Crystallography Reports, Vol. 45, No. 1, 2000, pp. 21–25. Translated from Kristallografiya, Vol. 45, No. 1, 2000, pp. 27–31.
Original Russian Text Copyright © 2000 by Smolin, Shepelev, Lapshin, Vasil’eva.
STRUCTURES OF INORGANIC COMPOUNDS
Structure of Selenium and Tellurium Clusters in Cavities
of NaX Zeolite
Yu. I. Smolin, Yu. F. Shepelev, A. E. Lapshin, and E. A. Vasil’eva
Institute of Chemistry of Silicates, Russian Academy of Sciences,
ul. Odoevskogo 24-2, St. Petersburg, 199155 Russia
Received June 20, 1997; in final form, February 10, 1998
Abstract—The structure of NaX zeolite crystals with the Se and Te atoms incorporated into the structure from
their vapors has been studied. It is shown that selenium atoms form clusters in the shape of six- and four-mem-
bered rings located in the cuboctahedral cavities of the structure framework. Single Se2 molecules are located
in large cavities, whereas Te atoms form four-membered rings located in cuboctahedra. Large cavities are occu-
pied by two alternating configurations of Te atoms forming either a chain consisting of 16 links or an eight-
membered ring. © 2000 MAIK “Nauka/Interperiodica”.
One of the methods for obtaining systems of crystals acquired the orange [NaX(Se)] or the brown
nanometer particles widely used in electronics and [NaX(Te)] color. To prevent possible dehydration, the
optics is the synthesis of semiconductor clusters in zeo- synthesized crystals were coated with lacquer films. As
lite cavities. The regular arrangement of such clusters the X-ray powder diffraction and other X-ray diffrac-
set by the structure of the zeolite matrix allows one to tion experiments showed, the treatment of zeolite crys-
study these clusters by well-developed diffraction tals in the Se and Te vapors leads to a certain degrada-
methods.
tion of the zeolite lattice—more pronounced for
NaX(Te) than for NaX(Se).
We had the aim to determine the structure and posi-
tions of semiconductor selenium and tellurium clusters
The unit-cell parameters determined on a diffracto-
formed in the cavities of NaX zeolite during adsorption meter are 25.06(1) Å for a crystal treated in selenium
of Se and Te vapors. Earlier [1], we obtained and stud- vapors and 25.14(1) Å for a crystal treated in tellurium
ied single crystals of the zeolite catalyst Te/NaX con- vapors. The space group for both crystals was deter-
taining tellurium ions coordinated with sodium ones. mined to be Fd3 and coincided with the space group of
Two positions of tellurium ions were established. One the initial NaX crystals.
is located at the center of a cuboctahedron (1.3 tellu-
The intensity measurements were performed on an
rium ions per unit cell), whereas the other, in a large
automated triple-crystal diffractometer operating in the
cavity (3.7 tellurium ions per unit cell).
mode of a normal beam (MoKα-radiation, graphite
The synthesis of semiconductor clusters in NaX was
performed by the modified multistage method sug-
gested elsewhere [1]; in this method, the last stage was
changed—the NaX(Te) crystals were treated in a
hydrogen flow. In the synthesis of clusters from vapors,
the initial matrices were single crystals of NaX zeolite
of the octahedral shape with a 0.17 mm-long edge and
the dehydrated unit-cell composition Na92Al92Si100O384
monochromator). However, the integrated intensities
were estimated by the well-known algorithm used in
the profile analysis [3]. The intensities obtained were
corrected for polarization and kinematic factors; no
absorption correction was introduced. Altogether, the
intensities of 330 nonzero nonequivalent reflections
were measured for NaX(Se) and 256 for NaX(Te) crys-
tals. In the following calculations, we used 307 and 236
[2]. Because of a small number of available single crys- reflections with I ≥ 3σ(I), respectively. The initial
tals, the crystals for the X-ray diffraction study were model structure consisted solely of the framework
treated together with the fine-crystalline (0.005–0.010) atoms [2]. The positions of the non-framework atoms
fraction of NaX zeolite in the vapors of a semiconduc- were determined from the difference electron-density
tor element. In each cycle of the synthesis, we used maps and the intermediate LSM refinements by the
100 mg of fine-crystalline zeolite and several single AREN-90 complex of programs [4] and the modified
crystals dehydrated by heating to 400°C mixed with the version of the ORFLS program [5]. The atomic factors
dried Se or Te powder in the weight ratios 7 : 1 and 6 : 1, of neutral atoms [6] and the Cruickshank weighting
respectively. The obtained NaX + Se mixture in a sealed scheme were used [7]. The positions of all the atoms
ampoule was heated for 24 h at 400°C and then for 24 h were refined in the isotropic approximation. The final
at 225°C. The NaX + Te mixture was heated for 48 h at values of the reliability factors were R = 0.051, wR =
540°C. As a result of the procedure, the synthesized 0.055 and R = 0.097, wR = 0.104 for the NaX(Se) and
1063-7745/00/4501-0021$20.00 © 2000 MAIK “Nauka/Interperiodica”