Structure, DFT Calculations, and Magnetic Characterization of Coordination Polymers of Bridged Dicyanamido-Metal(II) Complexes

Round 1

Reviewer 1 Report

Authors reported the synthesis and characterizations of three coordination polymers and one mononuclear complex with 4-methyoxypyridine-N-oxide ligand. Obtained complexes were characterized by the spectroscopic and magnetic measurements. This manuscript is well written, while several improvements are needed. 

 

1). Authors discussed the IR and absorption spectral features of coordination polymers and mononuclear complex. However, their spectra are not given in the manuscript and SI. Authors should add their spectra in the manuscript or SI.

 

2). In the DFT calculations, authors only described the potential energy surfaces of complexes 1, 2, and 3. However, their geometries are “fragment structures”, which are cut out of their coordination polymers. Therefore, reported absolute values of the potential energy surfaces are not correct because their calculations are not involved the intra-molecular (surrounding) coordination effects. By using the results of molecular orbitals (DFT calculations), authors should discuss the magnetic properties of complexes 1 and 2. In addition, authors should estimate the J values of complexes 1 and 2 by using the approximately spin projection method. 

 

3). In conclusion, authors mentioned that “complexes 1 and 2 display weak antiferromagnetic coupling (small |J| values)”.  However, the J value of 1 is not reported in this manuscript. Authors should estimate the J value of 1.

Author Response

Thank you very much for fine handling of our Ms and we like to expand our appreciation to the reviewers who did excellent job in careful referring of the Ms and their positive constructive comments/suggestions.  Here are our comments to all the points they addressed.  Changes in the Ms were highlighted in yellow.

Comments and Suggestions for Authors

Authors reported the synthesis and characterizations of three coordination polymers and one mononuclear complex with 4-methyoxypyridine-N-oxide ligand. Obtained complexes were characterized by the spectroscopic and magnetic measurements. This manuscript is well written, while several improvements are needed. 

 

1). Authors discussed the IR and absorption spectral features of coordination polymers and mononuclear complex. However, their spectra are not given in the manuscript and SI. Authors should add their spectra in the manuscript or SI.

 

The IR of the four complexes under investigation are now inserted in the supplementary material section IR (spectra are given as figures S1-S4 in supplementary section) and the electronic spectra of the solid complexes 1,2 and 4. Complex 3 is a Cd(II)-d¹⁰ CP where it does not exhibit d-d transition and as a result, it was not measured; it will not only shows the ligand transitions.

 

2). In the DFT calculations, authors only described the potential energy surfaces of complexes 1, 2, and 3. However, their geometries are “fragment structures”, which are cut out of their coordination polymers. Therefore, reported absolute values of the potential energy surfaces are not correct because their calculations are not involved the intra-molecular (surrounding) coordination effects. By using the results of molecular orbitals (DFT calculations),

 

Whilst the suggested calculations are beyond the scope of our resources, we have indeed explored the short-range anti-ferromagnetic couplings in our model structures by exploring the high-spin configurations minimum energy structures and comparing them with those of the low-spin configuration. The returned results show that the quartet configuration for 1 and the sextet configuration for 2 are more stable when compared to the singlet configuration. This agrees well with the experimental results which showed anti-ferromagnetic coupling in both 1 and 2 (please see p-15). Due to the limited resources at the moment, we apologize for being unable to evaluate J values and correlate it to the experimental values. We hope that this will be acceptable.

 

authors should discuss the magnetic properties of complexes 1 and 2. In addition, authors should estimate the J values of complexes 1 and 2 by using the approximately spin projection method. 

 

The J value of compound 1 had been roughly estimated (Please see the 2^nd half of the paragraph in p-8 and Fig. 5) and the corresponding value for 2 was evaluated before,

 

3). In conclusion, authors mentioned that “complexes 1 and 2 display weak antiferromagnetic coupling (small |J| values)”.  However, the J value of 1 is not reported in this manuscript. Authors should estimate the J value of 1.

 

This was fixed in the magnetic properties section and values were added in the abstract too.

Author Response File: Author Response.doc

Reviewer 2 Report

In the paper by Mautner et al. “Structure, DFT Calculations and Magnetic Characterization of Coordination Polymers of Bridged Dicyanamido-metal(II) Complexes” (magnetochemistry-501047) three coordination polymers of metal(II)-dicyanamido (dca) complexes with 4-methoxypyridine-N-oxide (MOP-NO) and the mononuclear [Cu(k¹dca)₂(4-MOP-NO)₂] were synthesized and characterized. The paper also reports their crystal structures, accompanied by a discussion with results of Density Functional Theory studies, and the results and discussion of the magnetic properties of some of them.

I have to make the following comments about it:

Introduction

At the beginning of the Introduction, 33 references are cited when presenting the topic of the work under consideration. It's a very large number for a manuscript, almost like a review. Almost half of them correspond to authors of the present manuscript, something that many scientific Journals would not accept. Therefore, I suggest that this number be shortened drastically.

The applications are well reviewed.

The text of lines 57 and 58 is badly written and should be corrected. In line 40 the acronym MOFs must be explicitly explained (this also applies to AF in line 184).

Discussion of the results

Which is the reason to comment only the spectra of two of the four coordination polymers studied? (lines 82-86)

The data of the M-O/N distances indicated in lines 92-93 are incorrect: they are all the same for compounds 1-3 and do not coincide with those read in the cifs or with those of the legends of the corresponding figures. On the other hand, in my opinion the information of the bond parameters in these figures is superfluous and should be eliminated.

In lines 122-123 it is stated that "For stacking reasons their methoxy groups are almost parallel to their pyridine rings with C-O-C-C torsion angles in the range from 3.2 to 5.8° ". Authors should explain what they understand by parallel. In this same sense, on line 145 they say “The 4-methoxy-goup of the 4-MOP-NO molecule deviates by 3.2° from its pyridine ring plane”. The authors should clarify this sentence because, in my opinion, this value corresponds to the C-O-C-C torsion angle that has nothing to do with the deviation of the substituent with respect to the heteroaromatic ring plane.

Following the authors, compound 1 exhibits an antiferromagnetic behavior. The magnetic susceptibility experimental data are analyzed using the Curie-Weiss law, leading to a value of q which indeed reflects such behavior. On the other hand, compound 2 also shows a weak antiferromagnetism. The experimental data are now analyzed by the equation for an infinite chain of classical spins, and the value obtained for J confirms again the behavior found. Moreover, for this compound, the authors analyze the magnetization at different external fields. My questions are: 1) why these two different treatments for both compounds 1 and 2, and 2) what happens with the other two coordination polymers 3 and 4? The answers to these questions must somehow be included in the manuscript for a better understanding of it and to avoid doubts about the experimental work carried out and its interpretation.

Conclusions

The authors write about the importance of the p-p interactions on the stability of crystalline structures. However, they do not refer to them along the manuscript, in particular in the Discussion of the results. This lack of important information must be corrected, indicating in which complexes they take place and the values of the distances to which they take place.

Figures

In my opinion, Figures S1-S4 (Supplementary Materials) can replace figures 1-4 of the manuscript. They provide the same structural information but incorporate the advantage that interactions between pyridine rings are reflected.

Minor points

In line 153 there is a write failure: it should say m_1,5 instead of m_1,2.

Line 173: a instead of s.

In line 178 Eq. 1 is cited, but the equation is not numbered.

In line 297 the meaning of the acronym DFT appears, when it has already been used several times. It must be moved to the first time it is mentioned in the text.

Ref 74 must be corrected.

In view of all these considerations, I recommend a major revision of the manuscript before its potential publication.

Comments for author File: Comments.pdf

Author Response

Comments and Suggestions for Authors

In the paper by Mautner et al. “Structure, DFT Calculations and Magnetic Characterization of Coordination Polymers of Bridged Dicyanamido-metal(II) Complexes” (magnetochemistry-501047) three coordination polymers of metal(II)-dicyanamido (dca) complexes with 4-methoxypyridine-N-oxide (MOP-NO) and the mononuclear [Cu(k¹dca)₂(4-MOP-NO)₂] were synthesized and characterized. The paper also reports their crystal structures, accompanied by a discussion with results of Density Functional Theory studies, and the results and discussion of the magnetic properties of some of them.

I have to make the following comments about it:

Introduction

At the beginning of the Introduction, 33 references are cited when presenting the topic of the work under consideration. It's a very large number for a manuscript, almost like a review. Almost half of them correspond to authors of the present manuscript, something that many scientific Journals would not accept. Therefore, I suggest that this number be shortened drastically.

 

The referee is absolutely right and some of our references were delated as well as the list of references were shorten.

 

The applications are well reviewed.

 

Thank you

 

The text of lines 57 and 58 is badly written and should be corrected. In line 40 the acronym MOFs must be explicitly explained (this also applies to AF in line 184).

 

Yes, referee was right and these were fixed.

 

Discussion of the results

Which is the reason to comment only the spectra of two of the four coordination polymers studied? (lines 82-86)

 

In fact, there was no specific reason other than the interesting topological geometries and structures of the three CPs 1-3.  However, the electronic spectra for complexes 3 and 4 were addressed in the last paragraph of p-4.  Please keep in mind that Mn(II) is a d⁵ metal ion and in octahedral environme show a series of very weak intense band due to spin forbidden which are not conclusive to correctly predict the geometry. Also, Cd(II) is a d¹⁰ that shows no electronic d-d transitions in the visible region and it UV spectral will provide the ligand electronic transitions which again not useful for predicting its geometry.

 

The data of the M-O/N distances indicated in lines 92-93 are incorrect: they are all the same for compounds 1-3 and do not coincide with those read in the cifs or with those of the legends of the corresponding figures. On the other hand, in my opinion the information of the bond parameters in these figures is superfluous and should be eliminated.

 

These were fixed. Thank you

 

In lines 122-123 it is stated that "For stacking reasons their methoxy groups are almost parallel to their pyridine rings with C-O-C-C torsion angles in the range from 3.2 to 5.8° ". Authors should explain what they understand by parallel. In this same sense, on line 145 they say “The 4-methoxy-goup of the 4-MOP-NO molecule deviates by 3.2° from its pyridine ring plane”. The authors should clarify this sentence because, in my opinion, this value corresponds to the C-O-C-C torsion angle that has nothing to do with the deviation of the substituent with respect to the heteroaromatic ring plane.

 

Very minor changes were made in these: torsion angles C-O-C-C torsion angles were inserted in the last part of the 1^st paragraph of p-7, together with pond angles in the 2^nd paragraph of p-8.

 

Following the authors, compound 1 exhibits an antiferromagnetic behavior. The magnetic susceptibility experimental data are analyzed using the Curie-Weiss law, leading to a value of q which indeed reflects such behavior. On the other hand, compound 2 also shows a weak antiferromagnetism. The experimental data are now analyzed by the equation for an infinite chain of classical spins, and the value obtained for J confirms again the behavior found. Moreover, for this compound, the authors analyze the magnetization at different external fields. My questions are: 1) why these two different treatments for both compounds 1 and 2, and 2) what happens with the other two coordination polymers 3 and 4? The answers to these questions must somehow be included in the manuscript for a better understanding of it and to avoid doubts about the experimental work carried out and its interpretation.

 

The J values of compounds 1 and 2 have been estimated by using in both cases Equations which were derived by Fisher. Compound 3 is a diamagnetic polymer Cd(II) and compound 4 is mononuclear: the coupling constant, J don’t exist.

 

Conclusions

The authors write about the importance of the p-p interactions on the stability of crystalline structures. However, they do not refer to them along the manuscript, in particular in the Discussion of the results. This lack of important information must be corrected, indicating in which complexes they take place and the values of the distances to which they take place.

 

In fact there was miss type and we are deeply apologize for this carless mistake. In fact, there is NO covalent π-π ring-ring stacking interactions along the chain direction of the adjacent pyridine rings. This was corrected in the conclusion. We are very thankful to reviewer for his focus and careful reading of the Ms in catching this non-intentional error.

 

 Figures

In my opinion, Figures S1-S4 (Supplementary Materials) can replace figures 1-4 of the manuscript. They provide the same structural information but incorporate the advantage that interactions between pyridine rings are reflected.

 

These was done, figures S1-S4 are now incorporated into the Ms with the new Figs 1-4.

 

Minor points

In line 153 there is a write failure: it should say m_1,5 instead of m_1,2.

Line 173: a instead of s.

In line 178 Eq. 1 is cited, but the equation is not numbered.

In line 297 the meaning of the acronym DFT appears, when it has already been used several times. It must be moved to the first time it is mentioned in the text.

Ref 74 must be corrected.

We apologize for these typos and not providing the meaning of the acronym of some abbreviations.  All of these were fixed as well as reference 74 (it is 64 now in the revised Ms)

In view of all these considerations, I recommend a major revision of the manuscript before its potential publication.

Author Response File: Author Response.doc

Round 2

Reviewer 1 Report

This manuscript was well revised. Thus, I think that present manuscript should be accepted as a paper for magnetochemistry.

Author Response

There was no comments.  Thank you for the reviewer for his effort.

Author Response File: Author Response.pdf

Reviewer 2 Report

The second version of the manuscript by Mautner et al. “Structure, DFT Calculations and Magnetic Characterization of Coordination Polymers of Bridged Dicyanamido-metal(II) Complexes” (magnetochemistry-501047) has been improved. However, there are still some unclear parts that need a minor but mandatory revision:

1) The text of lines 84-85 is badly written and it was not corrected by the authors. It seems as the sentence was unfinished.

2) New information about the UV-VIS spectra of the complexes is now provided (text and Figures). The values of the reported absorption bands for compound 4 (1320 and 570 nm) do not coincide with those inferred from Figure S7. The same is applicable for compound 2 (Figure S6). On the other hand, in line 121 the authors say “The very weak intense bands are …”. Bands corresponding to forbidden transitions are very weak, so the word intense should not appear.

3) Figures S5-S7, corresponding to VIS-UV spectra, are of very low quality. In particular, the magnitudes and numbers are barely visible.

4) With respect to the paragraph “The N(1)-O(1)-Cu(1) bond angle is 118.39(6)°. The 4-methoxy-goup of the 4-MOP-NO molecule deviates by 3.2° from its pyridine ring plane. The 4-MOP-NO molecule forms a C(6)-O(2)-C(3)-C(4) torsion angle of 3.2°. The N(1)-O(1)-Cu(1) bond angle is 118.39(6)°” (lines 178-181), the following must be taken into account to be corrected: The first and last sentences are identical. One of them must be removed and, without further comments, the two can be deleted. Its content is irrelevant (the value corresponds approximately to the tetrahedral angle of the central oxygen atom). The two central phrases of the paragraph say the same. At least one of them must be eliminated, but I suggest eliminating the two since the allusion to the referred torsion angle is already indicated in lines 155-156 of the manuscript.

5) In my first report I referred to the importance of p-p interactions, which the authors only addressed in the Conclusions of the paper but not in the text. The changes they have made in the new version of the manuscript continue in this same line. On the other hand, in these conclusions it is not clear if for compound 1 p-p interactions between rings occur. If so, the authors should give information such as the distance at which they take place. In the cif of this compound I am not able to locate this type of interactions at the typical distances at which they take place.

Author Response

Comments and Suggestions for Authors

The second version of the manuscript by Mautner et al. “Structure, DFT Calculations and Magnetic Characterization of Coordination Polymers of Bridged Dicyanamido-metal(II) Complexes” (magnetochemistry-501047) has been improved. However, there are still some unclear parts that need a minor but mandatory revision:

1) The text of lines 84-85 is badly written and it was not corrected by the authors. It seems as the sentence was unfinished.

Thank you for catching this error. This was fixed

2) New information about the UV-VIS spectra of the complexes is now provided (text and Figures). The values of the reported absorption bands for compound 4 (1320 and 570 nm) do not coincide with those inferred from Figure S7. The same is applicable for compound 2 (Figure S6). On the other hand, in line 121 the authors say “The very weak intense bands are …”. Bands corresponding to forbidden transitions are very weak, so the word intense should not appear.

Yes, the reviewer is absolutely right and we are very grateful for his careful revision.  The solid spectra of the three complexes were remeasured and new figures are now replacing the old series. The values of the absorption bands are now corrected in the Ms and also line 121 was fixed too.

3) Figures S5-S7, corresponding to VIS-UV spectra, are of very low quality. In particular, the magnitudes and numbers are barely visible.

Ad 2) and 3) RESPONSE: The UV-VIS spectra of compounds 1,2, and 4 were re-measured and revised Figures S5-S7 with improved quality included in the Supplementary Material. The section of UV-VIS spectra was adjusted taking into account revised data and above comments.

4) With respect to the paragraph “The N(1)-O(1)-Cu(1) bond angle is 118.39(6)°. The 4-methoxy-goup of the 4-MOP-NO molecule deviates by 3.2° from its pyridine ring plane. The 4-MOP-NO molecule forms a C(6)-O(2)-C(3)-C(4) torsion angle of 3.2°. The N(1)-O(1)-Cu(1) bond angle is 118.39(6)°” (lines 178-181), the following must be taken into account to be corrected: The first and last sentences are identical. One of them must be removed and, without further comments, the two can be deleted. Its content is irrelevant (the value corresponds approximately to the tetrahedral angle of the central oxygen atom). The two central phrases of the paragraph say the same. At least one of them must be eliminated, but I suggest eliminating the two since the allusion to the referred torsion angle is already indicated in lines 155-156 of the manuscript.

Ad 4) RESPONSE: As suggested we cancelled this paragraph completely.

5) In my first report I referred to the importance of p-p interactions, which the authors only addressed in the Conclusions of the paper but not in the text. The changes they have made in the new version of the manuscript continue in this same line. On the other hand, in these conclusions it is not clear if for compound 1 p-p interactions between rings occur. If so, the authors should give information such as the distance at which they take place. In the cif of this compound I am not able to locate this type of interactions at the typical distances at which they take place.

THANKS FOR YOUR CAREFUL REVISION, as we really have overlooked the pi-pi- interactions in the structures of 1-3.  According to PLATON runs we have included a revised paragraph at end of structural description of 1-3 and added also a new Table 1 for the ring-ring interactions. Also the Conclusions were re-written and Tables, References etc. adjusted.

Author Response File: Author Response.pdf