used (see Computational details). This is bound to be reflected in the results of
ELF-analysis.
Topological analysis of ELF performed for XO1NO2 molecules shows an
interesting topological structures. Only single local maximum, the non-bonding
V(N) attractor, in the N–O1 bonding region can be been found for both conformers
of FONO and ClONO and for anti isomers of BrONO and IONO (see Table 19.3).
The V(N) attractor is situated in the vicinity of the C(N) core attractor. This position
of the single V(N) attractor supports ELF-topology of type III for the N–O bond as
described above. The DFT(B2PLYP)/aug-cc-pVTZ results for the syn conformers
of BrONO and IONO show the protocovalent N–O1 bond with two non-bonding
attractors, V(O1) and V(N).
Our previous studies [20, 28] related to FONO where a correlated wave function
from the CCSD/aug-cc-pVTZ//CCSD(T)/aug-cc-pVTZ was used [28], showed the
protocovalent N–O1 bond for syn isomer (r(N–O1) = 1.467 Å) and only single
V(N) attractor for anti conformer (r(N–O1) = 1.500 Å). Analysis of ELF-topology
evolution for the N–O1 bond during dissociation process confirmed that only the
V(N) attractor is observed at equilibrium. The V(N,O1) attractor expected for
‘normal’ covalent bond and two attractors V(N), V(O1) of the protocovalent bond
are observed for shorter distances than that optimised for the equilibrium structure.
The discrepancy between the DFT(B2PLYP) and CCSD results for FONO shows
that the level of calculations plays important role in the study of the nature of the
N–O1 bond in XO1NO2. Similar conclusion can be drawn from topological
analysis of ELF performed for the ClONO and BrONO molecules using the various
wave functions [23].
Table 19.3 N–O bond lengths and mean electron populations,
N, for the localisaton basins for the
N–O1 bond in halogen nitrites XONO (XO1–NO2; X = F, Cl, Br, I) and peroxynitrous acid
HOONO (HOO1–NO2)
No
Molecule
Conformer
r(N–O1) [Å]
V(O1) [e]
V(N) [e]
V(N,O1) [e]
1
FONO
syn
1.490
–
0.41
–
anti
1.533
–
0.37
–
2
ClONO
syn
1.496
–
0.42
–
anti
1.554
–
0.33
–
3
BrONO
syn
1.403
0.33
0.52
–
anti
1.533
–
0.37
–
4
IONO
syn
1.348
0.50
0.62
–
anti
1.504
–
0.43
–
5
HOONO
syn-syn
1.393
–
–
0.91
syn-perp
1.505
–
0.46
–
anti-perp
1.498
–
0.46
–
The topological analysis of ELF performed at the B2PLYP/aug-cc-pVTZ level for XONO (X = F,
Cl, Br) and HOONO molecule and the B2PLYP/aug-cc-pVTZ(H,N,O),TZVPPall(I)//
B2PLYP/aug-cc-pVTZ-PP level for IONO
19 Diversity of the Nature of the Nitrogen-Oxygen Bond …
539
ELF-analysis.
Topological analysis of ELF performed for XO1NO2 molecules shows an
interesting topological structures. Only single local maximum, the non-bonding
V(N) attractor, in the N–O1 bonding region can be been found for both conformers
of FONO and ClONO and for anti isomers of BrONO and IONO (see Table 19.3).
The V(N) attractor is situated in the vicinity of the C(N) core attractor. This position
of the single V(N) attractor supports ELF-topology of type III for the N–O bond as
described above. The DFT(B2PLYP)/aug-cc-pVTZ results for the syn conformers
of BrONO and IONO show the protocovalent N–O1 bond with two non-bonding
attractors, V(O1) and V(N).
Our previous studies [20, 28] related to FONO where a correlated wave function
from the CCSD/aug-cc-pVTZ//CCSD(T)/aug-cc-pVTZ was used [28], showed the
protocovalent N–O1 bond for syn isomer (r(N–O1) = 1.467 Å) and only single
V(N) attractor for anti conformer (r(N–O1) = 1.500 Å). Analysis of ELF-topology
evolution for the N–O1 bond during dissociation process confirmed that only the
V(N) attractor is observed at equilibrium. The V(N,O1) attractor expected for
‘normal’ covalent bond and two attractors V(N), V(O1) of the protocovalent bond
are observed for shorter distances than that optimised for the equilibrium structure.
The discrepancy between the DFT(B2PLYP) and CCSD results for FONO shows
that the level of calculations plays important role in the study of the nature of the
N–O1 bond in XO1NO2. Similar conclusion can be drawn from topological
analysis of ELF performed for the ClONO and BrONO molecules using the various
wave functions [23].
Table 19.3 N–O bond lengths and mean electron populations,
N, for the localisaton basins for the
N–O1 bond in halogen nitrites XONO (XO1–NO2; X = F, Cl, Br, I) and peroxynitrous acid
HOONO (HOO1–NO2)
No
Molecule
Conformer
r(N–O1) [Å]
V(O1) [e]
V(N) [e]
V(N,O1) [e]
1
FONO
syn
1.490
–
0.41
–
anti
1.533
–
0.37
–
2
ClONO
syn
1.496
–
0.42
–
anti
1.554
–
0.33
–
3
BrONO
syn
1.403
0.33
0.52
–
anti
1.533
–
0.37
–
4
IONO
syn
1.348
0.50
0.62
–
anti
1.504
–
0.43
–
5
HOONO
syn-syn
1.393
–
–
0.91
syn-perp
1.505
–
0.46
–
anti-perp
1.498
–
0.46
–
The topological analysis of ELF performed at the B2PLYP/aug-cc-pVTZ level for XONO (X = F,
Cl, Br) and HOONO molecule and the B2PLYP/aug-cc-pVTZ(H,N,O),TZVPPall(I)//
B2PLYP/aug-cc-pVTZ-PP level for IONO
19 Diversity of the Nature of the Nitrogen-Oxygen Bond …
539