and 0.95-nm KaoliniteâHydrazine Intercalation Complexes - American

8080

J. Phys. Chem. B 2000, 104, 8080-8088

Infrared and Inelastic Neutron Scattering Study of the 1.03- and 0.95-nm Kaolinite-Hydrazine Intercalation Complexes Cliff T. Johnston,*,† David L. Bish,‡ Juergen Eckert,§ and Lori A. Brown¶ Crop, Soil and EnVironmental Sciences, 1150 Lilly Hall, Purdue UniVersity, W. Lafayette, Indiana 47907-1150, EES-1, MS D469, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, LANSCE, MS H805, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, and Department of Chemistry, Arizona State UniVersity, Tempe, Arizona ReceiVed: March 22, 2000; In Final Form: June 13, 2000

The interaction of hydrazine with kaolinite was studied using a combination of infrared (IR) spectroscopy, inelastic neutron scattering (INS), and X-ray powder diffraction. Under ambient temperature and pressure conditions, anhydrous hydrazine is readily intercalated into the interlamellar region of kaolinite resulting in a kaolinite-hydrazine (KH) intercalation complex with a 001 d-spacing of 1.03 nm. Under reduced pressure, the surface loading of hydrazine is reduced to 0.5 hydrazine molecules/unit cell, and the 001 d-spacing of the KH complex undergoes a partial collapse to a highly ordered KH complex with a 001 d-spacing of 0.95 nm. This transition from 1.03 to 0.95 nm is accompanied by strong perturbations in the IR and INS spectra for vibrational modes of both the kaolinite and the intercalated hydrazine species. The transition from the 1.03 complex to the 0.95-nm KH complex is made possible by the keying of one of the hydrazine amine groups into the siloxane ditrigonal cavity of the kaolinite surface as evidenced by changes of the IR active stretching and bending modes of the inner OH group. The IR and INS spectra reveal strong hydrogen bonds between the intercalated hydrazine molecules and the kaolinite surface itself. The strongest hydrogen bonds are intermolecular hydrogen bonds formed between intercalated hydrazine molecules for the 1.03-nm KH complex and are manifested by a strong, broad band at 2975 cm-1 in the IR spectrum. This band is absent in the IR spectrum of the 0.95-nm KH complex and is replaced by a band at 3270 cm-1, indicating a net increase in the distance between intercalated hydrazine molecules. Additionally, strong intercalation-induced perturbations occurred for the twist, scissor, asymmetric and symmetric wag modes, and torsional modes of hydrazine for both the 1.03- and 0.95-nm KH complexes.

Introduction Recently, there has been considerable interest in the intercalation of organic molecules into layered structures.1-6 Combining the structural support and the rigidity of the two-dimensional phyllosilicate (i.e., clay) support with the functionality of an intercalated organic compound is creating new types of materials for heterogeneous catalysis, nanocomposites, mesoporous materials, environmental chemistry, polymers, pharmaceuticals, and chromatography.1,7-9 One particular class of clay-organic complexes of recent interest is the intercalation complexes of kaolin group minerals.6,7 Kaolinite, Si2Al2O5(OH)4, is a 1:1 phyllosilicate made up of one tetrahedral sheet linked to one octahedral sheet (Figure 1). A unique feature of kaolinite is that its interlamellar region is bounded by two different types of surfaces. In Figure 1, the upper surface is made up of basal oxygens attached to silicon atoms, and this surface is called the siloxane surface. The lower surface is composed of hydroxyl groups coordinated to aluminum atoms. These Al-OH groups form hydrogen bonds with the opposing basal oxygens of the siloxane surface. Together, these surfaces create an interlamellar region with dipolar character. Direct intercalation of guest species into the interlayer region of kaolinite is restricted to a relatively small group of polar †

Crop, Soil and Environmental Sciences. Earth and Environmental Sciences 1 (EES-1). § Los Alamos Neutron Science Center (LANSCE). ¶ Department of Chemistry. ‡

compounds including hydrazine,10-14 dimethyl sulfoxide,15-18 potassium acetate,10 formamide and related amines.19-22 Upon intercalation the 001 d-spacing of kaolinite is increased from 0.71 nm to values ranging from 0.95 to 1.2 nm. The increase in the 001 d-spacing corresponds roughly to the monolayer thickness of the guest species. Successful intercalants are small polar molecules that can disrupt the electrostatic and hydrogenbonding interactions between layers23 (Figure 1) and that are small enough to reside in the expanded interlamellar region. The stretching and bending modes of the hydroxyl groups of kaolinite have been shown to be sensitive indicators of guesthost interactions in the interlamellar region.10,13,16,21,22 In particular, the ν(O-H) bands of kaolin group minerals are characterized by a set of five well-resolved bands that span a region of 80 cm-1. The positions and relative intensities of these ν(O-H) bands have been used extensively to study kaolinite intercalation complexes.10,11,13,16,21,22 In this study, IR and inelastic neutron scattering (INS) methods were used to study the 1.03- and 0.95-nm kaolinitehydrazine (KH) complexes to better understand the interaction of the intercalated hydrazine species with the kaolinite interlayer surface. Optical vibrational spectra (i.e., IR and Raman) of clayorganic complexes are limited by the opacity of the clay substrate in the low-frequency region and it is often difficult to separate the vibrational bands of the adsorbed species from those of the substrate itself. INS methods were used to obtain more direct information about the lower-frequency vibrational modes

10.1021/jp001075s CCC: $19.00 © 2000 American Chemical Society Published on Web 07/28/2000

Spectroscopic Study of Kaolinite-Hydrazine Intercalate

J. Phys. Chem. B, Vol. 104, No. 33, 2000 8081

Figure 1. [100] projection of the kaolinite structure.55

of the intercalated species. INS methods are highly sensitive to vibrational modes involving proton motion. Because most of the vibrational modes of hydrazine, N2H4, involve motion of the hydrogen atoms, this molecule has a high INS cross-section allowing the hydrazine modes to be detected in the presence of kaolinite. INS methods are also useful to study vibrational modes of the kaolinite structure itself which involve motion of the hydrogen atoms such as the Al-(O-H)-Al deformation modes. In addition to the spectroscopic data, powder X-ray diffraction methods were used to study the two KH intercalation complexes and to monitor the intercalation reaction. Motivation for studying the KH complex is derived from earlier studies that indicated keying of hydrazine molecules into the kaolinite interlayer surface.13,14 Similar arguments have been proposed for related kaolinite intercalation complexes. Based on cross-polarization NMR studies, one carbon atom of intercalated dimethyl sulfoxide (DMSO) was found to key into the siloxane ditrigonal cavity of kaolinite.24 Similar keyed structures have been proposed to account for the partially hydrated kaolinite complexes with 001 d-spacings ranging from 0.84 to 1.03 nm.25-29 Costanzo and Giese characterized the 0.84nm synthetically hydrated kaolinite complex using spectroscopic and structural methods.27,28 In this complex, one water molecule is proposed to reside in the base of each siloxane ditrigonal cavity and is referred to as “hole” water. The “normal” 1.0-nm kaolinite-water intercalation complex (i.e., halloysite) contains “hole” water and more mobile, loosely bound water, whereas the 0.84-nm kaolinite-water complex contains only hole water. Penetration of guest species into the siloxane surface of 2:1 phyllosilicates also has been demonstrated for both organic and inorganic species. For example, the recently reported crystal structure of the tetramethyl ammonium (TMA)-vermiculite complex shows the penetration of one of the methyl carbon atoms into the siloxane ditrigonal cavity.30 IR studies of the ν(O-H) bands of amine-treated 2:1 phyllosilicates also have suggested that penetration of the siloxane ditrigonal cavity by amine groups has occurred.31 More recently, attention has focused on the extent of penetration of lithium cations into the siloxane ditrigonal cavities of expandable 2:1 phyllosilicates32-34 using NMR and IR methods. Although described frequently, the underlying details of how guest species interact with the siloxane ditrigonal cavity of 1:1 or 2:1 phyllosilicates are not well understood.

Experimental Details The kaolinite specimen studied was KGa-1 kaolinite collected from Washington County, Georgia, obtained from the Source Clays Repository of The Clay Minerals Society. A complete description of the physical properties of this clay sample has been given by van Olphen and Fripiat,35 and Raman and IR spectra of this clay have been reported.36 The KGa-1 kaolinite was used as received from the Source Clays Repository. Supported deposits of the KGa-1 kaolinite were prepared by placing a 2-mL aliquot of a dilute aqueous suspension of KGa-1 kaolinite (solids concentration ) 0.1% w/w) on a 25 mm × 2 mm ZnSe disk and allowing the suspension to dry. The 1.03nm KH complex was prepared by placing a few drops of anhydrous hydrazine on the KGa-1 deposit to wet the solid deposit completely. The hydrazine-coated deposit was then placed in a sealed desiccator. The supported KH deposit was analyzed by powder X-ray diffraction to determine the extent of intercalation. After 2 h, approximately 95% of the kaolinite was intercalated by hydrazine forming the 1.03-nm KH intercalate. The 0.95-nm KH complex was prepared by placing the 1.03nm KH complex under a vacuum in an IR gas cell. The gas cell was placed in the sample compartment of a Bomem DA3.10 Fourier transform infrared (FTIR) spectrometer. FTIR spectra of the KH complex were obtained as the pressure in the cell was reduced to 10-3 Torr. The presence of the 3628 cm-1 band in the FTIR spectrum of the evacuated KH intercalate indicated that the complex had collapsed to an 001 spacing of 0.95 nm.13,14 The Bomem DA3 spectrometer used a Ge-coated KBr beam splitter and a mercury-cadmium-telluride (MCT) detector with a low-frequency cutoff of 500 cm-1. An unapodized spectral resolution of 1.0 wavenumber was used with a Hamming apodization function. Sample Preparation for INS and X-ray Analyses. Ten grams of KGa-1 kaolinite were placed in a 250-mL roundbottom flask fitted with Solv-Seal® fittings and caps. Anhydrous hydrazine (24 mL) was added to the flask, and the resulting slurry was stirred with a spatula. The round-bottom flask was sealed and the slurry was allowed to sit for 24 h. A portion of this slurry was placed in a cavity in a stainless steel mount, and the X-ray diffraction pattern of this complex was obtained at room temperature and 1 atm of pressure. Powder X-ray diffraction (XRD) patterns were measured on a Siemens D 500 θ-2θ diffractometer using Cu KR radiation,

8082 J. Phys. Chem. B, Vol. 104, No. 33, 2000 incident- and diffracted-beam Soller slits, and a Kevex PSi detector. All measurements were conducted in the step-scanning mode, with a 0.02°2θ step size. Initial XRD measurements scanned over a 2θ range of 2-70°, but detailed measurements to evaluate the degree of intercalation were made repeatedly from 6 to 14°2θ, with a count time of 1 s/step. An Anton Paar TTK controlled-environment stage fitted with Mylar windows was used to control the sample temperature and atmosphere/ vacuum, and the temperature was controlled to better than (0.5 °C using a Pt resistance thermometer. The Anton Paar stage was used to measure powder XRD patterns of the KH complexes at reduced pressure. The 0.95-nm KH complex was formed in situ in the Anton Paar cell under a vacuum; after a vacuum of 100 mTorr had been achieved, essentially all the 1.03-nm KH complex had collapsed to 0.95 nm. For the INS measurements, a portion of the 1.03-nm KH complex used for the XRD analysis was used. The 0.95-nm KH complex, however, could not be prepared in situ. A 5-g portion of the 1.03-nm complex was placed in a separate 250mL round-bottom flask and evacuated to a pressure of 10-3 Torr. The complex was then back-filled with dry argon gas to a pressure of 1 atm. Back-filling the evacuated 0.95-nm KH complex with argon prevented the reexpansion of the KH complex to 1.03 nm. This sample was then transferred to and sealed in an aluminum sample holder for the INS studies. All INS samples were cooled in a closed-cycle He refrigerator to a temperature of 15 K for data collection. Powder XRD patterns of the 0.95-nm KH complex were obtained from samples taken just after the INS data collection to ensure that the 0.95-nm KH complex had not reexpanded. The INS spectra were collected on the Filter Difference Spectrometer at the Manuel Lujan, Jr., Neutron Scattering Center of Los Alamos National Laboratory. This time-of-flight instrument uses a pulsed “white” neutron beam incident on the sample along with a low-energy band-pass Be filter after the sample to define the energy of the detected neutrons. The INS spectra shown in Figures 8-10 were obtained by a numerical deconvolution37 of the instrumental response from the observed neutron time-of-flight spectra. The typical energy resolution that can be achieved in this manner is approximately 1.5-2% of the energy of a particular band in the spectrum. It should be noted that intensities in INS vibrational spectra38 are dominated by those vibrational modes that involve large displacements of H atoms, such as torsions, wagging and rocking modes of H-containing groups. This occurs because the incoherent neutron scattering cross-section for H is more than 10 times as large as that of any other nucleus in these compounds. Relative INS intensities for a particular mode are also directly proportional to the number of scatterers, for example, the number of OH groups at crystallographically distinct sites. Results and Discussion Synthesis of the 0.95-nm KH Intercalate. Controlledenvironment, powder XRD patterns of the KH complex in the 7.0-13 °2θ range are shown in Figure 2. Exposure of KGa-1 kaolinite to liquid hydrazine (anhydrous) resulted in the formation of a KH intercalation complex with a 001 d-spacing of 1.03 nm (Figure 2A), in agreement with earlier studies.10,11 Intercalation was ∼95% complete within 2 h of exposure to liquid hydrazine as determined by the relative intensities of the 001 reflections at 8.57 °2θ (1.03 nm; KH intercalate) and 12.36 °2θ (0.71 nm; kaolinite). In previous studies, we demonstrated that the 1.03-nm KH complex can be partially collapsed to 0.95

Johnston et al.

Figure 2. Controlled-environment powder XRD patterns of the KH complex. The bottom diffraction pattern (A) corresponds to the KH complex at ambient pressure. XRD patterns (B-D) were obtained under a mild vacuum of 0.01 Torr for 10 (B), 15 (C), and 20 (D) min, respectively.

nm by evacuation.13,14 The XRD data of these previous studies were limited, however, because the XRD patterns were not collected under vacuum. Similar poorly resolved XRD patterns of KH complexes heated to 100 °C, revealing 001 d-spacings of 1.03, 0.95, 0.88, and 0.76 nm have been reported recently.39,40 Increased angular resolution of the 001 d-spacings was obtained in the present study by using a controlled-environment XRD stage that permitted collection of powder XRD patterns of samples under vacuum. Evacuation of the 1.03-nm KH complex using a roughing pump (0.01 Torr) for 20 min resulted in the complete loss of the 8.58 °2θ, reflection (1.03-nm KH complex) with a concomitant increase in intensity of a new reflection at 9.39 °2θ corresponding to the 0.95-nm KH complex (Figure 2B-D). Compared with the broad reflections reported previously,13,14,39,40 use of the controlled-environment XRD stage permitted the 1.03- and 0.95-nm KH complexes to be completely resolved. In contrast to the powder XRD pattern of the 1.03nm KH complex, that of the 0.95-nm KH complex is reasonably well-ordered as evidenced by the lack of 2-D diffraction effects and the presence of hkl reflections. These results are in agreement with a recent thermal study of the KH complex.20 At 25 °C the KH complex was characterized by a d-spacing of 1.04 nm. Upon heating the sample to 40-70 °C, the 1.04-nm reflection was reduced in intensity and a new, sharp reflection, corresponding to a d-spacing of 0.96 nm. The temperatureinduced collapse of the KH complex20 is in agreement with our XRD results obtained under reduced pressure (Figure 2). Upon further heating to temperatures between 70 and 150 °C, the d-spacing of the complex was reduced further to 0.85 nm followed by complete collapse of the clay back to 0.72 nm at temperatures >150 °C. Vibrational Spectra of the 1.03- and 0.95-nm KH Intercalates. FTIR spectra in the 800-4000 cm-1 region of the 1.03and 0.95-nm KH intercalates are shown in Figure 3. The intercalation-induced spectral perturbations can be divided into two groups. First, the influence of hydrazine on the positions and relative intensities of the ν(OH) bands of kaolinite.10,11,13,14 Second, the vibrational modes of the intercalated hydrazine molecules (e.g., torsions around the N-N bond, H-N-H twists, and N-N stretching vibrations) are influenced by the clay surface. The frequencies observed in the IR and Raman spectra



TABLE 1: Observed Vibrational Bands for the KH Complex in the 900-4000 cm-1 Region FTIR 1.03-nm KHa

0.95-nm KHa

Raman kaolinite36

kaolinite36

1.03 nm KH14

hydrazine14

871

899

904 940 1010 1040 1091 1125

913 940 1017 1044 1095 1124

1305 1355 1473 1593 1616 1628 2975

1276 1366 1471 1580 1613

3198

3214 3270 3302

918 941 1011 1033

915 940 1018 1040

948 1088 1130 1273 1313

1102

1114 1283 1335

1618

2964 3196

3303 3312

3283 3302 3311

3200 3283 3347

3363 3368

3363

3362

3402 3465 3568 3620 3654 3695

3620 3268 3653 3670

3620

3621

3620

3652 3668

3695

3695

3652 3668 3688 3696

3692

Figure 3. FTIR spectra of the 1.03- (A) and 0.95-nm (B) KH complexes in the 4000-800 cm-1 region.

of the KH complexes, kaolinite and liquid hydrazine are summarized in Table 1. Fundamental frequencies and assignments of hydrazine, including matrix-isolated hydrazine, obtained in a previous study are given for reference in Table 2. INS data along with proposed assignments are summarized in Table 3. ν(OH) Region. FTIR spectra in the 3800-2800 cm-1 region for the 1.03- and 0.95-nm KH complexes and nonintercalated kaolinite are shown in Figure 4A-C. It is readily apparent that the ν(OH) bands of kaolinite are strongly influenced by the presence of hydrazine in the interlayer region (Figure 4A). The 3620 cm-1 band of kaolinite (Figure 4C) has been assigned to the inner-hydroxyl group of kaolinite, and the 3652, 3668, and

assignment δ(Al-OH) inner OH perturbed by hydrazine δ(Al-OH) inner OH-kaolinite δ(Al-OH) inner surface OH-kaolinite ν(Si-O) kaolinite ν(Si-O) kaolinite ν5(N-N) hydrazine ν(Si-O) kaolinite HNH twist ν4 or ν11 HNH twist ν4 or ν11 HNH twist ν4 or ν11 HNH scissor ν3 or ν10 HNH scissor ν3 or ν10 HNH scissor ν3 or ν10 ν(NH) hydrazine-hydrazine ν(NH) ν(NH) ν(NH) ν(NH) s-s-HNH stretch ν(NH) s-a-HNH stretch ν(NH) liquid hydrazine ν(NH) a-s-HNH stretch ν(NH) a-a-HNH stretch ν(OH) inner surface H-bonded to hydrazine ν(OH) inner surface H-bonded to hydrazine ν(OH) inner surface H-bonded to hydrazine ν(OH) inner OH ν(OH) inner OH perturbed by hydrazine ν(OH) inner surface OH ν(OH) inner surface OH ν(OH) inner surface OH ν(OH) inner surface OH

3695 cm-1 bands correspond to the ν(O-H) modes of the innersurface hydroxyl groups (Figure 1).36,41,42 The FTIR spectrum of the 1.03-nm KH complex is characterized by a reduction in the intensities of the 3652, 3668, and 3695 cm-1 bands, and by the appearance of two new bands at 3465 and 3568 cm-1. The appearance of two red-shifted ν(O-H) bands with a separation of 103 cm-1 indicates the formation of H-bonds with two distinct N-O bond lengths for the 1.03-nm KH complex. According to published correlations,43 this 103 cm-1 separation corresponds to N-O (Nhydrazine-OAl-OH of kaolinite) distances which differ by approximately 0.07 Å.44 In other words, there are two unique environments for the nitrogen atoms of hydrazine. The 3620 cm-1 band, assigned to the inner-OH group of kaolinite (Figures 1 and 4C), is not measurably perturbed by the presence of hydrazine. This is consistent with the recessed location of the inner-OH group between the octahedral and tetrahedral sheets (Figure 1). Upon partial collapse of the KH intercalate to 0.95 nm, the position of the inner-hydroxyl ν(O-H) band shifted to 3628 cm-1 with a shoulder at 3620 cm-1. In addition, the 3465 and 3568 cm-1 bands disappeared, there was a loss in intensity in the 3650-3670 cm-1 region, and a broad, complex feature centered at 3270 cm-1 appeared (see below). The decrease in the 001 d-spacing forces the intercalated hydrazine species into closer proximity with the kaolinite surface, giving rise to the pronounced red-shift of the hydrogen-bonded ν(OH) bands at 3465 and 3568 cm-1 to the broad absorption feature in the 3100-3400 cm-1 region. Upon partial collapse of the 1.03-nm KH complex to a 001 d-spacing of 0.95, the ν(O-H) band of the inner-OH group blue-shifted from 3620 to 3628 cm-1. In earlier studies, we assigned the 3628 cm-1 band to the penetration of the siloxane ditrigonal cavity (SDC) by the one

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Johnston et al.

TABLE 2: Vibrational Band Assignments for Hydrazine symmetry description/PEDa

mode

IR N2H4/Ara

IR N2H4/N2a

IR solidb

IR liquidb

A. s-a-HNH str(96) s-s-HNH str(96) s-sci(100) s-HNH twi(91) NN-str(78) + s-wag(17) s-wag(79) + NN str(20) torsion(100)

ν1 ν2 ν3 ν4 ν5 ν6 ν7

3390 1299 1086 810 388

3387 1595 1314 1091 -

3200 1603 1304 1126 884 627

3189 1806 1283 1098 871 -

1493 1098 780 377

B. a-a-HNH str(86) a-s-HNH str(89) a-sci(99) a-HNH twi(94) a-wag(95)

ν8 ν9 ν10 ν11 ν12

3398 3313 1262 953

3396 3301 1595 1267 983

3310 3310 1655 1350 1066

3332 3310 1608 1324 1042

3350 3297 1608 1275 937

a

IR vaporc

Raman liquid

theorya

3325

3277 3189 1628 1295 1111 882

3410 3317 1639 1290 1087 841

3336

3415 3309 1624 1258

1628 1295 1000

Ref 46. b Ref 45. c Ref 56.

TABLE 3: INS Frequencies and Tentative Assignments kaolinite

KH, 0.95 nm

KH, 10.4 Å

64,75 120,127,135 166,190,224

67,79 120,135,148

assignment

252

T R (x or y) R R

300

torsion(νE) I

330,356 410

torsion(νE) II torsion (ν7) III

265 296 318 412 441 487 571 645 895,918,945

585 646 765,805 895

1305 1620

530 583 648 770,791 908, 870(sh) 1027 1070 1119 1320 1615

torsion(νI) I torsion(νI) II (kaolinite) (kaolinite) ν6 δ(O-H) ν(Si-O) ν12 ν5 ν4, ν11 ν3, ν10

Figure 4. FTIR spectra of the 1.03- (A) and 0.95-nm (B) KH complexes, and nonintercalated kaolinite (C) in the 3700-2800 cm-1 region. Overlaid spectra B and C are plotted in the inset box.

end of the hydrazine molecule.13,14 Partial penetration of hydrazine into the SDC results in increased electrostatic repulsion between the inner-OH group and the -NH2 group of hydrazine, which is manifested by an 8-cm-1 shift to higher energy. Frost et al. assigned this band to red-shifted inner-surface

Figure 5. FTIR spectra of the 1.03- (A) and 0.95-nm (B) KH complexes in the 3410-3270 cm-1 region. For comparison, the spectrum of matrix-isolated hydrazine in a N2 matrix at a dilution ration of 1:2000 at 12 K is shown at the top (C).

ν(OH) bands.39 However, we assign the 3628 band to the ν(OH) of perturbed inner-OH groups (Figure 1) based upon the following evidence. First, the line width of the ν(OH) band assigned to the inner-OH group is significantly narrower than that of the inner-surface ν(OH) bands. The 3628 cm-1 band is narrow and well-resolved unlike the inner-surface ν(OH) bands. Second, the appearance of the 3628 cm-1 band corresponds directly with the formation of the 0.95-nm KH complex observed with XRD (Figure 2). Third, the hydrazine molecule is too large to be accommodated in an interlamellar region that has a gallery height of 0.24 nm without partially keying into the kaolinite surface, that is, penetrating the SDC. Fourth, redshifted ν(OH) bands of the 1.03-nm KH complex are clearly identified at 3568 and 3465 cm-1 in agreement with the earlier study of Ledoux and White.10 Finally, the Al-OH bending band of the inner OH is clearly perturbed by the partial collapse of the KH complex from 1.03 to 0.95 nm (see below), which supports the assignment of the 3628 cm-1 band to the innerOH group. ν(N-H) Region. Two types of ν(N-H) bands are present in the spectra (Figures 4 and 5) of the 1.03- and 0.95-nm KH intercalation complexes. The spectrum of the 1.03-nm KH complex has a prominent, broad band at 2975 cm-1 and a broad underlying feature at 3214 cm-1 (Figure 4A). Partial collapse

Spectroscopic Study of Kaolinite-Hydrazine Intercalate of the KH complex to 0.95 nm eliminated the 2975 cm-1 feature, but the very broad band centered at 3270 cm-1 remained (Figure 4B). In addition to these broad bands, a set of sharp, well-defined ν(N-H) bands was present at 3368, 3363, 3312, and 3303 cm-1 in the spectrum of the 1.03-nm KH complex (Figures 4B and 5B) whereas only two bands at 3363 and 3303 cm-1 were evident in the 0.95-nm complex (Figures 4A and 5A). The FTIR spectrum of matrix-isolated hydrazine is shown for comparison (Figure 5C). This matrix isolation spectrum corresponds to hydrazine molecules diluted at a ratio of one hydrazine molecule per 2000 argon atoms trapped on a cold ZnSe window at 12 K.45 Under these conditions, the hydrazine molecules are separated from each other and have little, if any, interaction with the matrix. The line widths and positions of these wellresolved ν(N-H) bands of hydrazine intercalated into kaolinite are surprisingly similar to those of matrix-isolated hydrazine. Observation of such narrow, well-resolved bands is very unusual in clay-organic complexes and indicates that the -NH2 groups corresponding to these bands are in a well-ordered, highly shielded environment. These observations may be interpreted in terms of two types of ν(N-H) bands in both the 0.95- and 1.03-nm KH complexes, corresponding to non-hydrogen-bonded and hydrogen-bonded -NH2 groups. The fact that both types of bands are present indicates that two very different environments for the -NH2 groups occur. The narrow ν(N-H) bands in the 3300-3370 cm-1 region are close in frequency to those of matrix-isolated hydrazine and thus indicate that the associated -NH2 groups have minimal interaction with the clay surface or with other hydrazine molecules. Because of the limited gallery height of the KH complexes (0.32 or 0.24 nm), the only opportunity for -NH2 groups not to interact with both sides of the kaolinite interlamellar surface is to key into the siloxane ditrigonal cavity or to be oriented parallel with the interlamellar surface and not interact with other guest intercalates. The second type of ν(N-H) bands are those corresponding to -NH2 groups that are involved in hydrogen bonding. In the IR spectrum of the 1.03-nm KH complex, these groups are represented by a strong, broad band centered at 2975 cm-1 (Figure 4A). This band is red-shifted by 275 cm-1 relative to the average position of the ν(N-H) bands of liquid hydrazine, indicating that these NH2 groups are significantly more strongly hydrogen bonded than those of liquid hydrazine molecules. There are two possible proton acceptors that can account for the strongly hydrogen-bonded -NH2 groups. The first are O atoms at the siloxane surface of the kaolinite structure (Figure 1), and the second is the lone-pair of electrons of adjacent hydrazine molecules. Formation of H-bonds with the siloxane O atoms would imply an N-H‚‚‚O distance of 0.285 nm based on correlations of ν(N-H) vs d(NO) for N-H‚‚‚O hydrogen bonds.44 In the latter case, the frequency of 2975 cm-1 corresponds to an N-N distance of approximately 0.297 nm which is considerably shorter than observed in solid hydrazine. Upon partial collapse of the 1.03-nm KH complex to 0.95 nm, the large, broad band at 2975 cm-1 is no longer present and the dominant feature in the spectral region is an equally broad, complex feature centered at 3270 cm-1 (Figures 3B and 4B). This apparent increase in frequency of the ν(N-H) bands in the 0.95-nm complex indicates that these -NH2 groups are less strongly hydrogen-bonded than those present in the 1.03nm KH complex. Formation of the 0.95-nm KH complex is accompanied by a reduction in height of the interlamellar gallery from 0.32 to 0.24 nm. Thus, the intercalated hydrazine molecules are brought into closer contact with the kaolinite surface. If the



2975 cm-1 band resulted from -NH2 groups hydrogen-bonded to the siloxane surface, then one would expect this band to shift to lower frequency. The blue-shift of the ν(N-H) band from 2975 to 3250 cm-1 upon formation of the 0.95-nm KH complex supports the assignment of the 2975 cm-1 band to intermolecular hydrogen bonding between adjacent hydrazine molecules. The crosssectional surface of hydrazine is 0.135 nm2 and the monolayer surface available on kaolinite is 0.458 nm2. Thus, three or four hydrazine molecules can be accommodated in the gallery of kaolinite to provide monolayer surface coverage, depending on the arrangement of hydrazine molecules in the gallery. This value is consistent with the surface loading of hydrazine values measured for the KH complex as a function of pressure. The surface loading of hydrazine for the 0.95-nm KH complex was determined to be 0.5 hydrazine molecules per unit cell.14 This reduction in surface loading is responsible for the loss of the 2975 cm-1 band as the intermolecular hydrogen bonding between hydrazine molecules is reduced. The large, broad band at 3270 cm-1 corresponds to spatially separated hydrazine molecules on the kaolinite surface with one end of the hydrazine molecule keyed into the siloxane ditrigonal cavity and the other -NH2 group interacting with the inner-surface OH groups of the kaolinite surface. H-N-H Twist and Scissor Modes. IR spectra of intercalated hydrazine in the NH2 deformation region [s- and asymmetric scissor modes (ν3 and ν10); s- and a-symmetric HNH twist (ν4 and ν11)] for the 1.03- and 0.95-nm KH complexes are shown in Figure 6. The HNH twisting mode (ν11 or ν4 mode) of hydrazine occurs at 1305 cm-1 in the spectrum of the 1.03nm KH complex and shifts to 1276 cm-1 in the 0.95-nm KH complex (Figure 6B). The position of this band in matrixisolation studies is shifted from 1299 cm-1 in an Ar matrix to 1314 cm-1 in a N2 matrix.45 Matrix-isolation spectra of hydrazine in Ar and N2 matrixes at higher concentrations (1: 200) have bands at 1326 and 1320 cm-1, respectively, and were assigned to the formation of a hydrazine aggregate based on their disappearance in less concentrated matrixes.45 The assignment of the 1305 cm-1 band to the HNH twist of aggregated hydrazine molecules is consistent with the matrix-isolation results. The shift of this band to 1276 cm-1 corresponds to that of isolated hydrazine molecules where intermolecular hydrogen bonding has been reduced. The scissor mode (ν10 mode) of hydrazine appears at 1616 cm-1 in the 1.03-nm complex and at 1613 cm-1 in the 0.95-

8086 J. Phys. Chem. B, Vol. 104, No. 33, 2000


Figure 8. INS spectra of kaolinite (A), 0.95-nm KH complex (B), and the 1.03-nm KH complex (C) throughout the range of 200-2000 cm-1.

nm complex. These positions compare with a value of 1595 cm-1 for matrix-isolated hydrazine (N2 1:2000; Table 2). Similar bands at 1612 and 1627 cm-1 were reported recently by Frost et al.39 and assigned to the HOH deformation bands of co-intercalated water molecules. In fact, they assigned all the bands present in the 1575-1680 cm-1 region to H-O-H bending bands and did not account for the ν3 and ν10 modes of hydrazine.45 We conclude that these assignments are incorrect on the basis of the following lines of evidence. First, the samples studied here do not contain water and give spectra similar to the spectra reported by Frost et al.39 Second, the most logical assignments of the bands in the 1600-1620 cm-1 region of the KH complex would be to either the ν3 or ν10 modes of hydrazine based on previous IR and Raman studies of hydrazine.45,46 Third, the line widths of the 1616 and 1613 cm-1 bands are considerably narrower than the intrinsically broad ν2 of water.47,48 ν(N-N) Region. The position of the ν(N-N) band of hydrazine (ν5) reported ranges from 1086 cm-1 for matrixisolated hydrazine45 to 1126 cm-1 for the bulk solid.46 This mode appears at similar frequencies in the IR (Figure 7) in both KH complexes, at 1095 and 1091 cm-1, and in the Raman spectrum at 1113 cm-1 for liquid hydrazine.14 The INS spectra (Figure 8) for the KH complexes show a broad structured band in this region with the highest-frequency component at 1119 cm-1, in agreement with IR and Raman data for ν5. These data indicate that the N-N bond length is not strongly influenced by the partial collapse of the KH complex from 1.03 to 0.95 nm.

Johnston et al.


Asymmetric and Symmetric Wag Modes of Hydrazine. The ν12 mode of hydrazine (asymmetric wag) occurs in the 937 to 1066 cm-1 region,45 depending on the state of hydrazine (liquid, vapor, matrix isolated, or solid). This mode can be readily assigned from the INS data because it is expected to have significant INS intensity. The INS spectra of both KH complexes (Figure 9) show a broad, structured band in the region between 1000 and 1150 cm-1, which can be resolved into three bands at 1027, 1070, and 1119 cm-1 (Figure 9C). The band at 1070 cm-1 may then be assigned to ν12, and that at 1119 cm-1 to ν5, in reasonable agreement with the IR data. We attribute the band at 1027 cm-1 to one of the ν(Si-O) modes which has gained INS intensity by virtue of its coupling with the hydrazine molecule. There are, however, noticeable differences in the relative intensities of the different parts of this INS band, particularly for ν(N-N). Because the normal coordinate analysis suggests that this mode has a significant amount of NH2 wag character, one may speculate that the potential energy distributions (PEDs) differ for the weakly and strongly bound hydrazine molecules. The resulting differences in the atomic displacements of the H atoms of hydrazine would thereby affect the INS intensities of some of the vibrational bands. The symmetric wag, ν6, was observed by Raman spectroscopy in the bulk solid46 at 780 cm-1 and may therefore be assigned to the broad INS band at about 785 cm-1. This band is split into two components for both KH complexes, 770 and 791 cm-1 for the 1.03-nm complex and 765 and 805 cm-1 for the 0.95nm complex. This splitting may reflect the fact that the interactions of the two ends of the hydrazine molecule with the host differ appreciably. Torsions. The most intense bands in the INS spectra usually arise from modes that involve large displacements of H atoms, such as torsions or low-frequency bending modes. Although an isolated hydrazine molecule has only one torsional mode (ν7), the intercalated molecule will have both an out-of-phase and in-phase torsion49 where the two ends of the molecules rotate in the opposite (νI) and same direction (νE), respectively. Both of these torsional modes are subject to an internal barrier to rotation and an external barrier at each end of the molecule. If the external barriers at the two ends of the molecule are the same, the two torsional modes νI and νE are related49 to ν7 as νI2 - νE2 ) ν72. On the basis of INS intensity considerations we can assign the strong bands at 296 and 487 cm-1 to νE and νI, respectively (Figure 10). The width of the latter band may well reflect some difference in the external potential at the two ends of the molecule, which would cause a splitting in the



torsional peaks. Nonetheless, the resulting value of 387 cm-1 for ν7 is in good agreement with the gas-phase value of 377 cm-1 (Figure 10). The torsional spectrum of the 1.03-nm complex is complicated by the presence of different types of hydrazine molecules, and the fact that those hydrazine molecules that are not tightly bound will recoil upon scattering of the neutrons50 may give rise to the large and very broad background visible in the spectrum of the 1.03-nm complex (Figure 10). Indeed, the INS spectrum in this case shows many overlapping bands in the torsional region, and it may not be possible to assign these in detail without detailed structural information on the location of all guest molecules. A difference spectrum, in which the spectrum of the 0.95-nm complex was subtracted from that of the 1.03-nm complex, does suggest, however, that there may be two additional types of hydrazine molecules in the latter. The largest difference is a broad, intense band centered at 410 cm-1 which may be assigned to ν7 for weakly bound molecules because this frequency is only slightly shifted from that of the gas phase (377 cm-1). In addition, there is a pair of bands of similar peak intensity at 340 (split into two components) and 530 cm-1. These may correspond to the in-phase and out-ofphase torsions of another type of molecule with a higher external barrier to rotation than the molecules in the 0.95-nm complex (296 and 487 cm-1), which could arise from the strong intermolecular H-bonding evident in this complex. Similar torsional frequencies have also been observed by electron energy loss spectroscopy51 for hydrazine adsorbed on Ni(111) surfaces. On the basis of experimental and theoretical studies,45 the structure of hydrazine in the gas and matrix-isolation phases is in the gauche form. This structure, however, does not provide for optimal bonding interactions with the kaolinite surface because of its dipolar character. The -NH groups of hydrazine could interact most favorably with the lone pair of electrons of adjacent hydrazine molecules and with the oxygen atoms of the siloxane surface. The lone pair of electrons, in contrast, would form favorable interactions with the Al-OH groups of the gibbsite layer and with -NH2 groups through intermolecular hydrogen bonding. The dipolar nature of the interlamellar surface of kaolinite may provide sufficient energy stabilization to allow the hydrazine molecule to undergo a rotation about the N-N bond to provide optimal contact with the kaolinite surface. ν(Si-O) Region. The most intense bands in the entire IR spectra of kaolinite and its hydrazine intercalates are the ν(Si-

J. Phys. Chem. B, Vol. 104, No. 33, 2000 8087 O) bands at 1010, 1040, and 1116 cm-1 (Figures 3 and 7). The positions of these bands are influenced by the presence of hydrazine and by the partial collapse of the 1.03-nm KH complex to 0.95 nm (Table 2). Kaolinite has two prominent ν(Si-O) bands at 1010 and 1034 cm-1, which shift to higher frequency upon formation of the KH complexes, that is, to 1010 and 1040 cm-1 for the 1.03-nm complex, and 1017 and 1044 cm-1 for the partially collapsed 0.95-nm KH complex (Figure 7). INS data show a relatively weak, broad band at about 1027 cm-1 for these modes, which is indicative of some interaction with H on the guest hydrazine molecules. The positions of the ν(Si-O) bands are also influenced by the presence of hydrazine. Changes to the framework vibrational modes of kaolinite may be attributed to small structural changes induced by the presence of hydrazine and by dielectric effects. Upon intercalation of hydrazine, the layers are separated by distances of 0.24 or 0.32 nm. In nonintercalated kaolinite, the inner-surface OH groups have predominantly electrostatic interactions with the opposing siloxane surface (Figure 1).52 These interactions are replaced in the KH intercalation complexes by -NH2 groups of the guest species. Additional support for this argument is provided by 29Si solid-state NMR data of the 1.03-nm KH complex.12 The 29Si resonance of the KH intercalate shifted to a higher field of -92.0 ppm (relative to tetramethylsilane) compared with the value for nonintercalated kaolinite of -91.5 ppm, indicating that the local environment around the silicon atoms in the KH intercalate was changed relative to that of kaolinite. δ(O-H) Region. The hydroxyl deformation, or bending modes, of the structural OH groups [δ(O-H)] are also influenced by the presence of hydrazine. These bands are usually strong in INS spectra but may be relatively weak in optical spectra. The δ(O-H) bands of nonintercalated kaolinite occur at 940 and 915 cm-1 in the IR spectra and have been assigned to inner-surface and inner-OH groups, respectively.53,54 For both the 1.03- and 0.95-nm KH complexes, the intensity of the innersurface δ(O-H) band at 940 cm-1 is strongly reduced, in agreement with the loss in intensity of the inner-surface ν(OH) bands. The band at 914 cm-1 is shifted to 904 cm-1 in the 1.03-nm complex, and it shifts to 913 cm-1 upon partial collapse to form the 0.95-nm KH complex. Two observations can be made about these deformation bands. First, they show considerably less structure than sharp ν(OH) bands, consistent with earlier studies of the deformation bands.47,48 Second, these results show that the inner-OH group is perturbed by the presence of hydrazine as evidenced by the shift from 904 to 913 cm-1 upon partial collapse of the KH complex from 1.03 to 0.95 nm. The shift in frequency of the inner-OH group may reflect the change in surface loading from 2 to 4 hydrazine molecules per unit cell to a value of ∼0.5 hydrazine molecules per unit cell. One would expect that some of the intensity of the deformation bands associated with the inner-surface OH groups at 940 cm-1 would return upon reducing the surface coverage of hydrazine; however, none was observed. The INS data, discussed below, indicate that some of the intensity of the 904 and 913 cm-1 bands may be due to perturbed inner-surface OH groups which are hydrogen-bonded to intercalated hydrazine molecules. The INS spectrum for kaolinite shows a broad band with at least three components at approximately 895, 918, and 945 cm-1, in good agreement with the IR data. The width of the INS band can be rationalized by the fact that there are four nonequivalent OH groups in the kaolinite structure.55 Upon intercalation of hydrazine, the high-frequency component at 945 cm-1 lost most of its intensity and the center of the band shifted

8088 J. Phys. Chem. B, Vol. 104, No. 33, 2000 to somewhat lower frequency at 908 cm-1 for the 1.03-nm complex and 895 cm-1 when partially collapsed. Intercalation of hydrazine therefore results in a slight frequency shift of the bending modes for the inner-OH groups and a strong reduction in intensity of the inner-surface OH bends in both IR and INS spectra. Summary The combined application of spectroscopic and crystallographic methods has provided new insight into the structure and bonding of the KH intercalation complex. The ability of hydrazine to intercalate into the kaolinite structure is attributed to hydrogen-bonding interactions of hydrazine with both the siloxane and gibbsite layers of kaolinite. Initially, a KH complex with a 001 d-spacing of 1.03 nm formed on intercalation. IR spectra of this complex reveal the presence of strong hydrogen bonds between intercalated hydrazine molecules. Upon lowering the surface coverage of hydrazine to 0.5 hydrazine molecules per unit cell, the d-spacing of the KH complex is reduced from 1.03 to 0.95 nm. Spectral evidence shows the penetration of the siloxane ditrigonal cavity by one end of the hydrazine molecule. Furthermore, the intermolecular hydrogen bonding between hydrazine molecules is reduced for the 0.95-nm KH complex. All the vibrational modes of hydrazine are strongly perturbed by the transition from the 1.03- to 0.95-nm KH complex. In particular, the INS data reveal strong splitting of the torsional mode suggesting that the conformation of the intercalated hydrazine species is changed from a “gauche” conformation to a “cis” conformation. These interactions result from the dipolar nature of the interlayer surface of kaolinite. The combined application of IR, INS, and XRD methods has provided detailed insight into the structure of the KH intercalation complexes. Finally, the “keying” mechanism of hydrazine into the siloxane ditrigonal cavity may have useful applications related to grafting organic molecules onto the inorganic substrates. Acknowledgment. The authors would like to thank E. Ong for assistance with the collection of the INS data. This work has benefited from the use of facilities at the Manuel Lujan Jr. Neutron Scattering Center, a National User Facility funded as such by the US DOE. References and Notes (1) Tunney, J. J.; Detellier, C. Chem. Mater. 1996, 8, 927. (2) Wang, Z.; Pinnavaia, T. J. Chem. Mater. 1998, 10, 1820. (3) Mercier, L.; Pinnavaia, T. J. Microporous Mesoporous Mater. 1998, 20, 101. (4) Chibwe, M.; Ukrainczyk, L.; Boyd, S. A.; Pinnavaia, T. J. J. Mol. Catal. A Chem. 1996, 113, 249. (5) Komori, Y.; Sugahara, Y.; Kuroda, K. J. Mater. Res. 1998, 13, 930. (6) Hayashi, S. Clays Clay Miner. 1997, 45, 724. (7) Komori, Y.; Sugahara, Y.; Kuroda, K. J. Mater. Res. 1998, 13, 930. (8) Guimaraes, J. L.; Peralta-Zamora, P.; Wypych, F. J. Colloid Inter. Sci. 1998, 206, 261. (9) Ogawa, M.; Kuroda, K. Chem. ReV. 1995, 95, 399. (10) Ledoux, R. L.; White, J. L. J. Colloid Interface Sci. 1966, 21, 127. (11) Barrios, J.; Plancon, A.; Cruz, M. I.; Tchoubar, C. Clays Clay Miner. 1977, 25, 422.

Johnston et al. (12) Thompson, J. G. Clays Clay Miner. 1985, 33, 173. (13) Johnston, C. T.; Stone, D. A. Clays Clay Miner. 1990, 38, 121. (14) Johnston, C. T. Spectroscopic Characterization of Minerals and Their Surfaces; Coyne, L. M., McKeever, S. W. S., Blake, D. F., Eds.; American Chemical Society Symposium Series 415; American Chemical Society: Washington, DC, 1990; p 432. (15) Hayashi, S. J. Phys. Chem. 1995, 99, 7120. (16) Olejnik, S.; Aylmore, L. A. G.; Posner, A. M.; Quirk, J. P. J. Phys. Chem. 1968, 72, 241. (17) Johnston, C. T.; Sposito, G.; Bocian, D. F.; Birge, R. R. J. Phys. Chem. 1984, 88, 5959. (18) Duer, M. J.; Rocha, J.; Klinowski, J. J. Am. Chem. Soc. 1992, 114, 6867. (19) Adams, J. M.; Jefferson, D. A. Acta Crystallogr. 1976, B32, 1180. (20) Ruiz Cruz, M. D.; Franco, F. Clays Clay Miner. 2000, 48, 63. (21) Olejnik, S.; Posner, A. M.; Quirk, J. P. J. Colloid Interface Sci. 1971, 37, 536. (22) Olejnik, S.; Posner, A. M.; Quirk, J. P. Spectrochim. Acta A 1971, 27A, 2005. (23) Giese, R. F. ReV. Mineral. 1990, 19, 29. (24) Hayashi, S. J. Phys. Chem. 1995, 99, 7120. (25) Costanzo, P. M.; Giese, R. F.; Lipsicas, M.; Straley, C. Nature 1982, 296, 549. (26) Costanzo, P. M.; Giese, R. F.; Lipsicas, M. Clays Clay Miner. 1984, 32, 419. (27) Costanzo, P. M.; Giese, R. F. Clays Clay Miner. 1985, 33, 415. (28) Costanzo, P. M.; Giese, R. F. Clays Clay Miner. 1990, 38, 160. (29) Lipsicas, M.; Straley, C.; Costanzo, P. M.; Giese, R. F. J. Colloid Interface Sci. 1985, 107, 221. (30) Vahedi-Faridi, A.; Guggenheim, S. Clays Clay Miner. 1997, 45, 859. (31) Fernandez, M.; Serratosa, J. M.; Johns, W. D. Reun. Hisp.-Belga Miner. Arcilla An. 1970, 163. (32) Alba, M. D.; Alvero, R.; Becerro, A. I.; Castro, M. A.; Trillo, J. M. J. Phys. Chem. B 1998, 102, 2207. (33) Karakassides, M. A.; Petridis, D.; Gournis, D. Clays Clay Miner. 1997, 45, 649. (34) Madejova, J.; Bujdak, J.; Gates, W. P.; Komadel, P. Clay Miner. 1996, 31, 233. (35) Van Olphen, H.; Fripiat, J. J. Data Handbook for Clay Materials and Other Nonmetallic Minerals; Pergamon Press: Oxford, 1979. (36) Johnston, C. T.; Sposito, G.; Birge, R. R. Clays Clay Miner. 1985, 33, 483. (37) Sivia, D. S.; Vorderwisch, P.; Silver, R. N. Nucl. Instrum. Methods Phys. Res. Sect. A 1990, 290, 492. (38) Eckert, J.; Kearley, G. J. Spectrochim. Acta A 1992, 48, 269. (39) Frost, R. L.; Kristof, J.; Paroz, G. N.; Kloprogge; J. T. J. Colloid Interface Sci. 1998, 208, 216. (40) Kristof, J.; Toth, M.; Gabor, M.; Szabo, P.; Frost, R. L. J. Therm. Anal. 1997, 49, 1441. (41) Ledoux, R. L.; White, J. L. Science 1964, 145, 47. (42) Michaelian, K. H. Can. J. Chem. 1986, 64, 285. (43) Novak, A. Struct. Bonding 1974, 18, 177. (44) Lautie, A.; Froment, F.; Novak, A. Spectrosc. Lett. 1976, 9, 289. (45) Tipton, T.; Stone, D. A.; KuBulat, K.; Person, W. B. J. Phys. Chem. 1989, 93, 2917. (46) Durig, J. R.; Bush, S. F.; Mercer, E. E. J. Chem. Phys. 1966, 44, 4238. (47) Venyaminov, S. Y.; Prendergast, F. G. Anal. Biochem. 1997, 248, 234. (48) Johnston, C. T.; Sposito, G.; Erickson, C. Clays Clay Miner. 1992, 40, 722. (49) Ludman, C. J.; Ratcliffe, C. I.; Waddington, T. C. J. Chem. Soc. Faraday II 1976, 72, 1741. (50) Jobic, H. Chem. Phys. Lett. 1984, 106, 321. (51) Bu, Y.; Shinn, D. W.; Lin, Y. C. Surf. Sci. 1984, 276, 184. (52) Giese, R. F. Bull. Mineral. 1982, 105, 417. (53) Farmer, V. C. The Infrared Spectra of Minerals; Farmer, V. C., Ed.; Mineral Society: London, 1974; p 331. (54) Johnston, C. T.; Agnew, S. F.; Bish, D. L. Clays Clay Miner. 1990, 38, 573. (55) Bish, D. L. Clays Clay Miner. 1993, 41, 738. (56) Giguere, P. A.; Liu, I. D. J. Chem. Phys. 1952, 20, 136.

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