Study on the nature of interaction of thiophene with various hydrides

Journal of Molecular Structure: THEOCHEM 911 (2009) 132–136

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Study on the nature of interaction of thiophene with various hydrides Junyong Wu *, Hua Yan, Yanxian Jin, Hao Chen, Guoliang Dai, Aiguo Zhong, Fuyou Pan School of Pharmaceutical and Chemical Engineering, Taizhou University, Linhai 317000, Zhejiang Province, PR China

a r t i c l e

i n f o

Article history: Received 17 April 2009 Received in revised form 3 July 2009 Accepted 6 July 2009 Available online 30 July 2009 Keywords: Ab initio calculations Intermolecular interactions SAPT

a b s t r a c t The nature of interactions of thiophene with various hydrides (Y) (Y = HF, HCl, H2O, H2S, NH3, PH3) is investigated using ab initio calculations. In contrast with the previous results on similar furan complexes, only the p-type is observed for the thiophene complexes. Variations in complexes geometry can be accounted for by the differences in the electrostatic potential on the aromatic ring. To further study the nature of the intermolecular interactions, an SAPT (the symmetry-adapted perturbation theory) energy decomposition analysis was carried out and the results indicate that the dispersion and electrostatic interactions dominate the thiophene complexes. Ó 2009 Elsevier B.V. All rights reserved.

1. Introduction Novel types of interactions involving heterocyclic aromatic rings and their derivatives have been an important subject in the past decade [1–9]. Compared to simple aromatic compounds, heteroaromatic rings not only offer a p-electron system as an attractive site for intermolecular interaction formation but also provide a site for intermolecular interaction formation at the nonbonding electron pair (n-pair) of the heteroatom [10–16]. So, it is interesting to understand the nature of heteroaromatic rings interactions. Our interest in thiophene–Y (Y = HF, HCl, H2O, H2S, NH3 and PH3) complexes stems from Legon and Millen proposed a set of rules to predict the angular geometry of complexes of the type B–HX [17], in which the Lewis base B are chosen as prototypes for different categories of electron donor. Thus, according to the rules, the angular geometry of a system containing in the presence of both n- and p-pairs (e.g., heteroaromatic rings), the angular geometry is determined by the n-pair. Subsequent studies, however, raise questions concerning the validity of these rules [11–13]. Cooke et al. conducted Fourier-transform microwave spectroscopy study of thiophene–HF [12] and thiophene–HCl [13], in which they found p-hydrogen-bonded complexes (to be denoted as p-type) with Cs symmetry. In both the thiophene–HF and thiophene–HCl experimental structures, the hydrogen halide subunit lies almost directly above the center of mass of the thiophene ring, with the H atom of the hydrogen halide pointing toward the p-electron density in the region of the sulfur atom. Despite the likely attractive interaction between the ring sulfur and the hydrogen of the hydrogen halide, Cooke et al. concluded

* Corresponding author. Tel.: +86 0576 85137265. E-mail address: [email protected] (J. Wu). 0166-1280/$ - see front matter Ó 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.theochem.2009.07.009

that this interaction (to be denoted as rs-type) is secondary due to the large internuclear distance RS–H observed in both the thiophene–HCl and thiophene–HF clusters [12,13]. The discrepancies between the experimental results and the rules proposed to predict the angular geometry of B-HX complexes demonstrate a need for further studies in this area. Therefore, we investigated the intermolecular interaction of thiophene with the first hydrides (HF, H2O and NH3) and the second hydrides (HCl, H2S and PH3) by using reliable ab initio calculations with large basis sets. Moreover, to further investigate the relative importance of electrostatic, dispersion, induction, and exchange-repulsion energies of these complexes, we have decomposed the interaction energies into these components using symmetry-adapted perturbation theory (SAPT) [18,19]. We believe that such a study would help us obtain a detailed understanding the nature of these interactions by a quantitative analysis of interaction components to enrich the knowledge on thus weak interactions and spur further experimental work in this area. 2. Theoretical methods Equilibrium geometries of the title system were fully optimized with the aug-cc-pVDZ basis set at the second-order Maller-Plesset (MP2) level using the GAUSSIAN 03 program package [20]. Harmonic frequencies were calculated to confirm the equilibrium geometries that correspond to energy minima. In the computation of the interaction energies, the counterpoise (CP) correction [21] was employed to eliminate the basis set superposition error (BSSE). To get more understanding of the interaction on the complexes, natural bond orbital (NBO) analysis [22] has been carried out at the MP2/aug-cc-pVDZ level. The molecular electrostatics potential map (MEP) of thiophene was calculated at the MP2/aug-cc-pVDZ.

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J. Wu et al. / Journal of Molecular Structure: THEOCHEM 911 (2009) 132–136

In this study, the SAPT calculations reported here used the correlation level technically designated as SAPT2, and they were carried out using the aug-cc-pVDZ basis set at the MP2/aug-cc-pVDZ geometry. The SAPT interaction energy can be represented as CORR HF Eint ¼ EHF int þ Eint , where Eint is the sum of all of the energy compoincludes only nents evaluated at the Hartee–Fock level and ECORR int those contributions which are not within Hartee–Fock binding energy. EHF int can be represented as: ð10Þ

ð10Þ

ð20Þ

ð20Þ

HF EHF int ¼ Eelst þ Eexch þ Eind;resp þ Eexch-ind;resp þ dEint;resp

mer correlation on the exchange-repulsion. Therefore, the SAPT interaction energy, Eint , is given by

Eint ¼ Eelst þ Eind þ Edisp þ Eexch where ð10Þ

ð12Þ

ð11Þ

ð12Þ

ð22Þ

ð22Þ

ð20Þ

ð20Þ

ECORR ¼ Eelst;resp þ Eexch þ Eexch þ t Eind þ t Eexch-ind þ Edisp þ Eexch-disp int ð22Þ

ð22Þ

where t Eind represents the part of Eind that is not included in ð20Þ Eind;resp . A more detailed description of SAPT and some of its applications can be found in some recent references [24–26]. SAPT calculations were performed using the SAPT2002 program [27]. To gain more insight the nature of the interaction, we further performed SAPT to analyze the interaction energy in terms of physically meaningful components such as electrostatic, induction, dispersion and exchange energies. The electrostatic component of the ð10Þ

ð12Þ

interaction energy, represented here by the sum of Eelst and Eelst;resp . The induction contribution to the interaction energy is mainly conð20Þ

tained in Eind;resp . This is a second-order energy correction that results from the distortion of the charge distribution of one monomer by the electrostatic charge distribution of other monomer, and vice versa. This mutual polarization of the monomer by the static electric field of the other is polarizabilities of the monomers. The leading intramonomer correlation contribution is conð22Þ

cluded in t Eind and accounts for only 2% of the induction energy. The attractive part of the induction energy is substantially quenched by the repulsive exchange-induction energy (repreð20Þ

ð22Þ

sented by Eexch-ind;resp and t Eexch-ind ). As noted by Jeziorski and coworkers [18], any quantitatively accurate calculation of the induction energy cannot neglect the exchange-induction contribution. To simplify the analysis, for the present purposes, we have designated the exchange-dispersion and exchange-induction terms as dispersion and induction, respectively. So, the induction energy ð20Þ

ð22Þ

ð20Þ

ð22Þ

terms calculated here are Eind;resp , t Eind , Eexch-ind;resp , and t Eexch-ind . The dispersion energy represented here by the sum of ð20Þ Eexch-disp , where ð20Þ Eexch-disp standing

ð20Þ Edisp

ð20Þ Edisp

and

is the second-order dispersion energy,

for the second-order correction for a coupling be-

tween the exchange-repulsion and the dispersion energy. The exð10Þ

ð11Þ

ð12Þ

change energy terms calculated here are Eexch , Eexch , Eexch and dEHF int;resp .

ð10Þ Eexch

accounts for the repulsion due to the Pauli exclusion principle and arises from the antisymmetry requirement of the ð11Þ

ð12Þ

wave function, Eexch and Eexch account for the effects of intramono-

ð12Þ

Eelst ¼ Eelst þ Eelst;resp ð20Þ

ð22Þ

ð2Þ ð20Þ

ð22Þ

Eind ¼ Eind;resp þ t Eind þ Eexch-ind;resp þ t Eexch-ind ð20Þ

The superscript (ab) denotes orders in perturbation theory with respect to the intermolecular interaction operator and the intramolecular correlation operator, respectively. It can be seen from the above equation that the HF interaction energy includes first-order polarization and exchange, and second-order induction and exchange-induction contributions. The subscripts ‘‘resp” indicate that the induction and exchange-induction contributions include the coupled–perturbed HF response [23]. dEHF int;resp contains the third- and higher-order HF induction and exchange-induction contributions. We have employed the SAPT2 approach, in which the correlais nearly equivalent to tive portion of the interaction energy ECORR int the supermolecular MP2 correlation energy and can be represented as:

ð1Þ

ð20Þ

Edisp ¼ Edisp þ Eexch-disp ð10Þ

ð11Þ

ð3Þ ð4Þ

ð12Þ

Eexch ¼ Eexch þ Eexch þ Eexch þ dEHF int;resp

ð5Þ

3. Results and discussions 3.1. Geometrical parameters, interaction energies, and vibrational frequencies The equilibrium geometries of the thiophene–HnX (X = F, O, N, Cl, S and P) complexes are shown in Fig. 1. These geometries are all of the p-type. The p-type geometry is characterized by a p–H bond formed between a hydrogen atom of HnX and the p-electron system of the aromatic ring, and exhibit C1 symmetry. Some selected structural parameters of the thiophene–HnX complexes are summarized in Table 1. For each of the thiophene–HnX complexes, R is the shortest distance between the hydrogen of hydrides and the thiophene ring (Fig. 1). For the C4H4S–HF, C4H4S–NH3, C4H4S–HCl, C4H4S–H2S and C4H4S–PH3 complexes, the hydrogen of hydrides is directed toward the midpoint of C4–C5 bond of the thiophene ring. For the C4H4S–H2O complexes, the hydrogen of H2O is directed toward midpoint of C2–C3 bond of the thiophene ring, represented by point B (Fig. 1). This contradicts the rules proposed by Legon et al., which would predict that H atom of HnX would interact with the n-pair of the S atom of thiophene and form a hydrogen bond. Although thiophene possesses both a p-electron system and an n-pair, the angular geometries for all of the thiophene–HX complexes obtained in this study appear to be determined by the pelectron system. By contrast, as shown in a recent study [28], the furan–HX complex geometries were determined by both the pelectron system and the n-pair. Furan and thiophene are both five-membered heteroaromatic rings with different heteroatoms. Fig. 2 shows a molecular electrostatic potential (MEP) map of furan and thiophene, which might provide an insight into the disparity between the results obtained for furan and thiophene. The MEP plot indicates a positive electrostatic potential (shown in blue), corresponding to the regions of the thiophene hydrogen atoms. Above the thiophene ring, regions of negative electrostatic potential (shown in red) are noticeable, with the negative potential increasing from the S atom to the C4 and C5 atoms. With the strongest negative potential occurring in the vicinity of C4–C5 bond. When compared to the electrostatic potential of furan, it is apparent that the relatively weak electronegativity of sulfur confers a strong aromatic character on the thiophene ring. Thiophene is not expected to undergo complex formation at the site of the npair. This result accounts for the absence of S–H interaction type equilibrium complex geometries. Furthermore, it can be seen from Table 1 thiophene–HnX complexes produce significant changes in the HnX subunit, compared to the corresponding bond length in the monomer. With the exception of C4H4S–NH3, the H–X bond length increases upon complex formation. For the C4H4S–NH3 complexes of both types, the H–X bond length in dimmers becomes slightly contraction. Addition-

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J. Wu et al. / Journal of Molecular Structure: THEOCHEM 911 (2009) 132–136

Fig. 1. Optimized geometries for the p-type complexes between thiophene and HnX. Point A is the center of geometry of thiophene ring.

Table 1 Some selected geometrical parameters (Å and deg) and harmonic stretching vibrational frequencies (cm1) for p-type complexes between thiophene and HnX.

R rH–X(comp) rH–X(free) DrH–X

a tfree tcomp Dt

C4H4S–HF

C4H4S–H2O

C4H4S–NH3

C4H4S–HCl

C4H4S–H2S

C4H4S–PH3

2.1252 0.9339 0.9246 0.0093 76.8 4086.2 3865.0 221.2

2.4187 0.9698 0.9659 0.0039 74.9 3937.7 3759.5 178.2

2.5978 1.0150 1.0201 0.0051 69.4 3636.2 3665.1 28.9

2.2490 1.2982 1.2879 0.0103 84.1 3023.1 2884.8 138.3

2.4699 1.3528 1.3496 0.0032 73.5 2779.5 2726.5 53.0

2.7025 1.4266 1.4265 0.0001 72.1 2469.0 2467.4 1.6

Fig. 2. Molecular electrostatic potentials of thiophene and furan obtained at MP2/aug-cc-pVDZ level.

ally, the corresponding harmonic vibrational frequencies are also shown in Table 1. With the exception of C4H4S–NH3 complexes, the frequency analysis reveals the red-shifting character for the p-type dimers. In agreement with the computed H–X bond elongation, the H–X stretching frequencies are lower in the dimers than the corresponding frequencies in the monomers. In the case of C4H4S–NH3 complexes, the frequency analysis reveals the blue-

shifting character. In agreement with the computed H–N bond contraction. Table 2 lists the interaction energies (DE), BSSE, interaction energies corrected for BSSE (DECP), zero-point vibrational energies (ZPVE), interaction energies corrected for both BSSE and ZPVE (DECP+ZPVE), dipole moments (l) obtained by MP2/aug-cc-pVDZ level. The importance of the inclusion of electron correlation in the

135

J. Wu et al. / Journal of Molecular Structure: THEOCHEM 911 (2009) 132–136 Table 2 Interaction energies without (DE) and with (DECP) BSSE correction, BSSE, ZPVE and interaction energies for both BSSE and ZPE (DECP+ZPVE). All energies are in kcal/mol, DEcorr is determined from the difference between MP2 and HF binding energies (not corrected), l is the dipole moment in debye. Complexes

DE

DEcorr

BSSE

DECP

ZPVE

DECP+ZPVE

l

C4H4S–HF C4H4S–H2O C4H4S–NH3 C4H4S–HCl C4H4S–H2S C4H4S–PH3

6.1209 4.893 4.206 6.407 5.266 4.3911

3.839 4.071 4.507 6.282 6.462 6.272

2.045 2.043 2.235 2.369 2.268 1.972

4.075 2.850 1.971 4.038 2.998 2.419

1.299 1.020 0.837 0.961 0.949 0.852

2.776 1.831 1.134 3.077 2.049 1.567

2.567 2.220 1.282 1.997 1.181 0.967

description of these complexes can be seen from the values of DEcorr. For the first-row hydrides, from HF to H2O to NH3, the interaction energies corrected for both BSSE and ZPVE of thiophene– HnX complexes decreases from 2.776 to 1.831 to 1.134 kcal/mol. For the second-row hydrides, from HCl to H2S to PH3 the interaction energies of thiophene–HnX complexes also decreases (3.077, 2.049, 1.567 kcal/mol). A plot of the ZPVE corrected interaction energies of these complexes (Fig. 3) evaluated at the MP2/aug-cc-pVDZ level reveals that all of the first-row hydrides complexes are more stable than the corresponding the second-row hydrides complexes. 3.2. NBO analysis The occupancy (d) of frontier molecular orbitals involving the charge-transfer (CT) between subsystems, the second-order perturbation energy lowering (DE2) due to the interaction of donor and acceptor orbitals, and the difference (De) of energies between acceptor and donor NBOs, provided by NBO analysis, are listed in Table 3.

From the Table 3, we can see that electron density is increased in the H–X antibonding orbitals of the proton donor. Since the chargetransfer accompanies the formation of intermolecular interaction and plays a major role in it, the donor–acceptor interaction stabilization energies DE2 can be taken as an index to judge the strength of the intermolecular interaction. For the thiophene–HnX complexes, the CT from the C4–C5 bond or C2–C3 of the electron donor in the thiophene is mainly directed to the H–X antibonding orbitals of the hydrides molecular, For the first-row hydrides, the donoracceptor interaction stabilization energies DE2 are computed to be 7.09, 3.06 and 1.21 for r(C4–C5)–r(H–F), r(C2–C3)–r(H–O) and r(C4–C5)–r(N–H) interactions, respectively. For the secondrow hydrides, DE2 are computed to be 6.54, 3.21 and 1.40 for r(C4–C5)–r(H–Cl), r(C4C5)–r(H–S), and r(C4–C5)–r(H–P) interactions, respectively. 3.3. SAPT studies The SAPT-derived components of the interaction energy are summarized in Table 4. Although MP2 is widely and successfully

Table 4 SAPT decomposition of the interaction energy (kcal/mol) for C4H4S–HnX complexes obtained at the SAPT2/aug-cc-pVDZ levela,b,c,d. Term

HF

a EHF int

2.079

0.246

1.133

0.445

1.908

2.584

ð10Þ

5.517

3.938

2.587

4.921

3.825

3.254

Eelst

ð10Þ

Eexch ð20Þ Eind;resp

NH3

HCl

H2S

PH3

7.024

5.240

4.518

8.474

7.324

6.883

5.160

2.301

1.451

4.014

2.880

-2.544

2.784

1.380

1.058

2.528

2.238

2.177

dEHF int;resp

1.211

0.627

0.406

1.621

0.949

0.677

b ECORR int

1.826

2.573

3.193

4.597

5.038

5.166

0.526

0.175

0.043

0.186

0.043

0.063

0.627

0.647

0.545

0.556

0.575

0.586 0.203

ð20Þ

Eexch-ind;resp

ð12Þ

Eelst;resp ð11Þ Eexch

þ

ð12Þ Eexch

0.061

0.169

0.222

0.138

0.186

t ð22Þ Eexch-ind

0.033

0.101

0.162

0.086

0.145

0.173

ð20Þ Edisp

3.475

3.801

4.133

6.037

6.420

6.507

t ð22Þ Eind

0.468

0.474

0.498

0.750

0.806

0.848

Eint ðSAPT2Þc

3.905

2.819

2.060

4.151

3.129

2.581

Eelst

4.991

3.763

2.630

4.735

3.782

3.317

6.440

5.260

4.657

7.409

6.950

6.792

Eind

2.348

0.989

0.453

1.538

0.683

0.397

Edisp

3.007

3.327

3.635

5.287

5.614

5.659

Eint ðMP2Þd

4.075

2.850

1.971

4.038

2.998

2.419

ð20Þ

Eexch-disp

Eexch

ð10Þ

ð10Þ

ð20Þ

ð20Þ

ð20Þ

a

HF EHF int = Eelst + Eexch + Eind;resp + Eexch-ind;resp + Eexch-ind;resp + dEint;resp .

b

ECORR int

=

ð12Þ Eelst;resp

c

Fig. 3. The BSSE and ZPVE corrected interaction energies (MP2/aug-cc-pVDZ) of all the thiophene–HnX complexes.

H2O

+

EHF int

ð11Þ Eexch

+

ð12Þ Eexch

+

t ð22Þ Eind

+

t ð22Þ Eexch-ind

ð20Þ

ð20Þ

+ Edisp þ Eexch-disp :

ECORR int

Eint ðSAPT2Þ = þ = Eelst + Eexch + Eind +Edisp ; Eelst , Eexch , Eind and Edisp as defined by Eqs. (2)–(5). d MP2/aug-cc-pVDZ counterpoise-corrected binding energies.

Table 3 Natural bond orbital analysis at the MP2/aug-cc-pVDZ Level (DE2 in kcal/mol, De in Hartree, Dq in au)a. Complexes

Donor NBOs

C4H4S–HF C4H4S–H2O C4H4S–NH3 C4H4S–HCl C4H4S–H2S C4H4S–PH3

C4–C5 C2–C3 C4–C5 C4–C5 C4–C5 C4–C5

a

r bond r bond r bond r bond r bond r bond

d 1.8849 1.8841 1.8855 1.8777 1.8835 1.8845

(1.8863) (1.8863) (1.8863) (1.8863) (1.8863) (1.8863)

Acceptor NBOs

d

H–F r antibond H–O r antibond N–H r antibond H–Cl r antibond H–S r antibond H–P r antibond

0.0116 0.0045 0.0022 0.0145 0.0077 0.0068

Data in the parentheses are the occupancy of corresponding NBO of isolated molecule. Dq is charge-transfer.

(0.0000) (0.0000) (0.0000) (0.0000) (0.0011) (0.0029)

DE 2

Dq

7.09 3.06 1.21 6.54 3.21 1.40

0.0108 0.0056 0.0052 0.0152 0.0091 0.0098

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J. Wu et al. / Journal of Molecular Structure: THEOCHEM 911 (2009) 132–136

used to calculate the interaction energy of various species, it is very approximate method, which gives rather inaccurate results for some stacked structures [29]. So we should be aware of the limitations of the MP2 method, especially discussing the p-type thiophene-hydride structures. However, It can be seen from Table 4 that the results of SAPT2 (Eint ðSAPT2Þ) are in good agreement with the results obtained at the MP2/aug-cc-pVDZ level, suggesting that MP2/aug-cc-pVDZ is a proper method to study the intermolecular interactions in these studied complexes. As shown in Table 4 and Fig. 4, in the thiophene–HnX complexes, the major attractive contributions to the total attractive energy emerge from the electrostatic energy Eelst and the dispersion energy Edisp , the induction energy Eind is rather small. For the C4H4S–HF and C4H4S–H2O, the major attractive contributions to the total attractive interaction energy emerge from the electrostatic energy Eelst , and contribute about 50.0% and 46.6% to the total attractive interaction energy, respectively. The dispersion forces play a secondary role in these dimers, and contribute about 29.3% and 41.2% to the total attractive interaction energy. For the C4H4S–NH3, C4H4S–HCl, C4H4S–H2S and C4H4S–PH3, the dispersion forces play a key role in these dimers, and contribute about 54.1%, 45.7%, 55.7% and 60.4% to the total attractive interaction energy, respectively. The electrostatic forces play a secondary role in these dimers, and contribute about 39.1%, 40.1%, 37.5% and 35.4% to the total attractive interaction energy. 4. Conclusions The nature and origin of interactions of the complexes of thiophene with various hydrides molecule HnX (HF, HCl, H2O, H2S, NH3 and PH3) were studied using MP2 calculations with aug-cc-

Fig. 4. The components (Eelst, Eind, Edisp, [Eexch]) of interaction energy for the thiophene–HnX complexes.

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