3034
J. Phys. Chem. 1984, 88, 3034-3038
The Reaction of Aromatic Molecules in the Interlayer of Transition-Metal Ion-Exchanged Montmorillonite Studied by Resonance Raman Spectroscopy. 1. Benzene and p -Phenylenes Y. Soma,* M. Soma, National Institute for Environmental Studies, Tsukuba, Ibaraki 305, Japan
and I. Harada Pharmaceutical Institute, Tohoku University, Aobayama, Sendai 980, Japan (Received: October 17, 1983)
By resonance Raman spectroscopy supplemented by visible, ESR, and infrared spectroscopy, the dark red complex formed when benzene, biphenyl, and p-terphenyl molecules are adsorbed on transition-metal (Cu2+,Fe3+,Ru3+,Pd2+)ion-exchanged montmorillonite at room temperature under a dry atmosphere has been identified to be the poly@-phenylene) cation. The chain length of the poly@-phenylene) cation is dependent on the parent molecules and the reaction conditions. The cation is reversibly reduced to poly@-phenylene)in the presence of water vapor. The enhanced contribution of the quinoid structure in the poly@-phenylene)cation as compared with the neutral poly@-phenylene)is revealed in their Raman spectra, especially in the shift of the inter-ring CC stretching vibration. Differences, as well as similarities, between adsorbed poly@-phenylene) (cation) and the bulk poly@-phenylene) (cation) are discussed.
Introduction A wide variety of organic molecules are known to interact with clay minerals, and formation of polymers is reported in some cases.’S2 Such clay-organic systems are very important in agriculture, industrial processes, and environmental aspects. Among the clay minerals, montmorillonite shows interesting behavior in clay-organic reactions because of the presence of interlayer exchangeable metal cations which compensate the positive charge deficiency in the aluminosilicate sheet and of the variable interlayer spacing to accommodate various ions or molecules. The reaction of benzene or certain aromatic molecules with Cu2+ion-exchanged montmorillonite has been demonstrated by Mortland and his co-workers3 and characterized by infrared spectroscopy. According to their observations two types of adsorbed species of benzene besides those physically adsorbed are found. The infrared spectrum of type I (green form) has absorption bands shifted not very much from those of physically adsorbed benzene or liquid benzene, whereas type I1 (red form), which is formed under a dry atmosphere, shows broad absorption bands quite different from the spectrum of liquid benzene. Besides, the transparency to an IR beam becomes significantly low when type I1 species is formed, and this is ascribed to a low-energy electronic transition in the IR frequency range. Although it seems that IR spectra alone do not offer sufficient information to clarify the structure of type I1 species, important observations indicating the strong chemical modification of benzene molecules in type I1 species have been reported. According to ESR studies, an organic free radical is formed and the Cuz+ ion is reduced to the Cut ion when type I1 species is formed on Cu2+-montmorillonite.4~5 Mortland and Halloran suggested polymerization of benzene via type I1 species on the basis of mass spectral analysis of extract from the complex.6 Stoessel and Guth obtained poly@-phenylene) (1) B. K. G. Theng, “The Chemistry of Clay-Organic Reactions”, Wiley, New York, 1974. (2) J. M. Thomas, J. M. Adams, S. H. Graham, and D. T. B. Tennakoon in “Solid State Chemistry of Energy Conversion and Storage”, J. B. Goodenough and M. S. Whittingham, Eds., American Chemical Society, Washington, DC, 1977, Adv. Chem. Ser. No. 163, Chapter 17. (3) M. M. Mortland, and T. J. Pinnavaia, Nature (London), 229, 75 (1971); T. J. Pinnavaia and M. M. Mortland, J . Phys. Chem., 75, 3957 (1971). (4) T. J. Pinnavaia, P. L. Hall, S. S.Cady, and M. M. Mortland, J . Phys. Chem., 78, 994 (1974). (5) J. P. Rupert, J . Phys. Chem., 77, 784 (1973). ( 6 ) M. M. Mortland and L. G. Halloran, Soil Sci. SOC.Am. J., 40, 367 (1976).
0022-3654/84/2088-3034$01 S O / O
from the complex by dissolving montmorillonite in hydrofluoric acid and then treating the mixture with hydrochloric acid.7 In our earlier report, resonance Raman spectroscopy has successfully showed that p-dimethoxybenzene is stably adsorbed as a cation radical in the interlayer of Cu2+- and Ru3+-montmorillonite under dry conditions and the structure is similar to that of the dimethoxybenzene cation radical in the solution.s In resonance Raman spectroscopy, the objective species which has an optical transition in “resonance” with the excitation source can be selectively excited, thus eliminating interference from vibrations of other species, e.g. physically adsorbed species. It is also free from the vibrations of adsorbate montmorillonite while only a limited frequency region of infrared spectra is available for the identification of adsorbed species on clay minerals because of the absorption of clay itself. Besides, the intensity of resonance Raman scattering is 103-106 times higher than that of normal Raman scattering, so that the improved detection limit of the adsorbed species on the solid surface can be obtained. We have extended the application of resonance Raman spectroscopy to demonstrate the formation of poly@-phenylene) from benzene adsorbed on Cu2+- and Ru3f-montmorillonites.9 In this report, the identification of the structure of benzene, biphenyl, or terphenyl adsorbed on transition-metal (Cu2+,Ru3+,Fe3+,PdZ+) ion-exchanged montmorillonites by resonance Raman spectroscopy supplemented by other spectroscopic techniques will be described more in detail, and the usefulness of this approach in the study of clay-organic interactions will be demonstrated.
Experimental Section The montmorillonite used was refined bentonite (mined in the Tsukinuno mine, Yamagata, Japan, and distributed as Kunipia G by Kunimine Ind.). The cation-exchange capacity of this montmorillonite was about 110 mequiv/l00 g of clay (the exchangeable cation being mostly sodium). Preparations of Cu2+, Ru3+, Fe3+, and Pd2+ ion-exchanged montmorillonites were as follows: Montmorillonite was suspended for 20 h in 0.01 M aqueous solution of CU(NO,)~,RuCl,, Fe(N03)3,or PdC12,each containing 2.5 times as much of the transition-metal ion as the amount of cations to be exchanged. The colloidal montmorillonite was separated by centrifugation, washed once by distilled water, followed by centrifugation again, and freeze-dried. X-ray photoelectron spectroscopic analysis of the ion-exchanged montmo(7) F. Stoessel, J. L. Guth, and R. Wey, Clay Miner., 12, 255 (1977). (8) Y. Soma, M. Soma, and I. Harada, Chem. Phys. Lett., 94,475 (1983). (9) Y. Soma, M. Soma, and I. Harada, Chem. Phys. Lett., 99, 153 (1983).
0 1984 American Chemical Society
The Journal of Physical Chemistry, Vol. 88, No. 14, 1984 3035
Benzene and p-Phenylenes
I
380 nm
30
20
10
5
x103 c m - l Figure 1. Absorption spectra of benzene adsorbed on Fe3+-montmorillonite in (1) dry air and (2) humid air.
rillonite ascertained the completion of the ion-exchange reaction by the absence of the sodium KLL Auger line. Similarly, chloride or nitrate was not observed for the ion-exchanged montmorillonite except for the case of Pd-montmorillonite where the C1 2p line was detected, and hence the significant portion of Pd must be associated with chloride. Benzene, biphenyl, terphenyls (purchased from Wako Chemical Ind.), and deuterated benzenes (purchased from Merk Sharp & Dohme Canada) of guaranteed quality were used as received. A thin self-supporting film of montmorillonite for IR measurement was prepared by evaporation of a suspension of montmorillonite on a polyethylene plate in a silica-gel desiccator. For Raman measurement the film was formed on the inner surface of a glass ampule (diameter 12 mm), and the montmorillonite suspension was evaporated by rolling the ampule on a hot plate. Benzene was adsorbed on montmorillonite films in a P205desiccator from vapor phase until the reaction was completed within 3-4 days. When adsorbates were solid at room temperature, as in the case of biphenyl or terphenyl, a hexane solution saturated with these compounds was added on the film of the clay and dried in a P205desiccator. IR spectra were measured in a vacuum-IR cell to control the humidity or to remove the physically adsorbed species. The sealed ampule was fixed on a sample-rotating device and spun at 1000 rpm during the Raman measurement. Raman spectra excited by an Ar ion laser were measured at room temperature on a J R S 400T Raman spectrometer. The extent of reaction between Cu- or Fe-montmorillonite and benzene (or biphenyl) under identical conditions was followed as the extent of the reduction of the paramagnetic Cu2+ (Fe3+) ion by ESR. It was estimated to exceed 90%. Therefore, the amount of the adsorbed molecule should be more than the amount of reduced metal ion (see Results and Discussion). The adsorbed amount of benzene under similar reaction conditions has been reported by RupertS5
Figure 2. Resonance Raman spectra of C6H6 adsorbed on PdZ+-, Ru3+-, and Cuzt-montmorillonites (type 11, excitation by Ar 514.4-nm line) and Raman spectrum of solid p-terphenyl.
Results and Discussion Benzene. A Cu2+- or Fe3+-montmorillonite film turns dark red (type IT) on benzene adsorption in an exhaustively dried atmosphere. This reaction rate is slow at room temperature, and it takes a few days to complete the reaction. This red benzenemontmorillonite complex (type 11) turns to yellow (type I) in humid air. Absorption spectra of benzene adsorbed on the Fe3+-montmorillonite (type I or type IT) shown in Figure 1 are similar to those of benzene on the Cu2+-montmorillonite;9 spectrum (1) is the typical one of type 11, and spectrum (2) measured in humid air is mostly due to type I species (the absorption maximum at 380 nm) with some contribution by the remaining type I1 species. A difference between Cu2+- and Fe3+-montmorillonite complexes is that a part of type I1 species on Fe3+montmorillonite does not turn to type I in humid air, and this irreversible portion increases upon repeating the reaction. This tendency is more evident in the benzene-Ru3+-montmorillonite complex. As shown in Figure 2, the Raman spectra of type I1 species of benzene adsorbed on Cuz+-, Ru3+-, and Pd2+-montmorillonites
Figure 3. Infrared spectra of benzene (C6H6,C6H,D, C6D6)adsorbed on Cu2t-montmorillonite in a dry atmosphere (type 11).
p-Torphrnyl
I
1500
'
"
'
,
"
"
1000
l
'
-
~
-1
crn
500
i
p
measured with the excitation wavelength at 514.5 nm are the same in that the observed bands of this species at 1601, 1324, 1240, and 806 cm-' show no shifts on changing metal ions in montmorillonite. The same spectrum was obtained also on Fe3+montmorillonite. The band intensities of type I1 species on Pd2+-montmorillonite in the UV and Raman spectra are weak, indicating that the formation of this species on Pd2+-montmorillonite is rather poor. The spectra are quite different from the spectrum of free benzene and similar to that of p-terphenyl (Figure
3036 The Journal of Physical Chemistry, Vol. 88, No. 14. 1984
Soma et al. The following reaction consistent with the above results is considered to take place in the interlayer of montmorillonite.
-
1221 1283
kMm+ + nChHh
A
I\
c 6 H6
1240
I
892
iroo 1500 is00 1100 900 7 0 0 cm-l Figure 4. Resonance Raman spectra of benzene (CsH6, C6D6)adsorbed on Cuz+-montmorillonite: type I, excitation by Ar 457.9-nm line; type 11, excitation by Ar 514.5-nm line. 2) and other p-phenylene molecules. The infrared spectra of benzene, monodeuterated benzene, and perdeuterated benzene adsorbed on Cu2+-montmorillonite (Figure 3) have two broad absorption bands due to ring stretching vibrations in the range of 1550-1350 cm-'. Besides, the band assigned to the Kekul6 vibration is observed around 1280 cm-'. These observations can be explained if a benzene ring has D2h symmetry. The observed Raman bands of type I1 benzene (Figures 2 and 4) can also be assigned consistently on the assumption that the benzene ring has DZhsymmetry and p-phenylene structure. In accordance with the assignment of the Raman spectrum of biphenyllo or the biphenyl anion radical," the bands at 1601 cm-' (1561 cm-' for C6D6), 1324 cm-' (1301 cm-' for C6D6), and 800 cm-' (777 cm-l for C6D6) are due to the ring stretching, the inter-ring C C stretching, and ring deformation vibrations, respectively. The C H (or CD) in-plane bending is observed at 1240 cm-' for C6H6 and at 903 cm-' for C6D6. Compared with the Raman spectra of the biphenyl anion radical measured with 441.6- and 632.8-nm excitation,I2 those of type I1 benzene in Figure 4 show more resemblance to the spectra of the biphenyl anion radical measured with 441.6-nm excitation. Therefore, the electronic transition showing the absorption around 510 nm of type I1 benzene would be of the same origin with that at 400 nm of the biphenyl anion r a d i ~ a 1 . l ~ From the result of the ESR experiment, type I1 species is considered as a cationic species and the reaction with water transforms it to a neutral product (type I).9 At the same time, the transition-metal ion which is reduced upon the formation of type I1 species is reoxidized. (10) G. Zerbi and S. Sandroni, Spectrochim. Acta, Part A , 24A, 511 ( 1967). (11) S. Yamaguchi, N. Yoshimizu, and S.Maeda, J . Phys. Chem., 82, 1078, (1978). (12) I. V.Aleksandrov, Ya. S.Bobovich, V.G. Maslov, and A. N. Sidrov, Opt. Spectrosc. (Engl. Trunsl.), 38, 387 (1975). (13) C. Takahashi and S. Maeda, Chem. Phys. Lett., 24, 584 (1974).
Recently, a thin film of poly@-phenylene) was synthesized by Tieke and his co-workers by the methods described by Kovacic.14 According to their results, red poly@-phenylene) films showing an absorption at 500 nm transformed to the pale brown polymer having an absorption maximum a t 380 nm when exposed to moisture. This spectral change during the reaction with water vapor is coincident with what is observed for type I and I1 benzene species in the interlayer of montmorillonite. The reaction by water vapor is much slower in type I and I1 benzenes, presumably because the rate is controlled by the diffusion of water in the interlayer of montmorillonite. Shacklette and co-workers synthesized AsFS-doped poly@phenylene) from AsFs-doped p-terphenyl or p-q~aterphenyl.'~ Absorption spectrum of this AsFS-doped poly@-phenylene) is consistent with the spectrum of type I1 benzene species, though in the latter the absorption at around 510 nm appears at a longer wavelength compared with that of the corresponding band in the AsFS-poly@-phenylene) complex. This would be due to the difference in the phenylene chain length.l5 I R spectra of bulk poly@-phenylene) and AsFs-doped p~ly@-phenylene)'~ are consistent with our spectra. It may be pointed out that the IR spectrum of type I species (and of poly@-phenylene)) in the frequency range available in the montmorillonite matrix closely corresponds to the spectrum of liquid benzene. This situation has led to the previous assignment of the type I species to the weakly chemisorbed benzene m ~ l e c u l e . ~ Raman spectra of poly@-phenylene) or doped poly@phenylene) have been scarcely investigated, except for the report by Tzinis and others.16 The Raman spectra of types 11and I C6H6 shown in Figure 4 resemble well those of AsFS-poly Cp-phenylene) and poly@-phenylene), respectively, where the band due to the inter-ring CC stretching is observed at lower frequency in adsorbed species, presumably reflecting the structural difference of poly@-phenylene) in the clay matrices from bulk polymers. On the basis of above-memtioned evidence, it is confirmed that type I1 benzene is the poly@-phenylene) cation and type I is neutral poly@-phenylene). The structural change between type I1 and I species is evident in the Raman spectra of Figure 4. Remarkable frequency shifts toward higher frequencies are observed in the inter-ring C C stretching and the CH in-plane bending vibrations when 'poly@-phenylene) is oxidized to the cationic form: Av = 30-40 cm-' in the inter-ring CC stretching and 10-20 cm-' in the C H in-plane bending vibrations for C6H6 and C6D6. These frequency shifts indicate that although the benzene ring is not affected significantly, the inter-ring C C bond is strengthened when poly@-phenylene) is oxidized to the cationic form. The remarkable positive frequency shift$ of the inter-ring CC stretching vibration in the conversion of neutral molecules to radical ions have been observed also in biphenyl type molecules: 1287 1326 cm-' in the biphenyl anion radical,13 1286 1338 cm-' in the benzidine cation radical,17and 1282 1343 cm-' in the 4,4'-dimethoxybiphenyl cation radical in the interlayer of Cu2+-montmorillonite.'8 This result is consistent with an ab initio SCF-LCAO-MO calculation on undoped and Li-doped p-q~aterpheny1.I~In this calculation, it is revealed
- -
-
(14) B. Tieke, C. Bubeck, and G. Lieser, Makromol. Chem., Rapid Commun., 3,261 (1982). (15) L. W. Shacklette, H. Eckhardt, R. R. Chance, G. G. Miller, D. M. Ivory, and R. H. Baughman, J . Chem. Phys., 73,4098 (1980). (16) C. H. Tzinis, R. H. Baughman, and W. M. Risen Jr., Office of Naval Research, Technical Report No. TR-80-01, 1980. (17) R. E. Hester and K. P. J. Williams, J . Chem. SOC.,Faraday Trans. 2, 77, 541 (1981). (18) Y. Soma, to be submitted for publication. (19) J. L. Brtdas, B. ThBmans, and J. M. AndrB, Phys. Rev. B Condens. Matter, 26,6000 (1982).
The Journal of Physical Chemistry, Vol. 88, No. 14, 1984 3037
Benzene and p-Phenylenes
cu-montmorillonite
i25onm
/
450
13loC 30
20
10
5
xi03
cm-1
Figure 5. Absorption spectra of biphenyl adsorbed on Fe3+-montmorillonite: (a) adsorbed at room temperature, (b) annealed at 120 'C under vacuum.
that charge transfer from Li reduces the inter-ring CC bond length and the benzene rings become coplanar. These modifications may affect equally the inter-ring C C stretching and C H bending vibrations to shift toward higher frequencies upon the oxidation of poly@-phenylene). Therefore, an enhanced contribution of the quinoid structure in the poly@-phenylene) cation may be considered in type I1 species.20 If one compares the inter-ring CC stretching vibrations of bulk poly@-phenylene) and AsFS-doped poly@-phenylene) with those of type I and iI species, the inter-ring CC stretching vibration of adsorbed species is observed at lower frequencies: Av = -47 cm-' for type I and -21 cm-l for type 11. This may be due to the geometrical constraint of adsorption site on a benzene ring in the interlayer of montmorillonite; a silicate layer of montmorillonite exposes the two-dimensional network of the si606 ring to the inner surface, and a benzene ring may be accommodated in the center of a s i 6 0 6 ring. In the synthesis of poly@-phenylene) from benzene by the treatment with aluminum chloride-cupric chloride, a benzene cation radical has been suggested to be the intermediate.21*22This reaction process would be considered to proceed also in the interlayer of montmorillonite under the reaction with the transition-metal ion. Biphenyl and Terphenyl. When biphenyl is adsorbed on Cu2+-montmorillonite at room temperature in a dry atmosphere, the color changes to yellowish brown. The absorption spectrum of this complex is shown in Figure 5a, which is similar to the spectrum of type I1 benzene species although both of two characteristic bands are observed at shorter wavelengths. However, they are at longer wavelengths than those of the biphenyl cation radical formed in the fluoromethane matrix, where two bands are observed a t 365 nm (having a shoulder at 387 nm) and at 703 nm.23 Annealing this complex under vacuum at 120 "C shifts these bands to longer wavelengths as shown Figure 5b, but still both bands are at shorter wavelengths than those of type I1 benzene species. When p-terphenyl is absorbed on Fe3+-montmorillonite, the result is much the same. Broad absorption bands were observed at around 420 and 1250 nm after being annealed under vacuum at 120 OC. The short-wavelength absorption associated with the transition of K electrons in phenylene rings shifts toward a longer wavelength as the phenylene chain length increases.15 Thus, it is considered that biphenyl and terphenyl cation radicals or their oligomer cations formed at room temperature further polymerize upon annealing above 100 "C but still have their phenylene chain lengths shorter than those of type I1 benzene. The IR spectrum of biphenyl adsorbed on Cu2+-montmorillonite at room temperature still have similarity to that of free biphenyl, and the annealing around 130 "C changes the spectrum to the (20) J. L. BrBdas, R. R. Chance, and R. Silbey, Phys. Rev.B Condens. Mutter, 26, 5843 (1982). (21) G . G.Engstrom and P. Kovacic, J . Polym. Sci., Polym. Chem. Ed., 15, 2453 (1977). (22) C. F. Hsing, P. Kovacic, and I. A. Khoury, J . Polym. SOC.,Polym. Chem. Ed., 21, 457 (1983). (23) T. Shida, private communication.
1758
w
1575
1530
1287
1
Figure 6. Infrared spectra of biphenyl adsorbed on Cu2+- and Fe3+montmorillonites: Cu2+-montmorillonite, adsorbed at room temperature and annealed at 131 OC under vacuum; Fe-'+-montmorillonite, adsorbed at room temperature.
~~~
1700
1500
1300
1100
900
cm
-,
roo
Figure 7. Resonance Raman spectra of Biphenyl on Cu2+-montmorillonite: (1) adsorbed at room temperature in dry atmosphere (excitation by Ar 457.9-nm line); (2) annealed at 100 "C under vacuum (excitation by Ar 514.5-nm line).
/ I
A
Figure 8. Resonance Raman spectra of biphenyl and benzene adsorbed on R~~~-montmorillonite: (1) biphenyl adsorbed and annealed at 130 OC (excitation by Ar 457.9-nm line), (2) biphenyl adsorbed at room temperature (excitation by Ar 457.9-nm line), (3) biphenyl adsorbed at room temperature (excitation by Ar 514.5-nm line), (4) benzene adsorbed at room temperature (excitation by Ar 514.5-nm line).
J. Phys. Chem. 1984, 88, 3038-3042
3038
observed in the adsorption of benzene. This also indicates that phenylene chain length in the adsorbed biphenyl is shorter. This may be caused from the limitation imposed on the adsorbed amount of biphenyl or terphenyl, being less than that of benzene, due to the geometrical restriction of the interlayer of the clay mineral. Raman spectrum of biphenyl adsorbed on Cu2+-montmorillonite at room temperature in a dry atmosphere and that after annealing at 100 O C are shown in Figure 7. Spectrum 1 was measured by 457.9-nm excitation, while spectrum 2 was measured by 514.5-nm excitation. Notably, the latter spectrum coincides well with that of type I1 benzene species. Changes in the Raman spectra upon annealing are shown in Figure 8 in detail. The bands at 101 1, 787, and 1322 cm-I of the adsorbate which were selectively measured by 457.9-nm excitation at room temperature (Figure 8, spectrum 2) disappear upon annealing at 130 OC (Figure 8, spectrum 1). Therefore, the bands would be due to those of the biphenyl cation radical or the cations of its oligomers. The corresponding bands of the biphenyl anion radical are observed at 1017, 721, and 1326 ern-'.'' The Raman spectrum in Figure 7 (spectrum 2) is strictly the same as that of type I1 benzene, and no shifts are observed in their bands, which suggests that the resonance Raman spectra of these poly@-pheny1ene)s in the observed range are not sensitive to the chain length. Raman spectra of 0-,m-, and p-terphenyl adsorbed on Fe3+-montmorilloniteand annealed in vacuum at 130 O C are shown in Figure 9. The spectra are different from each other while the spectrum of adsorbed p-terphenyl is the same as that of type I1 benzene, which supports the mechanism that terphenyls para polymerize regularly at terminal benzene rings. In summary, benzene and phenylene molecules are observed to be polymerized to poly@-phenylene) cations in the interlayer of transition-metal ion-exchanged montmorillonites under the mild reaction conditions. These poly@-phenylene) cations are reduced in the presence of water vapor to poly@-phenylene) molecules accompanied by the reoxidation of metal ions. Registry No. Cu, 7440-50-8; Fe, 7439-89-6; Ru, 7440-18-8; Pd, 7440-05-3;C6H6, 7 1-43-2;biphenyl, 92-52-4;p-terphenyl, 92-94-4; oterphenyl, 84-15-1;m-terphenyl, 92-06-8;poly@-phenylene),25 190-62-9.
pTerphenyl
'
JV
1500
1000
500
o-Terphenyl
cm
-1
wave number cm-' Figure 9. Resonance Raman spectra of p - , 0-,and m-terphenyls adsorbed
and annealed under vacuum at 130 OC on Fe3+-montmorillonite (excitation by Ar 514.5-nm line). one similar to that of type I1 benzene species (Figure 6). On Fe3+-montmorillonite, the change to type I1 species proceeds considerably even at room temperature. The intensity of the band at 747 cm-I, which is attributed to the CH out of plane deformation of monosubstituted benzene, is weakened after the annealing but still remains, whereas the corresponding band is not
Electron Spin Resonance and Dielectric Relaxation Studies of Pyridine-Intercalated Cd2P2S6 E. Lifshitz, A. E. Gentry, and A. H. Francis* Department of Chemistry, University of Michigan. Ann Arbor, Michigan 48109 (Received: November 1 , 1983)
The transition-metal chalcogenophosphates (M2P2S6)crystallize in a layered structure of the CdC12 type. In the layered M2P2S6structure, adjacent planes of sulfur atoms are only weakly bound by van der Waals interactions and, therefore, can accommodate guest species (I) between the layers to form intercalation compounds, M2P&(I)x. The temperature dependence of the ESR spectra of Mn2+impurity centers in the metal plane of the host lattice has been utilized to investigate structural modifications associated with the progress of the intercalation reaction with pyridine. Temperature-dependent dielectric relaxation measurements have been used to study the dynamical behavior of the pyridine intercalate in Cd2P2S6.The experimental results indicate that intercalated pyridine is weakly bonded and dynamically disordered at room temperature. ESR spectroscopy has revealed structural disorder in the host lattice resulting from intercalation with pyridine.
Introduction Transition-metal chalcogenophosphates from a series of lamellar, broad-band semiconductors with general chemical formula M2PzS6 ( M = Mn, Fe, Cd, Fe, Ni, Mg and X = S, Se). The MzP& layered structure may be viewed as the MS, structure in which one-third of the metal has been replaced by a P2 atom pair.'f2 0022-3654/84/2088-3038$01.50/0
X-ray powder patterns of intercalated M2P2S6compounds indicate a monoclinic unit cell closely related to the unit cell of the host material.I4 The a and b parameters (intraplane dimensions) (1) V. W. Klingen, R. Ott, and H. Hahn, Z . Anorg. Allg. Chem., 396,271 (1973), (2) V. W. Klingen, G. Eulenberger, and H. Hahn, Z . Anorg. ANg. Chem., 401, 97 (1973).
0 1984 American Chemical Society
