Arrangement and mobility of Li-ions in X- and Y-zeolites

Arrangement and mobility of Li-ions in X- and Y-zeolites

132 Notes 1. inorg, nucl, Chem. Vol. 42, pp. 132-133 © Pergamon Press Ltd., #¢80. Printed in Great Britain 0022-1902/80/0101-0132502.00/0 Arrangem...

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Notes

1. inorg, nucl, Chem. Vol. 42, pp. 132-133 © Pergamon Press Ltd., #¢80. Printed in Great Britain

0022-1902/80/0101-0132502.00/0

Arrangement and mobility of Li-ions in X- and Y-zeoHtes (Received 30 October 1978; received for publication 9 May 1979) In the last few years many publications have appeared on determination of the structure of cation exchanged X- and Y-zeolites [1, 2]. Tung [3] has shown that the mobility of cations also has an important influence on the catalytic and adsorptive properties of zeolites. Dyer [4] made self-dittusion measurements of cations in hydrated forms of zeolites. Reports on the mobility of cations in dehydrated X- and Y-zeolites were given by Stamires [5], Vucelic [6], and Schoonheydt [7] by means of dielectric studies and electrical conductivity measurement. Pfeifer [8] and Freude [9] have used the NMR for the determination of proton mobility in decationed Yzeolites. About the mobility and arrangement of Li-ions in A-zeolites we have reported in [10, 11]. Lechert et al. [12] made NMR-studies on NaLiX-zeolites. In this report we give some informations about our 7Li-NMRmeasurements on NaLiX- and NaLiY-zeolites. EXPERIMENTAL The ion exchange was carried out by means of LiCIsolution. We used NaX (Si/AI = 1.35) and NaY (Si/A1 = 2.6). All samples obtained were filtered, washed with distilled water, dried, and kept over saturated NH4C1solution. The degree of ion exchange was determined by chemical analysis and flame photometry. The compositions of the samples are given in Table 1. The samples were activated at 673 K for 20 hr in vacuum (pressure about 0.01 Pa). 7Li-NMR-spectra were measured using a wide-line-spectrometer KRB 35/62 at 21 MHz. The line width 6Hp of the peak to peak distance of the NMR-signal was (1.8+0.1) G at room temperature. We cannot observe a small component analogue (Lechert [12] and Vucelic [6]) at these degrees of exchange. The second moment of all samples was (0.73=t=0.07) G z at room temperature. The frequencies from 21 to 9 MHz have no influence on the second moment as shown in Table 2. That means, that the quadrupolar interaction is negligible.

E

2.0

D

1.0

--

"1-

0.7

--

0.5

--

Table 1. Used samples for 7Li-NMR-measurements Degree of Li-exchange

Sample NaLi45X NaLi65X NaLi53Y NaLi55Ca8X NaLi50Cal6X NaLi55Zn8X

45 65 53 55 8%Ca 50 16%Ca 55 8 % Z n

Composition per unit cell

Na45Lia7X Na2s.6Li53.4X Na25.4Li28.6Y Na3o.4Li45.sCaa.3X Na2sLi41Ca6.sX Naao.nLi45.sZna.3X

X = (A102)82(8iO2)110. y = (AIO2)54(5iO2)138.

For determining the activation energy (E A) and correlation times (~'c) of thermal motion we measured the temperature dependence of the line width. Figure 1 shows the dependence of 8Hp plotted against 1/T for samples NaLi 65X and NaLi 45X. From the bend-point we calcu1 lated the correlation time ( T c = ~ where M 2 second moment, VLi--magnetogyric ratio) and we determined by the slope of the temperature dependent part of the curve the activation energy. The results are shown in Table 3.

Table 2. The second moment at 21 MHz, 16 MHz, and 9 MHz Frequency [MHz]

Second moment [G2]

21 16 9

0.73 0.77 0.70

.o/S I t.5

I 2~o*c 2 .o

I 2.~ T-~.I0 3 ,

I

I

3.0

3.5

K -~

Fig. 1. Temperature dependence of the line width 8Hp of the NMR signal of 7Li in (3, NaLi45X; O, NaLi65X. The dotted line curve shows the bendpoint at 210°C of which we obtained the correlation time ~'c-

133

Notes Table 3. Activation energy and correlation times Sample NaLi45X NaLi65X NaLi53Y NaLi50Ca8X NaLi55Ca16X NaLi55Zn8X NaLiA

EA[kJ/Mol] rc[fZs] at 473 K 13 13 14 19 19 20 30

120 120 145 160 160 165 110

fact to the positions of the divalent cations. Haber [16] and Angell [17] have reported that these divalent cations occupy SI positions at low cation content. The field of the cations is shielded in this position. Consequently they have not an influence on the mobility of the Li-ions in the large cavity.

Acknowledgements--We wish to thank Prof. H. Pfeffer, Dr. D. Freude and Dr. H. Schmiedel for helpful discussions.

[11]

Sektion Chemic, der Karl-MarxUniversitiit Leipzig, D D R 701 Leipzig, Liebigstral3e 18, German Democratic Republic

RESULTS A N D DISCUSSIONS The second moment for 7Li-NMR-spectra in NaLiXand NaLiY-zeolites is the same as in NaLiA-zeolites. That means it is independent of the silicon-aluminium ratio. According to the equation of van Vleck [13] M2[G 2] = 126 ~ rk-6[/~ -6] k we calculate a mean Li-Al-distance of (2.35 +0.03)/~. If we set the Li-ions on S(I) or S(II) opositions we get a Li-Al-distance of [14] LiI-AI = 3.57 A and Lin-AI = 3.1 A. The positions SI should not be occupied [15] by Li-ions. Analogue to A-zeolites we assume, that all Liions in X- and Y-zeolites must be displaced in the direction of the Al-ions. Kiselev [18] found by means of water adsorption studies, that the small Li-ions have another arrangement in X-zeolites as the other alkali metal ions. The correlation times of Li-ions in A-zeolites is nearly the same as in X- and Y-zeolites as shown in Table 3. The activation energy is about 13 kJ/mol. In an earlier work [11] we have shown that the magnetic correlation time of Li-ions can be set equal the mean life time on a cation position. As the Li+-ions cannot occupy type I sites [19], we assume a cation jumping process of a site II cation to a neighbouring site III in the large cavity analog the cation migration in A-zeolites. We found in A-zeolites [11], that small amounts of divalent cations (Be 2+, Mg 2÷, Ca 2+, Sr2+) strongly reduce the mobility of Li+-ions. The activation energy increase of 30 kJ/mol to about 60 kJ/mol. In contrast to the Azeolites we find at X- and Y-zeolites no significance influence of Ca 2+- and Zn2+-ions (see Table 3) at these degrees of exchange on the Li-mobility. The mean life time of Li-ions at 473 K is nearly unchanged and the activation energy increase only slightly. We attribute this

H. HERDEN G. KORNER SCHOLLNER

REFERENCES 1. J. V. Smith, Adv. Chem. Ser. 101, 171 (1971). 2. L. Broussard and D. P. Shoemaker, J. Am. Chem. Soc. 82, 1041 (1960). 3. S. E. Tung,and E. Mclninch, J. Catal. 10, 166 (1968). 4. A. Dyer, R. B. Gettins, and R. P. Townsend, J. Inorg. Nucl. Chem. 32, 2395 (1970). 5. D. N. Stamires, J. Chem. Phys. 36, 3174 (1962). 6. D. Vucelic, N. Juranic, S. Makura and M. Susie, J. Inorg. Nucl. Chem. 37, 1277 (1975). 7. R. A. Schoonheydt, and J. B. Uytterhoeven, Adv. Chem. Set. 102, 456 (1971). 8. H. Pfeifer,, Adv. Chem. Set. 121, 430 (1973). 9. D. Freude, W. Oehme, H. Schmiedel and B. Staudte, J. Catal. 49, 123 (1977). 10. R. Sch611ner and H. Herden. A C S Syrup. Set. 40, 357 (1977). 11. D. Freude, H. Herden, H. Pfeifer, H. Schmiedel and R. Sch611ner, Z. phys. Chem., Leipzig 259, 444 (1978). 12. H. Lechert, W. D. Basler, and H. W. Henneke, Bet. Bunsenges. phys. Chem. 79, 563 (1975). 13. J. H. van Vleck, Phys. Rev. 77, 1168 (1948). 14. E. E. Genser, J. Chem. Phys. 54, 4612 (1971). 15. H., Lechert, W. Gunsser and A. Knappwost, Bet. Bunsenges. phys. Chem. 72, 84 (1968). 16. J. Haber, J. Pfaszynski and J. Sloczynski, Bull. Acad. Polan. Sci. 23, 709 (1975). 17. C. L. Angell and P. C. Schatter, J. Phys. Chem. 70, 1413 (1966). 18. M. Dzhigit, A. V. Kiselev, K. N. Mikos, G. G. Muttik, and T. A. Rahmanova, Trans. Faraday Soc. 67, 458 (1971). 19. H. Herden, to be published.

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J, inorg, nucl. Chem. Vol. 42, pp. 133-135 (~3 Per g amo n Press Ltd., 1980. Printed in Grea t Britain

A novel series of bis(8X-guanosine) copper(ll) complexes (Received 9 March 1979) The importance of transition metal ions in the replication and transcription processess of DNA is well documented [1]. Interest in the specific interactions between copper(II) and nucleic acid constituents arose, in part, when copper(II) was shown to lower the "melting

temperature", T,,, of DNA (i.e. the temperature at which DNA unwinds into single strands), and to induce the reversible unwinding of DNA [2, 3]. As part of our continuing effort to systematically elucidate the nature of the chemical interactions in the solid