The Role of Methyl Substitution in Spin Crossover of Fe(III) Complexes with Pentadentate Schiff Base Ligands

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The authors present in this paper the use of a pentadentate chelating ligand containing a secondary bridgehead nitrogen atom and its chemically modified form in which a methyl group has been bonded to the central nitrogen atom. It was shown that complexes based on secondary amines exhibit thermally induced spin crossover whereas the one based on methyl derivatives remain in HS form down to 2 K. Theoretical considerations showed that Fe-N distances in HS complexes are slightly longer which remains in general agreement with results of magnetic studies.

In my opinion the manuscrict can be considerated for publication in “Inorganics”. I have a several comments.

1.      1. The term “spin crossover” describes the ability to change the spin state, while "spin equilibrium" rather refers to the occurrence of an equilibrium state, e.g. at a specific location (temperature, pressure) of the curve describing the temperature or pressure dependence. The authors use the term "spin equilibrium" to emphasize the absence of cooperative effects. I am not convinced that such extremely mild spin transitions are not the result of anticooperative effects. Therefore, it seems to me that distinguishing "spin crossover" from "spin equilibrium" in this particular case can not be justified.

2.      2. It seems to me that the term "ligand driven" is misleading and should not be used. "Ligand driven" rather means structural changes of the ligand forced by an external stimulus (e.g. light) involving a change in the spin crossover properties. In the case of the ligands used by the authors, we do not deal with such a dynamic phenomenon.

3.      3. The authors note that “The only exception to the purely HS behavior in the 1b-4b compounds (magnetic data are depicted in Supplementary, Fig.S1-S3) was 2b, in which a very gradual decrease of ueff/uB began at 130K upon further cooling (down to 5.7 uB at 15K, Fig.3).” In my opinion, a figure in the format of molar fraction of HS form versus temperature or product of molar susceptibility and temperature versus temperature may be more useful. The authors should include such figures in the SI file.

4.      4. For compound 2a (symbols are too small) there is some anomaly at 50 K. Is this related to the presence of oxygen?

Author Response

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Reviewer 2 Report

Comments and Suggestions for Authors

The Manuscript by Nemec et al., on "Ligand driven spin crossover and spin equilibrium in a series 2 of Fe(III) complexes with pentadentate Schiff base ligands" shows a series of Fe(III) complexes with their synthesis, structural characterizations,  theoretical calculations and magnetic measurements. The work looks really tedious, however the manuscript needs to be majorly revised and address the following comments for taking into consideration - 

1. The ligand system is a real confusion for the readers. The authors should really find a way to represent the scheme 1. Its not exaggeration to say that it takes more than 15 min to understand the ligand system.

2. According to the description, only 4 crystal structures were obtained. But the experimental (synthesis) part doesn't clarify that and its confusing.

3. If the other crystals were not obtained, how was the structure and composition obtained? Just elemental wouldn't suffice. Any other kind of confirmation for ex, MS ?
Even for the complexes with the crystal structure, PXRD would help to confirm the purity.

4. Line 105 - say having interaction in should promote cooperativity and thus SCO, but it was not found.  Where as the other compounds didn't show interactions but still showed SCO Why?

5. XRD data has Alert B. Authors should address them

6. Figure 1: Colour code and counter ions are missing. mention the temperatures as well as they are not same for all for example its 300 K for 4b and 100 K for 3b.

7. Authors mentioned that Magnetization data was measured, but was not included in the MS or SI. Authors should it include it.

* Table S1A and B has errors to be fixed -  like abs. coefficients and wavelength. Please fix them. MW of 4b aswell

*Line 228 - why prime on chi in formula ?

(I'm not an expert on theoretical calculation to comment on)

Author Response

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Round 2

Reviewer 2 Report

Comments and Suggestions for Authors

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Comments for author File: Comments.pdf

Author Response

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