DFT study of donor-acceptor complexes of the non-transition and transition elemants by NBO approach Текст научной статьи по специальности «Физика»

НАУЧНЫЕ СТАТЬИ

ХИМИЯ, ФИЗИКА, МАТЕМАТИКА, ТЕХНИКА

УДК 541,6

O.Kh. Poïeshchuk*, E.L. Kalinina*, G. Frenking**

DFT STUDY OF DONOR-ACCEPTOR COMPLEXES OF THE NON-TRANSITION AND TRANSITION

ELEMENTS BY NBO APPROACH

*Tomsk State Pedagogical University **Fachbereich Chemie, Philipps-Universitaet Marburg, Germany

Introduction

Compounds of non-transition and transition elements containing tin, antimony, titanium and niobium atoms were studied by nuclear quadrupole resonance spectroscopy and Mqssbauer effect. The parameters like quadrupole splitting or quadrupole coupling constant (QCC) as well as Mussbauer isomeric shifts on the nuclei 127I, 35Cl, 8lBr, 93Nb, 121Sb and »»Sn were determined. The studies of the electronic density distribution in the complexes and environment of the central atom were performed mainly on the basis of semi-empirical calculations. The correlation between the experimental and calculated Mussbauer isomeric shifts or QCC can be significantly improved by the application of non-empirical methods. A good test of ; various non-empirical methods could be the quality of reproduction of NQR parameters.

Usually such an analysis is performed on the basis of the Townes-Dailey approximation [1], which allows a comparison of QCC obtained from experimental and calculated with using the density ma-; trix values. This theory reduced to the following:

a) the inner-core electrons of the relevant atom do not contribute to the electric field gradient, the deviation of the inner shell from spherically being negligible;

b) the QCC is conditioned only by p-electrons of the valence shell of the atom under study. The contribution of the bond orbital may be partitioned into net atomic and overlap contributions, and these may be neglected;

c) the contributions from the electrons belonging to other atoms are completely compensated by the corresponding nuclear contributions. The contribution from one valence shell p-electron is assumed to be constant for each type of an atom.

As a result the main idea of the Townes-Dailey approximation is that the basic contribution to the electric field gradient comes from p-valence electrons of the atom considered. Therefore, we expected that

the best QCC values (i.e. the closest to the experimental results) could be calculated using a nuclear core pseudopotentials. In the earlier papers one of the author were calculated the QCC by ab initio methods using HONDO and GAUSSIAN'94 packages [2, 3] for heavy nuclei, such as iodine, tin and antimony in some complexes containing these elements. Direct calculations of the electric field gradient on iodine, tin and antimony atoms have shown that the use of a pseudopotentials for these atoms does not lead to QCC values reliable enough. The results obtained for chlorine and nitrogen atoms in the extended basis set i.e. 6-311G* were in a good agreement with experimental values.

The focus of the present paper is the comparison in the QCC on the central atoms calculated by pseudopotentials and all-electron basis sets, to obtain reliable values of the electronic density distribution on atoms as well as the electric field gradients on the nuclei. Besides we will look the trend in the donor strengths of Lewis bases on going from such weak donor as OSCl2 to strong donor as pyridine. According to Gutmann s approach [4] the strength of a coordinated bona aepends on the donicity of the donor and on the accepticity of the acceptor unit. Since no values are available for the latter, only the relative effect of the donicity can be followed towards a given acceptor component. In the capacity of such acceptor antimony pentachloride be used much.

Theoretical methods

The full optimisations of geometry were carried out using the B3LYP method with the Becke's exchange B3 functional [5] and LYP correlation functional [6] achieved within the GAUSSIAN'98. The calculations were carried out with standard basis set II [7], which has a relativistic effective core potential with a (211/ 211/1) valence basis set for Ti, Nb, Sb, and Sn, 6-311G (2d, p) all-electron basis set for the H, C, N, S, P, O, CI elements or 3-21G* basis set for all atoms. The

QCC values were obtained from the principal components of the electric field gradient tensor along the principal axes. We have been used NBO approach [8] for the analysis of the bonding situation of the complexes.

Results and discussion

A comparison of the geometrical parameters calculated by B3LYP/II and B3LYP/3-21G* with the experimental data for complexes containing a halogen, antimony, tin, titanium and niobium atoms showed that the bond lengths metal-halogen have been overestimated for the both calculation methods. However, for B3LYP/II calculations the co-ordinating bonds lengths larger than the experimental ones. On the other hand the results of B3LYP/3-21G* calculated indicated the high reliability of the calculations. We can see that using the both calculation methods, a good agreement between the experimental and the calculated valence angles was obtained.

These results encouraged us to perform the calculations of QCC of chlorine, nitrogen, antimony, tin and niobium atoms for the studied complexes using the B3LYP/II and B3LYP/3-21G*. It should be pinted out that correlation between experimental [9-12] and calculated NQR frequencies was obtained for B3LYP/II:

v(cal.)(MHz)=0.63+1,08v(exp.) (MHz) (r=0.995; s=0.9; n=24) (1)

and

v(cal.) (MHz) = 2.14+0.88v(exp.) (MHz) (r=0.997; s=0.6; n=30) (2)

for B3LYP/3-21G* calculations. It is necessary also to note, that such a correlation is valid for all complexes studied, in spite of the different environment of the halogen atoms concerned.

Analogous correlations were found between the calculated and experimental QCC [9,11, P] for studied complexes containing antimony and niobium atoms at the B3LYP/3-21G* level: e2Qq Sb(cal.)(MHz)=29.6+0.69e2QqJ5b(exp.) (MHz) (r=0.970; s=23; n=18), (3)

e2Qq Nb(cal.)(MHz)=l 1,2+0.34e2QqaNb(exp.) (MHz) (r=0.978; s=2.3; n=8). (4)

The last correlation included the niobium containing complexes (Table 1) and dimers [13].

The QCC values for Sb and Nb atoms were lesser from B3LYP/II calculations. It is very important conclusion because Townes-Dailey theory [1] developed for NQR takes point to the absence of the contribution of the core electrons into the electric field gradient.

Table 2 gives the energies calculated at the B3LYP/II level using B3LYP/II optimized geometries and the experimental Gutmann's donor numbers (DN) [4] for SbCl5L complexes. There is no essential difference between the using of dissociation

(D ) and ZPE (Do) corrected energies for the correlations between experimental DN and calculated energy values. The calculated by B3LYP/II bond dissociation energies of the SbCl5L complexes (D^ and Do are in a good agreement with the experimental enthalpy complex formation (DH) values [4]: -AH(kcal/mol)=2.0+1.3De(kcal/mol) (r=0.970; s=2.8; n=10), (5)

-AH(kcal/mol)=2.8+1.3Do(kcal/mol)

(r=0.970; s=2.9; n=10). (6)

On the other hand calculated B3LYP/3-21G* D

> e

values were far from DN values.

An interesting feature seems to be the electron density distribution on atoms in the complexes investigated. The changes in the electronic density distribution upon complex formation (charge donation), the polarisation, and the bond order of the donor-acceptor bonds, calculated by NBO (Table 3) indicate that all complexes with Me2S have the highest covalent character. We think that it may be connect with the lowest ionization potential for this donor (8.65 eV) in comparison with another donors (>9.5 eV). The most important seems to be the increase or the invariably of the positive charge on antimony and tin atoms upon complex formation with the exception of Me2S complexes. This conclusion was confirmed by X-Ray Electron and Fluorescence spectra for these complexes [2,14]. In niobium and titanium Complexes (with the exception of NbCls OP(CH3)3 complex) the positive charges on the central atoms decrease upon complex formation. From a view of donor the negative charge on the nitrogen and dxygeri atoms increases (in antimony, tin and titanium complexes) upon complex formation as a result of the transfer of electron density from another donor's atoms. It may be explained by the increasing of the electrostatic interactions upon complex formation. Indeed we can see (Table 3) that the polarization of the metal-chlorine bonds increase upon complex formation in these complexes. On the other hand in niobium complexes the negative charge on the co-ordinating donor atom decreases upon complex formation. At the same time the polarization of the niobium-chlorine bonds (Table 3) decreases to the same direction.

We did hot find the correlation between charge donation and calculated dissociation energies of the main group and transition metal complexes that agree with the paper [15] on the aluminium containing complexes. The calculated hybridization at the central atoms of the antimony complexes (Tables 3 and 4) shows the large 5d population on the equatorial metal-chlo-rine and metal-ligand bonds. For tin complexes the obtained results agree with sp hybridization for main-group chemistry. In the case of the titanium and niobium complexes metal-chlorine bonds include s- and d-orbitals of the central transition metal atoms just as

Table 1

Theoretical and experimental parameters [16] of the calculated complexes

Complex M-CI(eq) [A] M-Cl(ax) [A] M-L |A] ZCi-M-L or ZM-L-L' [deg]

Exp. 3-21G* II Exp. 3-2 JG* II Exp. 3-21G* II Exp. 3-21G* II

SbCUOPCl, 2.33 2.39 2.39 2.33 2.36 2.34 2.17 2.21 2.48 145 152 147

SbCl5NCCH3 2.36 2.39 2.39 2.35 2.36 2.35 2.23 2.29 2.41 85 88 83

SbClsPy 2.41 2.41 2.38 2.37 2.30 2.38 84 89

SbClsS(CH3)2 2.41 2.41 2.36 2.36 2.74 2.78 86 86

SbC)5OSCl2 2.39 2.38 2.35 2.32 2.29 2.89 83 80

SbCl5OS(CH3)2 2.41 2.41 2.37 2.37 2.11 2.19 86 85

SbClsOHCH3 2.40 2.40 2.36 2.35 2.18 2.35 86 85

SbCl502NCH3 2.39 2.39 2.36 2.34 2.25 2.51 81 79

SbCl5OP(CH3)3 2.34 2.40 2.41 2.34 2.38 2.38 1.94 2.08 2.15 139 144 141

SbCl5ONCH(CH3)2 2.33 2.39 2.39 2.35 2.43 2.43 2.05 2.14 2.23 124 130 128

SbClsOSeCl2 2.34 2.41 2.40 2.32 2.36 2.35 2.08 2.12 2.29 121 113 116

SbCl3NH2C6H5 2.33 2.43 2.40 2.52 2.44 2.42 2.52 2.56 2.78 83 78 79

SnCl4[NCCH3]2 2.34 2.39 2.38 2.36 2.41 2.39 2.335 2.34 2.51 167 174 169

SnCl4[S(CH3)2]2 2.46 2.43 2.46 2.43 2.69 2.73 90 90

SnCI,[OS(CH3)2]2 2.37 2.40 2.41 2.48 2.41 2.46 2.38 2.41 2.44 2.43 2.11 2.14 2.23 87 86 86

SnCl4[OPCI3]2 2.31 2.36 2.38 2.41 2.33 2.41 2.25 2.30 2.24 2.29 144 151 139 159

SnCl4[OSeCl2]2 2.36 2.42 2.35 2.41 2.49 2.46 2.12 2.17 2.38 121 113 119

TiCl4[NCCH3]2 2.215 2.22 2.23 2.265 2.29 2.295 2.18 2.23 2.22 2.23 2.27 166 157 170

TiCl4[OPCl3]2 2.20 2.20 2.23 2.20 2.23 2.235 2.29 2.28 2.22 2.13 2.16 2.26 2.42 152 153 138

TiCl4[S(CH3)2]2 2.27 2.31 2.28 2.31 2.60 2.63 92 91

TiCl4[0(CH3)2]2 2.24 2.27 2.35 2.11 146

TiCl4[OS(CH3)2]2 2.26 2.31 2.31 2.40 1.97 2.04 125 148

TiCl4Py2 2.30 2.30 2.19 96

NbClsNCCHj 2.36 2.35 2.30 2.28 2.32 2.34 82 82

NbCl5OPGl3 2.33 2.36 2.36 2.33 2.30 2.27 2.17 2.26 2.41 145 152 148

NbCl5S(CH3)2 2.36 2.36 2.31 2.28 2.79 2..85 109 109

NbCl5OS(CH3)2 2.39 2.37 2.32 2.30 2.10 2.19 128 127

NbCljPy 2.37 2.36 2.32 2.30 2.38 2.46 81 80

NbCl5OP(CH3)3 2.38 2.30 2.13 147

Table 2

Calculated total energies Ew [HartreeJ and zero-point vibrational energies [kcal/mol] at B3LYP/1I; experimental energy of complex formation -AH [kcal/mol], theoretically predicted binding energies Df [kcal/mol] and ZPE corrected values D, [kcal/mol]

for SbClsL complexes

L ZPE De D0 -All .

OSCb 3700.57063 8.3 1.0 0.7 0.4

CH;,CN 2439.48453 33.1 11.0 9.9 14.1

(CH,)2S 2784.76514 52.5 14.8 13.5 23.5

uPCI., 4104.07695 10.3 5.9 5.3 11.7

(CH3)2SO 2859.99034 54.5 25.2 23.9 29.8

Py 2555.05915 60.9 21.6 20.0 33.1?

CH30H 2422.45724 37.7 16.0 14.3 20.0

OSeCI, 5703.90770 7.8 6.6 5.8 12.2

(СНз)зРО 2843.17233 78.3 26.5 25.4 38.6м

(CH3)2NCHO 2555.29099 69.0 10.4 8.9 26.5

WON for SbCI5OP[N(CH3)j]3.

Table 3

Changes in the effective NAO charge (in e) and Wiberg bond orders calculated by B3LYP/II upon complex formation1'1

Complex Aq(D->A) AqM Aqa AqL WD.A

SbCIjOPCIj 0.05 -0.02 0.07 0.08 0.12

SbClsNCCH3 0.14 -0.01 0.15 0.12 0.22

SbClsPy 0.20 -0.01 0.21 0.09 0.28

SbClsS(CH3)2 0.38 0.17 0.21 -0.23 0.42

SbClsOSCl2 0.02 0.01 0.01 0.06 0.05

sbasos(CH3)2 0.20 -0.08 0.28 0.03 0,27

SbCh'OHCH, 0.13 -0.03 0.16 0.03 0.19

SbCls02NCH3 0.11 0 0.11 0.02 0.15

SbCl5OP(CH3)j 0.19 -0.09 0.28 0.05 0.27

SbCl5'OSeCl2 0.07 -0.03 0.10 0.15 0.22

SbCl,'ONH(CH3)j 0.17 -43.07 0.24 0.07 0.25

SnCl4[NCCH3]2 0.23 0.01 0.22 0.08 0.18

SnCl4[S(CH3)2]2 0.68 0.32 0.36 -0.18 0.43

SnCl4[OS(CH3)2]2 0.33 -0,09 0.42 0.04 0.23

SnCl4[OSeCI2]2 0.08 -0.04 0.12 0.14 0.18

TiCl4[NCCH3]2 0.36 0.21 0.15 0.03 0,30

TiCl4[S(CH3)2]2 0.80 0.38 0.42 -0.25 0.49

TiCl4[OPCl3]2 0.26 0.14 0.12 0.02 0.20

NbCl5OPCl3 0.13 0.08 0.05 0.04 0.19

NbCb'NCCHj 0.18 0.12 0.06 0.05 0.29

NbCls'OS(CH3)j 0.26 0.04 0.22 -0.05 0.37

NbCI5S(CH3)2 0.33 0.22 0.11 -0.22 0.38

NbClsPy 0.36 0.46 -0.10 -0.07 0.20

NbCl5'OP(CH3)j 0.29 0 0.29 -0.06 0.40

«Donor-acceptor charge donation Aq(D-»A); partial atomic charges q of the donor atom (Aqt) and the central atom (AqM), and the chlorine atoms of the acceptor (Aqa); Wiberg bond orders (WMJ of the donor-acceptor bond. The negative sign of Aq corresponds to a decrease in the electron density on the atoms upon complex formation.

donor-acceptor bonds contain essential contribution only for some complexes, while the NbCl5L complex-of the p-orbitals of the titanium atoms. The NBO es with all calculated donor ligands have lone-pair method finds the Sb-D, Sn-D and Ti-D bond orbitals orbitals at their donor atoms.

Table 4

Results of the NBO analysis at the B3LYP/II and B3LYP/3-21G* levels for metal-chlorine bonds"

Complex Basis set M(x)-Cl(y)

%x(eq)/(ax) %s(x) (cq) %p(x)(eq) %d(x)(eq) %s(xXax) %p(x) (ax) %d(x)(ax>

SbCl5 3-2 IG* II 73.46/77.25 73.79/77.97 20.39 20.30 65.98 66.20 13.63 13.50 20.15 19.62 50.00 50.00 29.85 30.38

SbClsOPCl3 3-2 IG* II 75.73/72.43 76.58/72.87 21.27 21.04 53.82 54.13 24.91 24.83 16.34 17.23 81.64 81.81 2.02 0.97

SbClsNCCH3 3-2 IG* II 77.48/72.44 77.14/73.25 18.48 20.95 56.30 53.92 25.23 25.13 19.78 16.21 73.02 82.77 7.20 1.03

SbCI5Py 3-2 IG" II 80.04/77.87 77.21/73.43 16.58 21.75 50.23 54.60 33.19 23.66 20.44 15.44 50.44 83.20 29.12 1.35

SbCl5S(CH3)2 3-2 IG* II 79.35/76.66 79.92/76.66 17.04 17.10 50.33 50.49 32.63 32.41 19.38 19.41 52.49 55.19 28.12 25.40

SbCl5OSCl2 3-21 G*a II 74.69/72.40 76.23/71.73 25.35 20.63 56.41 54.65 18.24 24.72 17.73 18.36 80.08 80.26 2.18 0.79

SbCl5OS(CH3)2 3-2 IG* II 81.41/78.23 81.45/78.61 15.58 15.89 49.89 51.16 34.53 32.95 20.07 19.86 49.86 55.51 30.07 24.63

SbClsOHCHj 3-21G* II 80.19/77.95 78.23/73.00 16.64 20.01 50.73 54.60 32.63 25.38 21.54 16.84 49.48 81.99 28.98 1.17

SbCls02NCH3 3-21G* II 76.89/73.02 77.05/72.78 20.95 20.61 53.81 54.13 25.24 25.26 16.18 17.28 81.73 81.78 2.09 0.96

SbCl5OP(CH3)3 3-21G* II 82.10/78.75 80.22/79.21 15.24 16.99 49.61 52.58 35.15 30.43 20.18 19.23 50.51 57.44 29.31 23.33

SbCl5OSeCl2 3-2 IG* II 75.84/73.21 76.20/73.23 22.98 22.20 53.39 54.17 23.63 23.64 15.48 16.38 81.89 82.43 2.63 1.21

SbCl5ONH(CH3)2 3-2 IG* II 77.00/73.93 77.32/74.00 21.82 21.62 53.39 53.80 24.79 24.58 15.10 15.53 82.42 83.17 2.48 1.30

Sncu 3-21G* II 77.14 78.24 24.99 25.00 74.09 74.33 0.92 0.68

SnCl4[NCCH3]2 3-2 IG* II 79.97/79.63 81.02/80.06 20.12 20.68 78.43 78.39 1.45 0.93 29.79 29.31 68.88 69.83 1.33 0.86

SnCU[S(CH3)2]2 3-2 IG* II 85.49 85.26 17.56 17.92 50.04 50.03 32.40 32.04

SnCUtOSCCHj^a 3-21G* II 86.52/86.48 82.36/83.01 17.97 31.63 50.45 66.86 31.58 1.52 17.71 18.22 51.38 80.27 30 9" 1

SnCl4rOPCl3]2 3-21G* 80.78/79.74 19.35 78.80 1.80 30.52 67.62 1.86

SnCl4[OSeCl2]2 3-21G* II 87.74/81.93 83,05/80.22 16.25 17.66 51.55 80.79 32.19 1.56 22.57 22.96 55.10 76.07 22.33 0.97

TiCl4 1 3^>TG*~ 11 82.98 79.28 25.01 24.99 0.07 0.29 74.91 74.74

TiCl4[NCCH3]2* 3-2 IG* II 86.41/89.05 84.69/87.08 27.85 24.93 0.37 7.38 71.78 67.69 17.33 11.43 1.41 15.33 81.26 73.24

TiCl4[OPC1,]: 3-2 IG* II 83.60/88.02 78.28/79.96 30.19 31.25 0.09 0.30 69.72 68.44 17.55 16.62 1.60 0.75 80.85 82.63

TiCl4[S(CH3)2]2 3-2 IG* II 85.65 79.81 31.82 33.82 0.44 1.39 67.84 64.79

TiCI4[OC(CH3)jl2 3-21G* 86.97/85.30 14.68 1.10 84.21 32.09 0.23 67.68

TiCI,[OS(CH;)2]; 3-21G* II 86.05 81.28/79.63 32.19 17.45 0.43 1.66 67.38 80.89 32.04 0.32 67.64

TiCl4Py3 3-21G* 89.19 14.93 2.91 82.16

NbCls 3-21G* II 94.70/78.26 81.42/93.74 10.25 20.20 29.30 3.40 60.45 76.39 38.40 0 0.16 8.47 61.44 91.53

NbCl5OPCl3 3-2 IG* II 79.07/76.19 77.95/77.16 15.88 16.30 0.42 0.09 83.71 83.62 33.04 31.21 0.15 0.06 66.81 68.73

NbClsNCCHj 3-21G* II 78.43/76.94 77.77/77.94 16.58 16.59 0.39 0.11 83.04 83.31 33.69 33.40 0.12 0.11 66.19 66.49

NbCl5OS(CH,)2 3-2 IG* 79.02 33.30 0.29 66.41

NbCl5S(CH3)2 3-2 IG* II 78.47/76.38 77.82/76.37 16.03 16.40 0.42 0.21 83.55 83.38 33.99 34.00 0.07 0.06 65.94 65.94

NbClsPy 3-2 IG* II 77.70/77.31 89.53/79.77 15.22 7.83 0.30 12.44 84.49 79.73 32.58 33.25 0.11 0.45 67.31 66.30

'"Polarization of the central atom-chlorine bond D(x)-Afy) in %x, hybridization of the D(x)-A(y) bond for equatorial and axial chlorine atoms separately.

Table 5

Results of the NBO analysis at the B3LYP/II and B3LYP/3-21G* levels for metal-ligand coordinating bonds'"

Complex Basis set D(x)-A(y)

%x %s(x) /upw %s(y> %p(y) %d(y)

SbCI5OPClj 3-21G* II 100 100 76.48 63.09 23.52 36.84 0 0.07

SbClsNCCH3 3-21G* II 75.93 100 8.10 46.15 91.90 53.84 0 0.01 26.06 56.40 17.53

SbCI.Py 3-21G* II 88.77 100 25.76 25.25 74.24 74.75 0 0 16.20 54.04 29.76

SbCl5S(CH3)2 3-21G* II 85.29 85.17 10.24 7 97 89.61 91.74 0.15 0.29 12.35 12.28 49.65 47.78 38.00 39.94

SbCl5OSCl2 3-21G*" 11 79.74 100 8.14 71.76 91.86 28.17 0 0.07 7.35 66.69 25.96

SbCl5OS(CHj)2 3-21G* II 90.07 93.04 21.09 19.37 78.91 80.50 0 0.12 15.97 14.08 53.65 60.16 30.38 25.76

SbCl5OHCH3 3-21G* II 91.86 100 33.56 28.44 66.44 71.53 0 0.03 14.45 59.38 28.18

SbCl502NCH3 3-21G* II 100 100 23.65 14.25 76.35 85.67 0 0.07

SbCl5OP(CH3)3 3-21G* II 90.80 93.36 23.85 21.06 76.15 78.89 0 0.06 16.55 13.62 57.16 65.60 26.30 20.78

SbCIsOSeCl2 3-21G* II 100 100 18.49 14.3 81.51 85.54 0 0.16

SbC 15ONH(CH3 )2 3-21G* II 100 100 23.04 15.66 79.69 84.25 0 0.08

SnCl4[NCCH3]2 3-21G* II 100 100 46.37 47.96 53.63 52.00 0 0.04

SnCl4[S(CH3)2]2 3-21G* II 87.76 87.35 15.19 13.53 84.67 86.20 0.13 0.28 14.99 14.82 50.19 50.01 34.82 35.17

SnCl4[OS(CH3)232 3-21G* II 92.77 100 22.79 56.15 77.21 43.74 0 0.12 16.59 53.34 30.07

SnCl4[OPCl3]2 3-21G* 11 100 65.37 34.63 0

SnCI4[OSeCl2]2 3-21G* II 93.36 100 12.86 71.58 87.14 28.35 0 0.07 16.14 48.54 35.32

TiCl4[NCCH3]2M 3-21G* II 66.09 62.94 49.37 57.58 50.63 42.41 0 0.01 22.04 39.41 38,05 19.50 39.91 41.09

TiCl4[OPCI,]2 3-21G* II 97.32 100 0 59.16 100 40.77 0 0.07 16.65 4.76 78.59

TiCl4[S(CH3)2]2 3-21G* IIм 86.93 80.57 63.35 6.98 14.96 13.78 92.88 84.80 85.95 0.13 0.24 0.26 35.72 16.58 40.22 0.48 17.08 41.90 63.79 66.34 17.88

TiCl4rOC(CH3)2l2 3-21G* 100 43.35 56.65 0

TiCl4[OS(CH3)2]2 3-21G* IIм 100 43.07 70.68 30.14 29.32 69.75 0 0.11 29.38 3.07 67.54

TiCl4Py2 3-21G* 100 26.70 73.30 0

"'Polarization of the donor-acceptor bond D(x)-A(y) in %x, hybridization of the D{x)-A(y) bond. №l3c-4e-bonds.

Conclusion

The calculations clearly show that the calculated by B3LYP/II and B3LYP/3-21G* >5CI frequencies correlate with the experimental values are the same. On the other hand the QCC values calculated with use of the pseudo potential for the central atoms provided much lower than the experimental ones. At the same time the QCC values of the central atoms calcu-

lated by B3LYP/3-21G* were well correlated with experimental values. The ZPE corrected complexa-tion energies of the SbClsL complexes do not upgrade the binding energies towards the experimental Gut-mann's donor numbers. The donor-acceptor bonds for all complexes have a high degree of ionic character. The Wiberg bond order values determine of the detection of the metal-ligand bond orbitals with the exception of niobium complexes by NBO approach.

The value of Wiberg bond order must be not lesser than 0.3. The donor-acceptor interactions of main-group elements such as Sb and Sn described in terms of the sp hybridization just as these interactions of transition metal elements mean sd hybridization.

Acknowledgements

This study was supported by the DAAD. Ex-cellent service was offered by the Hochschulrechenzentrum of the Philipps-Universitaet Marburg.

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YflK 541.49

O.Kh, Poleshchuk*, E.L. Kalinina*, B. Nogaj**

INVESTIGATION OF TIN AND ANTIMONY COMPOUNDS USING NQR, X-RAY ELECTRON AND QUANTUM-CHEMICAL CALCULATIONS

*Tomsk State Pedagogical University

"•Institute of Physics, Adam Mickiewicz University, Poznac, Poland

This paper is a part of the systematic studies performed by us for understanding the electronic structure of organic compounds of tin and antimony. It was shown in our previous papers that the NQR, X-Ray electron and fluorescence spectroscopies provides a simple way to characterise the electronic properties for qualitative interpretations of the structure, chemical reactivity and aspects of bonding [1-5]. In this paper we try to explain the relations between 35C1-NQR frequency and the energies of the internal levels in the tin and antimony compounds.

It is well known, from Townes-Dailey approximation [6], that the "CI-NQR frequencies are proportional to the degree of ionic character of the bonds. The latest one is dependent on the effective charge on the atoms and therefore is proportional to the energies of the internal levels.

We report analogous relations for Sn and Sb compounds with organic ligands. The calculations were performed by the NDDO method in PM3 modifica-

tion in the basis of sp valent orbitals using MOPAC program [7]. The geometry of the studied compounds optimized by quantum-chemical methods is consistent with that determined in experiment for the same compound in gas phase [8].

The calculated by Koopmans ionization potentials of the valent orbitals were compared with energy orbitals from photoelectron spectra [9]. A good correlation was found between the ionization potentials calculated by PM3 method and experimental values following from the photoelectron spectra. Analysis of this correlation leads to the following relation:

lP«'-1.06IP;:-0.88 (r=0.997, s=0.09). (1)

Table 1 presents the effective charge calculated by PM3 method, the experimental X-Ray electron spectroscopy (ESCA) levels [8] and the experimentally found [5] and calculated 35C1-NQR frequencies. The following relations between the energy of ESCA levels of CI and Sn atoms and the effective charge were derived: