agreement with the experimental counterparts, which can be explained by the fact
that both structures belong in fact to high-silica zeolites. In the experimental spectra
of pentasils, bands in 1400–1000 cm
−1 range are associated with vibrations m as Si–
O–Si, bands in the range 900–450 cm
−1 with vibrations m s Si–O, and bands
occurring below 450 cm
−1 with vibrations d Si–O–Si.
Visualizations of vibrations related to bands in the pseudolattice range of ferrierite spectrum have shown that despite the presence of rings with higher multiplicities (6- and 10-membered) in ferrierite, bands in this range are associated with a
5-membered ring, except for bands at around 600 cm
−1 that can be associated with
vibration of deformed (flattened) 6-membered rings. The characteristic RO S5R
vibration should be assigned to a maximum at approximately 470 cm
−1 , consisting
of several component bands.
The sequence of individual band arrangement in MOR spectrum is analogous to
the sequence of bands in FER spectrum, which confirms the belonging of both
structures to the same group. Differences appear only in the number and position of
characteristic RO-type bands. In mordenite structure, besides 5-membered rings
there are also 4- and 12-membered rings. As with ferrierite, MOR vibration visualizations indicate that all pseudolattice bands are associated with 5-membered ring
vibrations, with the exception of a few bands that should be associated with
4-membered rings. The problem, however, is to identify the RO S5R band due to
the presence of 4-membered rings. The rigid arrangement of this ring causes that
during the RO S5R vibration one of the walls is almost “rigid,” which means that
one can only talk about “pseudoring” vibration. According to [31], the band
associated with this vibration is one of the components of the complex envelope of
the experimental spectrum with a maximum at about 450 cm
−1 .
The next and last structure discussed in this study is a HEU-type framework,
which represents the most common natural zeolite–clinoptilolite. Its structure can
be successfully reproduced based on 4–4=1 unit. In the theoretical spectrum of such
unit, band related to characteristic vibrations of S4R and S5R rings has been
identified [48]. These calculations were verified experimentally, assigning those
vibrations’ positions in the ranges 790–690 and 675–590 cm
−1 , respectively. These
results were confirmed in the latest calculations carried out for periodic model [31].
The analysis of the presented results indicates (Fig. 10.10) that the modeling of
periodic structures provides theoretical spectra reflecting significantly more accurately the experimental ones than respective spectra of individual SBUs (Fig. 10.6).
In the case of FER-, MOR-, or HEU-type structures, the proposed aluminum-freeframework models render the experimental spectrum to a very large extent, which
suggests that the presence of aluminum and/or extra-framework ions does not
introduce significant structural deformation. The same applies to structures built
with D6R, i.e., faujasite and chabazite. In the case of the LTA structure, the theoretical spectra are more consistent with experimental ones after considering the
aluminum atoms in tetrahedral positions and the presence of extra-framework ions
(results presented below), which suggests that in high alumina zeolites ion
exchange will have a significant impact on the position and shape of bands in
pseudolattice range.
318
M. Król et al.
that both structures belong in fact to high-silica zeolites. In the experimental spectra
of pentasils, bands in 1400–1000 cm
−1 range are associated with vibrations m as Si–
O–Si, bands in the range 900–450 cm
−1 with vibrations m s Si–O, and bands
occurring below 450 cm
−1 with vibrations d Si–O–Si.
Visualizations of vibrations related to bands in the pseudolattice range of ferrierite spectrum have shown that despite the presence of rings with higher multiplicities (6- and 10-membered) in ferrierite, bands in this range are associated with a
5-membered ring, except for bands at around 600 cm
−1 that can be associated with
vibration of deformed (flattened) 6-membered rings. The characteristic RO S5R
vibration should be assigned to a maximum at approximately 470 cm
−1 , consisting
of several component bands.
The sequence of individual band arrangement in MOR spectrum is analogous to
the sequence of bands in FER spectrum, which confirms the belonging of both
structures to the same group. Differences appear only in the number and position of
characteristic RO-type bands. In mordenite structure, besides 5-membered rings
there are also 4- and 12-membered rings. As with ferrierite, MOR vibration visualizations indicate that all pseudolattice bands are associated with 5-membered ring
vibrations, with the exception of a few bands that should be associated with
4-membered rings. The problem, however, is to identify the RO S5R band due to
the presence of 4-membered rings. The rigid arrangement of this ring causes that
during the RO S5R vibration one of the walls is almost “rigid,” which means that
one can only talk about “pseudoring” vibration. According to [31], the band
associated with this vibration is one of the components of the complex envelope of
the experimental spectrum with a maximum at about 450 cm
−1 .
The next and last structure discussed in this study is a HEU-type framework,
which represents the most common natural zeolite–clinoptilolite. Its structure can
be successfully reproduced based on 4–4=1 unit. In the theoretical spectrum of such
unit, band related to characteristic vibrations of S4R and S5R rings has been
identified [48]. These calculations were verified experimentally, assigning those
vibrations’ positions in the ranges 790–690 and 675–590 cm
−1 , respectively. These
results were confirmed in the latest calculations carried out for periodic model [31].
The analysis of the presented results indicates (Fig. 10.10) that the modeling of
periodic structures provides theoretical spectra reflecting significantly more accurately the experimental ones than respective spectra of individual SBUs (Fig. 10.6).
In the case of FER-, MOR-, or HEU-type structures, the proposed aluminum-freeframework models render the experimental spectrum to a very large extent, which
suggests that the presence of aluminum and/or extra-framework ions does not
introduce significant structural deformation. The same applies to structures built
with D6R, i.e., faujasite and chabazite. In the case of the LTA structure, the theoretical spectra are more consistent with experimental ones after considering the
aluminum atoms in tetrahedral positions and the presence of extra-framework ions
(results presented below), which suggests that in high alumina zeolites ion
exchange will have a significant impact on the position and shape of bands in
pseudolattice range.
318
M. Król et al.