American M ineralogist, Volume62, pages 784-792,1977

Hydroxyl groupsand water in palygorskitel

C. SenNe,G. E. VnNScoyoc ANDJ. L. AHlnIcus Department of Agronomy, Purdue Uniuersity West Lafoyette, Indiana 47907

Abstract

lnfraredspectra ofthe coordinatedwater in palygorskitewere studied at differentdegrees of exchangeof deuteronsand protons.The singlepeaks observed for thebending fundamental of isotopicallydiluted HrO and DzO showthat all the coordinatedwater moleculesare equiva- lent, as suggestedby Bradley'sstructure determination. The doubletsobserved for the three fundamentalsof isotopicallydilute HDO showedthat the coordinatedwater molecules are asymmetric(C, symmetry).Response of palygorskitefilms to the angleof orientationin- dicatedone of the OH stretchingmodes to haveits transitionmoment nearly perpendicular to the [00] plane. The orientation effect results from one of the protons on each of the coordinatedwater molecules forming a hydrogenbond directed towards the hexagonalholes of oxygensfprmed by the Si-O-Siconnections between the amphibolechains, and it explains the distortedcharacter of thiswater. Deuteration and orientationstudies also verified that the two OH stretchingbands of the distortedwater are truly uncoupled. Georgiapalygorskite is shownto be completelydioctahedral, and a modelis presentedto explain its octahedralcation occupancyand the frequencyof the structural hydroxyls. Infraredadsorption bands around 3700 cm-'indicated the presence of someSiOH groupsin the mineral.These groups are less abundant in palygorskitethan in ,indicating that palygorskitehas lessexposed edges.

Introduction The presenceof SiOH groupsat sepiolitecrystal (1975). A largenumber of infraredstudies have been pub- edgeswas illustrated by Ahlrichset al. Similar lishedon hydroxylgroups and water in layersilicates. SiOH groups are found in .An ex- However,little is known about thesegroups and planptionof their relativeabundance and of the ori- moleculesin fibrous silicatessuch as sepioliteand entationof the hydroxylwill be presented. palygorskite.X-ray diffractioninvestigations have in- The originalchemical analysis published by Brad- dicatedthat palygorskitebelongs to the spacegroup ley(1940) on palygorskiteand later reviewed by Drits C"n-C2/m,with two formulaunits per primitivecell and Aleksandrova(1966) shows that an averageof (Bradley,1940). In the structuralscheme of Bradley, four of the five octahedralcation sitesare occupied. the eight oxygenatoms of water (Ow) have been Therefore,some dioctahedral character has been sug- 1975). placedin equivalentpositions, suggesting only one gestedfor the mineral(Henin and Caillere, infraredvibrations kind of coordinatedwater molecules. Recently, Prost The intensityand positionof the well (19'75)has shown each coordinated water molecule to of the structuralOH in palygorskite,as as the have be distortedby meansof hydrogenbonding through particulararrangement of the octahedrallayer, postulates one of its protons.Our detailedstudy substantiates been consideredin developingthe con- the presenceof hydrogenbonding of the waterand cerningthe di-trioctahedralcharacter. showsthe orientationof the protonsin the structure. Methodsand materials Also, important conclusionsabout the uncoupled was characterof the HDO and HrO moleculeswill be The Georgia palygorskite(attapulgite) ob- considered. tained from the Mineral Respository,Depart- ment of Geology,University of Missouri,Columbia, 'Journal Paper 6444,Purdue University Agricultural Experi- Missouri. Characterizationof the sampleby X-ray mentStation, West Lafayette,Indiana. diffraction and infrared analysisshowed it to be of SERNAET AL,: PALYGORSKITE

high purity. Only slight evidence of an expanded coordinated to the edge cations of the octahedral phase () was observed after treat- sheetexposed on the externalsurface and in the chan- ment of the samplewith ethyleneglycol. The C.E.C. nels (zeolitic water). This physically adsorbedwater of the sample as determined by summation of the can be removed under vacuum ( ( l0-5 mm Hg) at cations on the exchange sites was 25.1 meq./100 room temperature; leaving the mineral with two wa- gramswith 16.1meq. Ca, 4.8 meq. Mg, 0.6 meq. K, ter molecules coordinated to each external octahedral 0.2 meq. Na, and 2.4 meq. H. The chemical formula cation (Fig. l). given by Bradley (1940) for Georgia palygorskiteis Under this evacuatedcondition a nonsymmetric (si7'.Al0 1?) (Al,36TioorFe3.+rrFe3lrMg,.rr) OroCao.r, absorption band appearc at 1624 cm-' due to the (OH),(OH,)n.nH,O. bending mode of the coordinated water. However, a Powderedpalygorskite sampleswere convertedto complex spectrumof stretchingbands of the coordi- a stablesuspension in water by ultrasonic treatment. nated water and the structural hydroxyls still existsin Self-supportingfilms (2 mg/cm") were prepared by the 3800-3300cm-' region (Fig. 2A). Becauseof the drying suspensionson a flat mylar surface. This more accessibleposition of the coordinated water should have resultedin a portion of the fibers molecules,they were easily deuteratedat room tem- having their [00] plane parallel to the film surface. perature, leaving three absorption bands at 3625, The films were mounted in aluminum foil holdersand 3595, and 3560 cm-' due to the structural hydroxyls placed in an evacuable infrared cell similar to that (Fig. 2B). The assignmentof these bands based on described by Angell and Schaffer (1965). Spectra position and chemicalcomposition will be considered were obtained using a Perkin-Elmer 421 spectro- later. Due to the isotopic exchange,an OD shoulder photometer. Deuteron and proton exchangestudies appearsat2745 cm 'and two bands at2700 and 2585 were made in a high vacuum system which gave a cm-1.At the sametime, a split (1220and 1205cm-1) vacuum of lessthan l0-5 mm Hg. is observedin the nonsymmetricbending mode of the Separationof the structural OH from the coordi- coordinatedDrO (Fig. 2B). Similar spectrahave been nated HrO was achievedthrough deuteration of the presented by Mendelovici (1973) for Georgia pal- coordinatedHrO by flushing the film repeatedlywith DrO vapor at room temperature.Separation of the structural OH and coordinated HrO was also achievedby deuteratingthe structural OH. Samples with structural OD and coordinated HrO were pro- duced without altering the structure of the palygor- skite by heatingthe sampleto 300'C in an atmosphere of DrO, cooling to 25"C, and then flushing several times with HrO vapor. The important feature of this approachis that the samplecan be studiedin both the OH and OD stretchingregions of the spectrumwith- out overlap of the structural hydroxyl and coordi- nated watet bands. Study of the coordinated water was conducted by progressiveproton or deuteron exchangein samples with structuralOD or OH, respectively.The D2O to

HrO ratio usedfor theseisotopic dilution studieswas H adjustedto produce the amount of exchangedesired. tro A 5 to I ratio was usedto observethe uncoupledOH "6 o HY.DROXYL and a 0.2 to 1 ratio for the uncoupled OD. O O llg Results and discussion o lr,nfl'r.z' osl A. Infrared spectra of palygorskite

Under atmospheric conditions palygorskite con- Fig. l. Palygorskite model (Bradley, 1940) modified to show (a) tains loosely adsorbedwater. It has been suggested the dioctahedral character, (b) the position of the protons in the that this water is -bondedthrough the water coordinated water, and (c) in the SiOH. 786 SERNA ET AL.: PALYGORSK(TE

U o z 3 F r = U' z f, F

2700

3400 3200 2800 2600 2400 1800 ti+oo WAVENUMBER(cni'r) Fig. 2. Spectraof palygorskiteunder vacuum with structuralhydroxyls as OH and coordinatedwater as (A) HrO and (B) DrO. ygorskite and by Prost (1975) for palygorskitefrom separation of ll5 cm-' was found in the HrO and Serradilla. DrO absorption bands of palygorskite (Table I ), Sampleswith structural OD (Fig. 3A-B) show fea- their suggestion does not seem to provide a general tures analogousto thosewith structural OH. A com- explanation for their observation.Other examplesof parison of the positions of the OH and OD absorp- better resolution in deuterated specimenshave been tions is presentedin Table I with the corresponding reported for adsorption of water on ZrO, (Agron et OH/OD frequencyratios. al., 1975), and for deuterated molecules like HrS (Forster and Schuldt, 1975). B. Coordinated water (l ) The bending fundamental of isotopically diluted Numerous studiesof the nature of water molecules HrO and DrO.,The vibrations of equivalent water in hydrated have been made using the iso- moleculesin a crystal may engagein dynamic cou- topic dilution technique.These studies have shown pling. This phenomenonis often referredto as corre- that the number and position of the infrared absorp- lation field splitting (Khanna et al.,1969). However, tion bands of the water molecules in crystals are this coupling can be eliminatedwhen the HzO or DzO affectedby inter- and intramolecularcoupling. Slight is isotopically diluted. As the coordinated water isotopic exchangecan eliminatethese couplings, thus molecules in palygorskite are isotopically diluted, a making it possible to observe the different number single absorption band appearsfor the bending fun- and kinds of uncoupledOH (or OD) vibrations that damentalat 1620cm-' for HzO or l2l5 cm-1 for DzO exist in the crystal (Falk and Knop, 1973). (Fig. 5B). These data indicate that the four water Although both protonated and deuteratedstudies molecules per half-unit cell of the palygorskite are gave similar results,much better resolution was ob- crystallographicallyequivalent. The results are also tained when the spectra were studied in the OD in good agreementwith the structuralmodel of Brad- stretchingregion (Fig. a). This phenomenonhas been ley (1940),in which the eight O, of the water per unit previously reported in a study of water in copper cell are placed in the same equipoint (Fig. l). chloride dihydrate by Fifer and Schiffer(1971). They From the correlation diagram for the site symme- suggestedthat the HrO stretching bands are more try of water, Cr, in associationwith the group factor difficult to discern than their DrO counterparts due to symmetry of palygorskite, C11,(Bradley, 1940), one the smaller zr-2, separationfor HrO. Since an equal would postulatethat correlationfield-splitting should SERNA ET AL.: PALYGORSKITE 787

U o sz F (t= z. F

3800 3600 3400 5200 2@O 2600 2400 1800 1600 1400 1200 looo WAVENUMBER(cm-I) Fig. 3. Spectraof palygorskiteunder vacuumwith structuralhydroxyls as OD and coordinatedwater as (A) HrO and (B) DzO causethe internalvibrations of a watermolecule to (2) The OH and OD fundamentals of HDO. Figure giverise to two coupledvibrations which are infrared 4 shows the spectrum of the OH and OD stretching active, Au and Bu (Table l). Thus the non- regions at various degrees of proton exchange. Ex- symmetricalcharacter of the bendingabsorption of changeof a small fraction of the HrO and DrO (or the HrO (Fig. 5A) and the comparabledoublet ob- vice versa)produced two stretchingabsorption bands servedfor the DzO(Fig. 5C)could be considered due due to uncoupledOD at 2670 and 2600 cm-'. At the to the vibrationalcoupling of the water molecules same time two bending HDO absorptions at 1445 presentin the unit cell. Someprevious examples of and 1425cm-' appear (Fig. 5A). Vibrations isotop- correlationfield splittinghave been found in water ically isolated are consideredto be uncoupled, since moleculesof severalcrystal hydrates (Seidl et al., coupling between OD (OH) and surrounding OH 1969;Holzbecher et al:, l97l). (OD) vibrations is extremelyweak comparedto cou-

Table l. Position ofstructural hydroxyl and coordinated water absorption bands in palygorskite

Structural Hydroxyl CoordlnatedWater

OH OD OH/OD Asslgnment Hzo Dzo 0H/0p Asslgnment 3705 2745 1.350 si0H 3620 2700 1.341 Unperturbed0H 2585 1.356 Hydrogenbonded 0H 3625 2686 1.350 Al2-0H 3505 3595 2660 I .349 (Al,rez+)-ox I 625* 1220 Bendlngmodes, Au and Bu (AL,Mg ) -0H I 205 3560 2640 1.349 1re]+,rez+y-oH (Fer+,Mg) -0H

*a nonsyrmetrlcpeak 788 SERNA ET AL,: PALYGORSKITE

increasein intensity of 2600 cm-1 occurs while the uncoupled OD at 2670 cm-'remains unchanged.A similar effectdue to orientation is also noted for the lower-frequencycoordinated water band in sepiolite, which is a trioctahedralfibrous silicatewith a similar structure to palygorskite(Fig. 78). This responseto orientation shows that one of the OH groups of the coordinated water in the palygorskite has its axis directedessentially perpendicular to the [100] plane. This leaves proton in favorableposi- LrJ orientation the a (J z tion to bond with thep-electronclouds which project F from F the surface into the hexagonal holes o= formed by thd Si-O-Si connectionsbetween the silica z chains of adjoining amphibole ribbons. Strong hy- E F drogen bonding of water molecules into the hex- agonal holes of and has pre- viously been suggested(Farmer and Russell, l97l). The low frequency of the OH (OD at 2600 cm-l) supportsthe presenceof this hydrogen bond. Hydro- gen bonding of one of the OH groups of the coordi- nated water in palygorskitehas been previously sug-

3500 z7@ 2500 WAVENUMBER(cml)

Fig. 4. Spectra of the progressiveH-D exchangein coordinated water of palygorskite with (A) increasing H exchange in the coordinated D,O, and (B) with increasing D exchange in coordi- nated HrO. Initial states shown in Figs. 38 and 2A, respectively.

pling between like oscillators. Therefore, the doublets UJ o observed for the three fundamentals (OH and OD z stretching, HDO F bending) of isotopically-diluted ts HDO indicate that the water moleculesin palygor- = skite are asymmetric (Seidl er al., 1969). z@ The lack of a frequencyshift during the progressive E F isotopic exchangein the uncoupledOD of the HDO (2670, 2600 cm-') and in the OD stretching of the D2O (2700, 2585 cm-l) is characteristic of water molecules without intermolecular coupling (Kling and Schiffer, l97l). The apparent change in fre- quency in the uncoupled OD at 2600 to 2585 cm-' during the isotopic exchangeis consideredto be due to the lack of resolution of the different proportions of HDO and DrO molecules. (3) Uncoupledcharacter of the HDO and DrO. An important feature which appearswhen the partially t800 1600 1400 1200 deuterated film is oriented at 40o (Fig. 6,4') is the WAVENUMBER(cnfr) significant increasein intensity of the lower frequency Fig. 5. Spectra of the bending mode of coordinated water absorption band (2600cm-1) of uncoupledOD. This palygorskite with increasing deuteration. SERNA ET AL,: PALYGORSKITE 789

coordinatedwater in palygorskiteis regardedto be a distortedwater molecule (C" symmetry),the fact that eachOH or OD behavesindependently shows its true uncoupledcharacter. This is not unexpected,since couplingcan be eliminatedby partial deuteration (Bellamy and Pace,1972). The important feature observedfollowing com- plete deuterationis that the coordinatedwater, as DzO,has the sameindependent response to orienta- tion (Fig. 68) that was observedin the uncoupled OD. This shows that there is almost no in- tramolecularcoupling present in the distortedwater moleculein palygorskite.Therefore, the two absorp- tion bandsat2700 and 2585cm-' correspondto the lrt() stretchingmotions of the two differentOD (or OH) z groupsof eachhighly distortedwater molecule. @ E, a water o The degreeof vibrational distortion of U' d) molecule,i.e., degreeof coupling betweenboth stretchingvibrations, in moleculesasymmetrically perturbedhas beenconsidered by the equationpro- posedby Kling and Schiffer(1971).

0 : (Lviro I Lv1e6)/2Auo"s 0 : Vzin undistortedmolecules (Cz symmetry)and d : I for a highlydistorted molecule (C, symmetry), where Avsoo - Luoroand the intramolecularcou- pling is negligible. Applyingthis equationto the coordinatedwater in palygorskitegives the valuefor the DzOspecimen of 0.80.This meansthat the water moleculeis highly distorted,and substantiatesthe relativeindependent 2900 2800 ?7o,0 2@o 2500 240,0 WAVENUMBER(cflf|) Fig. 6. Spectraof (A) uncoupledOD from HDO and (B) un- coupledOD from DrO.

gested by Prost (1975). He assignedthe hydrogen bond of the distorted water moleculeinward toward U one of the oxygen atoms of the octahedral sheet.This I z assignmentis based on an appropriate O-O bond o E distance predicted from the frequency of the un- ao coupled OD applied to the Nakamoto et al. (1955) relationship. However, this bond orientation would place the proton in close proximity to both the Mg and Si atoms of the lattice, where repulsiveforces on the proton would exist.The model we have presented in Figure I placesthe hydrogen-bondedproton in the hexagonal hole formed by adjoining amphibole rib- bons, and placesthe other proton into the open chan- 5700 3600 5700 36@ nel. Both protons would thus be accessibleto zeolitic WAlBlltlBER (cn-r) water, and the hydrogen-bondedproton would show Fig. 7. Effect oforientation on evacuatedfilms of(A) deuterated an orientation affect as noted. In addition, if the palygorskite and (B) non-deuterated sepiolite. SERNA ET AL: PALYGORSKITE

behavior of both OH groups as shown by the orienta- uable information about the orientation of their OH tion effects. However, some slight coupling must ex- groups. These studieshave shown that in trioctahe- ist, which is supported by the small difference in dral minerals the transition moment of the OH frequency betweenthe uncoupled OD of the HOD, groups is essentiallyperpendicular to the plane of the 2670 and 2600 cm-1, and the uncoupled OD of the layer, whereasin dioctahedralminerals it is tilted out D2O,2700and 2585cm-1 (Bellamyand Pace,l97l ). ofthe cleavageplane (Serratosaand Bradley, 1958). Kling and Schiffer(1971) found and discusseda sim- Oriented self-supportingfilms permit a similar study ilar distortion for the water molecules in calcium of the OH groups in the fibrous silicates.Figure 7 sulfatedihydrate. showsthe effectof orientation on the intensity of the structural hydroxyl bands in palygorskite and the groups. C. SiOH structural hydroxyl and coordinated water bands in The infrared study of hydroxyls in sepioliteshas sepiolite.In agreementwith its trioctahedral charac- shown the presenceof structural SiOH groups near ter, sepiolite shows an appreciable increase in in- 3700 cm-1 as a consequenceof the large number of tensity of its OH groups at 3680 cm-1. However, no crystal edge sites (Ahlrichs et al., 1975). The fibrous orientation effectis shown for the three OH absorp- morphology of palygorskite (similar to sepiolite) tion bandsin palygorskite,which suggestsa complete would also predict a large number of SiOH groups to dioctahedral character for the mineral. This seems complete the coordination of the tetrahedra at the inconsistentwith the chemicalanalysis, but aswill be edge sites.Therefore, the shoulder observedaI 3705 shown below this inconsistencyis only apparent. cm-', or at 2745 cm-' following isotopic exchange, Figure 8 presentsa schemedf the octahedrallayer must be due to SiOH groups in the crystals(Table I ). in palygorskite.If we considerthat the two octahedra The high frequency of SiOH and its ease of per- holdingthe coordinatedwater at the edgeofthe chan- turbation can be easily explained by its location at nel in each half-unit cell are always occupied by cat- crystal edges,a very isolated site. ions, then whereverthe other two octahedralcations The relative abundanceof thesegroups in sepiolite are placedthe palygorskitewill be a completelydioc- has been suggestedas a measure of the degree of tahedral mineral, since only two out of the three crystallinity of this mineral (Ahlrichs et al., 1975). octahedronsbelow the hexagonalhole will be occu- The low intensity of the SiOH band in palygorskite pied. indicates less edge surface or fewer imperfections The cation ordering in the octahedral layers can than was observed for the several . The be considered by taking into account the position lower specificsurface area of this mineral,195 m2/g, and intensity of the structural OH. The chemical (Barrer and MacKenzie, 1954) in contrast to sepio- composition of the octahedrallayer of Georgia paly- lite, 320 m2/g, (Fernandez Alvarez, l97l) also sug- gorskite per three half-unit cells is (Alo.orFelj, gestsit to have fewer imperfections or fewer exposed Fe3.+orTio'Mgu ,n). In agreement with its dioctahedral edges. characterthe mineral doesnot show an absorption at An increasein intensity of the SiOH groups is 3680 cm 1, which is known to be due to 3 Mg in a observedwhen the sampleis oriented at 40", showing trioctahedral mineral (Ahlrichs et al., 1975). There- that its OH axis is essentiallyperpendicular to the fore, most of the Mg cations must be placed at the [100] plan (Fig. 68). The position of the protons in edgeof the channelsholding the coordinatedwater (6 the coordinated water producesa specialorientation Mg per three half-unit cells).This model, with water of the proton of the SiOH groups, due to repulsion all coordinated to the same cation (Mg), is in good effects(Fig. lC). Similar behavior is shown by the agreementwith the observationof only one kind of SiOH (3720 cm-') in sepioliteminerals (Fig. 7B). coordinatedwater moleculein palygorskite,and with the sharpnessof the stretching absorption bands of D. Structural hydroxyls in the octahedral sheet this water. Ordering in the cation positions,as shown Although Bradley's model for palygorskite is es- here for Mg, is now being commonly found in the sentiallycorrect, most of the chemical analysesshow layer silicates,as a consequenceof the refinementof four cations per half-unit cell. Therefore, as has been structuresin subgroup symmetry (Bailey, 1975). pointed out, the mineral must have some dioctahe- The remaining cations (Aln orFesf,rFe';lorTio r,) draf character(Rautereau and Mifsud, 1975:Henin must be placed in the 6 inner octahedralpositions, and Caillere, 1975). and must be responsiblefor the infrared absorptions Infrared studiesoflayer silicateshave provided val- at 3625.3595.and 3560cm '. The absorotionat 3625 SERNA ET AL.: PALYGORSKITE 791

water are not coupled and therefore are independent vibrators. (5) The OH bond of the SiOH group at the crystal edges is oriented nearly perpendicular to the [100] plane, and it is less abundant than in sepiolite, in- dicating fewercrystal imperfections or edgesurfaces. (6) The Georgia palygorskite shows complete dioctahedalcharacter, and its three stretchingvibra- tions from structural OH can be assignedto (1) AI,-OH, (2) (Al,Fe'z+)-OHor (Al,Mg)-OH, and (3) aMs_ (Fe3+,Mg)-OHor (Fe3+,Fe'+)-OH. @ Ar.Fd:Fe"or Mq O VACANT Acknowledgments Q nvonoxvt- H The senior author gratefully acknowledges the support of the H COORDINATED Commission for Cultural Exchange between the and A WATER \+H , which enabled him to be a visiting scientistfrom the Depart- mento de Fisico-Quimica del Instituto de Edafologia C.S.l.C. Madrid. This researchwas partially funded by the Indiana Elks ga ______-> Purdue CancerGrant. Fig. 8. Arrangement of cations in the octahedrallayer of pal- ygorskite illustrating its dioctahedral character (three half-unit References cells). Agron, P. A., E. L. Fuller,Jr. and H F Homes (1975)I.R. studies of water sorption on ZrO" polymorphs I J. Colloid Interface cm-' is well establishedas being due to Alr-OH Sci.,52 , 553-56I . Ahlrichs, J. L., C. Serna and J. M Serratosa(1975) Structural (Russell and Fraser, l97l). This would be in agree- hydroxyls in sepiolites Clays Clay Miner , 23, l19-124. ment with the high amount of Al present in.the Angell, C. L. and P. C. Schaffer (1965) Infrared spectroscopic palygorskite.The lessintense hydroxyl peaksat 3595 investigations of zeolites and adsorbed molecules. J. Phys. and 3560 cm-1 are not as well established,but are Chem . 69. 3463-3470. characteristicof dioctahedralminerals (Farmer et al., Bailey, S. W (1975) Cation ordering and pseudo-symmetryin layer silicates.Am Mineral 60, 175-178. analyzedbiotites the absorp- , 1971;Farmer,1974).In Barrer, R M and N Mackenzie (1954) Sorption by attapulgite. tion at 3600 cm-' was considered(Al,Fe'+)-OH and Part l. Availability of intracrystallinechannels. J. Phys Chem., the band at 3550cm-1 was considered(Fe3+, Fe'+)- 58, 560-568 OH. In ,a dioctahedralmica, absorption Bellamy, L. J. and R. J. Pace(1972) The effectsofnon-equivalent bandsat 3603 and 3557cm 'have beenassigned to hydrogen bonding on the stretching frequenciesof primary aminesand of water SpectrochimActa, 28A, 1869-1876. (Al,Mg)-OH and (Mg,Fe'*)-OH, respectively.Ap- Bradley, W. F. (1940) Structureof attapulgite.Am Mineral , 25, plications of these assignmentsto palygorskite are 405-4I 0. summarizedin Table l. Drits, V. A. and V. A. Aleksandrova(1966) The crystallochemical nature of palygorskite Zap. Vses.Miner. Obshch, 9J, 551-560. Conclusions Falk, M. and D Knop (1973) Water in stoichiometrichydrates. Chapter II in F. Franks, Ed Lltater,a ComprehensiueTreatise, coordi- , Interpretation of the infrared spectraofthe p 55-l 13. Plenum Press,New York, London. nated water moleculesand hydroxyl groups in pal- Farmer, V. C. (1974) The layer silicates.Chapter XV in V. C. ygorskite provides the following conclusions: Farmer, Ed , The Infrared Spectra of Minerals. p 331-364 (l) There is only one kind of coordinated water Mineral Soc.. London molecule in palygorskite,according to isotopic dilu- - and J. D. Russell (1971) Interlayer complexesin layer silicates,the structure of water in lamellar ionic solutions. Zrans. tion studies. Faraday Soc ,67, 2737-2749 (2) This water has C" symmetry and is coordinated W. J. McHardy, A.C. D. Newman, J. L. Ahlrichs mainly to Mg cations located in the channelsat the and J. Y. H. Rimsaite (1971) Evidenceof loss of protons and edgesof the octahedral sheets. octahedral iron from oxidized and vermiculites. Mineral. (3) The coordinatedwater is orientedwith the tran- Mag., 38, l2l-13'7. (1971) y de sition moment of its hydrogen-bondedhydroxyl per- Fernandez Alvarez, T. Superficie especifica estructura poro de la sepiolita calentada a diferentes temperaturas. Proc pendicular to the [00] plane and its other hydroxyl Reunion hispano-belga de minerales de la arcills, Madrid, directedtoward the channels. 203-209. (4) The two stretching frequencies of the distorted Fifer, R. A. and J. Schiffer(1971) Intermolecular coupling of water SERNA ET AL.: PALYGORSKITE

molecufes in copper chloride dihydrate. J. Chem. Phys., 54, frequenciesas a functionof distancesin hydrogenbonds. J. Am. 5097-5102. Chem.S oc., 77, 6480-6486. Forster,H. andM. Schuldt(19-75) Infrared spectroscopic study of Prost, R. (1975)Etude de I'Hydration desArgiles: InteractionEau- the adsorptionof hydrogensulfide on zeolitesNaA andNaCaA. Mineral et Mecanismede le Retention de I'Eau. Ph.D. thesis, J. ColloidInterface Sci., 52,380-385. Universityof ParisVI, . Henin,S. and S. Caillere(1975) Fibrous minerals. Chapter IX in Rautureau,M. and A. Mifsud (1975)Precisions apportees par les J. E. Gieseking,Ed., Sol Components,Vol. 2. p. 335-349. analysesthermiques de la sepioliteet de la palygorskite,sous Springer-Verlag,New York. vide et dans les conditionsnormales. C. R. Acad. Sci. Paris. Holzbecher,M., O. Knop and M. Falk (1971)Infrared studies of 281D, l07t-1074. water in crystallinehydrates: Sodium nitroprussidedihydrate, Russell,J. D. andA. R. Fraser(1971) I. R. spectroscopicevidence Na,[Fe(CN)'NO].2H,O. Can.J. Chem.,49, 1413-1424. for interactionbetween hydronium ions and latticeOH groups Khanna,R K., C. W. Brownand L. H. Jones( 1969)Laser Raman in montmorillonite.Clays Clay Miner., i,9,55-59. spectraof a singlecrystal of sodiumnitroprusside and thevibra- Seidl,V., O. Knop andM. Falk(1969) Infrared studies of waterin tional frequenciesof the Fe(CN)uNO'2-ionInorg. Chem.,8, crystallinehydrates: gypsum, CaSOo 2H,O. Can. J. Chem.,47, 2195-2200. 1361-1368. Kling, R. and J. Schiffer(1971) Intra and intermolecularinter- Serratosa,J. M. and W. F. Bradley(1958) Determination of the actionsin and betweenwater molecules in calciumsulfate dihy- orientationof OH bond axesin layer silicatesby infraredab- drare.J Chem.Phys., J4, 5331-5338. sorption.,J. Phys.Chem.,62, 1164-1167. Mendelovici,E. (1973) Infrared study of attapulgiteand HCI treatedattapulgite. Clays Clay Miner., 2l, ll5-119. Manuscript receiued,September 27, 1976;accepted Nakamoto,K., M. Margoshesand R. E. Rundle(1955), Stretching for publication,March 22, 1977.