26
2 Actual Potentials of Theoretical Chemistry: What Can Be Obtained
Table 2.7 CT-complex with the interaction energy E and its decomposition obtained by HF/431G. Energies are in kcal/mol
D–A
CT type
R(D–A)
(in Å)
E
ES
EX
PL
CT
MIX
H 3 N–BF 3
n → σ*
1.60
−71.5
−142.3
136.3
−42.7
−52.7
29.9
H 3 N–BH 3
n → σ*
1.70
−44.7
−92.9
86.9
−17.2
−27.1
5.6
OC–BH 3
σ → σ*
π* ← π
1.63
−28.5
−60.9
98.9
−61.8
−68.3
63.6
HF–ClF
n → σ*
2.74
−3.4
−3.6
1.8
−0.2
−1.4
0.1
H 3 N–F 2
n → σ*
3.00
−1.1
−0.8
0.6
−0.3
−0.6
0.0
C 6 H 6 –F 2
π → σ*
3.3
−0.3
−0.2
0.3
−0.0
−0.4
0.0
Adapted with permission from Morokuma (1977). Copyright 1977 American Chemical Society
CT the second largest. The energy decomposition is useful to understand the origin
of various H-bonds.
There are CT-complexes consisting of combination of various electron donors
(D) and acceptors (A). Calculation data of interaction energies E in several CTcomplexes and the energy decomposition results are listed in Table 2.7 (Morokuma
1977). Compared with the H-bond, the interaction energies are almost the
same or rather larger. For instance, in the combination of NH 3 –BF 3 , E reaches
−71.5 kcal/mol being comparable with the usual covalent bond. Contributions from
ES and CT terms are appreciable in the combination of NH 3 and borane compounds.
Theoretical calculations reveal that the CT in these complexes takes place from the
lone pair of amine (n) to σ-antibonding MO of BF 3 or BH 3 (σ*). It is of interest to
point out that there are two ways of the CT directions in carbonyl (CO) and borane
(BH 3 ) complex, namely, σ → σ* from CO to BH 3 , and π → π* from BH 3 to CO.
These two-way CT directions are called “donation” and “back-donation” as is often
encountered in the organometallic compounds. These donations eventually make the
CT term considerably larger than those with the ordinary one-way donation.
The interatomic or intermolecular van der Waals interactions range
ca. 0.01 – 0.1 kcal/mol and are much weaker than the weak bonds mentioned above
providing no more perceivable bond. Origin of this interaction energy is classified into
a couple of ingredients such as coming from orientation, induction, and dispersion
interactions. The most essential and universal van der Waals interaction consists of
the dispersion term between any atoms and between molecules involving both polar
and non-polar ones.
The van der Waals interaction is said to be of importance in many chemical
phenomena in (i) adsorption of molecules on surface such as catalyst, zeolite, or
metal organic frameworks (MOF), (ii) π-π stacking of planar molecules such as
pentacene crystal, graphite, or even aggregate of carbon nanotubes, and (iii) source
of miscellaneous adhesion found in stick tape, glue, or other adhesive substances.
Theoretical treatment of these interactions should be treated by the perturbation
method in principle, but this method has recently been also incorporated into the
2 Actual Potentials of Theoretical Chemistry: What Can Be Obtained
Table 2.7 CT-complex with the interaction energy E and its decomposition obtained by HF/431G. Energies are in kcal/mol
D–A
CT type
R(D–A)
(in Å)
E
ES
EX
PL
CT
MIX
H 3 N–BF 3
n → σ*
1.60
−71.5
−142.3
136.3
−42.7
−52.7
29.9
H 3 N–BH 3
n → σ*
1.70
−44.7
−92.9
86.9
−17.2
−27.1
5.6
OC–BH 3
σ → σ*
π* ← π
1.63
−28.5
−60.9
98.9
−61.8
−68.3
63.6
HF–ClF
n → σ*
2.74
−3.4
−3.6
1.8
−0.2
−1.4
0.1
H 3 N–F 2
n → σ*
3.00
−1.1
−0.8
0.6
−0.3
−0.6
0.0
C 6 H 6 –F 2
π → σ*
3.3
−0.3
−0.2
0.3
−0.0
−0.4
0.0
Adapted with permission from Morokuma (1977). Copyright 1977 American Chemical Society
CT the second largest. The energy decomposition is useful to understand the origin
of various H-bonds.
There are CT-complexes consisting of combination of various electron donors
(D) and acceptors (A). Calculation data of interaction energies E in several CTcomplexes and the energy decomposition results are listed in Table 2.7 (Morokuma
1977). Compared with the H-bond, the interaction energies are almost the
same or rather larger. For instance, in the combination of NH 3 –BF 3 , E reaches
−71.5 kcal/mol being comparable with the usual covalent bond. Contributions from
ES and CT terms are appreciable in the combination of NH 3 and borane compounds.
Theoretical calculations reveal that the CT in these complexes takes place from the
lone pair of amine (n) to σ-antibonding MO of BF 3 or BH 3 (σ*). It is of interest to
point out that there are two ways of the CT directions in carbonyl (CO) and borane
(BH 3 ) complex, namely, σ → σ* from CO to BH 3 , and π → π* from BH 3 to CO.
These two-way CT directions are called “donation” and “back-donation” as is often
encountered in the organometallic compounds. These donations eventually make the
CT term considerably larger than those with the ordinary one-way donation.
The interatomic or intermolecular van der Waals interactions range
ca. 0.01 – 0.1 kcal/mol and are much weaker than the weak bonds mentioned above
providing no more perceivable bond. Origin of this interaction energy is classified into
a couple of ingredients such as coming from orientation, induction, and dispersion
interactions. The most essential and universal van der Waals interaction consists of
the dispersion term between any atoms and between molecules involving both polar
and non-polar ones.
The van der Waals interaction is said to be of importance in many chemical
phenomena in (i) adsorption of molecules on surface such as catalyst, zeolite, or
metal organic frameworks (MOF), (ii) π-π stacking of planar molecules such as
pentacene crystal, graphite, or even aggregate of carbon nanotubes, and (iii) source
of miscellaneous adhesion found in stick tape, glue, or other adhesive substances.
Theoretical treatment of these interactions should be treated by the perturbation
method in principle, but this method has recently been also incorporated into the