Stabilizing small particles of lithium hydroxide with adsorbed water molecules: a quantum chemical study
Quantum chemical calculations have been carried out of the energetic and geometric characteristics of the lithium hydroxide molecular models within the frameworks of both semiempirical (the MNDO method) and ab initio (the STO-3G and 6-31G basises being used) approaches. The adsorption of water molec...
Збережено в:
| Дата: | 2002 |
|---|---|
| Автор: | |
| Формат: | Стаття |
| Мова: | Англійська |
| Опубліковано: |
Chuiko Institute of Surface Chemistry National Academy of Sciences of Ukraine
2002
|
| Онлайн доступ: | https://surfacezbir.com.ua/index.php/surface/article/view/85 |
| Теги: |
Додати тег
Немає тегів, Будьте першим, хто поставить тег для цього запису!
|
| Назва журналу: | Surface |
| Завантажити файл: |  |
Репозитарії
Surface| _version_ | 1869291173818925056 |
|---|---|
| author | Grebenyuk, A. G. |
| author_facet | Grebenyuk, A. G. |
| author_institution_txt_mv | [
{
"author": "A. G. Grebenyuk",
"institution": "Інститут хімії поверхні НАН України"
}
] |
| author_sort | Grebenyuk, A. G. |
| baseUrl_str | |
| collection | OJS |
| datestamp_date | 2018-11-27T09:42:19Z |
| description | Quantum chemical calculations have been carried out of the energetic and geometric characteristics of the lithium hydroxide molecular models within the frameworks of both semiempirical (the MNDO method) and ab initio (the STO-3G and 6-31G basises being used) approaches. The adsorption of water molecules has been shown to result in stabilizing small particles of the compound. The vibrational spectra of the LiOH microcrystallites have been also examined. |
| first_indexed | 2025-07-22T19:30:09Z |
| format | Article |
| fulltext |
82
STABILIZING SMALL PARTICLES OF LITHIUM
HYDROXIDE WITH ADSORBED WATER MOLECULES:
A QUANTUM CHEMICAL STUDY
A.G. Grebenyuk
Institute of Surface Chemistry, National Academy of Sciences
Gen. Naumov str. 17, 03680 Kyiv-164, UKRAINE
Abstract
Quantum chemical calculations have been carried out of the energetic and geometric
characteristics of the lithium hydroxide molecular models within the frameworks of both
semiempirical (the MNDO method) and ab initio (the STO-3G and 6-31G basises being used)
approaches. The adsorption of water molecules has been shown to result in stabilizing small
particles of the compound. The vibrational spectra of the LiOH microcrystallites have been
also examined.
Introduction
Molecular models of solids are widely used now as effective tools for the study of their
bulk and surface physicochemical properties [1]. The simulation of the compounds having
structures with the great atomic coordination numbers is of particular interest because the
taking frontier conditions into account in such cases meets definite difficulties and is a
non-trivial problem [2].
The aim of this work is the construction and quantum chemical analysis of the
molecular models of lithium hydroxide, the selection of them as objects for investigation being
conditioned by its relatively simple structure and practicality [3]. This compound has a layered
tetragonal system lattice with a “wafer” structure [4]. The coordination environment of any
lithium atom is a distorted tetrahedron and any hydroxyl group has four lithium atoms as the
nearest neighbours, all OH groups being stationed in the layers alternatively on either side of
the plane of lithium atoms. Hydrogen bonds are absent between the layers.
The geometrical structure as well as the force field and vibrational spectra of the
Li2(OH)2 molecule were examined theoretically in [5]. The detailed studies of the lithium
hydroxide tetramers [6] and hexamers [7] lead the authors to the conclusion that small clusters
of this compound must have equilibrium structures significantly distinct from that of the
crystal. In this connection a question arises what factors cause stabilizing small lithium
hydroxide clusters – precursors of the crystal.
There is a natural assumption that water molecules connected in definite way with the
surface of lithium hydroxide microcrystallites can be ones of such factors. Their presence may
be conditioned, firstly, by hygroscopic moisture, secondly, by the formation of condensation
water, due to the equilibrium
2 LiOHsolid « Li2Osolid + H2Ogas,
thirdly, due to the presence of the admixture of the crystal hydrate LiOH·H2O.
It is obvious that the firmer is the connection between water molecules and
microcrystallite surface, the greater is their stabilizing effect. On evidence derived from [8, 9],
83
water molecules are the most tied ones on the oxide system surface when adsorbed on the
“pared” Lewis surface sites formed at the expense of an elimination of the OH group that is the
same for two metal atoms.
Models and Methods
The lithium hydroxide molecular models examined were built with consideration for the
suggestions described above (see Fig.). Their structure and properties were studied by the SCF
MO LCAO quantum chemical method within the frameworks of semiempirical MNDO
approximation [10] by means of the program [11], and also in an ab initio way with use of the
STO-3G and 6-31G basises, operating under the program [12].
Fig. Molecular models for LiOH (big balls depict lithium atoms).
84
Results and Discussion
Let us consider at first the results obtained within frameworks of the MNDO method.
A comparison of the experimental [4] parameters of the lithium hydroxide crystalline lattice
with theoretical ones (see Table 1) shows that as a whole a semiquantitive agreement is
observed between them that is only slightly affected by the model dimensions. Enlarged values
of Li-O and Li-H distances as compared with the experimental ones engage our attention
whereas the calculated values for the Li-Li separations fall far short of those in the crystal. As a
consequence, the values of the Li-O-H angles are overestimated considerably. It seems likely
that these deviations can be explained by shortcomings of the MNDO method parameterization
what results in an overestimation of the values of coordination bond lengths.
Table 1. The averaged values of the equilibrium interatomic distances (pm) and valence
angles (degrees) in the molecular models and in the crystal of lithium hydroxide
(on evidence derived from the MNDO method).
Models
Interatomic distances
Valence angles
Li-Li Li-O Li-H O-H Li-O-Li O-Li-O Li-O-H
(LiOH)2 237 193 272 92 76 104 142
(LiOH)4 261 211 282 93 79 100 133
(LiOH)2·2H2O 315 228 282 95 88 92 115
(LiOH)8·2H2O 301 212 288 93 90 90 138
(LiOH)18·2H2O 305 216 281 94 90 90 125
(LiOH)32·2H2O 309 222 276 94 88 88 116
Exp. [4] 355 196 250 92 129 129 115
The values of the formation enthalpies of the lithium hydroxide molecular models
calculated by the MNDO method (see Table 2) can be used for the evaluation of the
corresponding theoretical value for the crystal of this compound provided the coordination
compositions of these models are taken into consideration. Really, symbolizing a contribution
into the models of the molecules with four-coordinated atoms (what answers the crystal) by
the letter x, that of the molecules with three-coordinated atoms being symbolized by the letter y
and the contribution of the Li2(OH)2·2H2O fragment - by the letter a, we will obtain a system
of equations:
18 x + 12 y + a = -13194 (1)
8 x + 8 y + a = -7454 (2)
2 x + 4 y + a = -3409 (3).
Subtracting both of the parts of the second equation from those of the first one and those of
the third equation from the second one, another system is arrived at:
10 x + 4 y = -5740 (4)
6 x + 4 y = -4045 (5),
85
whence it follows that the required x value is of -424 kJ/mol what is fitted well with the
experimental value that is equal to 440 kJ/mol [3]. The value y (-376 kJ/mol) coincides
practically with the specific (attributed to the single molecule) formation enthalpy calculated
for the globular model of Li4(OH)4 (-379 kJ/mol), and the value a (-1058 kJ/ mol) is somewhat
lesser than the corresponding one for the model of Li2(OH)2·2H2O (-1124 kJ/mol).
Table 2. The coordination composition and the values of the formation enthalpies calculated
by the MNDO method (DHf, kJ/mol) of the lithium hydroxide molecular models
(upper indices indicate the atomic coordination numbers)
Models DHf
Li22(OH)2
2 -688
Li34(OH)3
4 -1516
Li32(OH)1
2(OH2)2
2 º Li2(OH)2·2H2O -1124
Li42(OH)4
2·Li34(OH)3
4·Li2(OH)2·2H2O -3409
Li48(OH)4
8·Li38(OH)3
8·Li2(OH)2·2H2O -7454
Li418(OH)4
18·Li312(OH)3
12·Li2(OH)2·2H2O -13194
A comparison of the calculated vibrational spectra of the lithium hydroxide crystal [13]
(see Table 3) shows the values of vibrational frequencies to be overestimated systematically.
When dimensions of the models increase, the number of absorption bands grows, nevertheless
for the most part they have very small intensivities (because of this, the values of frequencies
are shown in the Table 3 for the most intensive bands), with the regions of vibrational
frequencies of the two-coordinated Li-OH and OH2 fragments differing from those of the
vibrations of the fragments with three- and four-coordinated atoms.
In order to improve the results obtained by the MNDO method, ab initio calculations
were carried out of the models including no more than eight lithium atoms, a minimal basis
(STO-3G) and expanded one (6-31G) being used. The results of calculations are shown in the
Table 4. A comparison of the data listed in the Table 1 and Table 4 testify the geometric
parameters of the crystal to be reproduced, as a whole, better in the ab initio calculations
rather in the semiempirical ones; in this case the change from the STO-3G basis to the 6-31G
one, as a rule, improves considerably the accordance with the experiment.
The values of total energies of the models can be used for an estimation of the lithium
hydroxide cohesion energy that is the difference between the compound formation enthalpy in
the gaseous state and that in solid one (on evidence derived from [14], it is of 238 kJ/mol).
Using the coordination formulae of the models with the compositions of Li2(OH)2·2H2O,
(LiOH)4, and Li8(OH)8·2H2O, it is an ease matter to find that the value
E = E[(LiOH)8·2H2O] – E [(LiOH)4] – E[Li2(OH)2·2H2O]
corresponds to the energy of two formula units of lithium hydroxide with four-coordinated
atoms, i.e. to that of the crystalline state.
86
Table 3. The experimental (crystal [13]) and theoretically calculated values of the vibrational
frequencies of the lithium hydroxide molecular models (n, cm-1)
Vibrations Exp. (LiOH)2·2H2O (LiOH)8·2H2O (LiOH)18·2H2O (LiOH)32·2H2O
A2u (OH) 3677 3898 3980 3965 3960
A1g (OH) 3664 3897 3949 3940 3938
Eg (T’)
620 860 827 818 802
519 593 717 697 666
A2u(T’) 495 518 586 527 508
Eu(T’) 440 461 503 451 485
Eu (R) 419 395 423 420 444
A1g (T’) 329 362 366 327 369
B1g (T’) 299 286 331 306 338
Eg (R) 287 270 289 293 299
Table 4. The results of ab inito calculations on interatomic distances (pm) and valence angles
(degrees) in the molecular models of lithium hydroxide
Models
Basis
Interatomic distances Valence angles
Li-Li Li-O Li-H O-H Li-O-Li O-Li-O Li-O-H
(LiOH)2 STO-3G 217 166 248 97 82 98 139
6-31G 222 177 257 94 78 102 141
(LiOH)4 STО-3G 230 177 252 98 81 98 131
6-31G 242 189 262 95 80 99 132
(LiOH)2·2H2O STО-3G 267 186 242 97 91 89 116
6-31G 278 202 257 95 87 93 114
(LiOH)8·2H2O STО-3G 325 187 243 97 121 121 114
6-31G 346 204 249 94 116 116 108
Thus, we have for the STO-3G basis
2 Е(STO-3G) = -805.189967 - (-327.623029) – (-313.693358) = -163.873590 а.u.,
87
cohesion energy
Еcohes (STO-3G) = Е(STO-3G) – ESTO-3G(LiOH) =
= ½ (-163.873590) – (-81.768565) = -0.16823 а.u. (-442 kJ/mol).
For the 6-31G basis
2 Е(6-31G) = -815.776997 - (-331.914765) – (-317.868806) = -165.99043 а.u.,
and cohesion energy
Еcohes (6-31G) = Е(6-31G) – E6-31G(LiOH) =
= ½ (-165.99043) – (-82.894883) = -0.10033 а.е. (-263 kJ/mol).
So, unlike those of the STO-3G basis, the calculations using the 6-31G basis let it
possible to reproduce both geometrical and energetic characteristics of the lithium hydroxide
crystal with small error. It should be noticed that the cohesion energy calculated by the MNDO
method (Еcohes (MNDO) = -424 – (-230) = -194 kJ/mol) is slightly lesser than the experimental
one (as an absolute quantity) whereas non-empirical calculations overestimates it.
Conclusions
An analysis of the calculated parameters of spatial structure, energetic and spectral
characteristics of the models examined indicates their stability (what is secured by the
adsorption of as few as two water molecules) and agreement with the experimental data. With
the availability of sufficiently large amount of molecules in such associates, they can be
considered as crystallites of the solid.
Acknowledgement
The author thanks Prof. M. W. Schmidt from the Iowa State University (Ames, Iowa,
USA) who placed at his disposal a Fortran codes of the GAMESS program for ab initio
quantum chemical calculations.
References
1. Sauer J. Molecular models in ab initio studies of solids and surfaces: from ionic crystals
and semiconductors to catalysts // Chem. Rev. – 1989. – V.89, N1. – P.199-255.
2. Grebenyuk A.G. Molecular models for hypervalent inorganic compounds //
Transactions of NaUKMA. – V.18. Chemical sciences. – 2000. – P.25-34
(In Ukrainian).
3. Plyushchev V.E. and Stepin B.D. Chemistry and technology of lithium, rubidium, and
caesium compounds. – Мoscow: Khimiya, 1970 (In Russian).
4. Göttlicher S., Kieselbach B. Die Elektronendichte in Lithium-hydroxyd (LiOH) // Acta
Cryst. A. – 1976. – V.32, Pt. 2. – P.185-192.
5. Solomonik V.G. and Pogrebnaya T.P. Ab initio study on geometric structure, force
fields and vibrational spectra of molecule Li2(OH)2 and ion Li2OH+ // Zhurn. Strukt.
Khimii. - 1983. – V.24, N1. – P.39-45.
88
6. Sapse A.-M., Raghavachari K., Schleyer P.Von Rague, and Kaufman E. Theoretical
studies of LiF, LiOH, and LiNH2 tetramers // J. Amer. Chem. Soc. – 1985. – V.107,
N23. – P.6483-6486.
7. Raghavachari K., Sapse A.-M., and Jain D.C. Clusters of ionic molecules: octahedral
vs. planar ring structures of LiF, LiOH, and LiNH2 hexamers // Inorg. Chem. – 1987. –
V.26, N16. – P.2585-2588.
8. Zelenkovskii V.M., Mardilovich P.P., and Zhidomirov G.M. Non-empirical calculations
of adsorbability of pared Lewis acid sites of alumina // React. Kinet. Catal. Lett. –
1989. – V.38, N1. – P.73-77.
9. Zolotovskii B.P., Paramzin S.M., Pelmenshchikov A.G., Paukshtis Е.А.,
Klevtsov D. P., Yermolayeva N.V., Buyanov R.A., and Zhidomirov G.M. Conformities
to natural laws of “pared” Lewis sites formation in alumina and of their adsorbabilities
// Kinet. i Kataliz. – 1989. – V.30, N6. – P.1439-1443.
10. Dewar M.J.S. and Thiel W. Ground states of molecules. 38. The MNDO method.
Approximations and parameters // J. Amer. Chem. Soc. – 1977. – V.99, N15. -
P.4899-4907.
11. Pilipenko A.T., Zayets V.A., Khavryuchenko V.D., and Falendysh E.R. // A program
realizing MNDO/HB method with analytical evaluation of the first derivatives and
calculation of vibrational spectra // Zhurn. Strukt. Khimii. – 1987. – V.28, N5. – P.155-
156.
12. Schmidt M.W., Baldridge K.K., Boatz J.A., Elbert S.T., Gordon M.S., Jensen J.H.,
Koseki S., Matsunaga N., Nguen K.A., Su S.J., Windus T.L., Dupuis M., and
Montgomery J.A. General atomic and molecular electronic-structure system: Review //
J. Comput. Chem. – 1993. – V.14, N11. – P.1347-1363.
13. Ryskin Ya.I. and Stavitskaya G.P. Unshared electron pairs in the crystal chemistry of
hydroxyl-containing compounds: vibrational spectra and structure of basic hydroxyls //
Vibrations of Oxide Lattices. – Leningrad: Nauka, 1980. – P.198-227 (In Russian).
14. Kireev V.A. Methods of Practical Calculations in the Thermodynamics of Chemical
Reactions. – Мoscow: Khimiya, 1970 (In Russian).
Models and Methods
Models and Methods
Models and Methods
Models and Methods
Models
Valence angles
Valence angles
Li-Li
Li-O
Li-H
Li-H
O-H
Li-O-Li
O-Li-O
Li-O-H
|
| id | oai:ojs.pkp.sfu.ca:article-85 |
| institution | Surface |
| keywords_txt_mv | keywords |
| language | English |
| last_indexed | 2025-07-22T19:30:09Z |
| publishDate | 2002 |
| publisher | Chuiko Institute of Surface Chemistry National Academy of Sciences of Ukraine |
| record_format | ojs |
| resource_txt_mv | surfacezbircomua/b9/cdae506501cdbde5efee48b6365e50b9.pdf |
| spelling | oai:ojs.pkp.sfu.ca:article-852018-11-27T09:42:19Z Stabilizing small particles of lithium hydroxide with adsorbed water molecules: a quantum chemical study Stabilizing small particles of lithium hydroxide with adsorbed water molecules: a quantum chemical study Stabilizing small particles of lithium hydroxide with adsorbed water molecules: a quantum chemical study Grebenyuk, A. G. Quantum chemical calculations have been carried out of the energetic and geometric characteristics of the lithium hydroxide molecular models within the frameworks of both semiempirical (the MNDO method) and ab initio (the STO-3G and 6-31G basises being used) approaches. The adsorption of water molecules has been shown to result in stabilizing small particles of the compound. The vibrational spectra of the LiOH microcrystallites have been also examined. Quantum chemical calculations have been carried out of the energetic and geometric characteristics of the lithium hydroxide molecular models within the frameworks of both semiempirical (the MNDO method) and ab initio (the STO-3G and 6-31G basises being used) approaches. The adsorption of water molecules has been shown to result in stabilizing small particles of the compound. The vibrational spectra of the LiOH microcrystallites have been also examined. Quantum chemical calculations have been carried out of the energetic and geometric characteristics of the lithium hydroxide molecular models within the frameworks of both semiempirical (the MNDO method) and ab initio (the STO-3G and 6-31G basises being used) approaches. The adsorption of water molecules has been shown to result in stabilizing small particles of the compound. The vibrational spectra of the LiOH microcrystallites have been also examined. Chuiko Institute of Surface Chemistry National Academy of Sciences of Ukraine 2002-06-12 Article Article application/pdf https://surfacezbir.com.ua/index.php/surface/article/view/85 Surface; No. 7-8 (2002): Chemistry, Physics and Technology of Surface; 82-88 Поверхность; № 7-8 (2002): Химия, физика и технология поверхности; 82-88 Поверхня; № 7-8 (2002): Хімія, фізика та технологія поверхні; 82-88 3154-8091 3154-8083 en https://surfacezbir.com.ua/index.php/surface/article/view/85/84 Авторське право (c) 2002 A.G. Grebenyuk |
| spellingShingle | Grebenyuk, A. G. Stabilizing small particles of lithium hydroxide with adsorbed water molecules: a quantum chemical study |
| title | Stabilizing small particles of lithium hydroxide with adsorbed water molecules: a quantum chemical study |
| title_alt | Stabilizing small particles of lithium hydroxide with adsorbed water molecules: a quantum chemical study Stabilizing small particles of lithium hydroxide with adsorbed water molecules: a quantum chemical study |
| title_full | Stabilizing small particles of lithium hydroxide with adsorbed water molecules: a quantum chemical study |
| title_fullStr | Stabilizing small particles of lithium hydroxide with adsorbed water molecules: a quantum chemical study |
| title_full_unstemmed | Stabilizing small particles of lithium hydroxide with adsorbed water molecules: a quantum chemical study |
| title_short | Stabilizing small particles of lithium hydroxide with adsorbed water molecules: a quantum chemical study |
| title_sort | stabilizing small particles of lithium hydroxide with adsorbed water molecules: a quantum chemical study |
| url | https://surfacezbir.com.ua/index.php/surface/article/view/85 |
| work_keys_str_mv | AT grebenyukag stabilizingsmallparticlesoflithiumhydroxidewithadsorbedwatermoleculesaquantumchemicalstudy |