121 Sb Mössbauer Studies on NO 2 SbF 6 Intercalated Graphite

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P. BOOLCHAND, University of P.C. EKLUND University of D. BILLAUD Universite de J.E. FISCHER University of

W. BRESSER, D. MCDANIEL Cincinnati, Cincinnati, OH Kentucky, Nancy,

Lexington, KY

45221

40506

France

Pennsylvania,

Philadelphia, PA

19104

ABSTRACT

We have examined graphite salts of the composition 121 C2 3 nSbF 6 (CH3 NO2 )I 7 n = 1,2 by Sb M6ssbauer spectroscopy at 4.2K. Thie spectra reveal a strong and narrow feature in the Sb5+ region and no evidence of any 3 features in the Sb + region. This result is in general accord with the expectation of only Sb5+ in the chemical form of SbF 6 anion in the intercalate layers.

INTRODUCTION The process of graphite intercalation has attracted much physical and chemical attention in recent years [1]. The intercalation of strong Lewis acids requires an oxidizing agent which may or may not be the species undergoing intercalation [2]. In the above context, of particular interest are the compounds prepared [3] by the action of nitronium salts NOX (X = SbF 6 ) dissolved in dry nitro-methane CH3 NO2 with graphite. In this instance, the chemistry of the oxidation process appears to be simple. One expects the oxidation of graphite to be carried out by N0 2+ ion and the SbF 6 anion to be intercalated. A particularly simnle and elegant microscopic probe for the test of this chemistry is the use of 12iSb Mossbauer spectroscopy [4] which is known to be sensitive to the chemical state of Sb. This paper describes the details of this study which to our knowledge, is the first of its kind on this graphite compound. SAMPLE PREPARATION AND CHARACTERISATION HOPG pieces of 5 x 5 x 0.2 mm3 dimensions were reacted with a saturated solution of NO2 SbF 6 salt dissolved in CH3 NO2 at 300K to yield stage 1 samples. Details of the preparations are discussed by Billaud et al. [3] Higher stage samples were obtained by reducing the salt concentration in CH3 NO2 . In each case X-ray (00k) reflections were used to establish the staging. Chemical analyses of the graphite salts prepared indicate that these are described by a general formula of C 2 3 n+SbF 6 -(CH 3 NO2 ) 1 . 7Sb MOSSBAUER SPECTROSCOPY RESULTS Spectra of the graphite salts of stage n = I and 2 were studied at 4.2K in a conventional spectrometer described elsewhere [4]. The spectra revealed no significant stage dependence and furthermore show (Fig. 1) a sharp narrow line having an isomer shift characteristic of Sb5+. For the sake of comparison we

Hat.

Res.

Soc.

Symp.

Proc. Vol.

20 (1983) OElsevier Science Publishing Co.,

Inc.

390 1 a spectrum of an SbF 5 intercalated graphite salt

have also shown in Fig.

obtained in our laboratory.[5] This latter spectrum displays in addition to the sharp narrow feature (near 2 mm/s) due to Sb5+, a broad and weak feature 3 characteristic of Sb + at -14 mm/s. The spectra were analysed in terms of a superposition of an 8 line quadrupole pattern keeping the ratio of the quadrupole moments Qe/Qo fixed at 1.34. A summary of the results appear in Table I below. TABLE I 121

Sb Missbauer resul