Enhancing Intramolecular Chalcogen Interactions in 1-Hydroxy-8-YH

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Enhancing Intramolecular Chalcogen Interactions in 1-Hydroxy-8-YH-Naphthalenes Derivatives Goar Sánchez-Sanz, Cristina Trujillo, Ibon Alkorta, and José Elguero J. Phys. Chem. A, Just Accepted Manuscript • DOI: 10.1021/acs.jpca.7b09678 • Publication Date (Web): 02 Nov 2017 Downloaded from http://pubs.acs.org on November 3, 2017

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The Journal of Physical Chemistry

Enhancing Intramolecular Chalcogen Interactions In 1-hydroxy-8YH-Naphthalene Derivatives Goar Sánchez–Sanz,a* Cristina Trujillo,b Ibon Alkorta,c José Elgueroc a

Irish Centre of High-End Computing, Grand Canal Quay, Dublin 2, Ireland & School

of Chemistry, University College Dublin, Belfield, Dublin 4, Ireland b

School of Chemistry, Trinity Biomedical Sciences, Trinity College Dublin, 152-160

Pearse Street, Dublin 2, Ireland c

Instituto de Química Médica, CSIC, Juan de la Cierva, 3, E-28006 Madrid, Spain

ABSTRACT: Forty-two peri-substituted naphthalene derivatives presenting chalcogen weak interactions have been studied. They correspond to O···Y interactions, Y being O, S and Se. While the O atom bear H or CH3 substituents (OH and OCH3 groups), the Y atom is substituted by H, F and CN in order to explore the effect of these electrondonating and electron-withdrawing substituents on the chalcogen bond strength. The effect of F and CH3 substituents on positions ortho/para (2,4,5,7 of the naphthalene ring) was also studied. Optimizations were carried out at the MP2/jul-cc-pVDZ and binding energies at the MP2/jul-cc-pVTZ followed by an MP2/CBS estimation. The main properties studied were geometries, energies (Eb, Eiso and Edef), the Molecular Electrostatic Potential (MEP), Electron density shifts and NBO E(2)energies and the relationship between these properties.

1. INTRODUCTION The importance of non-covalent interactions has been highlighted in several publications along the last decades.1 Amongst all the existing non-covalent interactions, hydrogen bonds are the most important since their relevant role on protein folding,2 amino acids stabilization,3 protein-protein interactions4 and other biological roles.5 Nevertheless, other interesting non-covalent interactions, such as halogen bonds,6 chalcogen bonds,7-12 tetrel bonds,13-16 and pnictogen (also called pnicogen)17-19 bonds have been subject of study by numerous groups. Amongst them, chalcogen bonds are one of the less studied, despite the abundance of chalcogen atoms, mainly oxygen and sulfur but also selenium, within biological environments. Mó, Yáñez and Sanz have

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intensively worked on chalcogen bonds, in particular intramolecular ones in different substrates such in β-chalcogeno vinylaldehydes20-21 and their corresponding saturated derivatives.22 The nature of chalcogen bonds have been also investigated amongst others by Iwaoka et al.,23 Shishkin,24 Scheiner,25 Guru Row26 and Mikherdov et al.

27

The

intramolecular interaction of organoselenium derivatives has been thoroughly reviewed by Mukherjee et al.28 We have been working intensively in the description of inter and intramolecular interactions,29 especially on chalcogen9, 30-34 and pnicogen bonds.35-38 In a recent paper, we studied the competition between hydrogen and chalcogen bonds in peri-substituted naphthalene derivatives, finding that chalcogen bonds involving HO···Y-H (Y = O, S and Se) presented positive (repulsive) interactions energies.34 That makes us wonder how we could modify the system in order to enhance those O···Y contacts. The main aim of the present research is to investigate how the intramolecular O···Y interaction can be modulated whether by substituting the H atom on each OH and YH groups or by introducing new substituents on the naphthalene ring. These different approaches are reported in Scheme 1. In the first analysis concerning 1-hydroxy-8-YH-naphthalene derivatives, substitution on the OH and YH groups would be considered, introducing methyl groups on the O side and electronwithdrawing groups, fluorine and cyano, on the Y side. For those compounds, the nomenclature will be OXYZ, where O is the electron donor, Y the electron acceptor (Y = O, S, and Se) and X refers to the substituents on the O side (X = H and CH3) and Z to the ones on the Y side (Z = H, F and CN). In a second approach, 1-hydroxy-8-YHnaphthalene derivatives R,R' disubstituted at positions ortho (2,7), para (4,5) and ortho/para (2,5 and 4,7) were studied. In those cases the nomenclature used is aROHbR'YH in which R and R' denotes the substituents in the ring (F or CH3) in the O and Y parts, respectively, and a or b indicates whether the substituents are in ortho (o) or para (p) positions. For example, oMeOHpFSH corresponds to a substitution of a methyl group on ortho position (2) on the oxygen (donor) ringside and a fluoro substitution on the para position (5) of the sulfur (acceptor) ring. Scheme 1. Schematic description of the systems considered: a) OXYZ system. X and Z' correspond to the direct substitution on the O or Y groups. b) aROHbR'YH systems: R and R' correspond to groups substituted on the naphthalene rings both in o (ortho) or p (para) position with respect to their respective OH or YH groups.


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2. COMPUTATIONAL DETAILS The structures of the systems were optimized at the MP239/aug-cc-pVDZ.40-41 Harmonic vibrational frequencies were computed at the same level used for the geometry optimizations in order to classify the stationary points as local minima with no imaginary frequencies. Single point MP2/aug-cc-pVTZ calculations were performed over the optimized geometries to obtain more accurate energies. Furthermore, the binding energies were also estimated at the MP2/CBS (complete basis set) limit using the method of Helgaker et al.42-43 from the calculated interaction energies with the julcc-pVDZ (X = 2) and jul-cc-pVTZ (X = 3) basis sets using α = 1.43 as defined in the literature:

∝ = EHF CBS +A

(1)

= EMP2 CBS +B

(2)

Calculations were performed using the Gaussian09 program.44 The interaction energy between the interacting groups has been obtained through the isodesmic reactions shown in Scheme 2 in two different ways: a) keeping the resulting fragment fixed in the optimized geometry of the XO···YZ system, in which the group OX and YZ have been substituted by a hydrogen atom located in the same bond axis than the O, S and Se atom with a C-H distance of 1.1 Å (Eb), and b) optimizing the geometry of the isolated fragments (Eiso). The differences between both quantities correspond to the deformation energy, in other words, to the penalty or re-organization energy, Edef. Scheme 2. Isodesmic reactions used to obtain the interaction energies.



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The Quantum Theory of Atoms in Molecules (QTAIM) methodology45-46 was used to analyze the electron density of the systems with the AIMAll program.47 The Natural Bond Orbital (NBO) method48 has been employed to evaluate atomic charges using the NBO-6 program, and to analyze charge-transfer interactions between occupied and unoccupied orbitals. The intramolecular Electron Density Shift (EDS) has been obtained using the fragmentation scheme reported in ref.29 This method proposes the calculation of the EDS of the intramolecular interaction by comparing the electron density of the interacting moieties substituted by hydrogen atoms as shown in Scheme 2. The EDS is calculated using Eq. 1

EDS = ρ(XO···YZ) – ρ(XO) – ρ(YZ) + ρ(HH) 4 Environment ACS Paragon Plus

Eq. 1

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Finally, the DFT-D3 program49 has been used to evaluate the dispersion interactions within the atoms involved in the chalcogen contact with B3LYP functional and BJ damping.50

3. Results and Discussion 3.1 Structure and energy 3.1.1 Energy benchmark The evolution of the interaction energy, Eb, and isodesmic energy, Eiso, in the XO-YZ systems with the size of the basis set has been investigated. For such purposes, Eb and Eiso values have been computed at the MP2/aug-cc-pVDZ, MP2/aug-cc-pVTZ and MP2/CBS. As observed in Table S1, values are very stable across the basis sets with no important variations. In spite that MP2/CBS values will be used from now on in the manuscript, is noteworthy that the observed differences between methods indicate that even at the lowest computed level, MP2/aug-cc-pVDZ, the interaction energy values obtained produce reliable results without paying the computational costs of larger basis sets.

3.1.2 Enhancing of O···Y interactions: σ-hole modulation As stated in the introduction, substitutions of the H atoms in HO and YH groups by different substituents (F, CN and CH3) have been carried out. The selection of the substituting groups is delicate and comprises a good balance between the electron withdrawing (donating) capacity, the size and symmetry of the group considered. Following our experience, F and CN groups present good electron withdrawing capacities, are small and very symmetric. Similar occurs with CH3 group as an electron donor. Furthermore, those groups reduce considerably the number of conformers to study. A total of 18 compounds have been generated, 6 by each O···Y possible pair, O···O, O···S and O···Se. Molecular graphs and Cartesian coordinates have been gathered in Figure S1 and intramolecular O···Y distances summarized in Table 1. As observed in all cases the systems present Cs symmetry. The intramolecular distances obtained between 2.444 to 2.574 Å, 2.451 to 2.703 Å, and 2.436 to 2.734 Å for O···O, O···S and O···Se interactions are shorter than the sum of the van der Waals radii of the atoms involved (vdWOO = 3.04 Å, vdWOS = 3.32 Å, and vdWOSe = 3.42 5 Environment ACS Paragon Plus


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Å).51 The range observed for O···O interactions is notably shorter than for O···S and O···Se. In OXOZ compounds the substitution of the H atom in Z position by an electronwithdrawing group (CN or F) decreases the intramolecular O···O distance by 0.033 and 0.099 Å, respectively. Similar substitution but by an electron-donating group (Z = CH3) also reduces the O···O distance but only 0.023 Å with respect to the OHOH compound. Taking into account two simultaneous substitutions lead to even shorter distances, reaching the minimum distance in OMeOF (2.444 Å). Similar evolution pattern, but more dramatic shortening are observed when more polarizable atoms, S and Se, are involved in the interaction. Intramolecular O···S and O···Se present decreases up to 0.252 and 0.298 Å in OMeYF with respect to their parent compounds. This shortening will be explained below in terms of the molecular electrostatic potential (MEP). Additional structural data, C-O···Y and O···Y-C angles, have been analyzed (Table 1). As a general feature, angles in the donor site (C-O···Y) are wider than in the acceptor site (O···Y-C). In almost all the compounds, both angles become wider compared with the OHYH compound, with the exception of OMeYH in which O···Y-C angle is slightly narrower than the corresponding parent compound. It is worth mentioning that in all the cases studied, the dihedral angle formed by C-O···Y-C is 0º indicating that both interacting atoms and its respective substituent groups are contained within the molecular plane defined by the naphthalene rings. It is worth noting that in case of sulfur derivatives, we have evaluated the addition of tight-d functions on the sulfur atoms to evaluate whether those functions have any impact on the optimized geometry. For such purpose, OHSF, OHSCN, OMeSH, OMeSF and OMeSCN have been re-optimized at the MP2/aug-cc-pV(D+d)Z level.51,52 The data obtained (Table S2) shows that the intramolecular O···S distances do not present large variations with respect to the MP2/aug-cc-pVDZ level. C-O···Y angles and C-Y···O angles are even less sensitive to the tight-d functions so is spite that tight-d function can impact on the geometry, in this particular case with very rigid systems, their influence is very limited. Table 1. O···Y distances (in Å) and C-O···Y and C-Y···O angles, in º, for all the OXYZ compounds at the MP2/aug-cc-pVDZ computational level. H

H

O O OHOCN

O···Y 2.574 2.541

C-O···Y 89.3 90.0

C-Y···O 89.3 90.2


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OHOF OMeOH OMeOCN OMeOF OHSH OHSCN OHSF OMeSH OMeSCN OMeSF OHSeH OHSeCN OHSeF OMeSeH OMeSeCN OMeSeF

2.475 2.551 2.521 2.444 2.703 2.637 2.522 2.660 2.594 2.451 2.734 2.646 2.500 2.687 2.594 2.436

90.6 91.3 91.8 92.6 99.5 100.4 103.5 101.8 102.6 105.9 102.7 104.1 106.8 104.9 106.3 109.5

92.3 88.6 89.5 91.7 76.7 78.2 78.3 76.2 77.9 78.5 73.5 75.1 75.9 73.3 75.0 75.9

An inspection of the Molecular Electrostatic Potential has been carried out to provide an insight on the intramolecular interaction. Note that the MEP on the intramolecular systems is difficult to interpret since the interacting areas, both electron lone pairs and σ-hole, are usually overlapped by the rest of the structure. In this particular case, an approximation has been used. The MEP on the 0.001 a.u. electron density isosurface for the isolated fragments on their optimized geometry (Scheme 2) has been obtained and their maxima and minima values corresponding to the O donor lone pairs and σ-hole on the acceptor gathered in Table S3. In terms of donors, the MEP minimum value (VS,min) corresponding to the OH and OMe donors show values of –0.037 and –0.044 a.u., which indicate that the latter will be better donor and thus the chalcogen O···Y distance should be shorter as previously observed. On the other hand, the evolution of the depth of the σ-hole on the electron acceptor is as follows: no maximum value (VS,max) was observed for the OH system while OF present very small negative values which show that these systems are poor acceptors in agreement with the polarization and electronegativity of the oxygen atom. When S and Se are considered, the VS,max associated to the σ-hole become more positive with Y = F and CN groups (in agreement with the electron-withdrawing nature of those groups) and more negative with CH3 (electron-donor group). This evolution is also in agreement with the interaction energy variation found for each system. However, in spite of the agreement between both quantities, no fair correlations were found between Eb or Eiso and VS,max



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values. Again, this indicates that there are several other factors which affects the interaction energy and which cannot be purely described as electrostatics or charge transfer. Regarding the interaction energy, the values of Eb are positive in all the OXOZ compounds (Table 2). However, negative values are observes in, OXYF, OMeSCN and OXSeCN derivatives, showing how the size of the Y atom influences the interaction energy, the bigger the atom, the more negative Eb. Considering the influence of the X and Z groups on the binding energy, Eb values become less positive with electronwithdrawing (F and CN) groups (EWG) on position Y due to the increase of the depth in the σ-hole that consequently enhances the O···Y interaction. When an electrondonating group (EDG), i.e. CH3, on position X is considered (OMeYH) there is an increase on the Eb values with respect to the respective parent compound OHYH (in case of OMeSeH both values are almost identical). This indicates that the sole increase of the electron donating ability on the donor side does not favor the interaction energy. However, when both EDG on X and EWG on Z are present, the binding energy decreases, and this decrease is more pronounced as the polarizability of the Y atom increases, reaching Eb its minimum values in the OMeSeF compound. Similar energy evolution was found for Eiso values across the chalcogen atoms. Finally, the deformation energy, Edef, is evaluated. The Edef takes into account any possible out-of-plane deformation upon complexation and also the in-plane deformation due to the attraction between the interacting atoms. In all the cases studied, the chalcogen interaction occurs within the molecular plane, which contains the whole molecule, so out-of-plane deformation does not contribute to Edef. As observed, Edef values are relatively small in all the cases. The maxima values for the deformation energy are found in those systems with F as an electron withdrawer in agreement with the largest variations of the O···Y intramolecular distances and the largest variation of the C-O···Y and O···Y-C angles. But in spite of the variation, values of Edef are relatively constant in all the cases, with a maximum value of 10.9 kJ·mol–1 in OHSeF. It is worth mentioning that selenium derivatives present larger Edef values than in sulfur ones for the OHYZ compounds while it is the other way around for the OMeYZ compounds. One might be tempted to claim that there is a discrepancy between the shortening of the intramolecular O···Y distance with respect to the OHSH compound and the positive values of the interaction energies found in the compounds. While the former clearly indicates the strengthening of the chalcogen bond, the later might give the impression of 8 Environment ACS Paragon Plus

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a non-attractive interaction. In fact, good linear correlations have been found between the intramolecular distance and both Eb and Eiso values for OXSZ and OXSeZ compounds as shown in Figure 1. Table 2. Interaction energies, Eb, Eiso, and deformation energies Edef, (kJ·mol–1) for the OXYZ compounds at MP2/CBS computational level. Y=O Compound Eb

Y=S

Y = Se

Eiso Edef

Eb

Eiso Edef

Eb

Eiso

Edef

OHYH

17.7 23.5 5.7

9.1

14.3 5.2

5.2

12.2

7.0

OHYF

12.5 21.6 9.1

–9.7

–1.9 7.7

–23.4 –12.5 10.9

OHYCN

14.3 19.1 4.8

7.0

14.2 7.2

–3.4

4.2

7.6

OMeYH

19.3 24.9 5.6

3.3

11.2 7.9

1.5

8.2

6.7

Me

F

10.5 20.6 10.1 –19.4 –10.6 8.8

–31.2 –23.0 8.3

Me

CN

13.3 18.9 5.7

–10.2 –2.3

O Y O Y

–2.0

6.5

8.5

7.9

Figure 1. Linear correlations between the O···Y intramolecular distance and Eb and Eiso values. Values on the graphs correspond to the r2 of each regression.



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The dispersion energy (Edisp) between the bulk OX and YZ have been estimated using the DFT-D3 program, with B3LYP functional and BJ damping. Table S4 contains the dispersion between chalcogen atom (on one side) and the substituent groups in the other side, i.e. between O and the Z groups, and between Y and the X ones. Also the dispersion interaction between both, X and Z groups with the naphthalene backbone. As observed, the dispersion term between O and X and between Y and Z is very small (0.20.6 kJ·mol–1). These values are larger with larger Y atoms, particularly in the interaction between Y and the methyl groups. Which is more important is the dispersion interaction between the X or Z groups and the naphthalene backbone that is relatively large (–3.0 to –10.5 kJ·mol–1) in methyl substituted derivatives. The total dispersion energy has been also examined and while a trend across the families is observed (OXOZ > OXSZ > OXSeZ) no acceptable correlations have been found between the Eb and Edisp. Natural bond orbital method has been used to evaluate the orbital interaction within the chalcogen bonds and how it varies with the substituents and the different Y atoms. In Table 3 the second order perturbation energies, E(2)corresponding to the donation from the oxygen lone pair, Olp, into the σ*Y-Z antibonding orbital are gathered. In OXOZ compounds only those fluorinated present a certain E(2), up to 5.6 kJ·mol–1 in OMeYF compound, while in OXYZ compounds (Y = S and Se), E(2)are much greater than in the oxygen derivatives. This is in agreement with the polarization and the depth of the σ-hole shown by MEP. In addition, linear correlations have been found between the Eint and E(2)values (Figure S2). Similar relationships were found in pnicogen derivatives of naphthalene.36 Table 3. Second order perturbation energy, E(2)(kJ·mol–1) corresponding to the donation from the oxygen lone pair into the antibonding orbital σ*Y-Z for OXYZ compounds at the B3LYP/aug-cc-pVDZ computational level. Olp→σ*O-Z

Olp→σ*S-Z

Olp→σ*Se-Z

OHYH

−

10.6

15.3

H

3.5

31.4

47.9 a

OHYCN

−

14.8

26.7

OMeYH

−

16.1

20.4

OMeYF

5.6

53.4

81.9a

O Y

F


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OMeYCN a

−

20.0

32.1

Donation into *Ylp, Y = S and Se

3.2 Ortho and para ring substitutions and the repercussion on the X…Y interaction Another possible modulation of the intramolecular chalcogen bond has also been explored through substitution of H atoms in ortho and para with respect to the corresponding O and Y groups by F and CH3 groups. Simultaneous substitutions in both rings have been considered with all the possible combinations. As stated before, the nomenclature followed is aROHbR'YH, in which a and b denote the ortho (o) or para (p) position on the ring of the substituent with respect to the O and Y respectively. Intramolecular O···Y distances have been gathered in Table 4. In the case of compounds with O···O interactions, oFOHoFOH and pFOHpFOH present an increase on the intramolecular distances with respect to the OHOH compound. On the other hand, both

ortho and para methyl-substituted derivatives show a decrease on the O···O distance. It seems that electron-withdrawing groups (EWG) in ortho and para of the aromatic rings destabilize the interaction while electron-donor groups (EDG) enhance it. When both EDG and EWG are combined, the observed values indicate that compounds with EWG substituted on ortho still present larger distances than the parent compound, no matter where the EDG is located. In the case of aROHbR'YH (Y = S and Se) compounds, the situation is slightly different. Only oFOHoFYH and oMeOHoFYH show larger distances that OHYH while the rest present shorter ones. Again, as it happens with oFOHoFYH compounds, the polarizability of the chalcogen atom acting as electron acceptor plays an important role in the interaction, as expected by the tunability of the σ-hole. As expected the effect on the ring is weaker than the direct substitution on the Y atoms and so the variation of the distances is less pronounced.

Table 4. O···Y distances (in Å) and C-O···Y and C-Y···O angles, in º, for all the

aROHbR'YH compounds at the MP2/aug-cc-pVDZ computational level. O···X C-O···X C-X···O F

H F

H

F

H F

H

oO oO pO pO Me

H Me

o O o O

H

2.595

87.6

87.6

2.829

89.8

89.8

2.563

89.6

89.6



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pMeOHpMeOH

2.499

90.1

90.1

Me

H F

H

2.597

90.3

86.9

Me

H F

H

2.568

89.9

89.1

pMeOHoFOH

2.589

89.9

87.4

o O oO o O pO Me

H F

p O pO

H

2.532

89.8

89.9

F

H F H

2.748

97.0

76.6

F

H F H

2.679

100.1

76.6

oO oS

pO pS oMeOHoMeSH

2.665

99.3

78.3

Me

H Me H

2.638

100.8

76.4

Me

H F H

2.709

99.9

75.9

Me

H F H

2.698

100.0

76.4

Me

H F H

2.702

99.6

76.1

Me

H F H

2.666

100.3

76.6

2.778

100.0

73.7

2.711

103.3

73.4

2.694

102.3

75.1

2.671

104.0

73.2

2.738

102.9

73.0

2.731

103.1

73.3

2.732

102.7

73.2

2.699

103.5

73.4

p O p S o O oS o O pS p O oS

p O pS oFOHoFSeH pFOHpFSeH oMeOHoMeSeH pMeOHpMeSeH oMeOHoFSeH oMeOHpFSeH Me

H F

H

p O o Se pMeOHpFSeH

In terms of the interaction energies, substitutions on the rings decrease neither the binding energy nor the isodesmic energy in any of the cases studied with respect to the parent OHYH compounds (Table5). This fact, in conjunction with the shortening on the intramolecular distances, point to a destabilization due to the steric repulsion between the substituting groups and the Y groups. On the contrary what occurred with the OXYZ compounds, the range of the binding energies are narrower indicating a mild effect of the substituent groups on the chalcogen bond. As happened with the OXYZ compounds, the polarizability of the chalcogen atom acting as electron acceptor determines the decrease on the interaction energy (both Eint and Eiso), but none are lower than the unsubstituted OHYH compound. Finally, the deformation energy is quite stable across the series with very small values, as in OXYZ compounds. As occurred in OXYZ, the chalcogen interaction takes place within the molecular plane that contains the whole molecule, so no out-of-plane deformation is observed. In general, Edef values do not show large variations due to the small structural


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changes are taking place upon interaction. aROHbR'OH compounds present the smallest Edef values, in agreement with the small variations of the intramolecular O···O distances. aROHbR'SH and aROHbR'SeH present very similar values between the corresponding compounds. However, in aROHbR'YH compounds is difficult to separate what part of the Edef corresponds to the contribution from the chalcogen interaction, and the intramolecular distance variation, and what is related to the re-organization of the R and R' groups. This is even more complicated in those compounds with groups in ortho, since they can interact with the H atom of the chalcogen atom. For that reason and as it was done for the OXYZ compounds, the dispersion energy has been estimated in

aROHbR'YH compounds. However, instead to evaluate the bulk interaction between the XO···YZ groups, we focused our attention in the total dispersion energy. The total dispersion energy will provide information on the effect of the rest of the groups on the rings. In Figure 2, Eb versus the Edisp has been plotted. While in OXYZ no correlations between both quantities were found, in aROHbR'YH there is a clear differentiation between aFOHbFYH, aMeOHbMeYH, and aMe(F)OHb

F(Me)

YH families. As observed the

evolution of the series is aFOHbFYH < aMe(F)OHb F(Me)YH < aMeOHbMeYH which indicate that methyl groups interact more with the H and C atoms of the naphthalene backbone than fluorine atoms. Besides, Edisp is greater than in the OHYH parent compound. Assuming that the chalcogen interaction is constant (i.e. that the electronwithdrawing/donating effect of each R (R') groups is much smaller than the chalcogen interaction) the increase (destabilization) of Eb might be due to the increase on the dispersion interaction between the groups and it is expected (as observed in Figure 2) that methyl substituted compound present larger dispersion interactions (between CH3 and the H atom of the naphthalene backbone) and therefore the chalcogen interactions show more positive binding energies.



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Figure 2. Linear correlations between the O···Y Eb and Edisp values for aROHbR'YH compounds. Labels on the data corresponds to substitutions on the orthoR-orthoR (oo), paraR-paraR (pp), paraMe-orthoF (po) and orthoMe-paraF (op) positions. Table 5. Interaction energies, Eb, Eiso, and deformation energies Edef, (kJ·mol–1) for the aROHbR'YH compounds at MP2/CBS computational level. Y=O

Y=S

Y = Se

Compound

Eint

Eiso

Edef

Eint

Eiso

Edef

Eint

Eiso

Edef

OHYH

17.7

23.5

5.7

9.1

14.3

5.2

5.2

12.2

7.0

17.7

21.9

4.2

10.7

16.4

5.8

7.1

13.4

6.3

F

H F

H

F

H F

H

oO oY pO pY

20.1

25.8

5.7

10.5

18.1

7.6

6.2

13.6

7.4

H

o O o Y

18.9

23.7

4.8

12.4

21.0

8.6

8.7

17.8

9.1

pMeOHpMeYH

21.8

29.0

7.2

10.9

20.7

9.8

6.6

15.8

9.1

oMeOHoFYH

18.6

23.2

4.6

10.4

17.8

7.4

7.4

14.5

7.1

oMeOHpFYH

19.2

24.4

5.2

10.1

17.1

7.0

6.0

13.1

7.1

pMeOHoFYH

18.3

23.4

5.1

10.7

18.3

7.6

7.3

15.0

7.7

pMeOHpFYH

20.5

26.7

6.3

10.7

19.7

9.0

6.2

14.6

8.4

Me

H Me


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Values of the E(2)provided by NBO analysis (Table 6) show that donations from the Olp into the σ*Y-H antibonding orbital take place. A significant increase of the charge transfer is observed with a maximum value for the pMeOHpMeYH compound (both for S and Se). This again indicates that in spite of the variation provoked by the ring substitutions on the E(2), no major changes are observed which evidence a strengthen of the interaction. Table 6. Second order perturbation energy, E(2)(kJ·mol–1) corresponding to the donation from the oxygen lone pair into the antibonding orbital σ*Y-X for the aROHbR'YH' compounds at the B3LYP/jul-cc-pVDZ computational level. Olp→σ*S-H Olp→σ*Se-H OHYH

10.6

15.3

H

oO oY

9.4

13.6

pFOHpFYH

12.6

17.7

oMeOHoMeYH

13.0

18.8

pMeOHpMeYH

14.4

20.0

oMeOHoFYH

F

H F

11.9

16.0

Me

H F

H

11.2

16.8

Me

H F

H

11.4

16.2

Me

H F

H

13.2

18.5

o O pY p O oY p O pY

3.3 Electron density properties A study of the topological analysis of the electron density of the intramolecular chalcogen interactions using Atoms in Molecules (AIM) theory has been carried out. The chalcogen contacts show the presence of a bond critical point (BCP) between both chalcogen atoms connected by a bond path. The values of the electron density at the BCPs, Laplacian and total electron have been gathered in Table S5. In OXOZ complexes the ρBCP values range between 0.0160 and 0.0201 a.u. These maximum and minimum values show a systematic increase when OXSZ (0.0194-0.0317 a.u.) and OXSeZ (0.0204-0.0361 a.u.) complexes are considered. In all the cases, the compound with the largest ρBCP value corresponds to the OHYF one. In the case of aROHbR'YH compounds values of each set, i.e. O:O, O:S and O:Se, the range of ρBCP values is narrower than in the OXYZ ones. In fact, the maxima and minima values of aROHbR'YH sets are smaller than the corresponding OXYZ compounds. This in 15 Environment ACS Paragon Plus


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conjunction with the binding (interaction) energy values in the latter compounds is stronger than in the formers. In all the cases studied here, ∇2ρBCP is positive and HBCP is positive, with the exception of OMeSF, OHSeF, OMeSeF in which small negative values of and HBCP are found. However, those small values do not indicate any partial covalent character in the chalcogen interactions.52 Exponential relationships between the ρBCP and the interatomic distance (Figure 3, l.h.s) are found in agreement with previous reports for hydrogen bonds53-57 or other weak interactions.13,

58

Additionally, linear relationships were found between the

interatomic distance and the Laplacian values (Figure 3, r.h.s).

Figure 3. Exponential relationships (left) between the O···Y intramolecular distance (dO···Y) and ρBCP and linear relationships between dO···Y and ∇2ρBCP.

Finally in order to provide a visual landscape of the electron density changes upon interaction, intramolecular electron density shift maps have been obtained for some representative cases, as per Figure 4. Blue regions correspond to negative values of the electron density shift, i.e. areas of electron density decrease, while yellow (positive) regions correspond to areas with an increase of the electron density. As observed in the


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OHSH case (Figure 4a), a blue region between both O and S atom, depletion on the electron density of the S atom which highlights the interaction between both atoms. This is coherent with the NBO small E(2)values (10.6 kJ·mol–1) and the positive values of the Eb (Table 2). Introducing a CH3 group in the donor site (Figure 4b) does not have much impact on the electron shift (also corroborated by the small E(2)values and positive Eb). However, when the F-group is added to the acceptor site (Figures 4c-d), there is an increase on the electron density (yellow area) nearby the O atom. This EDS maps pattern was also found for different chalcogen,9, hydrogen bonds

29, 59, 61

29, 59

pnicogen35-37,

60

and

in different systems. This is also in agreement with the increase

on the E(2)values and negative Eb values in Table 3. So, even in weak interactions EDS maps provide, if not quantitative, a qualitative vision of the electron density changes occurred upon interaction.

a) OHSH

c) OHSF

b) OMeSH

d) OMeSF

Figure 4. Electron density shift maps for the OHSH, OHSF, OMeSH, and OMeSF compounds on the 0.001au electron density isosurface at the MP2/jul-cc-pVDZ computational level.



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CONCLUSIONS Different series of substitutions on peri-1,8-substituted naphthalene derivatives have been carried out in order to explore how the chalcogen interactions between the O and Y atoms (Y = O, S, and Se) can be modulated. Using our previous experience, we have directly substituted the H atoms of the OH and YH groups by electron-donor (CH3) and electron-withdrawing (F, CN) groups. It is observed that the inclusion of an electronwithdrawing group in the electron acceptor site increases the interaction energy becoming more negative as the polarizability of the atom increases. This is in agreement with an interaction through the σ-hole; and is also corroborated by a shortening on the intramolecular O···Y distances, an increase on the electron density at the BCP and on the second order perturbation energy E(2)provided by the NBO analysis. Furthermore, a different approach was explored. Substitutions have been made on the aromatic rings both in ortho and para position with respect to their respective OX and YZ groups, in order to evaluate the influence of these substitutions on the intramolecular chalcogen interactions. It was observed that the inclusion of such groups has a negative effect on the binding energies, mainly provoked by dispersion interactions between the substituting groups and the rest of the atoms. However, in terms of distances, in S and Se derivatives there is a decrease on the intramolecular distances supported by an increase on the electron density at the BCP and an increase on the donations into the σ-hole (shown by the NBO analysis). Nevertheless, the mentioned shortening is milder than in the direct substitution on the OX groups. This might indicate that a) chalcogen interactions are, as expected, governed by σ-holes and b) that modifications on the naphthalene backbone can have implications on the chalcogen bonds in peri-substituted positions. Finally, electron density maps have been used to qualitative visualize the electron density changes upon interactions, indicating that in OXYZ systems the inclusion of a fluorine atom in the electron acceptor site causes an increase on the electron density changes as predicted by the previous calculations.

ASSOCIATED CONTENT Supporting Information Benchmark of the interaction energies, molecular electrostatic potential values, dispersion interaction energies, electron density properties at the BCP, molecular graphs


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and linerar relationships between interaction energies and second order orbital interaction energies can be found in the supporting information. The Supporting Information is available free of charge on the ACS Publications website at DOI:

AUTHOR INFORMATION Corresponding Author *E-mail [email protected] ORCID: 0000-0002-1390-4004 Notes The authors declare no competing financial interest.

ACKNOWLEDGEMENTS We thank the Ministerio de Ciencia e Innovación (Project No. CTQ2015-63997-C2-2P) and the Comunidad Autónoma de Madrid (Project FOTOCARBON, ref S2013/MIT2841) for continuous support. Thanks are given to the CTI (CSIC), to Irish Centre for High-End Computing (ICHEC) for the provision of computational facilities.

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TOC Graphic


Enhancing Intramolecular Chalcogen Interactions in 1-Hydroxy-8-YH

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