Stabilization of {Ag₂₀(S^tBu)₁₀} and {Ag₁₉(S^tBu)₁₀} Toroidal Complexes in DMSO: HPLC-ICP-AES, PL, and Structural Studies

Round 1

Reviewer 1 Report

 

In this work, the authors present the formation of both {Ag19(S-tBu)10} and {Ag20(S-tBu)10} in DMSO. While the single crystal structure results shows that the two clusters coexist in the single crystal with {Ag19(S-tBu)10} being the major component, the authors managed to perform a chromatography separation and successfully identified the two species with HPLC-ICP-AES. The authors further studied the photoluminescence properties of the silver cluster and proposed a charge transfer mechanism. In general, it is a well-conducted research and it can be published after taking the followings comments into consideration:

1.       1 The authors explained that the application of HR-ESI-MS could be challenging. However, has the authors considered the coupling of HPLC with ESI-MS, which may improve the signal quality a lot?

2.       2 The temperature-dependent photoluminescent properties are quite interesting. However, there exist several photoluminescent mechanisms for silver clusters and the authors explained the photoluminescence from LMCT. Have the authors considered the possibilities of core excitation or LMMCT?

3.     3   While the authors use the Gauss approximations to fit the photoluminescence bands, it is recommended to provide the original fitting using photon energy (eV) in the x-axis (at least provide such information in SI).

Author Response

In this work, the authors present the formation of both {Ag19(S-tBu)10} and {Ag20(S-tBu)10} in DMSO. While the single crystal structure results shows that the two clusters coexist in the single crystal with {Ag19(S-tBu)10} being the major component, the authors managed to perform a chromatography separation and successfully identified the two species with HPLC-ICP-AES. The authors further studied the photoluminescence properties of the silver cluster and proposed a charge transfer mechanism. In general, it is a well-conducted research and it can be published after taking the followings comments into consideration:

1. The authors explained that the application of HR-ESI-MS could be challenging. However, has the authors considered the coupling of HPLC with ESI-MS, which may improve the signal quality a lot?

 

Thank you very much for the comments. It is very perspective to combine HPLC and ESI-MS to study such systems and we are working in this direction. There is only one big problem for ESI-MS which is DMSO. This solvent is not compatible for our machine (the same to mentioned here: https://www.chem.ualberta.ca/~massspec/ESIsol.htm) and we really tried to use DMSO/CH3CN mixtures but the addition of CH3CN always gave some precipitation (most likely due to the ligands exchange). This is a problem and we will publish its possible solution separately.

 

2. The temperature-dependent photoluminescent properties are quite interesting. However, there exist several photoluminescent mechanisms for silver clusters and the authors explained the photoluminescence from LMCT. Have the authors considered the possibilities of core excitation or LMMCT?

 

Thank you for the comment! It is not so simple to answer this without calculations. We planned to do this but it will be published separately. At the moment we added this to the main text: Taking this into account the luminescence can be induced by several ways: i) emission of {Ag₁₉} and {Ag₂₀} with the possible intercluster transition; ii) emission from the same centers of both clusters caused by LMCT from S 3p to Ag 5s [33] together with {Ag₁₉} and {Ag₂₀} intracluster CC transition (or ligand-to-metal−metal charge transfer (LMMCT [10.1021/ja407911b])).

 

3. While the authors use the Gauss approximations to fit the photoluminescence bands, it is recommended to provide the original fitting using photon energy (eV) in the x-axis (at least provide such information in SI).

 

Thank you very much for suggestion. We added all original fitting into the SI file.

 

Reviewer 2 Report

1. Related studies on nanoclusters and nanocluster co-crystallization have been reported before this work, such as Martin Jansen (e.g., 10.1002/chem.200902538), Zheng Nanfeng (e.g., 10.1038/s41467-018-05584-9) and Wang Quan-Ming (e.g. 10.1002/chem.201202115) for their work. So it is suggested that the authors should add them to the references.

2. It is also suggested that this paper should have further discussed how the Ag-S clusters are converted to each other.

3. The study of this work focused on the crystal structures of Ag19 and Ag20, but the authors did not properly resolve and refine the crystal data. The cif files I received did not fully identify the atomic types, which led to an inappropriate interpretation of the A errors in the checkcif report that could have been eliminated with proper refinement. 1) In 1, there is a "PLAT430_ALERT_2_A Short Inter D.. .A Contact O5 . .O7A . 2.05 Ang.", the two parts with occupancy of 0.3 and 0.7 cannot be reasonably assigned to the normal structure of nitrate and are not divided into two PARTs, which is chemically unreasonable. Of course, the authors did not divide the disordered nitrate containing N6 into two PARTs either. Although the two disordered states of the nitrate containing N6 are chemically reasonable, it is not reasonable in crystallography. It is suggested that the authors should use the method of splitting the PART of tert-butyl where C23 is located to deal with all the disorders. 2) "PLAT971_ALERT_2_A Check Calcd Resid. Dens. 0.34Ang From W2 9.07 eA-3", this problem is not due to "strong x-ray"。 It should there is an O atom between W2 and Si1, but the authors did not identify it in the structure, except that there are many other atoms in the crystal data that have not been correctly identified. 3) The space group of structure 2_sq needs to be carefully checked again, which probably does not belong to the Ia space group but has a higher symmetry. In conclusion, this structure has not completed the resolution and refinement required for publication.

Author Response

1. Related studies on nanoclusters and nanocluster co-crystallization have been reported before this work, such as Martin Jansen (e.g., 10.1002/chem.200902538), Zheng Nanfeng (e.g., 10.1038/s41467-018-05584-9) and Wang Quan-Ming (e.g. 10.1002/chem.201202115) for their work. So it is suggested that the authors should add them to the references.

 

Thank you very much for the suggested citations. These items have been added to the references list.

 

2. It is also suggested that this paper should have further discussed how the Ag-S clusters are converted to each other.

 

This is a complicated point. We can only use structural data for [NO₃@Ag_19.2(S^tBu)₁₀(DMSO)_5.2(NO₃)_8.2]·3DMSO to mark disordered and defective positions of Ag atoms in the cluster core. Probably the loss of these atoms or groups generates silver clusters of lower nuclearity. Some discussion has been added to the main text. To answer this question a lot of additional studies should be provided.

 

3. The study of this work focused on the crystal structures of Ag19 and Ag20, but the authors did not properly resolve and refine the crystal data. The cif files I received did not fully identify the atomic types, which led to an inappropriate interpretation of the A errors in the checkcif report that could have been eliminated with proper refinement.

 

2. i) In 1, there is a "PLAT430_ALERT_2_A Short Inter D.. .A Contact O5 . .O7A . 2.05 Ang.", the two parts with occupancy of 0.3 and 0.7 cannot be reasonably assigned to the normal structure of nitrate and are not divided into two PARTs, which is chemically unreasonable. Of course, the authors did not divide the disordered nitrate containing N6 into two PARTs either. Although the two disordered states of the nitrate containing N6 are chemically reasonable, it is not reasonable in crystallography. It is suggested that the authors should use the method of splitting the PART of tert-butyl where C23 is located to deal with all the disorders.

 

The structural refinement has been improved.

 

1. ii) "PLAT971_ALERT_2_A Check Calcd Resid. Dens. 0.34Ang From W2 9.07 eA-3", this problem is not due to "strong x-ray". It should there is an O atom between W2 and Si1, but the authors did not identify it in the structure, except that there are many other atoms in the crystal data that have not been correctly identified.

 

First of all, this is not a common crystal structure which can be properly refined, this is a complicated co-crystalline associate combining these features:

1. i) fast decrease of the reflections intensity after d = 1Å; ii) full positional disordering of each Ag-atom coordination environment; iii) highly disordered solvent molecules of crystallization and nitrate anions; iv) positional disordering of POM anions. Such problems resulted in unstable refinement of “light” atoms. This density can be assigned only as POM rotational disordering. Oxoligands can not be refined properly.

 

iii) The space group of structure 2_sq needs to be carefully checked again, which probably does not belong to the Ia space group but has a higher symmetry. In conclusion, this structure has not completed the resolution and refinement required for publication.

 

Yes, it is possible to generate solution in C2/c. But refinement gives only W-atoms with crazy thermal ellipsoids. No any Ag-atoms were determined due o high orientational disordering. To fix this I used structural solution in low symmetry group and it generates silver clusters with right geometry and StBu ligands location. Due to a lot of structural features this is only a crystal structure model using only to answer for: i) speciation in solution; ii) stability of the Ag20-xS10 cluster core toward presence of possible POM template, iii) the use of POM to extract low nuclearity silver cluster from the reaction solution.

 

 

 

 

 

 

 

 

 

Reviewer 3 Report

I think the author's findings are very valuable for the field of metal clusters chemistry. Especially, HPLC technique is very suitable for the separation of different species. However, I have a question about such separation. If the two clusters are equilibrium species, why can you separate them by HPLC? Because the abundance ratio of equilibrium species is depended on the concentration of each species. At the moment of separating cluster, the concentration will be changed, resulting in new equilibrium bias. Can we say it is a equilibrium species? If the authors can discuss about the separation mechanism and equilibrium state, the manuscript will be better one.

 

I found some errors or incomprehensible point. Please correct the following points.

1. Line 89-90. "Ag atoms are marked in indigo": In Figure 1, the color of indigo also indicates Nitrogen. Please distinguish them.

2. Line 114. "3⁶ plane net topology": I guess most of the readers of this manuscript are not mathematician. So suitable reference may be needed.

3. Figure 3: I guess "Ag 328.0 nm" means ICP-AES emission wavelength of Ag atom. However it will be little difficult to understand. Please add more information about it in your manuscript.

4. Figure 4, 5: Only "a" and "b" will be required, not "1a" and "1b".

Author Response

I think the author's findings are very valuable for the field of metal clusters chemistry. Especially, HPLC technique is very suitable for the separation of different species. However, I have a question about such separation. If the two clusters are equilibrium species, why can you separate them by HPLC? Because the abundance ratio of equilibrium species is depended on the concentration of each species. At the moment of separating cluster, the concentration will be changed, resulting in new equilibrium bias. Can we say it is a equilibrium species? If the authors can discuss about the separation mechanism and equilibrium state, the manuscript will be better one.

 

I found some errors or incomprehensible point. Please correct the following points.

1. Line 89-90. "Ag atoms are marked in indigo": In Figure 1, the color of indigo also indicates Nitrogen. Please distinguish them.

 

Thank you for suggestion. Fig. 1 has been changed for clarity.

 

2. Line 114. "3⁶ plane net topology": I guess most of the readers of this manuscript are not mathematician. So suitable reference may be needed.

 

Thank you very much for the comment! This reference - 10.1098/rsta.1980.0150 has been added to the references list.

 

3. Figure 3: I guess "Ag 328.0 nm" means ICP-AES emission wavelength of Ag atom. However it will be little difficult to understand. Please add more information about it in your manuscript.

 

Thank you very much for the comment! We added this to the main text: “The eluting species are detected by monitoring the silver atomic emission line at 328.0 nm following the separation by high-performance liquid chromatography.”

 

4. Figure 4, 5: Only "a" and "b" will be required, not "1a" and "1b".

 

Thank you very much for the comment! This was fixed!

 

Reviewer 4 Report

In this work, Abramov and co-workers reported a novel co-crystal system. Then, PL properties of Ag_19.2 and Ag_17.8 were studied. The results are very attractive, for example, Ag₁₉ and Ag₂₀ were separated by chromatographic technique. The CT between the silver thiolate cluster and POM unit led to an apparent increase in the low-energy PL intensity band at 717 nm. However, certain problems in the article may require further research or explanation. Therefore, I think the job is appropriate for publication but minor revision is needed.

1.    The stability of Ag₂₀, Ag_19, and Ag_17.8 should be provided in the DMSO solution. For instance, time-dependent UV-vis spectra and images of the color change of the Ag complexes should be provided.

2.     The fluorescence quantum yield of Ag_19.2 and Ag_17.8 should be measured and provided.

3.     The fluorescence properties of co-crystallization of Ag_19.2 and Ag_17.8 were studied in this paper. Probably, the following literature should be referenced: Nanoscale, 2022, 14, 8842.

Author Response

In this work, Abramov and co-workers reported a novel co-crystal system. Then, PL properties of Ag_19.2 and Ag_17.8 were studied. The results are very attractive, for example, Ag₁₉ and Ag₂₀ were separated by chromatographic technique. The CT between the silver thiolate cluster and POM unit led to an apparent increase in the low-energy PL intensity band at 717 nm. However, certain problems in the article may require further research or explanation. Therefore, I think the job is appropriate for publication but minor revision is needed.

1. The stability of Ag₂₀, Ag_19, and Ag_17.8 should be provided in the DMSO solution. For instance, time-dependent UV-vis spectra and images of the color change of the Ag complexes should be provided.

 

Thank you very much for the comment! Fortunately, we keep samples in time and we added the HPLC-ICP-AES and UV data for the sample aged for 3 month. Indeed, this works and we found 3^rd signal in our chromatogram and additional peak in UV-VIS spectrum. These data have been added to the main text.

 

2. The fluorescence quantum yield of Ag_19.2 and Ag_17.8 should be measured and provided.

The fluorescence quantum yields for both complexes are significant less than 1%. The correct values could not be determined due to the technique and method limitations of Horiba Quanta-phi. In particular, the limitation on the absorption coefficient of the investigation compounds does not allow the use of a large amount of the sample, which would make it possible to qualitatively record the luminescence spectrum. 

 

3. The fluorescence properties of co-crystallization of Ag_19.2 and Ag_17.8 were studied in this paper. Probably, the following literature should be referenced: Nanoscale, 2022, 14, 8842.

 

The citation has been added to the references list.

 

 

 

 

Round 2

Reviewer 2 Report

Please delete figure 2 since there no crystal data of [Ag_17.8(NO₃)_3.8(StBu)₁₀][SiW₁₂O₄₀]·30DMSO in this version. And future  modification  related the crystal structure of [Ag_17.8(NO₃)_3.8(StBu)₁₀][SiW₁₂O₄₀]·30DMSO also need to done for the whole the manuscript.

Author Response

Please delete figure 2 since there no crystal data of [Ag_17.8(NO₃)_3.8(StBu)₁₀][SiW₁₂O₄₀]·30DMSO in this version. And future  modification  related the crystal structure of [Ag_17.8(NO₃)_3.8(StBu)₁₀][SiW₁₂O₄₀]·30DMSO also need to done for the whole the manuscript.

 

Both comments are strange. Probably this is misunderstanding. As mentioned in the manuscript we obtained crystalline material 2 after the addition of [H4SiW12O40] into the reaction mixture. Its crystal structure can not be well-refined due to the complicated disordering of all structural units. All the problems with the refinement are presented in XRD part. We used the structural model only to answer for: i) speciation in solution; ii) stability of the Ag20-xS10 cluster core toward presence of possible POM template, iii) the use of POM to extract silver cluster with low nuclearity from the reaction solution.

There is no any discussion concerning geometry or interatomic distances for this structural model. Only packing topology of main structural units is presented just to show double complex salt nature of the isolated complex. Our manuscript is about solving this problem by using: x-ray powder diffraction, elemental analysis, IR and luminescence to understand the nature of extracted silver clusters. Taking into account all the results we summarized presence of Ag18StBu cluster in the structure of 2.