Heteronuclear Bimetallic Complexes with 3d and 4f Elements

Round 1

Reviewer 1 Report

The manuscript by Chalmers et al. describes the synthesis and (structural) characterization of 3 novel heteronuclear bimetallic Schiff base complexes. The research is properly conducted and presented in a clear way and is definitely suitable for Molbank. However, I have some minor questions which need to be addressed before acceptance:

1) what about the structure(s) of the bulk (green powder) material? In my experience, these bulk materials often contain different structures/phases, which can differ entirely from the determined crystal structures. If would be a good idea to perform powder XRD analysis on the bulk materials and - if there's multiple/different phases - try to match (phase & match) these to any structures. 

2) in the CCDC, there's a number of similar structures (with different solvent molecules instead of MeOH). I would recommend to perform a CCDC survey and at least look for similar (isostructural?) entries with similar packing arrangements? 

3) the (short) introduction contains 3 references (1998-2001) to standard work of Piguet, Bünzli,...  Isn't there any more recent reviews on such materials? This would make the research also more relevant. 

Author Response

We thank you kindly for your response and your suggestions for our manuscript. Please see our detailed responses to your points below.

1) what about the structure(s) of the bulk (green powder) material? In my experience, these bulk materials often contain different structures/phases, which can differ entirely from the determined crystal structures. If would be a good idea to perform powder XRD analysis on the bulk materials and - if there's multiple/different phases - try to match (phase & match) these to any structures.

We carried out PXRD analysis on the bulk powders (between 5 and 70 2theta) and found comparison of those with the patterns calculated from the single crystal CIF confirms both the purity and identity of the complexes, and the structures we report matches the bulk. We have included the PXRD images in the Supporting Info.

2) in the CCDC, there's a number of similar structures (with different solvent molecules instead of MeOH). I would recommend to perform a CCDC survey and at least look for similar (isostructural?) entries with similar packing arrangements?

We thank the reviewer for drawing our attention to these. An overview of the structurally-characterised, closely related complexes has been included in Section 2.2.

3) the (short) introduction contains 3 references (1998-2001) to standard work of Piguet, Bünzli,...  Isn't there any more recent reviews on such materials? This would make the research also more relevant.

We have expanded the introduction and discussion sections to reflect other work in this area, including some recent reviews and advances.

Reviewer 2 Report

The manuscript describes the synthesis of Heteronuclear Bimetallic Complexes with 3d and 4f Elements. These Complexes were characterized by single-crystal X-ray diffraction, UV-vis spectrophotometry, mass spectrometry, and IR spectroscopy. The experimental results and their discussion were well presented, mainly in the crystal structure description. Therefore, I recommend this paper to be published in molbank after minor revisions.

1.  The introduction looks like the “abstract” section so I recommended to modify the introduction. It should detail the compositions, applications and the history of such complexes.

2.  How pure are these complexes? I wonder if they can be characterized by XRPD.

3.  If they exhibit a good homogeneity, they can be later undergoing further properties and applications to be studied.  

4.  Since there are many groups working on mixed metal coordination polymers, the citations should be wide. I suggested http://hdl.handle.net/10261/112969,    https://doi.org/10.3390/polym8030086 to be cited.

Author Response

We thank you kindly for your response and your suggestions for our manuscript. Please see our detailed responses to your points below.

The introduction looks like the “abstract” section so I recommended to modify the introduction. It should detail the compositions, applications and the history of such complexes.

We thank the reviewer for drawing our attention to these. We have expanded the introduction and discussion sections to reflect other work in this area, including some recent reviews and advances. An overview of the structurally-characterised, closely related complexes has been included in Section 2.2.

2. How pure are these complexes? I wonder if they can be characterized by XRPD.

We carried out PXRD analysis on the bulk powders (between 5 and 70 2theta) and found comparison of those with the patterns calculated from the single crystal CIF confirms both the purity and identity of the complexes, and the structures we report matches the bulk. We have included the PXRD images in the Supporting Info.

3. If they exhibit a good homogeneity, they can be later undergoing further properties and applications to be studied.

Thank you for your comment and suggestion. This is something we will consider for future research projects.

4. Since there are many groups working on mixed metal coordination polymers, the citations should be wide. I suggested http://hdl.handle.net/10261/112969, https://doi.org/10.3390/polym8030086 to be cited.

We have included these citations as suggested in our revised introduction.

Reviewer 3 Report

Review on molbank-2146197 (only crystallographic sections)

The manuscript is mostly sound, with some corrections needed.

Regrettably and unnecessarily the 3 data sets are only collected up to 2theta 50-51 degrees. Why?

The present treatment of the methanol H(O) atoms is not the best idea. The refinement with DFIX 0.98 leads to considerably shorter O-H bond lengths from 0.898 to 0.932 A. Why this very large DFIX-value? A free refinement would give 0.71 to 0.75 A – surely too short then. Refinement with the two commands FREE CU1 O41 and HFIX 147 O41 results in better and more comparable geometries. Relevant geometric parameters in the manuscript as well as lines 207-208 must then be rewritten.

Para 2.2, line 93: must read “bond lengths”.

Ditto, line 106-107: these Ce and Pr dimers lie around a crystallographic inversion center, so text should read “… ligands (O41-H41…O33A(symmetry code)) forming centro-symmetric dimers …” .

Ditto, line 113: As for Nd there are no centro-symmetric dimers it should read “… nitrato ligand (O41-H41…O11A(symmetry code)), their … “.

Figure 1: Label for all atoms necessary.

Caption:  Must read “Molecular structure …” and “Anisotropic displacement ellipsoids … “. There are no “thermal” ellipsoids.

Figure 2: wrong oxygen labels – for the Ce and Pr structure shown the O-H…O involved acceptor oxygen atom  is O33, not O11. Add nitrogen labels, too.

Table S1: Add 2theta max for data collection as well as associated h,k,l ranges. Number of parameters for 1-Nd is only 392 (397 for others), why?

Author Response

We thank you kindly for your response and your suggestions for our manuscript. Please see our detailed responses to your points below.

Regrettably and unnecessarily the 3 data sets are only collected up to 2theta 50-51 degrees. Why?

These are older datasets which the processing software automatically truncated at 2theta values of between 50.7 and 50.9 degrees. While this is not ideal, and it would be better to include all data collected, reprocessing to include small amounts of high angle data would likely not significantly improve the quality of the structures.

The present treatment of the methanol H(O) atoms is not the best idea. The refinement with DFIX 0.98 leads to considerably shorter O-H bond lengths from 0.898 to 0.932 A. Why this very large DFIX-value? A free refinement would give 0.71 to 0.75 A – surely too short then. Refinement with the two commands FREE CU1 O41 and HFIX 147 O41 results in better and more comparable geometries. Relevant geometric parameters in the manuscript as well as lines 207-208 must then be rewritten.

We thank the reviewer for their valuable comments. The DFIX value was chosen to reflect the known O-H bond length determined from neutron data. In these structures, as the refined distances do not end up accurately reflecting this, the refinements have been modified in line with the suggestion, although the O-H distances have been set to the average distance from neutron crystallography (0.967 Angstrom). Geometric data related to this, and the specified lines have been amended.

Para 2.2, line 93: must read “bond lengths”.

Ditto, line 106-107: these Ce and Pr dimers lie around a crystallographic inversion center, so text should read “… ligands (O41-H41…O33A(symmetry code)) forming centro-symmetric dimers …” .

Ditto, line 113: As for Nd there are no centro-symmetric dimers it should read “… nitrato ligand (O41-H41…O11A(symmetry code)), their … “.

Figure 1: Label for all atoms necessary.

Caption:  Must read “Molecular structure …” and “Anisotropic displacement ellipsoids … “. There are no “thermal” ellipsoids.

Figure 2: wrong oxygen labels – for the Ce and Pr structure shown the O-H…O involved acceptor oxygen atom  is O33, not O11. Add nitrogen labels, too.

We thank the reviewer for pointing these out, the manuscript has been amended as suggested by all points above.

Table S1: Add 2theta max for data collection as well as associated h,k,l ranges. Number of parameters for 1-Nd is only 392 (397 for others), why?

We thank the reviewer for bringing these omissions to our attention. Table S1 has been updated to include this information. It is not clear why the original refinements gave a different number of parameters for 1-Nd although it appears to have been due to some problem with placing hydrogens. Following their removal and replacement, this structure showed the same number of parameters as the other two.

Reviewer 4 Report

Manuscript ID: molbank-2146197

Authors: Brian A. Chalmers, David B. Cordes, Lauren Bertram, Daniel J. Harraghy, Rachel C. Reid, Iain A. Smellie, Anna E.
Tarcza, Brodie J. Thomson

Title: Heteronuclear Bimetallic Complexes with 3d and 4f Elements

This paper describes the synthesis and characterisation of new 3d-4f heteronuclear bimetallic complexes. The paper provides new experimental data that sustain the purpose of work.

However, there are some improvements/corrections to do:

-           In Introduction the information regarding 3d-4f dinuclear complexes are scarce (only one sentence) and the references mentioned are old. This domain of coordination chemistry is very interesting, a lot of paper were published in the last years, even some reviews. This part should be revised.

-           In Synthesis and Characterisation caption, the UV-Vis part, there is no assignment for the complexes visible bands (page 2, row 60).

-           In Materials and Methods caption (page 6, rows 165-166) only the first three IR bands were assignated. Please complete the assignments.

Author Response

We thank you kindly for your response and your suggestions for our manuscript. Please see our detailed responses to your points below.

In Introduction the information regarding 3d-4f dinuclear complexes are scarce (only one sentence) and the references mentioned are old. This domain of coordination chemistry is very interesting, a lot of paper were published in the last years, even some reviews. This part should be revised.

We have expanded the introduction and discussion sections to reflect other work in this area, including some recent reviews and advances.

In Synthesis and Characterisation caption, the UV-Vis part, there is no assignment for the complexes visible bands (page 2, row 60).

The assignment of the bands in the complexes has been updated based on the literature, and citations included.

In Materials and Methods caption (page 6, rows 165-166) only the first three IR bands were assignated. Please complete the assignments.

The relevant IR bands (C=N, C-O, NO2) etc. have been added in the materials and methods section.

Round 2

Reviewer 3 Report

Review on molbank-2146197 revised version (only crystallographic sections)

Most problems have sufficiently been treated but there are still severe H41-atom refinement problems.

Authors explain the former DFIX parameters with D-H distances known from neutron diffraction experiments – these of course lead to larger values as with neutron diffraction you “see” “real” nuclear-nuclear distances. However, X-rays “see” electron density and especially for H-atoms this one-electron-density is always moved towards the donor atom, so refinements must result in shorter D-H distances and it makes not only no sense to introduce the “neutron distances” but is a fundamental (X-ray)refinement mistake which generates systematic errors. (In discussion you could use “corrected” D-H parameters, but this is not common in X-ray world and has to be pointed out very clearly.)

Thus refinement must! be carried out with commands FREE CU1 O41 and HFIX 147 O41 and not with AFIX 147 0.96 which introduces the wrong neutron diffraction distance. Then correct all D-H and associated H…A geometric parameters.

Some more corrections (still) needed:

For figure 1 all atoms must show labels.

Figure 2, second part: Still wrong labels. Either it shows the Pr-compound (as may be read from the caption), then O11 and Ce labels are wrong (must read O33 and Pr1) or it shows the Nd-compound, then it must read Nd1, not Ce1.

Author Response

Thank you kindly for your response.

Thus refinement must! be carried out with commands FREE CU1 O41 and HFIX 147 O41 and not with AFIX 147 0.96 which introduces the wrong neutron diffraction distance. Then correct all D-H and associated H…A geometric parameters.

Response: The structures have now been refined with the default HFIX/AFIX distance. Associated hydrogen bond parameters have been updated.

We have also amended the figure 2 as suggested. I think there was confusion as Track Changes mode was showing the original and the replaced file.