The geometry and optimization of La-MPBCP or
[La-MPBCP]+3 systems
The studied La-MPBCP or [La-MPBCP]+3 systems in
this work are not planar, they belong to the C3V point
group. For both systems, the lanthanum atom was preferably adsorbed in
the middle of the cavity. The coordination sphere about the lanthanum
possesses a trigonal pyramidal geometry, with La-N bond lengths of (2.58
Å) La-MPBCP and (2.80 Å) [La-MPBCP]+3, these
values were consistent with similar experimental bond data (2.86-2.68 Å)
reported before. 47-48. The coordination is better in
the neutral system as expected by the formation of stronger bonds and a
N-La-N bond angle of 118°. The optimized structures are depicted in
Figure 3. The La-MPBCP system undergoes a considerable distortion in
order to keep the nitrogen donors close to the lanthanum center and this
system shows a greater stiffness caused by the N-La interaction,
allowing the lanthanum atom to lie closer to the plane of the MPBCP.
Adsorption energy values, as well as some important parameters for both
systems, are listed in Table 1.
The highest occupied molecular orbital, HOMO, and the lowest unoccupied
molecular orbital, LUMO are the main orbitals that participate in the
chemical stability they are shown in Figure 4, and the corresponding
energy levels are listed in Table 1. The HOMOs are predominantly
localized on the MPBCP ligand, while the LUMOs are localized mainly on
lanthanum atoms. The energy gap between HOMO and LUMO of the MPBCP is
4.22 eV and our calculated band gaps for La-systems show that the
coordination of lanthanum atom on the ligand affect the non-conductor
character of MPBCP. The [La-MPBCP]+3 system
exhibits lower band gaps of 1.39 eV, indicating character de
semiconductor and more excitability system. (see Table 1)
The predicted IR spectrum of MPBCP, La-MPBCP and
[La-MPBCP]+3 system shows bands associated
respectively to the stretching modes of N-H, C-H, La-N of group of
pyrrole and benzene ring. The IR data calculated of the MPBCP exhibit
bands at 1507 cm–1 and 3207 cm–1, due to the pyrrole ν(C=N) group and
ν(C-H) bond of benzene. The band corresponding to the C=N group was
considerably shifted to the lower frequency 122 cm–1(1360 cm–1) and 120 cm–1 (1377
cm−1) in their corresponding La-MPBCP and
[La-MPBCP]+3 system indicating the involvement of
the nitrogen atoms in the coordination. The presence of two bands at
1135, 323 cm–1 and 917, 306 cm–1attributed to ν(La–N) respectively. The calculated for assignments for
the MPBCP, La-MPBCP and [La-MPBCP]+3 system in gas
phase are collected in Table 2.
The study of natural bond orbitals shows the lone pairs from nitrogen
atoms participate as donors, while the lanthanum atom as acceptor see
Figure 3c and3d. Charges on La
atoms are +2.30, +2.40 in La-MPBCP and
[La-MPBCP]+3, respectively. Charges on N atoms in
the cavity are -0.79 to -0.81. The nitrogen atoms in
[La-MPBCP]+3 system has the most negative charge,
it is clear that this systems is the electron-deficient La site.