Copper(II) Carboxylates with 2,3,4-Trimethoxybenzoate and 2,4,6-Trimethoxybenzoate: Dinuclear Cu(II) Cluster and µ-Aqua-Bridged Cu(II) Chain Molecule

Round 1

Reviewer 1 Report

The Ms submitted by Dr. M. Mikuriya reports the synthesis and structural characterization of two the complexes [Cu2(234-tmbz)₄(H₂O)₂] (6) and [Cu(246-tmbz)₂(H₂O)₄] (7), which were derived from the carboxylic acids 2,3,4-trimethoxy- (234tmbz) and 2,4,6-trimethoxy-benzoic acid (H246tmbz), respectively. The former compound was a dinuclear with the acid bridging two Cu²⁺ ion simultaneously, typically as in the classical example of Cu(II) acetate, with strong antiferromagnetic coupling, whereas compound 7 was a polynuclear with H₂O are doubly bridging the Cu²⁺ ions and this complex reveals weak antiferromagnetic behavior. Obviously, this is continuation of previous work of Prof. Mikuriya in this field. The characterization of the compounds was done in very well and results were nicely presented.  However, I must indicate to the following points:

1)  I would recommend addressing complex 7 as a polynuclear, [Cu(246-tmbz)₂(H₂O)₄]_n or catena-[Cu(246-tmbz)₂(H₂O)₄] instead of a mononuclear as it was indicated in the abstract and in some parts of the Ms as this is more accurate way to describe the structure of the complex, in addition showing the bridging bonding for the H₂O: [Cu(246-tmbz)₂(µ-H₂O)₂(H₂O)₄]_n . This formula will attract the eyes to the compound because there are not too many examples where H₂O is acting as a bridging ligand.

2) Figure 4 for ORTEP view of [Cu2(234tmbz)4(CH3OH)₂] (6) is wrong and it should be for [Cu2(234-tmbz)₄(H₂O)₂] (6). This happens when cut/paste is used! Please correct. Also, in Fig. 7, I would suggest using a better drawing for the Fragment of the polynuclear chain molecule in 7, with emphasize on the bridging H₂ 

3) Another point which I must address is the large amounts of self-citations, at least 35 references out of 58 (60%) is too much and accordingly some of these references (at least half) should be deleted.

4) I would like to suggest the authors to give an interpretation in the conclusion for the different behavior of the two complexes and in relation to other trimethoxybenzoic acids.

Comments for author File: Comments.docx

Author Response

Author’s Reply to the Review Reports

Referee 1

The Ms submitted by····.  The characterization of the compounds was done in very well and results were nicely presented.  However, I must indicate to the following points:

Thank you very much for understanding our work.

1. I would recommend addressing complex 7 as a polynuclear, [Cu(246-tmbz)₂(H₂O)₄]_n or catena-[Cu(246-tmbz)₂(H₂O)₄] instead of a mononuclear as it was indicated in the abstract and in some parts of the Ms as this is more accurate way to describe the structure of the complex, in addition showing the bridging bonding for the H₂O: [Cu(246-tmbz)(µ-H₂O)₂(H₂O)₄]_n. This formula will attract the eyes to the compound because there are not too many examples where H₂O is acting as a bridging ligand.

We agree with this opinion.  Therefore, we changed the description about the complex 7 to [Cu(246-tmbz)(µ-H₂O)₂(H₂O)₂]_n. The description for the ligand 246-tmbz is better than 246tmbz.  So, we changed the ligand description to 246-tmbz or 234-tmbz.

2. Figure 4 for ORTEP view of [Cu2(234tmbz)4(CH3OH)2] (6) is wrong and it should be for [Cu2(234-tmbz)₄(H₂O)₂] (6). This happens when cut/paste is used!  Please correct.  Also, in Fig. 7, I would suggest using a better drawing for the Fragment of the polynuclear chain molecule in 7, with emphasize on the bridging H₂.

Our description was unclear for the formula of the crystals of 6, misleading the comment, although the description in Figure 4 caption is not wrong.  The difference came from the recrystallization solvent.  So, we added the comments on this difference using 6’ for the crystals of 6 in the crystal structure description in section 2.4 and the experimental part in section 4.

As for Fig. 7, we revised the figure to show the H₂O-bridgings in clear using pale blue for H atoms and using better view.  In line with this, we revised Figure 5 also.

3. Another point which I must address is the large amounts of self-citations. At least 35 references out of 58 (60%) is too much and accordingly some of these references (at least half) should be deleted.

I am sorry for such too much self-citations.  According to the suggestion, we deleted references, 12-15,17-22, 24, 25, 27, 28, 34, 36, 37, and 50.  The revised manuscript became smart.  Thank you.

4. I would like to suggest the authors to give an interpretation in the conclusion for the different behavior of the two complexes and in relation to other trimethoxybenzoic acids.

According to the suggestion, we rewrote the description in the conclusion.

Reviewer 2 Report

This is a fine work performed with due care and firm grip of the methods employed. My only notice pertains to the lack of mentioning that both molecular units adopt perfect (i.e. crystallographic) twofold rotor symmetries. For non-crystallographer readers this may not be apparent. (The both Z = 4 values are only informative for those who know that in space group 15 the general positions value is 8.)

So it would have been nice to mention this explicitly e.g. in the Figs. 4 and 6 legends at least (where the symmetry relations are clearly and righteously described). Moreover explicit mentioning of the molecular subunit symmetries also aids in interpreting spectral and magnetic properties as well.

Author Response

Author’s Reply to the Review Reports

Referee 2

This is a ····.  My only notice pertains to the lack of mentioning that both molecular units adopt perfect (i.e. crystallographic) twofold rotor symmetries.  For non-crystallographer readers this may not be apparent. (The both Z = 4 values are only informative for ···.)

So it would have been nice to mention this explicitly e.g. in the Figs. 4 and 6 legends at least (where the symmetry relations are clearly and righteously described).  Moreover explicit mentioning of the molecular subunit symmetries also aids in interpreting spectral and magnetic properties as well.

Thank you very much for understanding our work.  We revised the structural description in section 2.4 according to the suggestion, showing the crystallographic inversion center and C₂ axis.

Reviewer 3 Report

The main focus of the manuscript by Mikuriya and co-workers is the synthesis of a new Cu(II) paddlewheel complex and of a new one dimensional Cu(II) coordination polymer and the characterization of their magnetic properties through magnetic susceptibility measurements.

I recommend publication in Magnetochemistry after the following comments and corrections have been thoroughly addressed and implemented in the manuscript.

I recommend the following changes:

• acetato at line 34 should be spelled acetate
• At line 35 …, which interact between each other by ..
• At line 79 … as a carboxylate ligand
• At line 127 carboxylato should be spelled carboxylate
• At line 131 ‘crystal water molecules’ should be written as ‘crystallization water molecules’ or ‘water molecules of crystallization’.
• At line 128 and 166 I suggest replacing 2.4 with section4
• At line 168 …was performed for complexes 6 and 7.
• At line 170 present complexes should become presented complexes
• At line 171 system should be replaced by the term lattice
• At line 172 change ‘that of the reported one for’ with ‘that of the one reported for’
• At line 174 carboxylato should be written as carboxylate
• At line 176 carboxylato should be written as carboxylate
• At line 180 ‘toward to the’ should become ‘toward the’
• At line 322 carboxylato should be deleted to leave ‘..of the benzoate moieties..’

The authors should state more explicitly the scope of their study in the introduction.

In the introduction at line 77 the statement ‘exploring a new aspect of these compounds’ should be explain or postponed to ca. line 89 after the magnetic fastener effect has been introduced.

When discussing in the manuscript the Cu-Cu distance in paddle-wheel structure and the distortion of Cu from the planar arrangement I recommend discussing and citing J. Phys. Chem. C 2017, 121, 44, 24853–24860 (DOI: https://doi.org/10.1021/acs.jpcc.7b07792) and J. Am. Chem. Soc. 2019, 141, 23, 9382–9390 (DOI: https://doi.org/10.1021/jacs.9b03643), where in particular in the latter the Cu-Cu paddle wheel distance and its dependence from the L2 apical coordination is characterized and analysed in detail. The distortion from the planar arrangement is understood to be due to electrostatic attraction between Cu2+ and apical ligand’s dipole moment (also the coordination of apical ligands weakens the Cu—Cu interaction which becomes indeed longer upon apical coordination: ..’’the polarization induced by the apical ligand induces charge accumulation in the M−M region, but this excess of electron density cannot contribute to strengthen the M−M interaction because it implies further accumulation in dz2 orbitals, which destabilizes even more the M−M bond’’ as quoted from J. Am. Chem. Soc. 2019, 141, 23, 9382–9390) i.e. trans effect rather than due to packing effects.

In Table 1 the values of r_int should be reported to give an idea of the crystal and data quality.

Complex 6 has no inversion centre at the Cu(II) ion, in addition is coordinated  by two different ligand species therefore the Jahn-teller theorem does not apply directly, the authors should instead talk about pseudo Jahn-Teller effect, also known as second order Jahn Teller effect. At line 182 ‘from the Jahn-Teller effect’ should be substituted by ‘from the pseudo Jahn-Teller effect’ Also at line 127, the authors should use pseudo Jahn-Teller effect because also in complex 7 there are two different ligand species.

To improve the fitting showed in blue in figure 8 the author should attempt to consider the magnetic interaction between paddlewheels with mean field correction:

Chi(mean field) = chi/(1-gamma.chi) where gamma= z.J’/(g^2.muB^2.N_A)

where z is the number of first neighbours paddle wheel (2 in complex 6).

The decrease of the antiferromagnetic coupling between Cu(II) within the paddle wheel depends on the ligand species coordinated at the apical paddle wheel positions (see Journal of Solid State Chemistry 253 (2017) 1–52 https://doi.org/10.1016/j.jssc.2017.05.023 and Journal of Applied Physics 87, 6007 (2000); https://doi.org/10.1063/1.372595). Also consider and discuss as motivation the effect of the Cu-Cu weakening and -COO geometry distortion, again due to the apical coordination, as discussed in J. Am. Chem. Soc. 2019, 141, 23, 9382–9390.

In Figure 8 and 9 the x axis should match the colour of the respective data plotted for sake of clarity.

The authors should comment on the possible magnetic superexchange pathways in 7 and on the reason as to why the magnetic interaction is weak (expected given that the magnetic orbitals lie in the equatorial plane). Could the superexchange involve the carboxylate groups e.g. Cu—O-C-O…HOH..O-C-O—Cu? In fact, the spin density is localized on the equatorial plane involving the oxygen of the carboxylate ligands. Is there a H-bond between carboxylate groups and water molecules that could define a superexchange pathway? This possibility should also be considered and discussed in the text.

Could the /Display/Voids in Mercury software help to determine the degree of porosity in complex 6?

In section 4 ‘Materials and Methods’ information on the kind (single crystal or polycrystalline powder) and on the mass of the samples used for the SQUID should be included. Moreover, if the purity of the polycrystalline powder was verified it should be mentioned.

Author Response

Author’s Reply to the Review Reports

Referee 3

The main focus of the manuscript by ··· I recommend publication in Magnetochemitsry after the following comments and corrections have been thoroughly addressed and implemented in the manuscript.

Thank you very much for understanding our work.

I recommend the following changes:

Acetate at line 34 should be spelled acetate

At line 35 ..., which interact between each other by ..

At line 79…as a carboxylate ligand

At line 127 carboxylato should be spelled carboxylate

At line 131 ‘crystal water molecules’ should be written as ‘crystallization water molecules’ or ‘water molecules of crystallization’.

At line 128 and 166 I suggest replacing 2.4 with section 4

At line 168…was performed for complexes 6 and 7.

At line 170 present complexes should become presented complexes

At line 171 system should be replaced by the term lattice

At line 172 change ‘that of the reported one for‘ with ‘that of the one reported for’

At line 174 carboxylato should be written as carboxylate

At line 176 carboxylato should be written as carboxylate

At line 180 ‘toward to the’ should become ‘toward the’

At line 322 carboxylato should be deleted to leave‘..of the benzoate moieties..’

First, I would like to thank for pointing out many improper description.  Most of these were occurred by the use of Nomenclature of Inorganic Chemistry: IUPAC Recommendations 2005, which recommends to use ‘acetato’ in place of ‘acetate’ for the ligand, for example.  But, the referee’s pointing out should be normal.  So, we corrected these according to the referee’s suggestion.

The authors should state more explicitly the scope of their study in the introduction.

In the introduction at line 77 the statement ‘exploring a new aspect of these compounds’ should be explain or postponed to ca. line 89 after the magnetic fastener effect has been introduced.

According to this suggestion, we added more description and changed the statement.

When discussing in the manuscript the Cu-Cu distance in paddle-wheel structure and the distortion of Cu from the planar arrangement I recommend discussing and citing J. Phys. Chem. C2017, 121, 44, 24853-24860 (DOI: https://doi.org/10.1021/acs.jpcc.7b07792) and J. Am. Chem. Soc. 2019, 141, 23, 9382-9390 (DOI: https://doi.org/10.1021/jacs.9b03643), where in particular in the latter the Cu-Cu paddle wheel distance and its dependence from the L2 apical coordination is characterized and analysed in detail.  The distortion from the planar arrangement is understood to be due to electrostatic attraction between Cu2+ and apical ligand’s dipole moment (also the coordination of apical ligands weakens the Cu-Cu interaction which becomes indeed longer upon apical coordination: ..”the polarization induced by the apical ligand induces charge accumulation in the M-M region, but this excess of electron density cannot contribute to strengthen the M-M interaction because it implies further accumulation in dz2 orbitals, which destabilizes even more the M-M bond” as quoted from J. Am. Chem. Soc. 2019, 141, 23, 9382-9390) i.e. trans effect rather than due to packing effects.

Thank you for valuable information.  According to the suggestion, we added this information.

In Table 1 the values of r_int should be reported to give an idea of the crystal and data quality.

According to the suggestion, we added the R_int values in Table 1.

Complex 6 has no inversion centre at the Cu(II) ion, in addition is coordinated by two different ligand species therefore the Jahn-teller theorem does not apply directly, the authors should instead talk about pseudo Jahn-Teller effect, also known as second order Jahn Teller effect.  At line 182, ‘from the Jahn-Teller effect’ should be substituted by ‘from the pseudo Jahn-Teller effect’ Also at line 127, the authors should use pseudo Jahn-Teller effect because also in complex 7there are two different ligand species.

Thank you for the point.  We agree with this and changed our description as suggested.

To improve the fitting showed in blue in figure 8 the author should attempt to consider the magnetic interaction between paddlewheels with mean field correction:

Chi(mean field) = chi/(1-gamma.chi) where gamma=z.J’/(g².muB².N_A)

where z is the number of first neighbors paddle wheel (2 in complex 6).

According to the suggestion, we performed the fitting with the mean field consideration and put the result in the text.  Therefore we used c_M in place of c_A for 6.

The decrease of the antiferromagnetic coupling between Cu(II) within the paddlewheel depends on the ligand species coordinated at the apical paddle wheel positions (see Journal of Solid State Chemistry 253 (2017) 1-52 (https://doi.prg/10/1016/j.jssc.2017.05.023 and Journal of Applied Physics 87, 6007 (2000): https://doi.org/10.1063/1.372595 ). Also consider and discuss as motivation the effect of the Cu-Cu weakening and –COO geometry distortion, again due to the apical coordination, as discussed in J. Am. Chem. Soc. 2019, 141, 23, 9382-9390.

Thank you for another point of view for discussion of the magnetic interaction. We added some comments concerning this.

In Figure 8 and 9 the x axis should match the colour of the respective data plotted for sake of clarity

In order to clarify the Figures, we plotted the experimental data as rhombuses.

The authors should comment on the possible magnetic superexchange pathways in 7 and on the reason as to why the magnetic interaction is weak (expected given that the magnetic orbitals lie in the equatorial plane).  Could the superexchange involve the carboxylate groups e.g. Cu—O-C-O…HOH…O-C-O—Cu? In fact, the spin density is localized on the equatorial plane involving the oxygen of the carboxylate ligands.  Is there a H-bond between carboxylate groups and water molecules that could define a superexchange pathway? This possibility should also be considered and discussed in the text.

Thank you very much for valuable suggestion.  We revised this part according to the suggestion.

Could the /Display/Voids in Mercury software help to determine the degree of porosity in complex 6?

According to the suggestion, we revised Figure 11.

In section 4 ‘Materials and Methods’ information on the kind (single crystal or polycrystalline powder) and on the mass of the samples used for the SQUID should be included.  Moreover, if the purity of the polycrystalline powder was verified it should be mentioned.

As for the magnetic measurement, we added some comments according to the suggestion.

Round 2

Reviewer 1 Report

The Ms is fine and accepted in the present form.

Author Response

Thank you very much for understanding our work.  During the correction process, we found an small error “63.35(9)°” at line 316 in the revised manuscript and corrected this to “64.0(2)°” in the 2^nd revised manuscript”.

Reviewer 3 Report

At line 126 only ref 29 should be cited.

Author Response

Thank you very much for pointing out this.  We corrected the citing. During the correction process, we found an small error “63.35(9)°” at line 316 in the revised manuscript and also corrected this to “64.0(2)°” in the 2^nd revised manuscript”.

Thank you very much.