The Spectroscopic Study of Oxonium in Minerals Lons

American Minerulogist, Volume 59, pages 8II-319, 1974

The SpectroscopicStudy of Oxoniumlons in Minerals

RoN,c,rnW.T. WnrrNsl, ABDULMATEEN2, Departmerutof Geology and Mineralogy, Uniuersity of Queensland, St. Lu:cia,Australiq

eNo Geopn W. WBsr CSIRO Diuision ol Tribophysics,Unioersity ol Melbourne, Parkaille, Australia

Abstract

Nuclear magnetic resonance (Nrvrn) and infrared spectroscopic studies of some mineral species in which the presence of oxonium ions has been pstulated show that it is often difficult to obtain direct evidence of their existence. Clear evidence of oxonium in syntbetic hydrogen uranospinite, ItO(UO"AsOn).3 H,O, was obtained by infrared spectroscopy, It was not possible either to confirm or disprove the existence of oxonium in synthetic members of the alunite-jarosite group by infrared spectroscopy.Although fine structure characteristic of the presence of oxonium was not obtained in Nrvrnspectra of the uranyl arsenatesor alunites, a comparison of 77 K and 298 K spectra for different species revealed a degree of non- vibrational motion in some or all of the protons at room temperature,

Introduction have appeared(Brasseur and Peters,1965; Kubisz, 1968;Mel'nikov and Mel'nik, 1969;Nyrkov, 1968). Oxonium ions have been recorded in a number The presenceof oxonium ions in inorganic com- of minerals including spodumene (Gordienko and pounds is often inferred but rarely demonstrated Kalenchuk, 1966), vermiculite (Bokii and Arkhi- by direct evidence.One such indirect approachhas penko, 1,962), mica (Brown and Norrish, 1952; beenthe demonstrationof isomorphousrelationships White and Burns, 1963), palygorskite (Tarasevich by synthesisof HsO., K*, or NH+. analogues.An and Ovcharenko,1965), amphiboles(Ginzburg and early exampleof this approachis the work of Kraus Yukhevich, 1962), uranophane(Smith, Gruner, and (1935) who was able to infer the presenceof oxo- Lipscomb, 1957), hydrated uranate minerals (So- nium in heteropolyacids on the basisof isomorphism bry, l97l), troegerite (Ross and Evans, 1964, of tungstoboric acid and its ammonium salt. It may 1965), hydrogenautunite (Ross, 1965), jarosite even be possible to show the existenceof a com- (Kubisz,1961; Brophy and Sheridan, 1965), alunite plete solid solution betweenH3O* and K* end mem- (Parker, 1962) and several other mineral phos- bers as in jarosite (Kubisz, 1961). Another indirect phates and arsenates(Tarte and Paques-Ledent, method is the interpretation of chemical analysesof 1968). minerals containing excess water together with a Many more minerals may reasonablybe expected cation deficiency (Brown and Norrish, 1952; Bokii to contain oxonium ions. either as an essentialcon- and Arkhipenko, 1962; White and Burns, 1963). stituent or in partial substitution for another cation Although X-ray structure determination may not (Kubisz, 1968), but it is not alwayseasy to obtain reveal hydrogen atom positions, the presenco of evidence supporting their presence.As a result of oxonium may be suggestedby symmetry considera- recent interest in the problem, severaluseful reviews tions. In this way Johansson(1963) was able to infer the presenc€of oxonium in basic gallium sulfate from the trigonal symmetry of its probable rPresent Address: CSIRO Division of Mineralogy, North Ryde, N.S.W., Australia. site in the crystal structure. Halla and van Tassel 2 Permanent Address: Pakistan Atomic Energy Commis- (1956) have inferred the presenceof H:JO.in the sion, Lahore, Fakistan. jarosite group using a similar argument.

8ll 812 WILKINS. MATEEN. WEST

The direct determination of oxonium involves the originalstructural study on alunite,KAlg(SO+)z obtaining some structural information on hydrogen (OH)u, and jarosite,KFe3(SOa)r(OH)u, showed ' atoms in the crystal. Neutron diftraction, proton that the compound 3Fe2Os' 4SOs 9 HrO was magnetic resonance,and infrared spectroscopyare isostructuralwith jarosite. therefore applicable techniques.The results, how- In the structure of alunite (Wang, Bradley, and ever, are not always unambiguous.Neutr,on diftrac- Steinfink, 1965), the potassiumion is situatedon tion may give clear results on pure oxonium com- a site of D37 slmmetry. It is surrounded by six po,undsbut positional or rotational disorder leads equivalent hydroxyl ions, alternatively 2.335 A to considerablecomplexities in interpretation (Nord- above and trelow the level of the potassiumion. The man, 1962). Proton magneticresonance spectra will K-OH bond distanceis 2.871A. The structureof give evidence of 2-spin or 3-spin systemsonly if the oxonium analogueof neither alunite nor jaro- the systemsare relatively isolated from each other. site has been studiedin detail, but the relatedgal- Infrared spectrashould give unambiguousconfirma- lium salt, 3GazOs' 4SOs' 9 H2O, has been investi- tion of the presenceof oxonium,but absorptionfrom gatedby Johansson(1963). He concludedthat the other co'mponentsin the compound may overlap site occupied by K- in alunite is occupiedby H3O- the regions of critical interest. This problem will be in this compound,despite the close juxtaposition of enlargedupon in the presentpaper. hydroxyl and oxonium ions. The purpose of this study was to examine,with All of the compoundsexamined were synthesized infrared and proton magnetic resonance spectro- fairly readily, thus enhancingtheir value for com- scopictechniques, examples from two mineral groups parative spectroscopicstudy. We will show that in which the circumstantial evidence for the pres- infrared results from hydrogen uranocpinite con- ence of oxonium is particularly clear. The two firm the presenceof oxonium ions, but do not un- groups selected were hydrogen uranospinite FIgO equivocally confirm oxonium in compounds of the (UO2AsO+). 3 HrO, abernathyiteK(UOzAsOa) ' alunite-jarosite group. The resonanceresults give 3 I{2O and related synthetic compounds,and syn- no evidenceof oxonium ions but a usefulcomparison thetic and natural examplesfrom the alunite-jarosite of the special significance of each technique is group. obtained. ' 3 HrO, The crystal structuresof K(UOzAsOn) ExPerimental NH+(UOzAsOn)'3H2O, and K(ftOXUO2AsOa)2' Hydr,ogenuranospinite3 was synthesizedaccording 6 HrO have been described by Ross and Evans method of Mrose (1953). Sodium,potas- (1,964). In these compoundsNHa*, Kt and H3O- to the calcium, and ammonium substitutedproducts play essentiallythe same role (Ross and Evans, sium, obtained by standing small amounts of the 1965). The positionsof the hydrogenatoms are not were hydrogenuranospinite in appropriatechlo' known, but layers which separatethe uranyl ar- synthetic ride solutions of molar concentrationfor a period senate sheets are composed of water molecules of four months. SubsequentX-ray difiraction exami- arranged in what appears to be a tetrahedrally nation showed that the substitution was substan- hydrogen-bonded pattern related to the pseudo- tially completein each case. structureof water (Gurney, 1953). One in four of Alunites and jarosites were prepared in several these moleculesare randomly substitutedby uni- The mostsuccessful results were obtained using valent cations,including oxonium. ways. a combinationof the methodsof Fairchild (1933) The alunite-jarosite group of minerals may be Brophy, Scott, and Snellgrove (1962). A representedby the formula,,4-R3-3(SO4)r(OH)uand ratio of 1:3 for K:Fe or Al in a O.2NFIzSOn where A' is usually NIfa*, K* or Na* and R3* is molar was heatedin sealedpyrex glasstubes at FeS*or A13..On the basisof solid solutionstudies, solution temperaturesbetween 110'C and 160'C for periods a deficiencyin the univalent cation content coupled g to 10 days.The productswere washedseveral with an analyticalexcess of water has generallybeen of interpreted to be due to replacementof l* cations by H3O. (Shishkin, 1951; Kubisz, 1964; Brophy " It seems probable that at least two distinct hydrous and Sheridan, 1965). The substitution may be uranyl arsenates occur as minerals (Shchipanova el al, complete, and several oxonium compoundsin this 1971). Until the position becomesclearer, we prefer not to group have been synthesized.Hendricks (1937) in use the name troegerite for our synthetic material. OXONIAM 1ON^' IN MINERALS 813

times with 0.2N HsSOa, then with distilled water and dried at 60'C. The supposedoxonium analogues formed when the syntheseswere repeated without H potassiumin the solution. 10gouss Proton magnetic resonance spectra were taken with a spectrometerwhich consistedof a marginal oscillator and a 12 in. electromagnetset at about 1650 gauss.The absoqptionline was obtained di_ rectly by continuous averagingtechniques using a Poe-S computer.All specimenswere examinedas ..OXONIUM'' powders at 77 K and 295 K. ALUNITE fnfrared spectrawere obtainedwith materialsdis- persed in very thin disks prepared frorn freshly dried KBr. Blank disks showedno appreciablewater absorption.Considerable care was taken with sam- ple preparation of the uranium compoundsbecause spectra are easily modified by excessivegrinding. Specimenslightly ground in an agate POTASSIUMALUN ITE mortar for no NOTTO SCALE rnore than a few secondsgave the most satisfactory spectra. Examination of each supposed oxonium compoundin nujol and in hexachlorobutadienepro- 0'05g vided no evidenceo,f exchange between H3Or and K- in the KBr discs.

Results HYDROGENURANOSPINITE

Nuclear Magnetic Resonance Spectra The lines obtained from the four samples at 295 K and 77 K are shown in Figure 1. The weight of the specimen was the same in each case and the lines are plotted on the same scale with the exception of ABERNATHYITE those from the two arsenate specimens at room temperature. The widths of the lines at half peak Ftc. 1. Proton magnetic resonance spectra of alunites and height are indicated. hydrous uranyl arsenatesat 77 K (left) and 298 K (right). The lines from hydrogen uranospinite and abernathyite at 77 K have the same width, height, and resonance in hydrated gallium sulfate (Kydon, integrated intensity. The second moment of each Pintar, and Petch, 1968) so that the assumption line is 24.5 (gauss)r. There is a significant difference that the state of water of hydration in the, two between these lines and the lines obtained at room systemsis similar is not justified. temperature. In this case the width of the line from Resonanceline-shapes in polycrystallinematerials abernathyite is about 1 gauss and that from hydrogen for systemsof two, three, and four identical nuclei uranospinite less than 0.05 gauss. are discussedby Andrew (1955). So-calledtwo- The lines from the two alunite specimens at 77 K spin systems such as II2O give rise to a double have the same shape and a second moment of 14.5 peaked resonanceline, and three-spinsystems such (gauss)'9but the peak height 4nd intensity for the as HrO* give rise to a triple peakedline. Crystalline oxonium specimen are about twice those from the nitric acid monohydrateand perchloric acid mono- potassium specimen. At room temperature both lines hydrate (Richardsand Smith, 1951; Kakiuchi et al, consist mainly of broad lines similar in shape to 1951) give rise to theoreticallypredicted triple- those observed at 77 K, but there is a narrower line peaked curyes showing that hydrogen is present in superimposed on each. The lines from these two these compoundsas HsOr ions. They are assumed alunite specimens are quite different from proton to be model oxonium compounds. 814 WILKINS, MATEEN, WEST -that It might be anticipated since both uranyl arsenates,but an Nun study on syntheticautunites, arsenatescontain structural water molecules, the the related uranyl phosphates (Sugitani, 1'971), differencesbetween their spectra would be due to shows that what is termed random motion of the -60oC. the oxonium ion contribution in hydrogen urano- moleculesceases completely at about spinite. The alunitesmake a similar pair with struc- The intensity measurementsat 77 K for the alu- tural hydroxyl ions in both materials and oxonium nites indicate that there are about twice as many in the analoguecompound. It is clear that the line protons in the oxonium compound as in the potas- shapesat 77 k are the samefor each pair and give sium compound whereasthe expectedratio is about no positive identification of oxonium ions in either 1.5. At room temperaturemost of the protons are uranyl arsenatesor alunites. An absence of fine in a situation similar to the low temperaturecondi- structure, however, does not necessarilyimply the tions, but some are associatedwith some form of absence of two- or three-spin systems since fine movement. The most likely interpretation is that structure will only be observed with a relatively the broader lines are associatedwith hydroxyl pro' simple unit cell, and when line-broadening inter- tons which are fixed in the crystal structure at room molecular effectsare small. The sheet arrangements temperatureand below, and the narrow line is from of water moleculesand oxonium ions, if present in protons in water moleculeswhich can rotate. the uranyl arsenates,and the juxtaposition of hy- Inlrared Spectra droxyls and oxonium, if presentin the alunites,could result in loss of fine structure in the resonance Vibrational Modes ol HzO and HsO'' Attempts spectra. to confirm the presenceof oxonium frequently re- The intensity measurementsat 77 K indicate that solve themselvesinto the question of whether water the uranyl arsenateshave a similar number of pre molecules,oxonium ions, or both are presentin the tons, but this is not co'nsistentwith the accepted compound being investigated. The oxonium ion, chemical formulae. The large value of the second H3O*, is isoelectronicwith NHB and the symmetry moment indicates that the protons are fixed in the of the free ion is Cg,. All four distinguishablenormal structure(Andrew, 1955). The main contributionto modes of vibration are infrared and Raman active. the line width at this temperatureis the intramolecu- By contrast, the water molecule has symmetry Ce, lar interaction within a water molecule with much with three normal modes of vibration, all infrared smaller contributionsfrom intermolecularinteraction and Raman active. Recorded frequenciesfrom the between different molecules.Sharpening of lines at rnost recent infrared observations on solid acid room temperatureimplies considerablemovement of monohydratesand solutions of the same acids are the water moleculesin both arsenates.The spectra summarizedin Table 1. indicate that eachmolecule in the abernathyitewater The most conspicuous differences between the sheetshas rotati,ronalmotion, which eliminates the spectra of the two speciesare that the stretching intramolecular effect. The even sharper line from frequencies (or,us) of the oxonium ion are lower, hydrogen uranospinite suggeststhat there is some the bending frequency (r+) of HeO. tends to be additional diffusional movement of each molecule higher than vs of water, though not invariably, and which eliminatesthe intermoleculareffect. The tem- v2of H3O* is unique.In a reviewof more than 450 perature at which water moleculesgo into rotational crystalhydrates Yukhnevich (1963) found that the motion has not been determined for the uranyl bending vibration, vs, of water occurs in the range 1590-1670 cm-', whereosra of H3O. in acid hy- and aqueous acid solutions occurs in the Trsr-e 1. Vibrational Frequencies of HgO* and ItO from drates Recent Infrared Observations range 1670-1750cm-l. However,in very rare cases frequencieshave been recorded outside the'selimits. CoDpouil state Hso- State Hzo We may anticipate,therefore, that even in the pres- !r(Ar) v2(Ar) vr(E) vr(E) Vl VZ V! ence of water molecules,oxonium ions will usually OHrClor* s 2820 IO2O 3220 1670 s(-78"c) 3400 1620 3220 show a distinguishableinfrared Electrum' 0ll3N0!** s 2780 1135 27aO 1680 The Ol{:l{SOt** s 2A40 1160 2840 t620 Abernathyite and Hydrogen Uranospinite.

2900 1205 2900 1750 1(250 C) 3400 1640 3400 tetrahedrally hydrogen-bondedarrangement of wa- solutlons in the model structuresof abernathyite *Fomier et aL.' 1969. ter molecules *rsavoi-e @d cigrere, 1.984. uranospinite,with random substitution ***FaLk ma cigwre, 1957. and hydrogen OXONIUM /ONS IN MINERALS 815

of oxonium ions for one in four water molecules Tlsre 2. Band Frequencies and Assignments for Hydrogen in the latter mineral, suggeststhat the infrared spec- Uranospinite and Abernathyite trum should be closely related to the spectra of oxoniumhalides in aqueoussolution (Fabbri, 1959; HaO (UOzAsOr).3HzO K (U0zAsOt).3Ha0 Asslgnnent -l -) -l -) Ferriso and Hornig, 1955). v (cn v (cm That this is indeed the case is shown in Figure 2 ^, 3400 tu 3500 Hz0 (vt,vr) where spectra of abernathyiteand hydrogen urano- tu 3400 Hro+ 1v1,u31 spinite are comparedwith liquid HzO and aqueous ^, 2300 H2O (v2 * vo) HCI spectra. Analysis of the synthetic abernathyite t7 40 Hg0 (vr) for potassium gave 6.91 percent K2O, which indi- 1635 r645 HeO (vz) cates a formula (IG.seI{gOuos)UO2AsO+. 3 HrO. t 150 uro* (u.) The differencesbetween 2+ the spectraof the two solids 950 953 UOz (vg) should be due mainly to presence the of II3O. in 9r8 900 U02 (v! ?) hydrogen uranospinite. 3- Bands below 1000 cm-l, 815 8r8 AsOq (v3) most of which occur in uranyl and in arsenatespec- 610 590 Hzo (vn) tra, can (JO2*e be assigredas or AsOs-aabsorptions 486 497 Aso"3- (v.) (Table 3- 2). An exception is the broad band in the 386 372 AsOq (vr) vicinity of 60O cm-', which, by reason of its shape and position, is likely to originate in the librational motion of I{zO (ya). why intensity is maintained in the O-H stretching Although absorptionin the O-H stretchingregion reglon during the initial stagesof water loss. remains quite intense,the identified oxonium vibra- Alunite and larosite. It is generally agreedthat tional bands are observed to disappear when the oxonium ions may substitute for potassium in the material is heatedat 350'C for one hour. Weight alunite and jarosite structures. Potassium occupies loss curves show that water loss occurs soon after a site of D3a symmetry. Degeneratevibrations of a the commencementof heating,suggesting that water C3, ion (HrO.) are not resolved in a crystal field content is not fixed at exactly three moleculesper of this symmetry. The usual four vibrations of this formula unit at ambient temperatures.Decomposi- ion should therefore still be observed,but v2,which tion of oxonium may occur accordingto the reaction coincides with the intense v3 atxorption of the sul- HBO. + 02- : HzO + OH-. This would explain fate ion, will be obscured. There is also overlap between the regions of stretching vibrations of hydroxyl ions and those of oxotdum ions. The fine structure visible in the 3000-3600 cm-l region of lx2otv2l jarosite and alunite (Figs. 3, 4), is probably due to

1".oti,.t trotv.tlx2otu2) 1

nrotrllxaotu.t lsro(uz)

Hzo

cn-! 3OOO 20@ lm EOO l40O l2m mC &O 6@ 4@

Fto. 2. Infrared spectra of compounds containing ILO. or H,O. (a) (trG"JI,Oo*)UO,AsO+.3H"O synthetic; (b) Fta. 3. Infrared spectra of synthetic and natural alunites. (H'O)UO,AsOn.3ILO synthetic; (c) aqueous HCI; (d) (a) (IIaO)AI"(SO.),(OH)" synthetic; (b) (lG *H"Oo.') water. Both (c) and (d) redrawn from data in Fabbri Al'(SO.),(OH)e synthetic; (c) natural alunite, Muzay, (re59). Hungary. 816 WILKINS, MATEEN, WEST

there is a correlation betweenthe degreeof potassium deficiency and intensity of absorption. It will be observedthat the 18 molar percent of oxonium impurity in the potassiumcompound has contributed intensityto the low frequencytail of the 1640 cm-l band. The spectra must either be interpreted as resultingfrom two different water moleculeenviron- ments or the minor absorptionsflanking the 1640 cm-1 band are due to the presenceof oxonium ions. Discussion The interpretationof our data on abernathyite and hydrogen uranospiniteis fairly straightforward. and natural jarosites' Frc. 4. Infrared spectra of synthetic between infrared spectra of (a) (H*O)Fes,'(SOn),(OH)usynthetic; (b) (K",,H"Oo'") The close similarities Fe3."(SO,),(OH). synthetic; (c) natural jarosite, Mt. Mor- hydrogen uranospinite and aqueoussolutions con- gan, Queensland,Australia. taining oxonium ions confirm the existenceof oxonium in an environment related to that of liquid coupling of the motions of adjacent hydroxyl ions. water. Nun spectra neither confirm nor disprove Variation in the sharpnessof the main absorption the existence of oxonium in this compound, but peak, and in the intensity of the low frequencytail, show the presenceof much proton mobility in the was observed in samples synthesizedat different interlayer at room temperatures.Our spectroscopic temperatures.Despite repeatedattempts to prove data are therefore consistent with the structural the presenceof an absorptionband (H.gO'rrv.q)in model of the interlayer proposed by Ross and the 2800-3000cm-1 region in the supposedoxonium Evans (1965). alunite (by comparing its spectrumwith the spectra The experimentalevidence on alunites and jaro- of synthetic potassiumalunites), it remained un- sites is much more difficult to interpret. Since the certain whether a distinct absorption due to HsO- characteristicr2 absorption of HsO. overlaps with existed.This leavesthe 1600-1700 cm-1region as v3 of the sulphateion, the infrared spectral analysis one of critical interest, since in these compounds dependson the proper interpretation of minor fea- only HaO- should absorb in this range. tures in the 1500-1700 cm-' region. The absorption The infrared spectraof both potassiumand oxo- at about L640 cm-', which occurs in the spectraof nium jarositesand alunites,however, show absorp most normal and oxonium alunites and jarosites tion at about 1640 cm-'. In addition,the FI3O*,Na*, and has no correlation with potassium deficiency, K*, Rb*, NH+* and Tl basic gallium salts of the can only be due to structural water molecules.The alunite type figured by Petrov, Pervykh, and Bol'- anomalous amount of water usually contained in shakova (1966) all absorbin this region. Several synthetic alunites and jarositeshas been the subject natural alunitesand jarosites,varying from opaque of comment (Parker, 1962; Brophy and Sheridan, to optically clear, all showed some absorption in 1965). The removal of this water by heating re- this region, even after drying at 160'C before the sults in substantial changesin cell dimensions.It spectrawere taken. must therefore be structurally combined, not ad- Since extinction coefficients for some oxonium sorbed or included water. The existenceof a tri- absorptionsare small (Tarte and Paques-Ledent, valent cation deficiency,tending toward the compo- 1968), it is necessaryto considerthe origin of other- sition KR3'2( SOn) B( OH ) r ( HrO ) * would explain this wise minor spectral features. It seemsmost likely excesswater content. A trivalent cation deficiency that weak bands at about 1400-1450 cm-' and is a feature of synthetic alunite analyses (Parker, 2OAO-240Ocm*1 are respectivelydue to carbonate 1962), and there is one analysis on record (by impurities and to overtones of sulfate stretching Parker in Brophy et al, 1962, Table 1) which vibrations.Associated with the prominent1540 cm-' shows a marked excessof water and deficiencyof band is anotherminor feature at l7?O cm-l in the aluminum that may representa substantialamount alunitesand 1575 cm-l in the jarosites.The latter of this substitution. band in particularcannot be easilydismissed, since The only infrared band which appearsto correlate OXONIUM IONS IN MINERALS 8t7 in intensity with the degreeof potassiumdeficiency component is present in both potassium and oxo- is the 1575 cm-' absorption in the jarosites. This nium alunite spectra,it seemsmost likely to be due band is outside the normal range of oxonium vr to rotational motion of some of the excesswater frequencies but there are some other well substan- molecules in the structure, depending on the type tiated (Paques-Ledent cases and Tarte, 1969) of substitution involved. The discrepancybetween where this is known to occur. Alternatively, this theoretical and observed relative intensities must band could result from the bending vibration of also be related to additional water substituted in water molecules situated within the site occupied these structures. by potassium in normal jarosites. Conclusion Due to strong intermolecularinteractions resulting from the relative structural complexity of common minerals which may contain oxonium, it is unlikely that nuclear magnetic resonancespectra will often change of some 12 orders of magnitude would be show fine structure characteristicof oxonium ions, necessary for both H3O. and OH- to exist in appre_ even if they should in fact exist in these materials. ciable concentration at equilibrium. This problem may be overcometo some extent by Perhaps for this reason,Hendricks (1937) pro. the use of single crystals. The exceptionsto these posed .Fe'ia(SOr)r the structural formula HzO observationsare where oxonium ions, perhaps in (OH)u .tIeO . . for the compound 3FezOa 4SO3 substitutionfor large univalent cations, are in struc- 9 HrO which has the jarosite structure. He believed tural isolation from other proton-containingspecies. the potassium sites in the jarosite structure to be On the other hand, nuclear magneticresonance gives occupied by water molecules with charge balance a powerful indication of the degree of mobility of maintained by the coupled substitution of water the protons, information which is difficult to obtain moleculesfor one in six hydroxyl ions. Subsquently in other ways. rnost authors have inclined to the opinion that F[O- Similarly, application of infrared spectroscopyto in the potassium site and OH- can exist in these the determination of oxonium is limited by the juxtaposition. compoundsin chemistry of the compound. From the exampleswe It is important to recognizethat wherever oxo- have studied,it is possibleto anticipateareas where nium and hydroxyl ions are supposedto coexist in infrared analysiswill be most fruitfully applied. The a mineral structure, indirect methods cannot distin- only oxonium frequency which cannot be confused guish whether the protons are arrangedinto groups with those deriving from water molecule vibrations of one and three (OH-, HrO-) or only groups of is vz at about 1150 cm-1. The absorptionband (HzO). two Indeed,if the protons are mobile, the correspondingto this frequencyis commonly broad exchangeHsO- + OH- = HzO + H:O may occur and weak. This frequencycorresponds, in part, with continuously and, if the period of existenceof the that of the intense asymmetricstretching vibration, ion or molecule is greater than the vibrational fre- 13,of some common tetrahedralanions such as sul- quency,it will be recordedin the infrared spectrum. fate, phosphate,and silicate and possibly with vi- In addition, the possible existence in these com- brations of other anions. In these materials. unless pounds of higher hydrates of H. such as HrOn. it is possibleto prove the presenceof a hydrogenic (Gilbert and Sheppad, 1973) cannot be entirely absorption in this reglon by deuterium substitution, overlooked although it does add further complexity attention must be concentratedon the 1500-1700 to the interpretation of the spectra.It would there- cm-l region in which the bending vibration of tIpO fore seem to be impmsible with the data at hand also occurs. This may lead to insuperabledifficul- to come to any firm conclusion. ties of interpretation, especiallyif water molecules The Ntun spectra do not provide evidence of are present as impurity, or if hydroxyl and oxonium oxonium ions in any of the compoundsstudied. It exist together in the same structure. Materials con- is possibleto distinguish,however, between protons taining only anions of heavy elements,such as ar- which are essentiallyin fixed positionsin the crystal senate, however, which have their highest funda- structure and those which are involved in some sort mental frequency vibration below 1000 cm-1, make of rotational or diffusional motion. Since the latter ideal subjectsfor infrared examination.Our investi- 818 WILKINS, MATEEN, WEST

in HCIO. gationsalso suggestthat mineralswith oxonium ions (1951) Proton magnetic resonance absorption and the structure of oxonium ion. I' Chem' in interlayer water molecule sheets are especially monohydrate 19, 1069. absorptions Phys. favorable for study, provided anion Kn-Lus, O. (1935) The crystal lattices of heteropoly acids allow observationof the 1100-1200 cm-r region. and their salts. I. The lattice of silicotungstic acid, borotungstic acid and ammonium borotungstate' Z' Kris- Acknowledgments tallogr. 9\ 4A2409. Kusrsz, J. (1961) Natural hydronium jarosites'Bull' Acad' pleased acknowledge the help of G. Hladky' We are to Polon. Sci., Ser. Sci. Chim. Geol. Geogr' 9, 195-2OO' provided assistancein many S. Bagley, and J. Milne, who (1964) Studium mineral6w grupy alunitu-jarosytu' benefited from a critical review by ways. The manuscript Prace Geologiczne, 22. J. C. Ward. (1958) The role of poeitive hydrogen-oxygen ions in minerals. Polska. Akad. Nauk. Prace Mineral' ll, References l-7 5. E. Psrcrr (1968) Nun ANDREw, E. R. (1955) Nuclear Magnetic Resonance' Cam- Kvoox, D. W., M. PINTAR,lNp H. gallium I' Chem' Phys' bridge University Press. evidence of H"O* ions in sulphate. Busseun, H., eNo L M. Prrpns (1965) Oxonium in cer- 4E,5348-5351. (1969) Oxonium tain uraniferous compounds' Z. Ktistollogr, 1221 469472' Mer'Nxov, V. S., eNo Yu. M. MEL'NIK (Luou), 23, 235-250' Borrr, G. B., lxo D. K. AnrcrrpeNro (1962) Oxonium in mineralogy. Mineral. Sb. minerals (XIII): ions in vermiculite. l. Structural Chem. 3, 67o-574' Mnose, M. E. (1953) Studiesof uranium 3E' 1159-1168' Bnoenv, G. P., E. S. Scorr, eNp R. A' SNBrrcnovB (1952) Synthetic uranospinites.Am. Mineral' of hydronium Solid solution between alunite and jarosite. Am- Mineral' NonoulN, C. E. (1962) The crystal structure -80'C. 15, 1U23' 47, rt2-t26. perchlorate at Acta Crystatlogr. problem in mineralogy' -, eNo M. F. SneRroeN (1965) Sulphate studies IV: NyRKov, A. A. (1968) Hydronium The jarosite-natrojarosite-hydronium jarosite solid solu- Mineral. Sb. &ttoo), 22,205-208. (1969) Spectre infra- tion series.Am. Mineral.50' 1595-1607. Peeuss-Leopxr, M., AND P. Tenre et GaAsO" BnowN, G., lxo K. NoRRIsH(1952) Hydrous micas. Mrn- rouge et structure des compos6s GaPO.'2HO eral. Mag.29,929-932. 2H"O. Spectrochim. Acta, A25, lll5-1125. in natural Flrrnr, G. (1959) Spettri ultrarossi di soluzioni acquose PARKER,R. L. (1962) Isomorphous substitution di acido cloridrico. Atti Accad. Nazl' Lincei, Rend', and synthetic alunite. Am. Mineral. 47' 127-136' N. Bor'srurove ClasseSci. Fis. Mat. Nat.26,671-678' Pnrnov, K. I., V. G. Penwxn, eNo K' basic gallium salts Fernorrro, I. G. (1933) Artificial jarosites-the separation (1966) Infrared absorption spectra of 11,742-745' of potassium from cesium. Am' Mineral lE' 543-547' of the alunite typ€. Rrrrs. l. Inorg. Chem. (1951) Nuclear mag- Ferx, M., rxp P. A. Grcusnne (1957) Infrared spectrum Rrcuenos, R. E., lxo J. A. S. Srvrlrn hydrates. Trans' of the HaO* ion in aqueous solutions. Can. I. Chem, 35, netic resonance spectra of some acid lt95-1204. Faraday Soc. 41, 126l-1274. as model com- FERRrso, C. C., eNo D. F. HonNIc (1955) The infrared Ross, M. (1965) The torbernite minerals Clay Min' spectra of oxonium halides and the structure of the ox- pounds for the hydrous layer silicates. Clays onium ion. I. Chem. Phys.23,1464-1468. erals, 20, 65. torbernite FounNIen, M., G. Mescnrnre, D. Rousserpt, eNo J. Po- exo H. T. EvlNs (1964) Studies of the and (1969) of oxonium ion vibrational minerals (I): The crystal structure of abernathyite rrBn Assignment '3H'O frequencies. C. R. Acad. Sci. Ser. C, 269,279-282 (Ft)' the structurally related compounds NH.(UO"AsO+) Mineral' 49, 1578- Grraenr, A. S., eNo N. Snepperp (1973) Infrared spectra and K(H"O)(UO,AsO.),'6H,O' Am' of the hydrates of hydrogen chloride and hydrogen 1602. - torbernite min- bromide. ,1. Chem. Soc. Faraday Trans. 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Sornv, R. (1971) Water and interlayer oxonium in hy- WANG,R., W. F. Bneorny, ANDH. SrBrNnrNr (1965) The drated uranates. Am. Mineral. 56. 1065-1076. crystal structure of alunite. Acta Crystallogr. lE,249'252. SucrreNr, Y. (1971) Nun study of water of crystallization Wnrrt, J. L., eNo A. F. BunNs (1963) Infrared spectraof pap. in minerals. Mineral. Soc. Iapan, Spec. l, 2.10. hydronium ion in micaceous minerals. Science, 141, 800- Tene,snvrcH,Yu. I., lNo F. D. OvcnenrNKo (1965) Ther- 801. mal dehydration of palygorskite as investigatedwith the Yurnxnvrcn, G. V. (1963) Advancesin the use of infrared aid of infrared spectroscopy. Dokl. Akad. Nazrt. S^S^SR, spectroscopy for the characterization of OH bonds. Rass. 16l, 1138-ll4l (in Russian). Chem. Rea.32,619-633. Tenrr, P., eNn M. TH. Pequns-LrorNr (196g) Spectre infrarouge et prdsence probable de I'ion hydroxonium dans des compos6s du type XPO4.2H"O et XAsO,,.2HO. Manuscript receiued, December 3, 1973; accepted Bull. Soc. Chim. Fr. (Spec. No.), llSO-1756. for publication, March 7, 1974.