**4. Concluding remarks**

corrections, which are more negative than that of interactions of CO2

COCHR2

It is important to investigate the strength of interactions between CO2

∙∙∙CO2

with the hydrocarbons such as CH4

complexes of CO2

as compared to CH3

in CO2

three CO2

*compounds*

*3.2.3. Interaction of nCO2*

three molecules of CO2

stability of complexes.

of the HCOOH∙∙∙CO2

−7.8 kJ.mol−1 for the complexes of CO2

116 Carbon Dioxide Chemistry, Capture and Oil Recovery

COCH3

Generally, the strength of CH3

surrounded by a number of CO2

of the system by adding more CO2

erative effects. The complexes formed by H<sup>2</sup>

*3.2.4. Concluding remarks on interaction capacity of CO2*

and amide groups have been paid much attention as CO2

other functionalized ones, when they interact with CO2

that there is a stronger interaction of CO2

and fluorocarbons. Thus, the interaction energies range from −3.7 to −4.9 kJ.mol−1 for the

pVDZ 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>

 *(n = 1:3) with model functionalized organic compounds*

as a solvent, it is imperative to consider aggregates in which a solute molecule is

CO, CH3

molecules, with small energy differences. The bonding features of the heterodi-

taining molecules, as well as the underlying their chemical nature. Due to a strong interest

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 coop-

are a host of different geometries adopted by the complexes of the carbonyl with two or

mers 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

The organic compounds functionalized by hydroxyl, carbonyl, thiocarbonyl, carboxyl

bonyl and thiocarbonyl compounds have presented a higher stability, as compared to

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

to be more important than the >C═O∙∙∙C Lewis acid-base interaction. We have also found

complex, where the role of the O─H∙∙∙O hydrogen bond was found

∙∙∙CO2

, C2 H6 , CF4 , C2 F6

, while it is slightly decreased with R = F, Cl and Br.

molecules, an unexplored area at present [69]. Expansion

molecules shows how the geometry and bonding in the

CHO, and (CH3

 *with model functionalized organic* 

with the >S═O and >S═S containing compounds


. This durability has been assigned

are studied using *ab initio* calculations by Scheniner et al. [69]. There

)2

with CH4−nFn (n = 0 ÷ 4) [57, 60] at the MP2/aug-cc-

complexes is gently increased when R = CH3

with hydrocarbons

; and from −2.4 to

and carbonyl-con-

CO with two and

.

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

