Научная статья на тему 'Study of the coordination effects for SnCl4, SbCl5 and TiCl4 complexes on the base of ab initio calculations'

Study of the coordination effects for SnCl4, SbCl5 and TiCl4 complexes on the base of ab initio calculations Текст научной статьи по специальности «Науки о Земле и смежные экологические науки»

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Аннотация научной статьи по наукам о Земле и смежным экологическим наукам, автор научной работы — Kalinina E.L., Shanina Yu.A., Poleshchuk O.Kh.

In this paper ab initio HONDO calculations of SnCI4, SbClg and TiCI4 with H2S complexes have been performed. All 35CI-NQR frequencies for above-mentioned nv-complexes are obtained by ab initio calculations. It was shown that ab initio calculations might be useful for the appropriate interpretation of experimental NQR frequencies. The optimized geometry of the complexes has been used to calculate the quadruple coupling constants, the ionization potentials, the MO composition and the orbital energies for each of the compounds investigated. Our calculations have been pointed out that TiCI4, SnCI4 and SbCI5 complexes are somewhat stabilized. The most stable complex is SbCI5 that is in a good agreement with the experimental data. The stability of the complexes depends both on the stabilization of the occupied donor molecular levels and the vacant acceptor and donor levels.

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Текст научной работы на тему «Study of the coordination effects for SnCl4, SbCl5 and TiCl4 complexes on the base of ab initio calculations»

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yflK 541.6

E.L. Kalinina, Yu.A. Shanina, O.Kh. Poleshchuk

STUDY OF THE COORDINATION EFFECTS FOR SnCl4, SbCl5 AND TiCl4 COMPLEXES

4 5 4

ON THE BASE OF AB INITIO CALCULATIONS

Tomsk State Pedagogical University

Introduction

The analysis of the coordination electronic effects, carried out on the base of X-ray fluorescence spectra [1, 2] and PM3 calculations [3] indicated to following. The redistribution of the electron density on donor and acceptor atoms and the donor-acceptor ability were different in the complexes consisting transition or non-transition elements. In these papers we had investigated the complexes of the transition and non-transition metal halogenides with the organic donors.

It seems interesting to calculate the structural and energetic characteristics by ab initio method. On the other hand the redistribution of electron density in these complexes has characteristic differences of transition from non-transition element complexes [1].

The aim of this paper was to obtain the results of ab initio HONDO calculations of SnCl4, SbCl5 and

TiCl4 with H2S complexes. The calculated characteristics of the molecular systems were compared with the experimental data by photoelectron, X-ray fluorescence and X-ray spectra.

Computation details

The ab initio molecular calculations were carried out by the program package HONDO [4] at the Har-tree-Fock (HF) 6-311G** level of theory. The values of the principal components of the diagonalized electric field gradient (EFG) tensors were calculated using IBM RS/6000 workstation running HONDO.

Results and discussion

Table 1 presents the experimental and the optimized bond length values of the acceptors, donor and valent HSH angles of H2S molecule. As follows

— 1 0

Table 1

The geometrical description of the compounds calculated

Compound IWIP, A Rs.„elp,Â[8] RM-ci"1! À Rs-hm1,A

SnCl4 2.282 2.280

SbCl5 2.277 2.292

2.329 2.350

TiCl4 2.185 2.184

SnCl62 2.350 2.470

TiCl62- 2.350 2.390

SbCl6- 2.360 1 2.380

H2S 1.335 1.333

SnCl42SH2 2.383

2.388

TiCl42SH2 2.298

2.283

SbCl5SH2 2.314

2.353

2.365

2.365

2.372

from Table 1 the agreement between the experimental X-ray bond lengths and the optimized values is good in the number of the similar complexes [5].

In the Table 2 are presented the experimental ionization potential values from photoelectron spectra [6] and the calculated energies of occupied molecular orbitals of free acceptors and donor. The electron structure of these molecules was investigated mainly by photoelectron spectra [7, 8]. Our calculations confirm the assignments of the experimental ionization energies. In tetrahedral halogenides of Sn and Ti the levels la, and lt2 are essentially 3s chlorine orbitals; M-Cl bonds provide the basic contribution in 2a, and 2t2 levels as a result of the interaction valent s, p and d orbitals of Sn and Ti atoms with 3s,p chlorine orbitals. The le, 3t2 and It, levels include the 3p_ chlorine group orbitals in SnCl4. There are two main bonding levels 2t2 (Tip,d0 -ClpCT ) and le (Tid^ -Clp^) in the TiCl4 molecule. The two highest occupied orbitals (It, and 3t2) are nQorbitals combination.

The localization of the levels in SbCl, molecule may be described in the following way. The 3a, slightly bonding level has Sbp large contribution. The MO 4a,, 2e and 3a, correspond to the Sbpcr -Clpcr bonds. The 4e level is provided with the Sb5d. -C13p!; interaction. The highest occupied 2e, 3a2, 3e, and 2a, orbitals include only combinations of the chlorine atom lone pairs electron (na).

In H2S the highest occupied molecular orbital lb, is really non-bonding (ns) and consist from the lone

Table 2

Photoelectron ionization potentials (IP) and occupied orbital energies (E) of the acceptors and donor

Symmetry IP, eV [6, 7, 8] Ei,eV Assignment

SnCl4

It, 12.13 13.2 nCi

3t2 12.42 13.4 nci

le 12.74 13.9 nci

2t2 14.29 15.4 Snp C1S. p

2a, 17.36 19.1 Sns Cls, p

lt2 - 30.1 CI,

la! - 31.1 Cls

SbCl5

2e" 11.47 12.6 nc.

4e' 11.87 13.0 Sbd Clp

3a2" - 13.0 nci

4a,' 12.24 13.3 Sbp Clp

3e' 12.74 13.8 nc,

le" 13.05 14.2 "ci

2a2" 14.95 14.8 nci

2e' 14.95 16.7 SbpCls,p

3a,' - 16.7 Sbp Cls, p

TiCl4

It, 11.69 12.9 nci

3t2 12.67 14.1 Tip Clp

le 13.17 14.5 Ti<j Clp

2t2 13.46 15.1 Tip, d Clp

2a, 13.88 15.5 Tis Cls> p

lt2 23.1 30.1 Cls

la, 24.5 30.5 CI,

H2S

lb, 10.47 10.4 ns

2a, 13.23 11.8 Ss.PHs

lb2 15.47 17.7 SpHs

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la, 19.5-31 26.7 Ss

3p electron pair of the sulfur atom. The next 2a, and lb2 orbitals correspond to Ss p-Hs bonding. The lowest valent la, level mainly contains the Ss orbitals with small addition of Ss -Hs bonding.

Fig. 1-3 and Tables 3-5 present complexes' energy diagrams and MO composition of the acceptors and donor orbitals. As follows from the energy diagrams, HOMO levels of the complexes are formed by nQ and ns orbitals. The next occupied level of SnCl4 2H2S (43) and SbCl5H2S (46) is formed by the vacant dM orbitals. There are 4 and 5 bonding MO levels, involving central atoms and ligand orbitals, which locate considerably in-depth (13.0-17.6 eV) in SnCl4 and SbCl5 complexes.

In TiCl4 complex there are three highest occupied levels corresponding to Ti -CI interaction with con-

— H

ш

-5

-10

-15

-20

-25

-30

43,44-

40,41"

39-

37 =

32,33« 30.31

28-

26,27-

25-

24-Г 22.23-21-

- SnP -Qsnrt

.Srip-Op Srip "СЦр

-avd-a,

=5np-Clp sn^j-a^p

Sspd"Hs"

ns-Hs-Ssfri'Hs*

na

/уПп 46 =

na 44,45-

Srip-Op "a

Srip-CIsp

Ssp-Hs"

41.42-

40-

-Sns-CUp 37.

Sp-Hs ~

Ss-Hs-

-eu

-Os

-Sns-as

SnCl/, SnC^^S

Fig, 1. The MO energy diagram of SnCI4-2SH2 complex

H2S

tribution of the sulfur atom orbitals. The levels contained Tid electrons lay some deeper. In SnCl4 complex the highest multicentral level (14.2 eV), includes both central acceptor M atom orbitals (Snsd) and lig-and orbitals (n ; similar level (13.0 eV) in SbCl5 complex involves Sopd and ns AOs. In TiCl4 complex two similar multicentral levels (13.4; 13.5 eV) involve Tipd and ns AOs. The lowest levels (18.2; 18.7 eV) are formed by lb2 orbital of H2S (Sp-Hs) in TiCl4 and SnCl4 complexes. In similar level of SbCl5 complex (19.3 eV) the Sd orbital contribution takes place.

The stabilization of the complexes are mainly defined by participation of the vacant acceptors and perhaps, donor orbitals in bonding (see Tables 3-5).

On the whole the complex energy stabilization is described by the formula:

AE = E - ДЕ..

(1)

where E.- molecule energies of the components, included in complexes, calculated in the same approximation as the energy of the complex (Ec). As follows from Table 6 the agreement between the calculated energy stabilizations and the experimental enthalpies of the complex formation is satisfactory, despite of the small difference of the large energy value.

In Ref. [9] we have introduced the concept of an energy level of a hypothetical electron lone-pair of a sulfur atom (Hns), whose energy depends only on

Fig. 2. The MO energy diagrams of SbCI5-SH2 complex

the charge on the sulfur atom. Hypothetical levels are introduced using the hypothetical orbitals (HO) concept by Jolly [10]. The HO's are molecular orbitals of the model fragments described by the colum-bic interaction.

We have previously obtained the correlation between the energy of the ns-lss transition in the SKß spectra of sulphides (containing a practically «pure» ns level) and ASKa values [9]:

Hns(Kp)eV = E(ns-lss) = 5.6 ASKa +2468.37 (2) r=0.97 s=0.06 n=26

In fact this level can be treated as a internal standard in the analysis of the changes in the spectral structure occurring upon complexation and caused only by orbital interactions devoid of the effect of charge change on the sulfur atom. It follows from Fig. 4 that the intensity of the short wave maximum A, which in the SKp spectra of sulphides corresponds to the transition from the ns level to the vacancy K of the sulfur atom, significantly decreases and is considerably shifted towards longer wave length with respect to the Hns (K„ level). The calculation explain this point: the intensity of the maximum A decreases

5

О

-5

-10

%

LU

-15

-20

-25

-30

T1CI4 na^HzS H2S

Fig. 3. The MO energy diagrams of TiCI4.SH2 complex

owing to the ns level of H2S molecule becomes compound with the ns and nC) AO participation in the complexes.

Thus, the enthalpy of complex formation of SnCl4, SbCls and TiCl4 with Me2S can be determined from change in the position of the center of gravity (CG) of the SK p spectrum (that is 3ps electron distribution) relative to the Hns(K8 level). It follows from Table 7 that the D C G valaes of the SK p spectra of the complexes decrease by 0.3-0.5 eV when compared to the values of the appropriate free ligands. Using the ACG values we could arrange the complexes of Sb, Sn and

Ti chlorides with Me2S according to their increasing stability as: Sn < Sb < Ti.

This ordering is consistent with the one according to increasing both enthalpy of complex formation and the calculated complexes energy stabilization (Table 6).

Table 8 presents the change in the electron density on the coordinated atoms and on the whole donor and acceptors molecules upon their compi-exation (the negative sign corresponds to the electron density decreasing upon complexation). From the data presented in Table 8 one can see that

Table 3

MO composition of SnCl4-2SH2 complex

N MO Ei, eV Assignment MO numbers

of the acceptor of the donor

37 19.4 Sns ClS]p Sp 25 9

38 18.3 SpHs - 7

39 18.2 Sp Hs - 7

40 17.6 Snp Ss, p Hs 29,38* 8, 10*

41 14.6 Snp Cl,, p 26, 38* -

42 14.6 Snp Cls, p 27, 38* -

43 14.2 Snj, d CI, Sj, p 37* 8

44 13.2 na ns 34 9

45 13.2 na 28 -

46 12.5 na 30 -

47 12.3 na"s 31 9

48 12.1 na«s 31 9

49 11.8 na 32 -

50 11.8 nans 33 9

51 11.6 nci 34 -

52 11.6 SnA Clp 35 -

53 11.2 na ns 36 9

54 11.1 nans 36 9

Table 5

MO composition ofTiCl4-2SH2 complex

N MO Ei, eV Assignment MO numbers

of the acceptor of the donor

41 18.7 SPHs - 7

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42 18.2 sp Hs - 7

43 17.1 Tls, d Ss, p Hs 41 8, 10*

44 16.4 Tip Ss, p Hs 32, 49* 8, 10*

45 14.6 Tl4s, d Cls,p Ss 34, 45* 6

46 14.3 Tig, d Cls, p 29 —

47 13.6 Tid nci 30 —

48 13.5 Tii no ns 31,42* 9

49 13.4 Tip Cls, p ns 32, 47* 9

50 13.3 TipCls,p 33 -

51 12.8 Tid na 35 -

52 12.1 Tip nci Ss,p 36,47* 8

53 12.0 nans 39 9

54 11.6 Tip nci 38 —

55 11.5 Tip nans 37,47* 9

56 11.4 na 39 —

57 11.2 ncins 37 9

58 11.0 na 40 —

Table 4

MO composition of SbCl5-SH2 complex

N MO Ei, eV Assignment MO numbers

of the acceptor of the donor

37 21.3 Sbs Cls, p 31 -

38 19.3 Sp, a Hs _ 7

39 17.5 Sbs, p Cis, p Ss, p H5 32,46* 8

40 16.3 Sbp Cls, p ns 32 9

41 16.1 SbpCls,p 33 -

42 15.6 Sbp Clp Ss, p 34,47* 8

43 14.2 na 37 -

44 13.7 nci 38 -

45 13.6 na Ss, p 39 8

46 13.0 Sbp, d Clp ns 34,36,47* 9

47 12.9 nans 39 9

48 12.8 nci ns 42 9

49 12.7 nans 42 9

50 12.7 na 40 _

51 12.6 Sbd na 41 -

52 12.4 nCi 43 _

53 12.3 na 44 -

54 12.1 nci 45 -

A

Fig. 4. SK spectra of the TiCI4-2SMe2 (1), SbCI5'2SMe2 (2), SnCI4-2SMe2 (3) complexes and Me2S (4), the solid line is the center of gravity (CG), broken line is the position of the K level

Table 6

The energy characteristics of the complex

Complex -Fc, a,e. —E ac, a.e. -E don, a.e. —AEC kcal/mol -AHda kcal/mol[12]

SnCl42SH2 2638.8527 1841.4343 398.7013 10 7.6a

SbCl5-SH2 2701.6250 2302.8844 398.7013 25 23.5b

TiCI4-2SH2 2693.0866 1895.6622 398.7013 14 23.0°

a The values for SnCI/2S(PhCH2)2 complex 6 The values for SbCI6-SMe2 complex c The values for TiCI4-2SEt2 complex

Table 7

Parameters determined from the X-ray spectra of the sulfur atoms

Compound ASKp.103,eV relative to S8 qs, e Hns(Kp), eV CG(SKp), eV ACG (SKp), eV

Me2S -0.063(6) -0.20 0.00(4) 2466.1 0.0

SnCl4-2SMe2 0.002(4) -0.10 0.36(8) 2466.3 0.2

SbCl5-SMe2 0.017(7) 0.05 0.45(5) 2466.15 0.4

TiCl4-2SMe2 -0.003(4) —0.07 0.33(6) 2466.0 0.5

The figures given in parenthesis are the mean square errors in the last significant digit ' The calculated values have been received for H2S complexes

Table 8

The charges transfer in the complexes

Complex AqM,e Aq accs e Aqs,e Aqd<m> e AqM/Aqacc, % Aqs/Aqdon, %

SbCl5-SH2 0.04 0.41 -0.25 -0.41 10 61

SnCl4-2SH2 0.18 0.56 -0.10 -0.28 32 36

TiCl4-2SH2 0.52 0.60 -0.13 -0.30 87 43

Table 9

Wiberg indices values of the free acceptors and donor and complexes

Complex WM-o (abs/rel) Ws-H WM_S

free complex free complex

SbCl5-SH2 0.990/100 0.924/93 0.979 0.941 0.579

SnCl4-2SH2 1.033/100 0.893/86 0.979 0.920 0.440

TiCl4-2SH2 1.241/100 1.170/94 0.979 0.928 0.440

the sequence of the electron transfer increasing to the acceptor (Ti < Sn < Sb) do not corresponds to the change of the complex energy stabilization. This confirms the our previous deductions [1] and results of the paper [11] that for nv-complexes sta-

bility charge transfer value isn't dominate characteristic.

The n-electron density of the donor can transfer as to d,.as to a ..„vacant orbitals. The electron transfer

M .MCI

to a. .„ orbitals must lead to the more weak M-Cl bonds

•MCI

(that is reflected of the decreasing of WMQ values) and to the less electron density transfer to the central M atom in comparison with the electron transfer to dM orbitals. From the data presented in Table 9 one can see that the n,.-->d., electron transfer dominates in TiCl .

b M 4

complex while n^cr,^ electron transfer dominates in SnCl4 and SbCl5 complexes. This may be explained by the fact that for non-transition elements dM orbitals are more diffusive and lay higher within energy scale than those for transition elements. This lead to the greater acceptor ability of dM orbitals of transition elements in comparison with that for non-transition ones.

Conclusions

Our calculations have been pointed out that TiCl4, SnCl4 and SbCL complexes are somewhat stabilized. The most stable complex is SbCl5 that is in good agreement with the experimental data. The complexes' stability depends on the stabilization of the complexes' levels in consequence of vacant acceptor orbitals participation in the bonding. The reasons of the electron distribution difference between complexes of transition and non-transition elements have been explained.

References

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2. Poleshchuk O.Kh,, Nogaj B., Kasprzak J. et al. // J. Mol. Struct. 1994. V. 324.

3. Poleshchuk O.Kh., Latosinska J.N. // Koord. Khim. 1996. V. 22.

4. Wardt W.R., Hay P.J. // J. Chem. Phys. 1985. V. 82.

5. Buslaev Yu.A. et al. // J. Coord. Chem. Rev. 1987. V. 82.

6. Nefedov V.I., Vovna V.I. // Electronnaya Structura Khimicheskich Soedinienii. Moskov, 1987.

7. Modelling of structure and Properties of Molecules / Ed. Z.B. Maksic, N.Y., 1993.

8. Burstein B.E., Green J.C., Kaltsoyamus N. et al. // Inorg. Chem. 1994. V. 33.

9. Dolenko G.N., Voronkov M.G., Elin V.P., Yumatov V.D. // J. Mol Struct. 1993. V. 295.

10. Jolly W.L. //J. Phys. Chem. 1981. V. 85.

11. Jonas V. et al. // J. Am. Chem. Soc. 1994. V. 116.

12. Hargittaii M. Structurnaya Khimiya Soedinenii Seri. M., 1988.

13. Guryanova E.N. et al. Donorno-Akceptornaya Swyaz. Khimiya, 1973.

УДК 533

О.К. Матвиенко*, В.М. Ушаков**

ЧИСЛЕННОЕ ИССЛЕДОВАНИЕ РАСПРОСТРАНЕНИЯ ПРИМЕСИ ЗАГРЯЗНЯЮЩИХ ВЕЩЕСТВ

В АТМОСФЕРЕ

'Томский государственный архитектурно-строительный университет "Томский государственный педагогический университет

В связи с обострившейся экологической ситуацией особое значение приобретают задачи моделирования выбросов вредных веществ в атмосферу и определения степени загрязненности окружающей среды для оценки степени воздействия на окружающую среду и выработки рекомендаций, позволяющих уменьшить это неблагоприятное воздействие.

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Образовавшиеся перегретые газы оказываются легче воздуха. В поле силы тяжести они поднимаются вверх, увлекая за собой пылевидные частицы, и формируют свободно конвективное движение в виде пылегазового облака. Поступившая из источника примесь переносится и рассеивается в атмосфере, где может претерпевать дополнительные изменения: выпадать на подстилающую поверхность, осаждаться на вертикальные препятствия, вымываться осадками, вступать в химическую реакцию.

Конкретные задачи, связанные с расчетом переноса примеси, могут быть классифицированы

на различной основе. Первым признаком классификации считается характер источника. Это может быть постоянно дымящая труба предприятия, которую можно считать точечным источником постоянного действия, кратковременный выброс из нее или взрыв. Другие признаки классификации могут быть связаны со временем осреднения, с расстоянием до источника и характером примеси.

На практике для описания поля концентрации примеси используют два типа моделей: основанные на решении полуэмпирического уравнения турбулентной диффузии (К-модели) или гауссовой модели [1].

В первой группе моделей концентрация примеси находится из уравнения

•л

+ ^у{йд - К - &-ас1 , (1)

где К - тензор коэффициента турбулентной диффузии, и - вектор скорости ветра, Р - мощность источника.

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