Table 2.
Structural, electronic, and energy characteristics of models of various associates in comparison with the initial models of MEA and H2O. An analysis of data presented in Table 2 allows us to conclude that association energy, which determines the stability of a complex, depends significantly on the structure of the complex and, to a large extent, on the number of hydrogen bonds. As the strength of the associate increases, the polarizability of N-H and O-H atoms involved in association increases, i.e., positive charges on hydrogen atoms and negative charges on oxygen and nitrogen atoms involved in the association increase. Lengths of hydrogen bonds in the most stable complexes are shorter, while bonds between atoms inside the molecule are lengthened. From the data in Table 2, it is obvious that all listed changes in structural and electronic characteristics are more pronounced in the MEA-10H2O associate, as well as in the associate of 10 water molecules (last 2 rows of Table 2). Structures of these associates, together with the theoretical vibrational spectra, are shown in Figure 5 and Figure 6. In these associates, oxygen atoms arise in water molecules with a negative charge equal to −1, and the total charge of two protons at such oxygen atoms is equal to +1.
| No. | Associate Model | E∆. kcal/mol | Bond Lengths (Å) | Charges on Atoms (e) | Angle H-N-Ho |
Dip. Moment (D) | |||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| MEA | H2O:O-H | HO⋯H | HN⋯H | MEA | H2O | ||||||||||
| O-H | N-H | N | HN | O | Ho | O | H | ||||||||
| 1 | MEA | - | 0.967 | 1.017 | - | - | - | 0.60 | +0.31 | −0.54 | +0.37 | - | - | 106.3 | 2.232 |
| 2 | H2O | - | - | - | 0.967 | - | - | - | - | - | - | - | +0.38 | - | 2.456 |
| 3 | 2 MEA | −3.73 | 0.950 | 1.00 | - | - | 2.090 | −0.78 | +0.31 | −0.68 | +0.36 | - | - | 106.9 | 0.516 |
| 4 | 3 MEA | −3.28 | 0.945 | 1.002 | - | - | 2.281 | −0.78 | +0.31 | −0.68 | +0.36 | - | - | 106.5 | 7.120 |
| 5 | 2H2O | −5.02 | - | - | 0.948 | 2.040 | - | - | - | - | - | −0.76 | +0.42 | - | 3.296 |
| 6 | MEA-H2O | −5.51 | 0.943 | 1.000 | 0.949 | 2.001 | - | −0.63 | +0.29 | −0.63 | +0.37 | −0.78 | +0.44 | 107.6 | 2.884 |
| 7 | MEA-2H2O | −9.11 | 0.968 | 1.020 | 0.983 | 1.815 | 2.359 | −0.61 | +0.33 | −0.57 | +0.40 | −0.84 | +0.45 | 106.9 | 3.589 |
| 8 | 3 MEA-3H2O | −17.87 | 0.955 | 1.002 | 0.957 | 1.878 | 2.007 | −0.77 | +0.30 | −0.72 | +0.38 | −0.75 | +0.41 | 106.2 | 3.650 |
| 9 | 10H2O | −59.70 | - | - | 0.995 | 1.645 | - | - | - | - | - | −1.06 | +0.66 | - | 7.660 |
| 10 | MEA-10H2O | −67.74 | 0.988 | 1.020 | 0.992 | 1.693 | 1.890 | −0.66 | +0.45 | −0.94 | +0.49 | −1.00 | +0.50 | 109.1 | 2.825 |