Reactions of the Uranyl Ion and a Bulky Tetradentate, “Salen-Type” Schiff Base: Synthesis and Study of Two Mononuclear Complexes

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The manuscript by Sotiris G. Skiadas et al. describes two new UO₂ complexes with tetradentate salen-type Schiff base ligand, which were characterized using single-crystal X-ray diffraction (including Hirshfeld surface analysis), IR, Raman, UV/Vis and emission spectroscopy. Crystal structures, H-bonding, and C-H…π interactions were described in detail. Additionally, the behavior of new compounds in solution was investigated using conductivity measurements, UV-Vis and NMR spectroscopy.

The authors performed interesting results, which are worthy of publication in Crystals. However, upon reading the manuscript, some questions arose that required consideration.

1. The Abstract is too long and contains too many details described in the main article. The text should be shortened, leaving the most important points.
2. Since the authors found that H₂L can crystallize in the form of different polymorphs, it would be interesting to study the product obtained using powder X-ray diffraction to find out which of the polymorphs (or their mixture) is isolated during the synthesis described on page 5. Were there any attempts to obtain single crystals of H₂L by recrystallization of the synthesized product, rather than by reaction with Sm(III)?
3. Raman spectrum for 1 (Fig. 18) and IR spectrum for 2 (Fig. 19) should be transferred to the ESI, since the corresponding spectra for 2 and 1 are given there.
4. The oxidation states of uranium should be denoted by Arabic numerals rather than Roman numerals (see the first paragraph of the Introduction).

Author Response

Dear Referee,

It is an honor for me to correspond with you.

First of all, we thank you very much for your time to study our ms, and for your valuable comments. We were glad to see that you reported warmly on our work.

We are uploading the revised versions of the main ms and its “Supporting Materials”. We are pleased to inform you that we have addressed ALL your revision points/comments/suggestions.

Please see below our point-by-point answers to your demands and concerns, and the way we have treated them in the revised material. For easy communication, each of your comments is written before our corresponding answer.

1. The Abstract is too long and contains too many details described in the main article. The text should be shortened, leaving the most important points.

We have condensed the “Abstract” by ca. 50%, and this is now more concise.

2. Since the authors found that H₂L can crystallize in the form of different polymorphs, it would be interesting to study the product obtained using powder X-ray diffraction to find out which of the polymorphs (or their mixture) is isolated during the synthesis described on page 5. Were there any attempts to obtain single crystals of H₂L by recrystallization of the synthesized product, rather than by reaction with Sm(III)?

The comments are correct. Thus: (i) The recrystallization of our crude H₂L from methanol gave the polymorph H₂L(B). We tried to recrystallize the crude H₂L (prepared as described in paragraph 2.10) from ethanol (the solvent in which the crude crystalline powder was synthesized) in the absence of Sm(III), but in vain. The crystals were of poor quality, not suitable for single-crystal X-ray crystallography. We have added new sentences in the revised paragraphs 3.1 (“Unfortunately, the…was not possible.”) and 3.3 (“Recrystalization of our crude product from MeOH…by unit cell determination).”), to describe the above experimental facts. (ii) We have studied the product obtained using pXRD and confirm that it is neither one of the polymorphs, nor a mixture of them, but seems to correspond to a third polymorph (unknown to date). To address this point, we added four new figures (Figures S10-S13) in the revised “Supplementary Materials”; the new data were obtained in the last week, i.e., during the revision process. To clarify this point, we added a new paragraph (“Experimental x-ray diffraction data…can give several conformers.”) in the end of paragraph 3.4 of the revised main ms. We have also added a new paragraph titled “2.12. Powder X-ray diffraction” with the experimental details of this new study.

3. Raman spectrum for 1(Fig. 18) and IR spectrum for 2 (Fig. 19) should be transferred to the ESI, since the corresponding spectra for 2 and 1 are given there.

We have transferred the old Figures 18 and 19 in the ESI; under the new numbering scheme, these figures have become S23 and S25, respectively.

4. The oxidation states of uranium should be denoted by Arabic numerals rather than Roman numerals (see the first paragraph of the Introduction).

We have performed the suggested corrections in the first paragraph of “Introduction”.

In summary, we do believe that -from your viewpoint- the ms is now absolutely ready for final acceptance by The Academic Editor.

Reviewer 2 Report

Comments and Suggestions for Authors

I have carefully read the manuscript that was sent to me for review. After reading it, I have the following comments and questions, which I have listed below.

1. The authors should clarify the following:

- the title of the manuscript;

- the parameters used to record the excitation and emission spectra in section 2.6.

- In Section 2.9, the type of solvent used;

- Which structures correspond to the ESI-MS signals in section 2.10 (line 224); the same applies to Figure 2.

2. The authors mention the 1H NMR spectrum of H2L in CDCl3 (line 394), but do not include it in the manuscript. This should be added.
3. From the caption of Figure 3, I can infer that using different lengths of excitation always resulted in emissions of the same intensity. Was this actually the case?
4. Line 774: On what basis did the authors determine the precise position of the bands in the excitation and emission spectra? Did they use spectral deconvolution? This comment applies to all excitation and emission spectra.
5. Line 793: The authors should supplement this section of the manuscript with information on the emission spectrum of the pure ligand recorded at λ(ex) = 400 nm.
6. Absorbance is a dimensionless quantity. Please correct this in Figures S18 and S22.

 

After making a few minor corrections to the text, I recommend printing this manuscript in “crystals”.

Author Response

Dear Referee,

It is an honor for me to correspond with you.

First of all, we thank you very much for your time to study our ms, and for your valuable comments. We were glad to see that you reported warmly on our work.

We are uploading the revised versions of the main ms and its “Supporting Materials”. We are pleased to inform you that we have addressed ALL your revision points/comments/suggestions.

Please see below our point-by-point answers to your demands and concerns, and the way we have treated them. For easy communication, each of your comments is written before our corresponding answer.

1. The authors should clarify the following:

- the title of the manuscript;

- the parameters used to record the excitation and emission spectra in section 2.6.

- In Section 2.9, the type of solvent used;

- Which structures correspond to the ESI-MS signals in section 2.10 (line 224); the same applies to Figure 2.

- We have modified the title of the ms, which is now more informative. The new title is “Reactions of the Uranyl Ion and a Bulky Tetradentate ‘Salen-Type’ Schiff Base: Synthesis and Study of two Mononuclear Complexes”.

- We have enriched the revised paragraph 2.6 with the requested details. The added information is “…with a Xenon flash lamp… ± 1.5 nm.”).

- We have added the requested information.

- We have assigned the extra peaks at m/z values of 1344.23, 863.25, 650.18 and 274.28 to combined or fragmented species. We considered it more appropriate to add the new information in the revised discussion paragraph 3.1 (“The signals at m/z values of…fragments of the original ligand.”). In the caption of Figure 2, we have added an explanatory sentence (“The assignments of the peaks are given in the text.”).

 

2. The authors mention the 1H NMR spectrum of H2L in CDCl3 (line 394), but do not include it in the manuscript. This should be added.

We have added two versions (whole spectrum, aromatic region) of the ¹H NMR spectrum of H₂L (CDCl₃) in the revised “Supplementary Materials” section. Under the new numbering scheme, the new figures have become Figure S4 and Figure S5.

 

3. From the caption of Figure 3, I can infer that using different lengths of excitation always resulted in emissions of the same intensity. Was this actually the case?

The comment is correct. Under excitation by using the different wavelengths mentioned in the caption of Figure 3, we always record emission with the same “structure” and intensity. We have added this information in the caption of Figure 3 in the revised ms. For clarity, this information has been added in paragraph 3.1 (“Using all these different wavelengths for excitation…and intensity.”).

 

4. Line 774: On what basis did the authors determine the precise position of the bands in the excitation and emission spectra? Did they use spectral deconvolution? This comment applies to all excitation and emission spectra.

As a matter of fact, the information of the old line 774 refers to the solid-state absorbance spectrum. For this particular spectrum, the bands’ position was determined after deconvolution. We have replaced the old Figure 18 with a new one (Figure S27 in the revised “Supplementary Sections” section). We mention this information in the caption of Figure S27, but also in paragraph 3.7 of the revised ms (“; the bands’ position was determined after deconvolution.”). For the UV-Vis solution spectrum, the maxima are written as recorded by the instrument. This information has been added in the experimental paragraph 2.9 of the revised ms (“The maxima are written as recorded by the instrument.”). Concerning the excitation and emission spectra, again the maxima are written as recorded by the instrument. This information has been also added in the experimental paragraph 2.6 of the revised ms (“The wavelengths of the excitation and emission maxima…by the instrument.”).

 

5. Line 793: The authors should supplement this section of the manuscript with information on the emission spectrum of the pure ligand recorded at λ(ex) = 400 nm.

The comment is correct. We can confirm that under excitation at 400 nm, we recorded emission with the same “structure” and a slightly lower intensity compared with the emission of Figure 3 (for which excitations at 355, 384, 418 and 457 nm were used). We have added this information in paragraph 3.9 of the revised ms (“It should be mentioned…or 457nm.”).

 

6. Absorbance is a dimensionless quantity. Please correct this in Figures S18 and S22.

The comment is correct; we apologize for this mistake. In the revised Figures S27 and S32, this mistake has been corrected and, thus, the absorbance appears dimensionless.

 

In summary, we do believe that -from your viewpoint- the ms is now absolutely ready for final acceptance by the Academic Editor.