Synthesis, Spectral Characterization, and Structural Modelling of Di- and Trinuclear Iron(III) Monensinates with Different Bridging Patterns
, Alia Tadjer 1, Svetlana Simova 2, Zara Cherkezova-Zheleva 3, Daniela Paneva 3, Radostina Stoyanova 4, Rositsa Kukeva 4, Petar Dorkov 5 and Ivayla Pantcheva 1,*Round 1
Reviewer 1 Report
Comments and Suggestions for AuthorsThis article describes the synthesis and characterization (IR, ESR, NMR, Mossbauer and EA) of two new iron complexes of an antibiotic. Computational and antibacterial aspects were also investigated. Complex 1 is described as a dinuclear species and complex 2 as a trinuclear one.
Since the complexes are non crystalline the spectral studies and literature behavior of structurally characterized related complexes are crucial in making structural inferences. Computational work may provide a basis for favoring one proposed structure from it alternatives.
The ligand employed, Mon-, has a carboxylate and a hydroxyl group. The former could be bidentate possibly bridging) and the latter is monodentate but possibly bridging as well. In addition the ligand can bind through both the carboxylate and the hydroxyl.
The manuscript needs some improvements before publication.
The authors should provide a sketch of all of the possible modes of binding of the ligand (similar to Fig 5 and 6) in the introduction and indicate which modes have been observed in their work or in examples from the literature for this or related ligands.
The authors should state in the introduction that the ligand provides only O donor atoms which suggests that the iron complexes would be high spin. Provide reference(s) to the spin state of other iron complexes of this or similar ligands that provide the same donor set.
P7 line 252. What is the 6th ligand of 1a? or is 1a a five coordinate species?
P7 formulation of complex 2 is 3 Fe(III) with 6 Mon- (-6), an oxide (-2) and a hydroxide (-1). The structure proposed in fig 6 has 2 waters and one hydroxide all three arranged in a symmetric manner. There is a known structure of a mixed valence Fe(II)/Fe(III) structure that is very close to Fig 6.
Fe(II) Fe(III)2(O)(OAc)6(H2O)3. Why is a mixed valence formulation rued out? The synthetic procedure used an iron(II) salt which could have undergone only partial oxidation. Can 2 be made from an iron(III) salt? If all of the iron atoms are iron(III) then it should be possible to make 2 from an iron(III) salt.
On page 9, line 298, the LS state is described as ST =0 in complex 1. There are two problems here: a) LS iron(III) is not possible with these donor atoms and b) and even if a low spin S=1/2 were possible ST = ½ + ½ =1. Similar concern for section 2.3.2. It is important to distinguish the spin state of an iron atom (with these ligands only HS seems possible) from the resultant spin of the whole under ferro- or antiferromagnetic coupling.
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Reviewer 2 Report
Comments and Suggestions for AuthorsThis manuscript by Petkov, Pantcheva and co-workers describes the synthesis of di- and trinuclear iron(III) complexes suported by monensinate ligands with different coordination patterns. The composition and structure of the two new compounds were established based on EA, IR, EPR, NMR, Mossbauer, and TG-DTA/MS techniques. The experimental methods were supplemented by molecular modelling (DFT calculations). It is a pity that the authors could not performe single crystal X-ray diffraction analysis to unambigously confirm the molecular structure of their complexes. In addition, the antibacterial activity of the two Fe(III) derivatives were investigated.
The present work is competently carried out, and the manuscript is well-written up, presented and organized. Overall, the matter contained in this manuscript deserves publication in Inorganics after addressing the issues listed below.
The elemental analysis of complex 1 is good and fits well with the expected composition. So, it is difficult to believe in a contamination with ca. 10 % of a mononuclear species. What about an equilibrium [FeCl(Mon)2]2 vs. 2 [FeCl(Mon)2] ?
Why the antiferromagnetic coupling values wher not determined using SQUID measurement for instance ?
The most intriguing part of this manuscript is the «diamagnetic» NMR spectrum of paramagnetic complex 1 containing high-spin Fe(III) ions ! This is completely unexpected for an esr-active compound. At which temperature have been obtained the NMR data reported in Table S1 ? Have the authors carried out VT NMR ?
The second sentence of the conclusion is confusing. It is not only because of the different oxidation states of the iron ions that the formed compounds are different. The experimental protocole used to prepare them is also completely different. This sentence must be rewritten.
Minor issues in the reference section:
[12] 3051 instead of 33051
[13] macrocylic should be macrocyclic
[23] Commun. Instead of Ccmm.
[24] M.; instead of M.,
[43] Chem. instead of Chemistry
SI:
«Synthesis,» is lacking in the title.
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Round 2
Reviewer 1 Report
Comments and Suggestions for AuthorsThe inclusion of Scheme S1 was useful.
In lines 347-348 you specify the % of AFM Sx to the spin state population.
what is the balance attributed to? HS ST= 15/2?
Why are the LS St=3/2 and AFMDb ( St=1/2) included? How can Fe(III) be LS with an all "O" donor set?
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