A Versatile Tripodal Ligand for Sensitizing Lanthanide (Ln^III) Ions and Color Tuning

Round 1

Reviewer 1 Report

The Manuscript describes the synthesis and Photoluminescent study of new Eu, Tb, and Ce complexes with BimOEt3 ligand. The Gd congener was also studied to reveal the excited singlet and triplet energy levels of the ligand. The Manuscript cannon be accepted in its present form and needs major revision:

1. The work suffers from a lack of characterization of the complexes. There is no study of their composition and purity. In fact, only the Y complex was characterized in CDCl₃ by NMR analysis. However, the absorption and emission spectra were registered in more polar solvents (ethanol and 2-methyl-THF) that could break the binding between the lanthanides and the ligand. Thus, it is incorrect to assert that the complexes are 2:1 LnIII-to-ligand ones.
2. PAGE 3, line 90: “This finding indicates that BimOEt3 can selectively bind early (CeIII) and mid (EuIII and TbIII) LnIII ions via its nitrogen and carbonyl groups, respectively.” and related sentences. This is incorrect to draw such a strong conclusion based on IR spectra and XRD data for only one crystal structure. Fig 2b reveals a two-peaked band for the Ce complex; the first peak is close to that for free BimOEt3, while the second – to the Eu and Tb complexes. One could conclude that all the complexes exhibit the same coordination type of BimOEt3, while the Ce sample contains an impurity of free BimOEt3. The NMR spectroscopy analysis for only the Y complex (that could exhibit coordination type in the solution than in the solid state) is also insufficient for drawing strong conclusions. Thus, I would recommend refraining from the conclusion about the metal-dependent coordination nature of the ligand. Otherwise, further study is needed to prove this.
3. The Authors claimed that they performed single crystal X-Ray diffraction study for the Ce(III) complex. Please deposit the corresponding cif file to the Cambridge Crystallographic Data Centre (CCDC) (or its analogues) and provide the corresponding CCDC number so that a referee has the opportunity to check the cif file.

 

Some minor points are:

1. PAGE 1, line 10: “The differences in emission quantum yields for the early-lanthanide (CeIII) and the mid-lanthanides (EuIII and TbIII) were attributed to the selective LnIII-coordination of the ligand” In my opinion, the differences are rather due to the different nature of the lanthanides. Please revise the sentence.
2. Please indicate the yield (in grams) of the complexes in the Supporting information.
3. Please indicate concentrations of the complexes in the solutions used for the photoluminescence study.
4. How was the fluorescence spectrum for the Gd complex (Fig. S5) recorded? Please indicate the time range in the Experimental Section. Is the “fluorescence spectrum” just a steady-state spectrum?
5. Fig. 6b: Please indicate the time range for the phosphorescence spectrum of the Ce complex.
6. Supporting Information, ¹H NMR data (P. 2) the number of hydrogen atoms is not a multiple of three in the case of 1.17 - 1.31, 3.82 - 3.96, 3.89, and 4.18 signals. Why? What do these signals correspond to?
7. Please list signals for 13C spectrum of BimOEt3 and for 1H and 13C spectra of the Y complex in the Supporting Information.
8. PAGE 2, line 70 “1→1* and 1*→1” and PAGE 4, line 124 “ф, and lifetimes, , of…” Some symbols are missing.

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 2 Report

This paper describes the syntheses and luminescent properties of lanthanide complexes with tripodal ligand. The findings are interesting. However, the cif file is not attached, although the crystallographic result is reported in this paper. Authors should attach the cif file of the cerium(III) complex and give CCDC number and the experimental procedure of crystallography in the text. Thus, this paper is worth publishing in Chemistry with minor revisions.

Author Response

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Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

The Authors responded to all the points. However, the structural data appeared in the new version of the Manuscript should be revised before publication:

1. Page 2, line 83: “The structures were solved by the intrinsic phasing and least-square refinements using SHELXTL”. According to the cif file, the phrase should be corrected: ”…using ShelXT and ShelXL” (Please note that SHELXTL is a different program of Bruker software).
2. The structure has a lot of level A and B alerts found by the Checkcif routine. Please resolve or explain them in the Manuscript or in the cif file:
3. Many atoms (e.g. C atoms of the ethylate groups and all atoms of triflates) have too high atomic displacement ellipsoid parameters. Probably, it is better to refine them in isotropic approximation.
4. The geometry of some triflates (S1 and S2/S2 ones) and ethyl groups (e.g. C29, C30 one) is doubtful. Please construct meaningful models with reasonable bond distances. Using some constraints and restraints on atomic distances should solve this problem.
5. The refinement seems to be unstable (absolute value of the parameter shift to su ratio of 3.098). This may be resolved after considering the above problems, but the Authors should ensure the small shift.
6. Some hydrogen atoms are missing resulting in the wrong chemical formula in the cif file. Please carefully place H atoms.
7. The structure contains large voids of 291 ų. Please resolve this problem (better to use Solvent Mask Procedure)

One minor point is:

Supporting Information, Page 3: Does the yield exactly amount to 45.0 mg for each compound? Please indicate the yield for each compound.

Author Response

Please see the attachment.

Author Response File: Author Response.pdf