**2. Computational details**

it is usually regarded as an environmentally benign solvent because of its less hazardous property. Furthermore, it is an attractive solvent owing to the ease of its removal capacity, abundance, inexpensive, and flexibility of the solvent parameters [2]. Consequently, super-

many chemical processes, and is expected to be useful in many applications of green chemistry such as extraction, separation, chemical reaction, and material processes [3–6]. Recently,

oligomers, and polymers, etc. [7–10]. It is noteworthy that due to a lack of polarity, sc-CO2 is a very feeble solvent for most polar solutes [11]. Nevertheless, due to the possession of a substantial quadrupole moment and a polar C═O bond, the majority of materials attached

efforts have been reported for the purpose of enhancement in applicability of sc-CO<sup>2</sup>

[3, 12]. Experimental works have aimed at better understanding of behavior of the sc-CO<sup>2</sup>

solvent because its full potential could not be realized without a thorough understanding of

economically and environmentally because most of them are fluorinated polymers. Thus, in attempts to avoid expensive cost and environmental impacts of the fluorous materials, during the last three decades, large-scale studies have focused on the design of nonfluorous CO<sup>2</sup>

philes, specifically hydrocarbon-based and oxygenated hydrocarbon-based polymers [21, 22]. In 1996, Kazarian et al. discovered the formation of Lewis acid-base (LA-LB) type of inter-

first time [23]. Soon later, Beckman et al. successfully synthesized copolymer of nonfluorous-

systems in the gas phase have been theoretically studied for the purpose of ranking in a database of a large variety of organic ligands, which would be valuable candidates for design-

low pressure. Accordingly, some extensive studies have been reported on the interactions of

with π-systems at level of theory and experiment [24–29]. In recent years, interactions of

CHO, CH3

chemistry is the interaction capacity of a solute molecule surrounded by a number of CO2 molecules. Despite the fact that numerous studies have been performed, a full understanding

we need more systematic studies to gain a better understanding on the nature of the interactions involved, rather than considering the origin for a few disparate systems. Furthermore, there is also a great interest in deep understanding of the origin of the interactions between

characteristics as a solvent remains a challenging task [1]. It is therefore clear that

at low pressure [21]. Interaction of CO2

ing new metal-organic framework materials with enhanced affinity for CO<sup>2</sup>

, H, F, Cl, Br; Z = O, S) [42] CH3

been carried out using quantum chemical methods. Today, the interest in CO2

by carbonyl functional or fluoride groups are soluble in sc-CO<sup>2</sup>

been reported during the 1990s [19, 20]. These CO2

simple functionalized organic molecules, including CH3

different types of organic compounds with CO<sup>2</sup>

[33–35], HCHO, CH3

solvent for organic compounds [13–18]. It might be assumed that CO2

its solvent behavior at molecular level. Accordingly, numerous results on the CO2

has been employed in direct sol-gel reactions for the synthesis of oxide nanomaterials,

) is well known as an efficient solvent over conventional organic ones in


with the O atom of a number of carbonyl compounds (>C═O) for the

OH, CH3

SZCH3

COOCH3

CH2

COCH3

at molecular level for an effective use of CO<sup>2</sup>

, CH3

at an acceptable level of low temperature and pressure conditions

. In the context, continuing

with delocalized π aromatic

OH [30–32], CH3

, CH3

(Z = O, S) [43] with CO2


is a green yet feeble


adsorption at

OCH3 ,

have

COOH [36–

computational

solvent

as


critical CO2

sc-CO2

(sc-CO2

106 Carbon Dioxide Chemistry, Capture and Oil Recovery

through the use of "CO<sup>2</sup>

action between CO2

CO2

CH3

OCH2

of the CO2

in different states.

ete-carbonate in sc-CO2

CH2

41], and XCHZ (X = CH3

OCH3

ing more soluble in sc-CO2

Geometrical parameters of all the considered structures including monomers and complexes are optimized using suitable quantum-chemical methods such as the molecular orbital theory (MO) and density functional theory (DFT) and large basis sets, depending on investigated systems, such as 6-311++G(2d,2p), 6-311++G(3df,2pd), aug-cc-pVDZ, aug-cc-pVTZ, which have succeeded in investigating noncovalent interactions, especially hydrogen bonds [44, 45]. Harmonic vibrational frequencies are subsequently calculated at investigated level of theory to ensure that the optimized structures are local minima on the potential energy surfaces, and to estimate their zero-point energy (ZPE). The stabilization energy of each complex is calculated using the supermolecular method as the difference in total energies between that of each complex and the sum of the relevant monomers at the selected level of theory. The interaction energy is corrected by zero-point energy (ZPE) and basis set superposition errors (BSSE). The latter is computed using the function counterpoise procedure of Boys and Bernardi [46]. The "atoms-in-molecules" (AIM) [47] analyses are applied to identify critical points and to calculate their characteristics including electron density (ρ(r)), Laplacian, electron potential and kinetic energy density, and total energy density. The GenNBO 5.G program [48] is used to perform NBO calculations, which is extensively applied to investigate chemical essences of hydrogen bonds and other weak interaction, and can provide information about natural hybrid orbitals, natural bond orbitals, natural population, occupancies in NBOs, hyperconjugation energies, rehybridization, and repolarization.

#### **3. Interaction capacity of CO2 with organic compounds**

#### **3.1. Interaction of CO2 with model hydrocarbons**

#### *3.1.1. Interaction of CO2 with saturated hydrocarbons and their substituted derivatives*

Saturated hydrocarbons are a primary energy source for our civilization. Fluorocarbons have been currently used as CO2 -philic functionalities in many potential applications of chemistry utilizing liquid and supercritical CO2 as a "green" alternative to conventional organic solvents for chemical processes [20, 49–52]. The miscibility and dissolution of organic molecules in sc-CO2 generally increase when the hydrogen atoms in molecules are substituted by fluorine atoms [49, 53]. It is crucial, therefore, to investigate interaction of CO2 with saturated hydrocarbons and its substituted derivatives. A study [54] on density-dependent 1 H and 19FNMR chemical shift of hydrocarbons and fluorocarbons in sc-CO<sup>2</sup> pointed out that there is a distinct difference in the chemical shift changes, as a function of density, for the two nuclei. In addition, the authors suggested a specific interaction of type "solute-solvent" in the system formed by the fluorocarbons and CO<sup>2</sup> , and a site specificity for the 19F shifts due to the surface accessibility of the individual fluorine atoms. In 1996, interactions between CO<sup>2</sup> with ethane (C2 H6 ) and hexafluoroethane (C<sup>2</sup> F6 ), in particular the (CO2 )n∙∙∙C2 H6 and (CO2 )n∙∙∙C2 F6 interactions, with n = 1–4, were examined using restricted Hartree-Fock method [55]. The interaction energy for the CO2 ∙∙∙C2 F6 complex was calculated to be −3.35 kJ.mol−1, while it was −1.26 kJ. mol−1 for the CO2 ∙∙∙C2 H6 complex, indicating that the interaction of CO2 with C2 F6 is stronger than that with C2 H6 . The obtained results showed key differences between the interaction of hydrocarbons and fluorocarbons with CO<sup>2</sup> . The interaction of the fluorocarbon with CO<sup>2</sup> is predominantly electrostatic in nature. Thus, the positively charged carbon atom in CO2 has a strong attraction with the negatively charged fluorine atoms of the fluorocarbons, resulting in a favorable binding energy of 3.14–3.35 kJ.mol−1 for each CO2 molecule in the first solvent shell. The interaction of CO2 with hydrocarbons is quite weak due to the noble nature of the hydrocarbons molecule. Nevertheless, Han and Jeong [56] pointed out that the results in Ref. [55] were incorrect because the calculations for interaction energy of the complexes were not corrected by the basis set superposition error.

calculations and studying effect of stepwise substitution of H atom of methane by fluorine, the authors explored origin of fluorocarbon and hydrocarbon interactions with CO<sup>2</sup>

results suggested an optimum density of fluorine atoms that can be viewed as a maximum

this work, the authors suggested the fundamentally different nature of interaction between

complex is also contributed by the C─H∙∙∙O weak hydrogen. In summary, these molecular modeling computations have shed some light on the interaction of hydrocarbons and fluo-

Unsaturated hydrocarbons is one of the most important classes of materials for synthesiz-

energy was evaluated to be *ca.* -4.70 kJ.mol−1 at M05-2x/6-311++G(d,p) and −5.99 kJ.mol−1 at

surface. The stability of complex is determined by weak C∙∙∙C interaction and is confirmed by AIM and NBO analyses. Indeed, AIM analysis shows the presence of this intermolecular

0.0067 and 0.0246 au. Furthermore, the NBO analysis also indicates that upon complexation

having electron-poor carbon atoms. In order to understand deeply origin of interaction of

our group in 2016 [1]. It is remarkable that the interaction energies corrected by both ZPE and

is in line with the report by Miller et al. that CO2

p∙∙∙π\* and π∙∙∙π\* interactions play more important role than the C─H∙∙∙O hydrogen bond in

Our group [1] continued to investigate the interactions of the 1,2-dihalogenated derivatives of

with saturated hydrocarbons.

, the complexes of C2

molecule plays both weak Lewis acid and base in these systems. In

Understanding Interaction Capacity of CO2 with Organic Compounds at Molecular Level:…

and fluorine in fluorocarbons, while the stability of complexes of hydrocar-

 *with unsaturated hydrocarbons and its substituted derivatives*

H2 ∙∙∙CO2

, which may help to explain the difference in solubility of various satu-

has been seen as a good solvent for this kind of synthesis. In 2009,


.

was investigated by Alkorta et al. [61] and interaction

transfers electrons to the anti-bonding orbital of C2

and CO2

with hydrocarbons and fluorinated hydrocar-

H4

complexes are in the range from −1.1 to −4.9 kJ.mol−1. The most stable

complexes. Remarkably, contribution of the π∙∙∙π\* interaction to

(from −3.7 to −4.9 kJ.mol−1 at the MP2/aug-cc-pVDZ) [56, 57,

in order to evaluate the substituent effects on the interactions.

, but is not parallel to its C─C axis [62]. Obtained results showed that the


H4 ∙∙∙CO2

is stable on the potential energy

ρ(r)) at its BCP to be

were investigated by

's main axis parallels

has been observed for

(−4.9 kJ.mol−1) is more stable

(X = F, Cl and Br) at the MP2/

with unsaturated hydrocarbons is

H2

, their stability is contributed by interaction of

http://dx.doi.org/10.5772/intechopen.71878

. It should be noteworthy that the stability of

CO2

CO2

carbon in CO2

bons and CO2

rocarbons with CO2

*3.1.2. Interaction of CO2*

ing polymers; and sc-CO2

interaction between C2

BSSE for the C2

structure of C2

the plane of C2

stabilizing the C2

bons such as CH4

stronger than that of CO2

ethylene (XCH═CHX) with CO2



complexes formed by fluorocarbons and CO<sup>2</sup>

H2

MP2/aug-cc-pVTZ, implying that the complex C2

the electron-rich carbon atom of CO2

unsaturated hydrocarbons with CO2

H4 ∙∙∙CO2

H4

H4 ∙∙∙CO2

, C2 H6 , CF4 , C2 F6

stabilization of the complex formed by CO2

than the complexes of interaction between CO2

the first time in this literature. The stability of complex C<sup>2</sup>

61]. This review indicates that interaction capacity of CO2

Six stable shapes of the optimized structures of XCH═CHX∙∙∙CO2

H4 ∙∙∙CO2

is thanks to two oxygen of CO2

rated hydrocarbons and their substituted derivatives in sc-CO2

with CO2

contact owing to the values of electron density (ρ(r)) and Laplacian (∇<sup>2</sup>

. The

109

In 1998, interactions of CO2 with small hydrocarbons (CH4 and C2 H6 ) and fluorocarbons (CF<sup>4</sup> and C2 F6 ) were reinvestigated using second-order many-body perturbation theory (MP2) methods by Diep et al. [57]. These authors surprisingly did not find any enhanced attraction between CO2 and perfluorocarbons relative to the analogous hydrocarbons as in the publication of Cece et al. [55]. On the contrary, interaction energies of the obtained complexes range from −3.31 to −4.90 kJ.mol−1, in which the interaction energies are slightly more negative for the CO2 -hydrocarbon complexes than for the corresponding CO2 -perfluorocarbon ones, suggesting that the interaction capacity of CO2 and hydrocarbons is stronger than that of fluorocarbons and CO<sup>2</sup> . Yonker and Palmer [58] studied the nuclear shielding of 1 H and 19F nuclei in CH3 F and CHF3 by NMR and molecular dynamics simulations. Obtained results showed that there is no distinct or specific interaction between fluoromethane and CO2 . A various work by Yee et al. [59] reported that the polarizability of CF4 and C2 F6 , which is derived from dielectric constant measurement, is larger than that of CH4 and C2 H6 , and noted that this reason should result in a proportional difference in the magnitude of the interaction between the induced dipoles. Consequently, they suggested that the repulsion of CO2 is greater for CF4 than for CH4 . However, Diep et al. [57] argued that only the electronic component of the total polarizability cited by Yee et al. [59] is the adequate reason for the induced dipole-induced dipole interactions between the molecules. They showed that the electronic polarizability is comparable between the perfluorocarbons and the alike hydrocarbons. The CO2 -philicity of fluorinated compounds with varying numbers of fluorine atoms in the system was investigated by Wallen et al. [60]. By using correlated ab-initio calculations and studying effect of stepwise substitution of H atom of methane by fluorine, the authors explored origin of fluorocarbon and hydrocarbon interactions with CO<sup>2</sup> . The results suggested an optimum density of fluorine atoms that can be viewed as a maximum CO2 -philicity, and CO2 molecule plays both weak Lewis acid and base in these systems. In this work, the authors suggested the fundamentally different nature of interaction between CO2 -fluorocarbon and CO<sup>2</sup> -hydrocarbon, in spite of comparable interaction energy. For complexes formed by fluorocarbons and CO<sup>2</sup> , their stability is contributed by interaction of carbon in CO2 and fluorine in fluorocarbons, while the stability of complexes of hydrocarbons and CO2 is thanks to two oxygen of CO2 . It should be noteworthy that the stability of complex is also contributed by the C─H∙∙∙O weak hydrogen. In summary, these molecular modeling computations have shed some light on the interaction of hydrocarbons and fluorocarbons with CO2 , which may help to explain the difference in solubility of various saturated hydrocarbons and their substituted derivatives in sc-CO2 .

#### *3.1.2. Interaction of CO2 with unsaturated hydrocarbons and its substituted derivatives*

for chemical processes [20, 49–52]. The miscibility and dissolution of organic molecules in

tinct difference in the chemical shift changes, as a function of density, for the two nuclei. In addition, the authors suggested a specific interaction of type "solute-solvent" in the system

), in particular the (CO2

tions, with n = 1–4, were examined using restricted Hartree-Fock method [55]. The interaction

complex, indicating that the interaction of CO2

strong attraction with the negatively charged fluorine atoms of the fluorocarbons, resulting

hydrocarbons molecule. Nevertheless, Han and Jeong [56] pointed out that the results in Ref. [55] were incorrect because the calculations for interaction energy of the complexes were not

methods by Diep et al. [57]. These authors surprisingly did not find any enhanced attraction

lication of Cece et al. [55]. On the contrary, interaction energies of the obtained complexes range from −3.31 to −4.90 kJ.mol−1, in which the interaction energies are slightly more nega-


results showed that there is no distinct or specific interaction between fluoromethane and

noted that this reason should result in a proportional difference in the magnitude of the interaction between the induced dipoles. Consequently, they suggested that the repulsion

tronic component of the total polarizability cited by Yee et al. [59] is the adequate reason for the induced dipole-induced dipole interactions between the molecules. They showed that the electronic polarizability is comparable between the perfluorocarbons and the alike

rine atoms in the system was investigated by Wallen et al. [60]. By using correlated ab-initio

. A various work by Yee et al. [59] reported that the polarizability of CF4

is derived from dielectric constant measurement, is larger than that of CH4

) were reinvestigated using second-order many-body perturbation theory (MP2)

and perfluorocarbons relative to the analogous hydrocarbons as in the pub-

predominantly electrostatic in nature. Thus, the positively charged carbon atom in CO2

with small hydrocarbons (CH4

atoms [49, 53]. It is crucial, therefore, to investigate interaction of CO2

F6

in a favorable binding energy of 3.14–3.35 kJ.mol−1 for each CO2

chemical shift of hydrocarbons and fluorocarbons in sc-CO<sup>2</sup>

formed by the fluorocarbons and CO<sup>2</sup>

108 Carbon Dioxide Chemistry, Capture and Oil Recovery

) and hexafluoroethane (C<sup>2</sup>

∙∙∙C2 H6

H6

shell. The interaction of CO2

In 1998, interactions of CO2

that of fluorocarbons and CO<sup>2</sup>

is greater for CF4

hydrocarbons. The CO2

and C2 F6

CO2

of CO2

between CO2

tive for the CO2

and 19F nuclei in CH3

∙∙∙C2 F6

hydrocarbons and fluorocarbons with CO<sup>2</sup>

corrected by the basis set superposition error.

ones, suggesting that the interaction capacity of CO2

F and CHF3

than for CH4

carbons and its substituted derivatives. A study [54] on density-dependent 1

accessibility of the individual fluorine atoms. In 1996, interactions between CO<sup>2</sup>

generally increase when the hydrogen atoms in molecules are substituted by fluorine

with saturated hydro-

pointed out that there is a dis-

) <sup>n</sup>∙∙∙C2 F6

F6

molecule in the first solvent

) and fluorocarbons (CF<sup>4</sup>

 and C2 F6

and C2

and hydrocarbons is stronger than


H

, which

H6 , and

with C2

, and a site specificity for the 19F shifts due to the surface

. The interaction of the fluorocarbon with CO<sup>2</sup>

and (CO2

)n∙∙∙C2 H6

with hydrocarbons is quite weak due to the noble nature of the

and C2

. Yonker and Palmer [58] studied the nuclear shielding of 1


by NMR and molecular dynamics simulations. Obtained

. However, Diep et al. [57] argued that only the elec-

H6

complex was calculated to be −3.35 kJ.mol−1, while it was −1.26 kJ.

. The obtained results showed key differences between the interaction of

H and 19FNMR

with ethane

interac-

is stronger

is

has a

sc-CO2

(C2 H6

energy for the CO2

mol−1 for the CO2

than that with C2

Unsaturated hydrocarbons is one of the most important classes of materials for synthesizing polymers; and sc-CO2 has been seen as a good solvent for this kind of synthesis. In 2009, interaction between C2 H2 with CO2 was investigated by Alkorta et al. [61] and interaction energy was evaluated to be *ca.* -4.70 kJ.mol−1 at M05-2x/6-311++G(d,p) and −5.99 kJ.mol−1 at MP2/aug-cc-pVTZ, implying that the complex C2 H2 ∙∙∙CO2 is stable on the potential energy surface. The stability of complex is determined by weak C∙∙∙C interaction and is confirmed by AIM and NBO analyses. Indeed, AIM analysis shows the presence of this intermolecular contact owing to the values of electron density (ρ(r)) and Laplacian (∇<sup>2</sup> ρ(r)) at its BCP to be 0.0067 and 0.0246 au. Furthermore, the NBO analysis also indicates that upon complexation the electron-rich carbon atom of CO2 transfers electrons to the anti-bonding orbital of C2 H2 having electron-poor carbon atoms. In order to understand deeply origin of interaction of unsaturated hydrocarbons with CO2 , the complexes of C2 H4 and CO2 were investigated by our group in 2016 [1]. It is remarkable that the interaction energies corrected by both ZPE and BSSE for the C2 H4 ∙∙∙CO2 complexes are in the range from −1.1 to −4.9 kJ.mol−1. The most stable structure of C2 H4 ∙∙∙CO2 is in line with the report by Miller et al. that CO2 's main axis parallels the plane of C2 H4 , but is not parallel to its C─C axis [62]. Obtained results showed that the p∙∙∙π\* and π∙∙∙π\* interactions play more important role than the C─H∙∙∙O hydrogen bond in stabilizing the C2 H4 ∙∙∙CO2 complexes. Remarkably, contribution of the π∙∙∙π\* interaction to stabilization of the complex formed by CO2 -philic compounds and CO2 has been observed for the first time in this literature. The stability of complex C<sup>2</sup> H4 ∙∙∙CO2 (−4.9 kJ.mol−1) is more stable than the complexes of interaction between CO2 with hydrocarbons and fluorinated hydrocarbons such as CH4 , C2 H6 , CF4 , C2 F6 (from −3.7 to −4.9 kJ.mol−1 at the MP2/aug-cc-pVDZ) [56, 57, 61]. This review indicates that interaction capacity of CO2 with unsaturated hydrocarbons is stronger than that of CO2 with saturated hydrocarbons.

Our group [1] continued to investigate the interactions of the 1,2-dihalogenated derivatives of ethylene (XCH═CHX) with CO2 in order to evaluate the substituent effects on the interactions. Six stable shapes of the optimized structures of XCH═CHX∙∙∙CO2 (X = F, Cl and Br) at the MP2/

aug-cc-pVDZ level are showed in **Figure 1**, which are denoted hereafter by **C1X**, **C2X** and **C3X** for *cis*-XCH═CHX∙∙∙CO2 pairs, and **T1X**, **T2X** and **T3X** for *trans*-XCH═CHX∙∙∙CO2 pairs.

*3.1.3. Interaction of CO2*

with enhanced CO2

ligands in MOFS

action capacity with CO2

CO2

ligand.

CO2

(C4 H5

of CO2

and S-C4

for T-C5

C4 H5 H5

N∙∙∙CO2

H5

N∙∙∙CO2

N∙∙∙CO2

ute to the interactions between CO2

 *with some model aromatic hydrocarbons*

tant chemicals and polymers. In 2009, interactions between CO2

interactions of these hydrogen atoms with oxygen atom of CO2

and three aromatic molecules, namely benzene (C6

are twice more negative than the most stable complex of the C2

, as illustrated in **Figure 2**.

(N) and −11.5 kJ.mol−1 for TC5

pairs. On the contrary, for the C5

results indicate that π∙∙∙π interaction between CO<sup>2</sup>

cavity, and hence it can be seen as a promising way to enhance the CO2

work materials [63]. The interaction energies for the complexes of CO2

with aromatic hydrocarbons is stronger than that of CO2

obtained the three most-stable side-on configurations, specifically S-C<sup>6</sup>

to the exposed aromatic N atom of the EDA-type interaction in S-C5

The side-on interaction is significantly weaker than the π∙∙∙π interaction in C<sup>6</sup>

Key aromatic hydrocarbons of commercial interests such as benzene, toluene, and xylene play a key role in the biochemistry of all living things. They are used to produce a range of impor-

tionalized aromatic molecules were investigated by means of using density functional theory by Torrisi et al. [24] with the aim of ranking a large variety of organic ligands in a database, which could be suitable candidates for designing new metal organic framework materials

zene derivatives including the electron-withdrawing halogen groups (tetrafluoro-, chloro-, bromo-, and dibromobenzene) and methyl electron donor (mono-, di-, and tetramethylbenzene) were considered since these substituents are very common components of aromatic

relatively strong destabilization of complexes formed, which is increased with number of substituting groups, and thus reduces the magnitude of the aromatic ring adsorption toward

substitution of hydrogen atom in aromatic ring by methyl group clearly strengthens its inter-

in which tetramethyl substitution manifests a maximum advantage of this particular class of

In 2013, Chen et al., by using high-level *ab initio* methods, suggested the π∙∙∙π interaction between

carbons calculated at MP2/aug-cc-pVTZ are in the range from −11.9 to −15.4 kJ.mol−1, which

CCSD(T)/aug-cc-pVTZ//MP2/aug-cc-pVDZ level). This result implies that interaction capacity

bons. These authors also optimized the side-on structures of all possible complexes to compare the interaction strength of side-on configurations and π∙∙∙π top-on configurations. This work

H5

H5

tion (−18.0 kJ.mol−1). The obtained results showed that the EDA-type interactions are not available in real MOF/ZIF materials because the central cationic metal of MOF/ZIF materials is linked

and MOFs/ZIFs.

N∙∙∙CO2

N∙∙∙CO2

N), which serve as common functional groups in metal-organic/zeoliticimidazolate frame-

. Nevertheless, a decrease of electron density of the aromatic ring induces an increase in acidity for some of the aromatic hydrogen atoms, which helps weak hydrogen bond-like

adsorption capacity at ambient pressure. Two groups of substituted ben-

Understanding Interaction Capacity of CO2 with Organic Compounds at Molecular Level:…

. The results of interaction energy showed that halogen substitution causes

, which is usually very accessible on the internal surface of a MOF

H6

), pyridine (C5

H6 ∙∙∙CO2

H5

and aromatic rings can significantly contrib-

pair the π∙∙∙π interaction [−11.6 kJ.mol−1

(C)] is weaker than the side-on interac-

N∙∙∙CO2

H4 ∙∙∙CO2

and a large number of func-

http://dx.doi.org/10.5772/intechopen.71878

111

formed. On the other hand,

H5

affinity of the MOF,

N), and pyrrole

with aromatic hydro-

system (−4.9 kJ.mol−1 at

with unsaturated hydrocar-

, S-C5 H5

> H6 ∙∙∙CO2

N∙∙∙CO2 ,

. In short, the

and

The obtained results showed that stability of the complexes **C1X** and **C3X** is determined by the C─H∙∙∙O hydrogen bonded interaction, whereas the presence of both the C─H∙∙∙O hydrogen bond and C─X∙∙∙C Lewis acid-base interaction leads to stabilization of the complexes **C2X**, **T1X** and **T2X**. For **T3X**, their stability is induced by a p∙∙∙π\* interaction from the lone pair n(O) to the π\*(C═C) orbital and a π∙∙∙π\* interaction from MO-π(C═O) to MO-π\*(C═C) orbital. The two H atoms in C2 H4 substituted by two alike halogen atoms X results in an additional presence of C─X∙∙∙C Lewis acid-base interaction, thus contributing supplementary to the stabilization of the investigated complexes. In general, the *cis*-XCH═CHX∙∙∙CO2 complexes are more stable than the *trans* counterparts. In addition, CH2 CH2 ∙∙∙CO2 is less stable than both t*rans*-XCH═CHX∙∙∙CO2 and *cis*-XCH═CHX∙∙∙CO2 . Thus, the interaction energies with both ZPE and BSSE corrections are calculated to be from −1.7 to −7.5 kJ.mol−1 for *cis*-XCH═CHX∙∙∙CO2 and from −4.4 to −6.8 kJ.mol−1 for *trans*-XCH═CHX∙∙∙CO2 . Hence replacement of the two H atoms in CH2 ═CH2 by the same halogen atoms actually increases the stability of complexes formed by interaction of XCH═CHX with CO2 and causes a decrease of the role of the π∙∙∙π\* interaction in stabilization of the parent C<sup>2</sup> H4 ∙∙∙CO2 complex in comparison with the XCH═CHX∙∙∙CO2 ones.

**Figure 1.** The stable geometries of the complexes of CO2 and XCH═CHX derivatives (X = F, Cl, and Br). (a) *cis*-XCH═CHX∙∙∙CO2 complexes, (b) *trans-*XCH═CHX∙∙∙CO2 complexes.

#### *3.1.3. Interaction of CO2 with some model aromatic hydrocarbons*

aug-cc-pVDZ level are showed in **Figure 1**, which are denoted hereafter by **C1X**, **C2X** and **C3X**

The obtained results showed that stability of the complexes **C1X** and **C3X** is determined by the C─H∙∙∙O hydrogen bonded interaction, whereas the presence of both the C─H∙∙∙O hydrogen bond and C─X∙∙∙C Lewis acid-base interaction leads to stabilization of the complexes **C2X**, **T1X** and **T2X**. For **T3X**, their stability is induced by a p∙∙∙π\* interaction from the lone pair n(O) to the π\*(C═C) orbital and a π∙∙∙π\* interaction from MO-π(C═O) to MO-π\*(C═C)

additional presence of C─X∙∙∙C Lewis acid-base interaction, thus contributing supplementary to the stabilization of the investigated complexes. In general, the *cis*-XCH═CHX∙∙∙CO2

energies with both ZPE and BSSE corrections are calculated to be from −1.7 to −7.5 kJ.mol−1

═CH2

ones.

**a)** *cis***-XCH=CHX···CO2 complexes**

complexes.

H4

complexes are more stable than the *trans* counterparts. In addition, CH2

the stability of complexes formed by interaction of XCH═CHX with CO2

decrease of the role of the π∙∙∙π\* interaction in stabilization of the parent C<sup>2</sup>

pairs, and **T1X**, **T2X** and **T3X** for *trans*-XCH═CHX∙∙∙CO2

and *cis*-XCH═CHX∙∙∙CO2

and from −4.4 to −6.8 kJ.mol−1 for *trans*-XCH═CHX∙∙∙CO2

substituted by two alike halogen atoms X results in an

by the same halogen atoms actually increases

and XCH═CHX derivatives (X = F, Cl, and Br). (a) *cis*-

pairs.

CH2

H4 ∙∙∙CO2

∙∙∙CO2

. Thus, the interaction

is less

. Hence

complex

and causes a

for *cis*-XCH═CHX∙∙∙CO2

orbital. The two H atoms in C2

110 Carbon Dioxide Chemistry, Capture and Oil Recovery

for *cis*-XCH═CHX∙∙∙CO2

stable than both t*rans*-XCH═CHX∙∙∙CO2

replacement of the two H atoms in CH2

in comparison with the XCH═CHX∙∙∙CO2

**Figure 1.** The stable geometries of the complexes of CO2

complexes, (b) *trans-*XCH═CHX∙∙∙CO2

XCH═CHX∙∙∙CO2

Key aromatic hydrocarbons of commercial interests such as benzene, toluene, and xylene play a key role in the biochemistry of all living things. They are used to produce a range of important chemicals and polymers. In 2009, interactions between CO2 and a large number of functionalized aromatic molecules were investigated by means of using density functional theory by Torrisi et al. [24] with the aim of ranking a large variety of organic ligands in a database, which could be suitable candidates for designing new metal organic framework materials with enhanced CO2 adsorption capacity at ambient pressure. Two groups of substituted benzene derivatives including the electron-withdrawing halogen groups (tetrafluoro-, chloro-, bromo-, and dibromobenzene) and methyl electron donor (mono-, di-, and tetramethylbenzene) were considered since these substituents are very common components of aromatic ligands in MOFS . The results of interaction energy showed that halogen substitution causes relatively strong destabilization of complexes formed, which is increased with number of substituting groups, and thus reduces the magnitude of the aromatic ring adsorption toward CO2 . Nevertheless, a decrease of electron density of the aromatic ring induces an increase in acidity for some of the aromatic hydrogen atoms, which helps weak hydrogen bond-like interactions of these hydrogen atoms with oxygen atom of CO2 formed. On the other hand, substitution of hydrogen atom in aromatic ring by methyl group clearly strengthens its interaction capacity with CO2 , which is usually very accessible on the internal surface of a MOF cavity, and hence it can be seen as a promising way to enhance the CO2 affinity of the MOF, in which tetramethyl substitution manifests a maximum advantage of this particular class of ligand.

In 2013, Chen et al., by using high-level *ab initio* methods, suggested the π∙∙∙π interaction between CO2 and three aromatic molecules, namely benzene (C6 H6 ), pyridine (C5 H5 N), and pyrrole (C4 H5 N), which serve as common functional groups in metal-organic/zeoliticimidazolate framework materials [63]. The interaction energies for the complexes of CO2 with aromatic hydrocarbons calculated at MP2/aug-cc-pVTZ are in the range from −11.9 to −15.4 kJ.mol−1, which are twice more negative than the most stable complex of the C2 H4 ∙∙∙CO2 system (−4.9 kJ.mol−1 at CCSD(T)/aug-cc-pVTZ//MP2/aug-cc-pVDZ level). This result implies that interaction capacity of CO2 with aromatic hydrocarbons is stronger than that of CO2 with unsaturated hydrocarbons. These authors also optimized the side-on structures of all possible complexes to compare the interaction strength of side-on configurations and π∙∙∙π top-on configurations. This work obtained the three most-stable side-on configurations, specifically S-C<sup>6</sup> H6 ∙∙∙CO2 , S-C5 H5 N∙∙∙CO2 , and S-C4 H5 N∙∙∙CO2 , as illustrated in **Figure 2**.

The side-on interaction is significantly weaker than the π∙∙∙π interaction in C<sup>6</sup> H6 ∙∙∙CO2 and C4 H5 N∙∙∙CO2 pairs. On the contrary, for the C5 H5 N∙∙∙CO2 pair the π∙∙∙π interaction [−11.6 kJ.mol−1 for T-C5 H5 N∙∙∙CO2 (N) and −11.5 kJ.mol−1 for TC5 H5 N∙∙∙CO2 (C)] is weaker than the side-on interaction (−18.0 kJ.mol−1). The obtained results showed that the EDA-type interactions are not available in real MOF/ZIF materials because the central cationic metal of MOF/ZIF materials is linked to the exposed aromatic N atom of the EDA-type interaction in S-C5 H5 N∙∙∙CO2 . In short, the results indicate that π∙∙∙π interaction between CO<sup>2</sup> and aromatic rings can significantly contribute to the interactions between CO2 and MOFs/ZIFs.

interactions formed in complexes, rather than considering the results obtained from few

C─H∙∙∙O blue-shifting hydrogen bond in stabilizing most of the complexes. However, the

gen bond. All interaction energies are significantly negative, indicating that obtained complexes are quite stable. Particularly, the interaction energies with both ZPE and BSSE corrections are in the range from −3.3 to −14.2 kJ.mol−1, in which the HCOOH∙∙∙CO2

The interaction energies of some considered complexes are more negative than the values

energy of −13.3 kJ.mol−1 with only ZPE correction, and −11.4 kJ.mol−1 with both ZPE and BSSE corrections is more negative than that of −11.3 kJ.mol−1 obtained with only BSSE correction at the MP2/aug-cc-pVTZ level [64]. Another example is that the BSSE corrected

MP2/6-311++G(2d,2p)//MP2/6-311++G(d,p) level [35] while it is −13.7 kJ.mol−1 with ZPE and BSSE corrections, and −16.3 kJ.mol−1 with only ZPE correction in the present work.

dehyde and thioformaldehyde [42]. The interaction energies (with ZPE and BSSE corrections)

ported that both O and S atoms act as Lewis bases and the >C═X (X = O, S) groups should

carbonyl compounds. Obtained results suggested that the Lewis acid-base and hydrogen bonded interactions should be the key factors in governing the solubility of isolated mono-

In 2014, we investigated the interactions between some carbonyl compounds including

denoted by **H1**, **H2**, **H3,** and **H4** at the CCSD(T)/6-311++G(3df,2pd)//MP2/6-311++G(2d,2p) level are gathered in **Table 1**. The results indicate that the stability of studied complexes is contributed by both Lewis acid-base and hydrogen bonded interactions. As shown in **Table 1**, the interaction energy for **H1** (−10.3 kJ.mol−1) is less negative than that reported in Ref. [40] (−11.1 kJ.mol−1) at CCSD(T)/aug-cc-pVTZ but is more negative than that in Ref. [64] (−8.8 kJ.mol−1) at MP2/aug-cc-pVDZ. Notably, complex **H3** is less stable than **H1** in this work, which is different from the results reported by Ruiz-Lopez et al [68]. By using the levels of theory MP2/aug-cc-pVDZ and CCSD(T)/aug-cc-pVDZ, the authors suggested

, in which the crucial role of the former is suggested. The function of these

and HCHS∙∙∙CO2

and −9.1 kJ.mol−1 for CH3

OH), methylamine (CH3

Understanding Interaction Capacity of CO2 with Organic Compounds at Molecular Level:…

OCH3

) [40] Obtained results showed that the Lewis acid-base inter-

pair is mainly determined by O─H∙∙∙O red-shifting hydro-

is likely to be the largest in all the considered compounds.

and some typically functionalized

http://dx.doi.org/10.5772/intechopen.71878

), formaldehyde

) and

113

pair

COCH3

pair. As a consequence,

), its interaction

are more negative

may be important in

NH2

), acetone (CH3

OH, CO2

with substituted derivatives of formal-

, respectively. The obtained results sup-


pair was computed to be −13.1 kJ.mol−1 at the

CHS∙∙∙CO2

are stronger than those of fluorocarbons and fluoro-

[41]. Interaction energies of obtained complexes which are

) plays a more dominant role compared to the

specific systems. We investigated complexes of CO<sup>2</sup>

(HCHO), formic acid (HCOOH), dimethylether (CH3

), C═O∙∙∙C(CO2

is the most stable, whereas the weakest one is the HCHO∙∙∙CO2

reported in the previous works [35, 64]. Thus, for the pair (CH3

OCH3

In 2011, our group investigated the interactions of CO2

CHO∙∙∙CO2

be considered as potential candidates for the design of CO2

) with CO2

interactions in the solvation of >C═O and >C═S compounds in sc-CO2

∙∙∙CO2

organic molecules such as methanol (CH3

methyl formate (HCOOCH3

action such as C─N∙∙∙C(CO2

stability of the HCOOH∙∙∙CO2

solubility of HCOOH in sc-CO2

interaction energy of the CH3

of −10.5 kJ.mol−1 for CH3

mers in sc-CO2

acetone (CH3

than for complexes of HCHO∙∙∙CO2

terms of the specific solute-solvent.

COCH3

between carbonyl compounds and CO2

**Figure 2.** Optimized structures of S-C6 H6 ∙∙∙CO2 , S-C5 H5 N∙∙∙CO2 , and S-C4 H5 N∙∙∙CO2 .

#### *3.1.4. Concluding remarks on interaction of CO2 with model hydrocarbons*

Interactions of CO2 with model hydrocarbons including saturated, unsaturated, aromatic hydrocarbons and theirs substituted derivatives were investigated using high-level *ab initio* methods. In general, the strength of the complexes increases in going from the interaction of the saturated hydrocarbons with carbon dioxide to unsaturated hydrocarbons with carbon dioxide and finally to the parent aromatic hydrocarbons with carbon dioxide. The stability of the obtained complexes is determined by the C─H∙∙∙O hydrogen bonded interaction, C─X∙∙∙C Lewis acid-base interaction, π∙∙∙π, p∙∙∙π\* and π∙∙∙π\* interactions. The contribution of the π∙∙∙π\* interaction to the formation of the complexes between CO2 -philic compounds and CO2 has been observed. The π∙∙∙π interactions were significantly stronger than the side-on hydrogenbond interactions but weaker than EDA-type interaction. The π∙∙∙π interactions can significantly contribute to adsorption of CO2 in practical applications. Consequently, approach to the increase in the aromaticity of the linker should be an effective way with purpose of increasing the CO2 adsorption in MOF/ZIF materials.

#### **3.2. Interaction of CO2 with model functionalized organic compounds and their substituted derivatives**

#### *3.2.1. Interaction of CO2 with model functionalized organic compounds*

Up to now, a large number of complexes for interactions of CO2 with simple functionalized organic molecules have been studied using quantum chemical methods [33–43]. In more recent investigations, the Lewis acid-base interaction between CO2 and some carbonyl-functionalized compounds has been reported [34, 44, 64–67]. The existence of the C─H∙∙∙O hydrogen bond in complexes was confirmed clearly by Wallen et al. [38, 39, 60]. However, it is necessary to perform systematic studies to elucidate the nature of the interactions formed in complexes, rather than considering the results obtained from few specific systems. We investigated complexes of CO<sup>2</sup> and some typically functionalized organic molecules such as methanol (CH3 OH), methylamine (CH3 NH2 ), formaldehyde (HCHO), formic acid (HCOOH), dimethylether (CH3 OCH3 ), acetone (CH3 COCH3 ) and methyl formate (HCOOCH3 ) [40] Obtained results showed that the Lewis acid-base interaction such as C─N∙∙∙C(CO2 ), C═O∙∙∙C(CO2 ) plays a more dominant role compared to the C─H∙∙∙O blue-shifting hydrogen bond in stabilizing most of the complexes. However, the stability of the HCOOH∙∙∙CO2 pair is mainly determined by O─H∙∙∙O red-shifting hydrogen bond. All interaction energies are significantly negative, indicating that obtained complexes are quite stable. Particularly, the interaction energies with both ZPE and BSSE corrections are in the range from −3.3 to −14.2 kJ.mol−1, in which the HCOOH∙∙∙CO2 pair is the most stable, whereas the weakest one is the HCHO∙∙∙CO2 pair. As a consequence, solubility of HCOOH in sc-CO2 is likely to be the largest in all the considered compounds. The interaction energies of some considered complexes are more negative than the values reported in the previous works [35, 64]. Thus, for the pair (CH3 OH, CO2 ), its interaction energy of −13.3 kJ.mol−1 with only ZPE correction, and −11.4 kJ.mol−1 with both ZPE and BSSE corrections is more negative than that of −11.3 kJ.mol−1 obtained with only BSSE correction at the MP2/aug-cc-pVTZ level [64]. Another example is that the BSSE corrected interaction energy of the CH3 OCH3 ∙∙∙CO2 pair was computed to be −13.1 kJ.mol−1 at the MP2/6-311++G(2d,2p)//MP2/6-311++G(d,p) level [35] while it is −13.7 kJ.mol−1 with ZPE and BSSE corrections, and −16.3 kJ.mol−1 with only ZPE correction in the present work.

*3.1.4. Concluding remarks on interaction of CO2*

cantly contribute to adsorption of CO2

interaction to the formation of the complexes between CO2

H6 ∙∙∙CO2 , S-C5 H5 N∙∙∙CO2

adsorption in MOF/ZIF materials.

Up to now, a large number of complexes for interactions of CO2

Interactions of CO2

**Figure 2.** Optimized structures of S-C6

112 Carbon Dioxide Chemistry, Capture and Oil Recovery

increasing the CO2

**3.2. Interaction of CO2**

**substituted derivatives**

*3.2.1. Interaction of CO2*

 *with model hydrocarbons*

H5 N∙∙∙CO2 .

, and S-C4

with model hydrocarbons including saturated, unsaturated, aromatic


with simple function-

and some

in practical applications. Consequently, approach

has

hydrocarbons and theirs substituted derivatives were investigated using high-level *ab initio* methods. In general, the strength of the complexes increases in going from the interaction of the saturated hydrocarbons with carbon dioxide to unsaturated hydrocarbons with carbon dioxide and finally to the parent aromatic hydrocarbons with carbon dioxide. The stability of the obtained complexes is determined by the C─H∙∙∙O hydrogen bonded interaction, C─X∙∙∙C Lewis acid-base interaction, π∙∙∙π, p∙∙∙π\* and π∙∙∙π\* interactions. The contribution of the π∙∙∙π\*

been observed. The π∙∙∙π interactions were significantly stronger than the side-on hydrogenbond interactions but weaker than EDA-type interaction. The π∙∙∙π interactions can signifi-

to the increase in the aromaticity of the linker should be an effective way with purpose of

 *with model functionalized organic compounds*

In more recent investigations, the Lewis acid-base interaction between CO2

alized organic molecules have been studied using quantum chemical methods [33–43].

carbonyl-functionalized compounds has been reported [34, 44, 64–67]. The existence of the C─H∙∙∙O hydrogen bond in complexes was confirmed clearly by Wallen et al. [38, 39, 60]. However, it is necessary to perform systematic studies to elucidate the nature of the

 **with model functionalized organic compounds and their** 

In 2011, our group investigated the interactions of CO2 with substituted derivatives of formaldehyde and thioformaldehyde [42]. The interaction energies (with ZPE and BSSE corrections) of −10.5 kJ.mol−1 for CH3 CHO∙∙∙CO2 and −9.1 kJ.mol−1 for CH3 CHS∙∙∙CO2 are more negative than for complexes of HCHO∙∙∙CO2 and HCHS∙∙∙CO2 , respectively. The obtained results supported that both O and S atoms act as Lewis bases and the >C═X (X = O, S) groups should be considered as potential candidates for the design of CO2 -philic materials. The interactions between carbonyl compounds and CO2 are stronger than those of fluorocarbons and fluorocarbonyl compounds. Obtained results suggested that the Lewis acid-base and hydrogen bonded interactions should be the key factors in governing the solubility of isolated monomers in sc-CO2 , in which the crucial role of the former is suggested. The function of these interactions in the solvation of >C═O and >C═S compounds in sc-CO2 may be important in terms of the specific solute-solvent.

In 2014, we investigated the interactions between some carbonyl compounds including acetone (CH3 COCH3 ) with CO2 [41]. Interaction energies of obtained complexes which are denoted by **H1**, **H2**, **H3,** and **H4** at the CCSD(T)/6-311++G(3df,2pd)//MP2/6-311++G(2d,2p) level are gathered in **Table 1**. The results indicate that the stability of studied complexes is contributed by both Lewis acid-base and hydrogen bonded interactions. As shown in **Table 1**, the interaction energy for **H1** (−10.3 kJ.mol−1) is less negative than that reported in Ref. [40] (−11.1 kJ.mol−1) at CCSD(T)/aug-cc-pVTZ but is more negative than that in Ref. [64] (−8.8 kJ.mol−1) at MP2/aug-cc-pVDZ. Notably, complex **H3** is less stable than **H1** in this work, which is different from the results reported by Ruiz-Lopez et al [68]. By using the levels of theory MP2/aug-cc-pVDZ and CCSD(T)/aug-cc-pVDZ, the authors suggested


**Table 1.** Interaction energies (kJ.mol−1) corrected for only ZPE and for both ZPE and BSSE of the complexes.

that **H1** is *ca.* 1.0 kJ.mol−1 higher in interaction energy than **H3**. These authors conclusively suggested that the >C═O group can be a valuable candidate in the design of CO2 -philic and adsorbent materials.

Further, interactions of CO2 with CH3 SZCH3 (Z = O, S) were also investigated by our group [43]. Three stable shapes of the complexes at MP2/6-311++G(2d,2p) are presented in **Figure 3**, denoted hereafter by **T1**, **T2** and **T3**. Interaction energies of complexes at two different levels of theory are also given in the **Table 2**.

also suggested a stronger interaction of CO2

Taken from MP2/aug-cc-pVTZ//MP2/6-311++G(2d,2p).

Taken from CCSD(T)/6-311++G(3df,2pd)//MP2/6-311++G(2d,2p).

∙∙∙CO2

pVDZ//MP2/6-31+G(d) reported in Ref. [38].

 *with model functionalized organic compounds*

action energy in obtained complexes between CO2

compounds. The complexes of the interactions of CO2

tion and storage materials in the future.

**Table 2.** Interaction energies corrected for ZPE (∆E<sup>0</sup>

SOCH3

For the CH3

complexes.

Source: Phuong et al. [43].

a

b

*CO2*

CH3

CH3

a CH3

of CH3

CH3

SOCHX2

tion with CO2

SOCHX2

COCH3

∙∙∙CO2

∙∙∙CO2

group of CH3

SOCHX2

from H *via* F to Cl to Br and finally to CH<sup>3</sup>

∙∙∙CO2

by two alike CH3

sequence from F, H, Cl, Br to CH3

SOCH3

also leads to a slight enhancement of stability of the CH3

complexes relative to CH3

one, and they both should be candidates for designing CO2

**Structures Z = O Z = S**

with the >S═O moiety compared to the >S═S

, in kJ.mol−1) and for ZPE and BSSE (∆E\*, in kJ.mol−1) of obtained

complexes, the strength of **T3** is close to that of **T1** reported by

with CH3

by two alike X groups significantly influences the strength

, F, Cl and Br groups, and the results showed that interaction

SSCHX2

∙∙∙CO2

. In Ref. [41], we replaced two H atoms in a CH3

Wallen et al. [38]. Thus, the interaction energies of **T1** in this work are −14.4 kJ.mol−1 at MP2/ aug-cc-pVTZ//MP2/6-311++G(2d,2p) and −14.5 kJ.mol−1 at CCSD(T)/6-311++G(3df,2pd)// MP2/6-311++G(2d,2p), which are in consistent with the value of −14.3 kJ.mol−1 at MP2/aug-cc-

**T1 T2 T3 T1 T2 T3**

Understanding Interaction Capacity of CO2 with Organic Compounds at Molecular Level:…

∆E<sup>a</sup> −17.2 −14.3 −17.4 −17.1 −13.8 −16.9 ∆E<sup>b</sup> −17.6 −14.8 −17.7 −16.8 −13.6 −16.4 ∆E\*<sup>a</sup> −14.4 −10.9 −13.7 −14.2 −9.8 −13.2 ∆E\*<sup>b</sup> −14.5 −11.3 −14.0 −13.5 −9.6 −12.0

We now continue to discuss in some details the effects of substitution to the overall inter-

Cl, Br; Z = O, S) were studied by our group and reported in Ref. [43]. In general, the

This firmly indicates that the >S═O, as compared to the >S═S, has a stronger interac-

interaction of the former than the latter in stabilizing the examined complexes. For the

energies of complexes are in the range from −9.2 to −10.7 kJ.mol−1 with both ZPE and BSSE

, which originates from a contribution of a larger attractive electrostatic

SOCH3

complexes, the strength is enhanced by the X substitution in the order

*3.2.2. Effect of various substituted groups to strength the complexes formed by interaction of* 

complexes are more stable than the CH3


http://dx.doi.org/10.5772/intechopen.71878

with model functionalized organic

∙∙∙CO2

complexes. The replacement

complexes in the

group of

(X = H, CH3

complexes.

, F,

SZCHX2

SSCHX2

. Therefore, the substitution of two H atoms in

∙∙∙CO2

adsorp-

115

The CH3 SZCH3 ∙∙∙CO2 (Z = O, S) complexes are in general stabilized by the Lewis acid-base, chalcogen-chalcogen and hydrogen bonded interactions. However, the crucial role contributing to the overall stabilization energy should be the Lewis acid-base interaction. The obtained results pointed out a slight difference in the interaction energies between the two employed levels of theory. Thus, the interaction energies of the examined complexes range from −13.8 to −17.2 and −9.8 to −14.4 kJ.mol−1 (at MP2/aug-cc-pVTZ//MP2/6-311++G(2d,2p)), and −13.6 to −17.7 and -9.6 to −14.5 kJ.mol−1 (at CCSD(T)/6-311++G(3df,2pd)//MP2/6- 311++G(2d,2p)) for only ZPE correction and for both ZPE and BSSE corrections, respectively (*cf.* **Table 2**). The results indicate that the formed complexes are significantly stable, and more stable than the complexes of the >C═O or >C═S functionalized compounds with CO2 reported in Refs. [38, 40, 42]. This implies a stronger interaction of CO2 with the >S═O and >S═S functional groups relative to the >C═O and >C═S counterparts. In addition, we

.

**Figure 3.** Stable shapes of complexes between CH3 SZCH3 (Z = O, S) and CO2


a Taken from MP2/aug-cc-pVTZ//MP2/6-311++G(2d,2p).

b Taken from CCSD(T)/6-311++G(3df,2pd)//MP2/6-311++G(2d,2p).

Source: Phuong et al. [43].

that **H1** is *ca.* 1.0 kJ.mol−1 higher in interaction energy than **H3**. These authors conclusively

**H1 H2 H3 H4**

[43]. Three stable shapes of the complexes at MP2/6-311++G(2d,2p) are presented in **Figure 3**, denoted hereafter by **T1**, **T2** and **T3**. Interaction energies of complexes at two different levels

chalcogen-chalcogen and hydrogen bonded interactions. However, the crucial role contributing to the overall stabilization energy should be the Lewis acid-base interaction. The obtained results pointed out a slight difference in the interaction energies between the two employed levels of theory. Thus, the interaction energies of the examined complexes range from −13.8 to −17.2 and −9.8 to −14.4 kJ.mol−1 (at MP2/aug-cc-pVTZ//MP2/6-311++G(2d,2p)), and −13.6 to −17.7 and -9.6 to −14.5 kJ.mol−1 (at CCSD(T)/6-311++G(3df,2pd)//MP2/6- 311++G(2d,2p)) for only ZPE correction and for both ZPE and BSSE corrections, respectively (*cf.* **Table 2**). The results indicate that the formed complexes are significantly stable, and more stable than the complexes of the >C═O or >C═S functionalized compounds with

and >S═S functional groups relative to the >C═O and >C═S counterparts. In addition, we

(Z = O, S) complexes are in general stabilized by the Lewis acid-base,


with the >S═O

(Z = O, S) were also investigated by our group

suggested that the >C═O group can be a valuable candidate in the design of CO2

**Table 1.** Interaction energies (kJ.mol−1) corrected for only ZPE and for both ZPE and BSSE of the complexes.

∆E −12.7 −11.3 −12.7 −4.7 ∆E\* −10.3 −9.4 −9.2 −2.4

SZCH3

reported in Refs. [38, 40, 42]. This implies a stronger interaction of CO2

SZCH3

(Z = O, S) and CO2

.

with CH3

adsorbent materials.

Source: Dai et al. [41].

The CH3

CO2

Further, interactions of CO2

SZCH3

of theory are also given in the **Table 2**.

114 Carbon Dioxide Chemistry, Capture and Oil Recovery

∙∙∙CO2

**Figure 3.** Stable shapes of complexes between CH3

**Table 2.** Interaction energies corrected for ZPE (∆E<sup>0</sup> , in kJ.mol−1) and for ZPE and BSSE (∆E\*, in kJ.mol−1) of obtained complexes.

also suggested a stronger interaction of CO2 with the >S═O moiety compared to the >S═S one, and they both should be candidates for designing CO2 -philic materials, CO2 adsorption and storage materials in the future.

For the CH3 SOCH3 ∙∙∙CO2 complexes, the strength of **T3** is close to that of **T1** reported by Wallen et al. [38]. Thus, the interaction energies of **T1** in this work are −14.4 kJ.mol−1 at MP2/ aug-cc-pVTZ//MP2/6-311++G(2d,2p) and −14.5 kJ.mol−1 at CCSD(T)/6-311++G(3df,2pd)// MP2/6-311++G(2d,2p), which are in consistent with the value of −14.3 kJ.mol−1 at MP2/aug-ccpVDZ//MP2/6-31+G(d) reported in Ref. [38].

#### *3.2.2. Effect of various substituted groups to strength the complexes formed by interaction of CO2 with model functionalized organic compounds*

We now continue to discuss in some details the effects of substitution to the overall interaction energy in obtained complexes between CO2 with model functionalized organic compounds. The complexes of the interactions of CO2 with CH3 SZCHX2 (X = H, CH3 , F, Cl, Br; Z = O, S) were studied by our group and reported in Ref. [43]. In general, the CH3 SOCHX2 ∙∙∙CO2 complexes are more stable than the CH3 SSCHX2 ∙∙∙CO2 complexes. This firmly indicates that the >S═O, as compared to the >S═S, has a stronger interaction with CO2 , which originates from a contribution of a larger attractive electrostatic interaction of the former than the latter in stabilizing the examined complexes. For the CH3 SOCHX2 ∙∙∙CO2 complexes, the strength is enhanced by the X substitution in the order from H *via* F to Cl to Br and finally to CH<sup>3</sup> . Therefore, the substitution of two H atoms in a CH3 group of CH3 SOCH3 by two alike X groups significantly influences the strength of CH3 SOCHX2 ∙∙∙CO2 complexes relative to CH3 SOCH3 ∙∙∙CO2 complexes. The replacement also leads to a slight enhancement of stability of the CH3 SSCHX2 ∙∙∙CO2 complexes in the sequence from F, H, Cl, Br to CH3 . In Ref. [41], we replaced two H atoms in a CH3 group of CH3 COCH3 by two alike CH3 , F, Cl and Br groups, and the results showed that interaction energies of complexes are in the range from −9.2 to −10.7 kJ.mol−1 with both ZPE and BSSE corrections, which are more negative than that of interactions of CO2 with hydrocarbons and fluorocarbons. Thus, the interaction energies range from −3.7 to −4.9 kJ.mol−1 for the complexes of CO2 with the hydrocarbons such as CH4 , C2 H6 , CF4 , C2 F6 ; and from −2.4 to −7.8 kJ.mol−1 for the complexes of CO2 with CH4−nFn (n = 0 ÷ 4) [57, 60] at the MP2/aug-ccpVDZ level. These results are in line with the suggestion on larger stability of carbonyl relative to fluorocarbons and other functionalized compounds in interacting with CO<sup>2</sup> . Generally, the strength of CH3 COCHR2 ∙∙∙CO2 complexes is gently increased when R = CH3 as compared to CH3 COCH3 ∙∙∙CO2 , while it is slightly decreased with R = F, Cl and Br.

relative to the >C═O and >C═S counterparts, and therefore it should be suggested that they would be potential groups attached on the surface of materials to adsorb CO2

Understanding Interaction Capacity of CO2 with Organic Compounds at Molecular Level:…

From the contents mentioned above, we can draw some key conclusions for this chapter:

and functionalized organic compounds along with its derivatives were investigated by using *ab initio* calculations. The obtained results show that interaction capacity between

plexes is found for interaction of aromatic relative to saturated and unsaturated hydrocarbons with carbon dioxide. In the case of interactions between functionalized organic

**ii.** The stability of examined complexes is determined by weakly noncovalent interaction including C─H∙∙∙O, O─H∙∙∙O of hydrogen bonds, X∙∙∙C Lewis acid-base interaction, O∙∙∙O chalcogen-chalcogen, π∙∙∙π, p∙∙∙π\*, and π∙∙∙π\* interactions. Remarkably, contribution of

has been revealed in our work. The π∙∙∙π interactions can significantly contribute to the

lecular interaction tends to decrease in going from >C═S∙∙∙C via > C═O∙∙∙C to >C═X∙∙∙C

with the >S═O and >S═S counterparts relative to the >C═O and >C═S ones is re-

**iii.** It is found that the functional groups such as carbonyl and sulfonyl give a more stable

the π∙∙∙π\* interaction to the complex formed between CO<sup>2</sup>

(X = F, Cl, Br). This observation points out enormous applicability of CO2

vealed, and they should be valuable candidates for synthesizing CO2

.

Department of Chemistry, Laboratory of Computational Chemistry and Modelling, Quy

is stronger than that of other functionalized compounds. Obtained results on interac-

into systems leads to an increase in the stability of complexes formed.

(n = 1–3) with functionalized organic compounds indicate that the addition

in MOF/ZIF materials. Obtained results show the strength of intermo-

than other functionalized groups, in which a stronger interaction

with various organic compounds including hydrocarbons

, interaction capacity of the carbonyl and sulfonyl compounds with

with model hydrocarbons, the larger stability of com-

is stronger than that of model hydrocarbons

http://dx.doi.org/10.5772/intechopen.71878




used to design CO2

with CO2

tion of nCO2

of more CO2

adsorption of CO2

based on thiocarbonyls.

interaction with CO2

finding new materials to adsorb CO<sup>2</sup>

Pham Ngoc Khanh and Nguyen Tien Trung\*

Nhon University, Quy Nhon, Binh Dinh, Vietnam

\*Address all correspondence to: nguyentientrung@qnu.edu.vn

of CO2

**Author details**

CO2

**4. Concluding remarks**

**i.** Interaction capacity of CO2

compounds with CO2


functionalized organic compounds with CO2

. For interactions of CO2

and

117

#### *3.2.3. Interaction of nCO2 (n = 1:3) with model functionalized organic compounds*

It is important to investigate the strength of interactions between CO2 and carbonyl-containing molecules, as well as the underlying their chemical nature. Due to a strong interest in CO2 as a solvent, it is imperative to consider aggregates in which a solute molecule is surrounded by a number of CO2 molecules, an unexplored area at present [69]. Expansion of the system by adding more CO2 molecules shows how the geometry and bonding in the heterodimer is affected by placement of the solute in an environment. This would make our simulation more akin to solvation phenomenon, and particularly the magnitude of cooperative effects. The complexes formed by H<sup>2</sup> CO, CH3 CHO, and (CH3 )2 CO with two and three molecules of CO2 are studied using *ab initio* calculations by Scheniner et al. [69]. There are a host of different geometries adopted by the complexes of the carbonyl with two or three CO2 molecules, with small energy differences. The bonding features of the heterodimers are generally carried over to these larger heterotrimers and tetramers, although the linear C═O∙∙∙C arrangement of the binary complexes is largely absent. The O∙∙∙O chalcogen bonds, absent in the heterodimers, play a major role in many of the larger complexes. The degree of cooperativity in these oligomers is generally rather small, with a maximal positive cooperativity of only 1.1 kJ/mol. The binding energies of heterotetramers complexes range from −39.0 to −50.7 kJ.mol−1, which are more negative than heterodimers (−8.8 to −12.5 kJ.mol−1) and trimers complexes (−23.1 to −34.2 kJ.mol−1). These results suggest that the addition of more carbon dioxide molecules into systems leads to a larger increase in stability of complexes.

#### *3.2.4. Concluding remarks on interaction capacity of CO2 with model functionalized organic compounds*

The organic compounds functionalized by hydroxyl, carbonyl, thiocarbonyl, carboxyl and amide groups have been paid much attention as CO2 -philic compounds. The carbonyl and thiocarbonyl compounds have presented a higher stability, as compared to other functionalized ones, when they interact with CO2 . This durability has been assigned to a main contribution of the >C═Z∙∙∙C (Z = O, S) Lewis acid-base interaction and/or an additional cooperation of the C─H∙∙∙O hydrogen bonded interaction, except for the case of the HCOOH∙∙∙CO2 complex, where the role of the O─H∙∙∙O hydrogen bond was found to be more important than the >C═O∙∙∙C Lewis acid-base interaction. We have also found that there is a stronger interaction of CO2 with the >S═O and >S═S containing compounds relative to the >C═O and >C═S counterparts, and therefore it should be suggested that they would be potential groups attached on the surface of materials to adsorb CO2 and used to design CO2 -philic materials.
