valuable.
I think that this manuscript is acceptable as is.

Author Response

No response is necessary.

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