STUDY OF ((NCS)x(H2O)6-xFe) Kx-2 FOR X = 6, 5, 4, 3 BY MÖSSBAUER SPECTROSCOPY

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STUDY OF ((NCS)x(H2O)6-xFe) Kx-2 FOR X = 6, 5, 4, 3 BY MÖSSBAUER SPECTROSCOPY

C. Lupiani, J. Vara, J. Sancho, R. Duo

To cite this version:

C. Lupiani, J. Vara, J. Sancho, R. Duo. STUDY OF ((NCS)x(H2O)6-xFe) Kx-2 FOR X = 6, 5, 4, 3 BY MÖSSBAUER SPECTROSCOPY. Journal de Physique Colloques, 1974, 35 (C6), pp.C6-251-C6-253.

�10.1051/jphyscol:1974633�. �jpa-00215790�

JOURNAL DE PHYSIQUE Colloque C6, suppl6ment au no 12, Tome 35, Dkcembre 1974, page C6-251

STUDY OF ((NCS),(H,O),-,Fe) K,-,

FOR X

⁼ 6 , 5 , 4 , 3

BY MOSSBAUER SPECTROSCOPY

C. LUPIANI, J. M. VARA, J. SANCHO and R. DUO Departamento de Investigaciones Quimicas

Centro Coordinado del C. S. I. C. y la Universidad Aut6noma de Madrid, Espagne

Rbum6. - Les complexes [Fe(NCS)x(H20)6-x]2-X ont BtB BtudiBs par spectroscopie Moss- bauer. Une relation linkaire a BtB trouvk entre 1'Bclatement quadrupolaire et le nombre de mole- cules d'eau pour X = 6, 5, 4 et 3. La variation de e avec 6 est Bgalement linBaire pour X = 6, 5,O.

Abstract. - The [ F ~ ( N C S ) X ( H ~ ~ ) ~ - ~ ] - X + ~ complexes have been studied by Mossbauer spec- troscopy. A linear relation between quadrupole splitting and the hydration number has been found for values of X = 6,5,4,3. The plot of ⁸ vs. 6 also yields a straight line for X = 6, 5,O.

The progress of the following reaction has been studied :

SO,H,O[F~(H~O),]

+

6 SCNK (1) Mossbauer spectra were made for varying reaction times. At room temperature (21 OC), the reaction is completed in 4 hours. The technique of freezing was used in studying this reaction.

The final product of the reaction

was identified by synthesizing the complex using conventional methods [I] and comparing Mossbauer spectra of (Fe(NCS),)K,. 3 H,O obtained by a solid- solid reaction or by the classic technique. At room temperature the value of the isomer shift is the same as that found by Sano and Kono [2].

Table I gives the values of the isomer shift, quadru- pole splitting, width at half height and percent of effect for the different complexes which appear during reac- tion (1).

In order to determine whether the coordination is made through nitrogen or sulphur. I. R. spectra were made in the zone between 4 000 and 400 cm-l. The band frequencies are : 2 070 cm-I (vs) C-N stretch ; 770, 740 cm-I (w) C-S stretch ; 475 cm-I (w) N-C-S bend. The frequency values are the same as those in the literature [3, 41 for the isothiocyanate group.

Three complexes appear during reaction (I) : (F~(NCS),)-~ (F~(NCS),(H,O))-3 and

The second of these could only be obtained as an intermediate step of a reaction between solids. The third was isolated and identified, and it was proved that of the two possible structures - c~s-(F~(NCS),(H,O)~)-~

and t r a n ~ - ( F e ( N C S ) , ( H , 0 ) ~ ) - ~ - only one is stable.

The complexes which appear during the reaction between S04Fe. 7 H 2 0 and SCNK, for a stochiometric ratio of

4,

are : (Fe(NCS),)-4 ; (Fe(NCS),(H20))-3 ; trans-(Fe(NCS)4(H20),)-2 ; and

C~S-(F~(NCS),(H,O))-~

.

The Mossbauer parameters of these complexes for different reaction times are given in Table 11.

SO4 F e - 7 H 2 0 + ~ S C N K

~ ~ ( N C S I J - ~ 5

"10

C

3 s

I [Fe('cs)5(H201]-

,

I ^"10

c F e ( N c s h ( ~ 2 0 ) 2 2 s P

CIS? _%

T e ~ p e r a t u r e re a c t i o n = 2 1 ° C

The s p e c t r e s be made a t Iiqutd nttrogen temperature SO'Fe 7H20-6 S C N K

0 . 5 0 1 . 2 6 0 . 2 6 0.0574 1.32 1.2 7 0.3 8 0.0 554

2.4L 1 2 7 0:71 0.0495

T:293 K

8 5 s 0.51 1.25 0.26 0.0497

1.32 1.2 6 0.3 8 0 0 497

2.44 1 . 2 7 0.5 5 0.0658

0.31

180s 0.52

I 2 5 0.35 0.0577 1.33 1.2 5 0.3 1 0.057 5

2.44 1.27 0.59 0.0552

1.17

Total 7 ~ 2 9 3 K

1.99for293 K l.09for 293 K 0.3lfor 293 K 0 . 0 6 5 4 f o i 293 K

OL5 0.0455

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1974633

C G-252 C. LUPIANI, J. M. VARA, J. SANCHO AND R. DUO

In this table it can be observed that for short reaction times the best fit is obtained by consider- ing four doublets, that is, only one structure for the (Fe(NCS)4(H20)2)-2 complex. As the reaction time increases, the best fit is obtained with five doublets, ^L that is, with the two possible structures of

m'm. /s e g.

The final product is the complex which has a quadru- pole splitting of (2.44

+

0.01) mm/s and an isomer shift of 6 = (1.27 k 0.01) mm/s.

In figure I we have shown the variation of the isomer shift of the different complexes as a func-

1 FIG. 2. - Quadrapole splitting vs. hydration number for the complexes : (F~(NCS)X(H~O)~-X)-X+~, X = 6 , 5 , 4 , 3 .

.21 ¹

⁾ a 2 are the delocalization factor and ^E,,, are lattice contributions.

The relation between the quadrupole splitting and the

1.1 - hydration number (Fig. 2) is linear. This leads us to

believe, according to expression (2), that the maximum contribution to the quadrupole splitting is determined

6-NCS- 5-NCS- L'NCS 3-NCS- OcNCS- by the scalar average of the iron-ligand bond properties.

O H 2 0 1 H 2 0 2 H 2 0 3 H 2 0 6 H 2 0

In the case of : (FeT6-n.nH20)"-4 for n = 0, 4, 6 ; FIG. 1 . - Isomer shift (with respect to (Fe(CN)6)&. 3 H20) vs. and (FeC16-n. ^nH20Y'-4 for = ' 9 2, ⁴³ a hydrationnumberforthecomplexes:(~e(~CS)~(~~0)~~~)-~+~, ~0rrelation has been found by Hazony et af. [7-91.

x

⁼ 6, 5 , 4 , 0 . In the complexes under study this correlation would be expected, due to the pseudohalide nature of the iso- thiocyanate group.

tion of the hydration number. Zero was taken as The plot of 6 vs. for the ( F ~ ( N C S ) , ( ~ ~ ~ ) ~ - , ) - X + 2

a reference for the measurement of the isomer shift for (Fe(CN6))K4.3 H 2 0 . All the isomer shifts were measured at 79 K and the terms relative to the second- order Doppler shift and zero point motion of Moss- bauer atom have not been corrected. In principle, a comparison between uncorrected isomer shifts should not be made. However, in our case there are two factors which lead us to believe that the error in this compa- ³ rison would be very small. In the first place, all our measurements were made at the same temperature.

Secondly, since all the complexes were present in the sample, it can be assumed that the J factor is the same for all of them. Under these conditions, the value of ² GZPM [5] is approximately the same for all the complexes.

Figure 2 shows the value of the quadrupole splitting as a function of the hydration number for the (Fe(NCS),(H,O), -,),+ complexes measured at 79 K. 1

For high-spin ferrous compounds, the expression for the quadrupole splitting is [6] :

x a 2 F(A ^{1, A 2} a 2

A,,

7') -k E,,, (2) FIG. 3. - 6 vs. E for the complexes ( F ~ ( N C S ) X ( H ~ O ) ~ - X ) -x+2.

STUDY OF ((NCS)X(~20)6 - x ~ e ) KX - Z FOR X = 6,5,4, 3 BY MOSSBAUER SPECTROSCOPY C6-253

complexes where X = 6, 5,0, is shown in figure 3. The b) The contribution of the bond in these complexes following conclusions can be deduced from this graph : must be very weak.

a) The electronic ground state of the complexes c) The main source of the differences in the quadru- [Fe(NCS),IP4 and [Fe(NCS),(H,0)]-3 must be a pole splitting values can be associated with differences

singlet. in the delocalization factor a'.

References

[l] ROSENHEIM, U. A., ROEDRICH, E., TREWENDT, L. Z., Anorg. [6] INGALLS, R., Phys. Rev. 133 (1964) A 787.

all. Chem. 207 (1932) 97. [7] AXTMAN, R. C., HAZONY, Y., HURLEY, J. W., Jr, J. Chem.

[2] SANO, H., KONO, H., Bull. Chem. Soc. Japan 38 (1965) 1228. Phys. 52 (1970) 3309.

[3] COTTON, F. A. et al., Inorganic Chemistry 1 (1962) 565. [8] HAZONY, Y. et al., Chem. Phys. Lett. 2 (1968) 440.

[4] SABATIN~, A., BERTINI, I., Inorganic Chemistry 4 (1965) 959. [9] AXTMANN, R. C., HAZONY, Y., HURLEY, J. W., Jr, Chem.

151 HAZONY, Y., J. Chem. Phys. 45 (1966) 2664. ^' Phys. Lett. 2 (1968) 673.