MÖSSBAUER ABSORPTION SPECTRA OF 119Sn IN THE SINGLE CRYSTALS OF (CH3)2Sn(NCS)2, (CH3)2SnCl2(C5H5NO)2, AND (CH3)3SnCn

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MÖSSBAUER ABSORPTION SPECTRA OF 119Sn IN THE SINGLE CRYSTALS OF (CH3)2Sn(NCS)2,

(CH3)2SnCl2(C5H5NO)2, AND (CH3)3SnCn

H. Negita, R. Boku, S. Ichiba

To cite this version:

H. Negita, R. Boku, S. Ichiba. MÖSSBAUER ABSORPTION SPECTRA OF 119Sn IN THE SIN-

GLE CRYSTALS OF (CH3)2Sn(NCS)2, (CH3)2SnCl2(C5H5NO)2, AND (CH3)3SnCn. Journal de

Physique Colloques, 1979, 40 (C2), pp.C2-403-C2-404. �10.1051/jphyscol:19792140�. �jpa-00218513�

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JOURNAL DE PHYSIQUE Colloque C2, suppldment au n o 3, Tome 40, mars 1979, page C2-403

MOSSBAUER

ABSORPTION

SPECTRA

OF I9sn

I N THE

SINGLE CRYSTALS OF

(cH~)~s~(Ncs)

2,

(cH,)

,snc12

(c~H~No), , AND (cH~)

3 ~ n ~ ~ H. Negita, R. Boku, and S. Ichiba

Department of Chemistry, FaeuZty of Science, Hiroshima University, Hiroshima 730, Japan RSsum6.- Les spectres d'absorption MSssbauer de "'~n dans des monocristaux de (CH3)2Sn(NCS)2,

(CH3)2SnC12(C5H5N0)2, et (CH3)3SnCn ont bti? mesur6s 2 110 K. Les analyses du rapport dtintensit6 du doublet quadrupolaire donnent les composants du tenseur de gradient de champ Slectrique (GCE).

Abstract.- The Gssbauer absorption spectra of '"~n in the single crystals of (CH~)ZS~(NCS)~, (CH~)ZS~C~Z(C~HSNO)~, and (CH3)3SnCN were measured at 110 K. The analysis of the intensity ratio of the quadrupole splitting doublet yields the parameters of the electric field gradient (EFG) tensor.

1. Introduction.- When a single crystal is used as an absorber in the Mijssbauer experiment, the parameters describing the magnitude and orientation of

the EFG at a nucleus can be deduced from the angular dependence of its spectrum. This method has been applied to iron compound /I/. However, it is neces- sary to take the effect of absorber thickness into account for the precise determination of the EFG parameters in iron and tin compounds 121-141. The present investigation is aimed to extend these re- searches to three kinds of tin compounds.

2. Experimental.- The single crystals were grown by the slow evaporation of solvent. The planes of the thin plates obtained for (CH3)2Sn(NCS)2, (CH3)zSnCla (CsHsNO)z, and (CH3)3 SnCN have the 001, 100, and 100 indices, and the surface densities were 24.0 (for the observation in the ac plane) and 19.2 (for the observation in the be plane), 16.3, and 25.4 mg/

cm2 of Sn, respectively. The Mzssbauer spectra were obtained according tq the procedure outlined previous- ly /&/, except absorber temperature was kept at llOK.

3. Results and discussion.- 3.1. (CH~)ZS~LNCS)~.- The compound crystallizes in the orthorombic space group of Pnnrm 151. We choose a (c, a, b)-axis system and define O and@ as the orientation angles of the in- cident radiation relative to (c, a, b). The EFG principal axis system (z, Y, 2) is related to (c, a, b) by the Euler transform D(a,$,y). Since the two sites in the unit cell are related by 180' rotation about the b axis, the density matrix for the combi- ned sites can be diagonal for observation in the ac plane, i.e. for0 = 90'. The resulting diagonal ele- ments are :

The area ratio in the quadrupole spectrum is then given by :

In equations (1) and (2), the notation conforms to that in reference /4/, except A=sin(@-a)cosy-cos(@a) cosBsiny, B=cos(@a)sin$, and C=cos(@a)cos$cosy+

sin( ta)siny.

Recoilless fraction was taken to be isotropic;

f' = 0.19. Since the crystal structure of the compound is similar to that of (CH3)2SnC12 161 in which the direction of the EFG principal axes has been de- termined, it can be inferred to vXx//c, V //a, and

YY

V //b. Equations (I) and (2) then give the observa-

ZZ

tion angle (0)versusarea ratio curves for various values of q. Figure I(a) shows the results for q =

0.35 and 0.40 along with the experimental values.

In the case of VZZ//b, the density matrix is diagonal for all directions of O and@, then equation (1) also holds, where A=sin0&in(@ -a) cosy-cos (@-a)cos~sinfl, B=cosO, and e s i n 0 E o s (@-a)cosBcosy+

sin(@-a)sind.~he observation in the bc plane was investigated to make sure whether the value of q obtained in the above case were reasonable. Figure

I(b) shows that 0.35 is better than 0.40 as the value of q.

3.2. ~~IX2lfinC1~(C~H!jN0)2

.-

The compound is tricli- nic, space group pi 1 7 1 . Equation (1) hblds for observation in the a'b' plane, if D(a,B,y) is taken as the Euler transform of the EFG principal axis system relative to (a' ,b' ,c ) where a' is parallel to a

' and b' in the be plane.

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:19792140

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0.6

-20 0 20 40

0 , degree

JOURNAL DE PHYSIQUE

50 70 90 110 130

0 , degree

Fig. I : The area ratio as a function of the observation angle O or in (CH3)2Sn(NCS)2. The y-ray is in the ae plane for (a) and in the be plane for (b).

The solid line is computed for ezq& > 0, f' = 0.19, a=OO, P o 0 , y o o , and n=0.35 or 0.40.

Recoilless fraction was estimated to f1=0.21 at 110 K. From the point charge model for trans- RzSnA2B2 species, it is expected that e 2 q ~ is posi- tive and that the x, y, and z principal axes of the EFG are approximately along the Sn-pyO,Sn-C1, and Sn-CH3 bond directions, respectively. This leads to a=6I0,

B=82', and y= 1 16O. The experimental values were compared with the computed values for various values of a, B,y, and 11. An accurate stimulation of the experimental data was obtained for a=6S0, &78", y=114', and

~=0.05 (see fig. 2). This support the fact that the above expection is correct.

-50 -30 -10 10 30 50

$, degree

Fig. 2 : The area ratio as a function of the observation angle 0 in ( C H ~ ) Z S ~ C ~ ~ ( C ~ H ~ N O ) ~ . T ~ ~ solid line is computed for e2q& > 0, f'=0.21, a=6S0, f3=78', y114', and q=0.05.

of the density matrix is the same as that of (CH3)-9 Sn(NCS)z because the two sites are symmetry by the 180' rotation about the a axis. It is expected from the symmetry of the crystal structure that the value of q is zero and that Vxx//a, V / / b , and VZZ//e.

YY

The recoilless fraction to the y-ray propaga- tion direction going in and out angle @ from the molecular symmetry axis is given by :

ft(@) = exp(f;, cos20+fisin20) (3) we estimated Inf;, = -1.72 and lnfi = -3.64 at 110 K from the data of Herber e t aZ. 191.

The area ratios calculated by substituting the above-mentioned parameters into equations ( 1 ) and (2) along with the experimental values are pre- sented in table I.

Table I : Area ratios for the single crystal of (CH3)3SnCN. Calculated values are based on a=oO, &90°, y=90°, and ll=O.

0 0 Exp t

.

^Calc.

(deg.) (deg

.

⁾ ^(Ao/Aa)

90 7 5 1 .50 ? 0.07 1.48 9 0 80 1.55 -C 0.09 1.57

90 85 1.61

+

^0.08 ^1.63

90 9 0 1.64 ? 0.09 1.65

It is found that the ratio of the high energy area to the low energy one, AH/AL, is equal to A /A and

0 Tl

not A / A

.

This implies that ezqQ is negative. The-

Tl u

refore, the electrostatic field has an oblate shape around the axis of cylindrical symmetry (CN-Sn-CN).

References

/I/ Zory, P., Phys. Rev.

240

(1965) A1404.

/2/ Housley, R.M., Grant, R.W. and Gonser, U., Phys Rev. 178 (1969) 514.

131 Gibb, T.C., J. Phys. C 7 (1974) 1001.

141 Negita, H., Boku, R., Nakamura, M. and Ichiba, S., Bull. Chem. Soc. Jpn. 50 (1977) 584.

/5/ Forder, R.A. and Sheldrick, G.M., J. Organomet.

Chem. 22 (1970) 61 1.

/61 Davies, A.G., Milledge, H.J., Puxley, D.C. and Smith, P.J., J. Chem. Soc. A (1970) 2862.

171, Blom, E.A., Penfold, B.R. and Robinson, W.T.,

' J. Chem. Soc. A (1969) 913.

181 Schlemper, E.O. and Britton, D. Inorg. Chem. 5 (1966) 507.

/9/ Herber, R.M. and Chandra, S., J. Chem. Phys. 53 (1970) 3330.

3.3. ( C H M n C N . - The compound forms orthorombic crystals in the space group Cmcm /8/. The treatment