AmericanMineralogist, Volume63, pages520-527, 1978

rhecrvstar structure *l',l;ff ca2HPO4so 4'4H2o', "t ;:[ll# ?ltrl:f,i:ilHff ,[*ate,

TosurnoSnrnn Depafiment of Oral Histology Nihon Uniuersity Matsudo School of Dentistry Mqtsudo, Chiba, Japan

Hrnossr Necntr

Geological and M ineralogical Institute Faculty of Science, Tokyo Uniuersity of Education Otsuka, Bunkyo, Tokyo, Japan

exo Tosuro Suoo Miyasaka3-20-7 Setagayo,Tokyo, Japan

Abstract

The syntheticcalcium phosphate-sulfate hydrate, CarHPOnSOr.4HrO, is monoclinic,space group Cc, a = 5.721(5),b : 30.992(5),c : 6.250(4)A,and B : 117.26(6)',Z : 4. The structurehas been determinedby the Pattersonmethod and refined by full-matrix least- squaresmethod to a conventionalR : 0.068,using 268 independent reflections. The structure possessesfour sheet-structureunits parallel to (010),in whichCa atomsare coordinated by six oxygenatoms belonging to (P,S)O.tetrahedra and two watermolecules at the surfaceof the sheet.Each sheetunit is analogousto thoseof brushiteand gypsum,but thereis a different mode of sheetstacking from thosein brushiteand gypsum.The mean 7-O bond lengths, I .50A at ?'(I ) siteand I .49A at T(2) site,are close to an averagedistance of P-O ( 1.54A)and S-O ( 1.46A)bond lengths. The distributionof P and S atomsin T sitesseems to berandom.

Introduction that X-ray powder diffraction patternsof ardealite, Ardealite, CarHPOnSOl.4HzO,is a rare phos- brushite,and gypsumare considerably different from phate-sulfate mineral first describedby Schadler eachother. Ferraris(1969) insisted that brushiteand (1932) from Cioclovina cave, Transylvania. This gypsum are not in a strict isostructuralrelation be- original material is found in closeassociation with causeof the different spacegroups: /a for brushite gypsum, CaSOn.2H2O,and brushite, CaHPOn. and I2/a for gypsum. Recent X-ray and neutron- 2H2O.Recently, one of the authors(T. Sakae)found diffractionanalyses have revealed that the configura- ardealite from the Onino-Iwaya limestonecave at tion of watermolecules in brushite(Curry andJones, Hiroshima Prefecture,Japan (in preparation). 1971)is quite differentfrom that of gypsum (Cole Beevers(1958) and Hill and Hendricks(1936) and Lancucki, 1974).The crystal-chemicalrelation pointedout that, becauseof a closesimilarity in their amongardealite, brushite, and gypsumis a matterfor chemical compositions,ardealite may belong to a further research. solid solution betweenbrushite and gypsum.In the The study of the crystal structureof ardealiteis crystalstructures of brushite(Jones and Smith, 1962) significantand interesting.It was difficult, however, and gypsumlAtoji and Rundle,1958), the corrugat- to obtain a singlecrystal of ardealitefor structural ing sheetsstack along the b axis.O'Daniel (1939) and determination.Single crystals obtained from syn- Baynham and Raistrick (1960), however,reported thetic materialhave been used in this structuredeter- 0003-0Mx / 78 / 0506-0520s02.00 5201 SAKAE ET AL.: CALCIUM PHOSPHATE-SULFATE HYDRATE 521 mination.These synthetic crystals almost agreewith hkl with h + k : 2n -r I and 0k0 with /c : 2n -r I tead natural ardealite in various properties, but are to the spacegroup of Cc or C2/c. The occurrenceof slightlydifferent from ardealitein their X-ray powder 0k0 reflectionswith k : 4n only (040,080,0120, etc.) patterns. suggestthat the periodicityalong the D axisoccurs at four times the elementaryunit, as describedlater. Experimental Latticeparameters are determined and refinedto a : 5.721(5),b : 30.992(5), 6.250(4)A,p Material 117.26(6)"by least-squaresmethod, using 16 reflec- Ca(OH)2, NarHPOn.l2H2O,and NarSOnwere tions measuredon a Phillipsfour-circle diffractome- usedas startingmaterials. Each of thesewere made ter (graphite-monochromatizedMoKo- radiation). up in water solutionswith the samemole concentra- For intensitymeasurement the o-?i scanningtech- tions.These solutions were mixed with eachother in nique wasemployed (0.05' per secondin <.r).Scan- the moleratio of Ca/(P + S) : l. The pH valuesof ning width wasdefined as a I b(tan|)where a = 1.5 the mixed solutionswere controlled by addingdilute andb : 0.5.The crystalwas so smallthat 400 reflec- hydrochloricacid. Varyingthe conditionsfrom pH 2 tionsto sin|/\: 0.7 werecollected with monochro- to 5; P/S, 0/10 to l0l0; mole conc.,0.25 to 0.5; matized Mo.l(a radiation. Finally, 268 independent temperatures,OoC to 50"C, three-componentmix- reflectionsof lf.l greaterthan 4loF,l wereused for turesof brushite,ardealite-like material, and gypsum the followingstructure determination. The data were were not found in precipitatesalthough two-com- correctedfor Lorentzpolarization factors, but not for ponent mixtures were found. In the seriesof syn- absorPtion(p : 15.35cm-'). thesesat pH 4, precipitatesare brushiteplus ardeal- ite-like material(P/S : 6/4), ardealite-likematerial Structureanalysis plus gypsum(P/S : 5/5), andgypsum (P/S : 4/6), The lattice parametersof the presentcrystal are as revealedby X-ray powder diffraction analysis.A similar to those of gypsum and brushite(Table I ), crystallineprecipitate from a solutionwith P/S : 9/1 exceptthe b dimension,which is nearlyequal to the and pH : 3, after standingfor 43 daysat 20oC, sum of the b dimensionsof gypsumand brushite. consistedof the ardealite-likematerial free from One-dimensionalPatterson synthesis along the 6 axis brushite and gypsum, as revealedby X-rays. This shows a similar pattern to those of gypsum and crystallineprecipitate was used for the presentstudy. brushite, but with a repeat of one-fourth of the b Chemicalcomposition of the productis asfollows: dimension.The resultslead to an assumptionthat the CaO,32.5; P2Ou,20.9; SOs, 23,2; ignition loss (below crystalhas also a sheetstructure, in which eachsheet 600oC), 22.9; total, 99.5 (weight percent). Several stacksalong the b axiswith a four-fold periodicityin crystalsin the product were analyzedsemi- contrast to a two-fold periodicity in gypsum and quantitativelyby the point-analysismethod employ- brushite. ing HnecHr-Krvrx Snna.Each of them had the mole The spacegroup is Cc in brushite(Ia by Jonesand ratio of Ca:P:S : 2:l:1. Althoughthe chemical Smith, 1962)and C2 / c in gypsum(12 I a by Atoji and compositionsof the crystalsare uniform, Weissen- Rundle,1958), and Cc or C2/c in the presentcrystal. berg photographsof the crystalsshow some differ- Ifthe structureis a sheetstructure analogous to those ences.Throughout the photographsthe cell dimen- of gypsum and brushite,a possiblespace group for sionsare the samebut the extinctionsare different. the crystalis Cc rather than C2/c, becausethe sym- Among them a crystalshowing the extinctionsset out metry of the structuremay be reducedon accountof belowwas usedfor the datacollection. Crystals with the presenceof H atoms,as in the caseof brushite. other extinctionsare alsobeing studied. Further, the Thus the spacegroup Cc was examinedin the first single crystal was analyzedby the point analysis stepof the crystalstructure analysisl. method,which confirmed that it hadthe moleratio of A structuremodel having the spacegroup Cc may Ca: P: S = 2: I : l. Thechemical formula was therefore be constructedin the followingtwo ways:(l) one- assumedto be CarHPO4SOo.4HrO. sheetstructure unit is locatedbetween n and c glide Data collection 1 The crystalis a triangularplate (fragment) For the sake of the comparison of lattice parameters between approx- the present crystal, brushite, and gypsum, Cc lattice was selected. imately0.015 mm thick,0.06mm alongthea axisand When Ia lattice for the present crystal is selected, the lattice param- 0.09mm along the c axis.The systematicextinctions eters are a : 6.248, c : 6.250A,and B : 125.52. 522 SAKAE ET AL.: CALCIUM PHOSPHATE-SULFATE HYDRATE

Table l. Crystallographicdata for CazHPOrSOn.4HrO,brushite, and gypsum

CaTHPOOSO Brush i te Gypsum 4.4HZO Beevers (1958) Cole + Lancucki This study Jones + snith (1962) (re74)

5.727(s)x A 5.81210.002 A 5.670r0. 002 A b 50.992(s 15. 180r0.003 15.201t0.002 c 6.2s0 (4 6.239!0.002 6. 533r0.002 R 1L7.26"(6 1t6.42"r0.03 118.60"t0.07

Cel1 volune 985.1(9) A' 493 A' 494.4 A" Chemical forrnula CazHP04SO4.4H2O CaHPOq .2HzO CaSOo.2HzO Ce11 content 4 4 Space group Cc fa I2/a *Estimated standard deuiations are giuen in paz,entheses and nefet, to the Last decimal place. planes, and the mode of sheet stacking is controlled least-squaresmethod using UNtcs program (Sakurai, by these symmetry operations; and (2) two-sheet 1967,after Onrr-s written by Businget al., 1962).The structure units are located on z and c glide planes neutralatomic scattering factors (International Tables respectively;in this casethe mode of sheetstacking is for X-ray Crystallography,1962) were usedfor Ca, P, not affected by the symmetry operations. In the S, and O atoms.Isotropic thermal factors were set at former, a strong peak should occur at (0,50,0), Ca, 1.4;P andS, 1.0;O, 2.0;HrO,2.5.Inthe succes- coordinates multiplied by 100, in three-dimensional sive refinements,an averagedfactor of P and S was Patterson synthesis, but such a peak could not be usedfor the atomsat the Z sites. observed.A strong peak at (8,17,16) may indicate The positional parameterswere divided into sev- that the positionsof Ca, P, or S atoms in the adjacent eralgroups, becatise the number of variableswere too sheetshave shifted to a and c directions. Such a shift many comparedwith the numberof reflections.Each cannot be expectedin the former but favors the latter. group of positionalparameters was refined separately At this stage of the three-dimensional Patterson syn- and resultedin a reductionof R to 0.070(wR,0.077). thesis,the structure model basedon the spacegroup A further cycleof refinementof all positionalparam- C2lc was considered unlikely, becausethere were no etersexcept for Ca(l ) reducedR to 0.069(wR, 0.077), 2-fold axis symmetry peaks of (8,17,16)and no re- and the refinementof isotropic temperaturefactors lated peaks on the Harker sectionat b/2. reducedR to 0.068(wR, 0.077).Refinement with Note that in brushite and gypsum the sheet struc- anisotropictemperature factors was not attempted, ture units are located on the c glide plane, but those becauseof the prohibitive number of least-squares in the second proposed model for the present crystal variablesnecessary for sucha model.At thelast stage are located both on the c and n glide planes.The sheet of refinements,Fourier differencesynthesis showed structure unit analogous to those of gypsum and no peak excepta ripple near the Z(1) site, which brushite can be located both on c and n glide planes seemedto be causedby the paucity of the data set. in the present cell, becauseof the similar cell dimen- The final positionalparameters and isotropictem- sions (Fig. I ). perature factors are shown in Table 2, along with The mode of sheet stacking is not defined for the their estimatedstandard deviations. The observed secondproposed model, but Ca or (P,S) atoms in the and calculatedF valuesare given in Table3, and the adjacent sheets may shift in accordance with the interatomicdistances and anglesin Table4. (8,17,16)vector componentsfound in the Patterson of the crystal structure map. Through several trials concerning this shift, a Discussionand description structure reduced the conventional R rapidly to The crystalstructure is shownin Figure2(3), where 0.178,whereas the other models hardly reducedR to a unit cell is projectedalong the c axisand compared less than 0.26 by a diagonal least-squaresmethod. with the crystal structuresof gypsum and brushite The positional parameterswere refined by full-matrix [Fig. 2(l) and2(2)]. The sheetson the c glideplanes SAKAE ET AL; CALCIUM PHOSPHATE-SULFATE HYDRATE s23 are similar to each other. The sheeton the n glide plane in the presentstructure was assumedto be identicalto that on the c glide plarie,and the refined structure does not differ significantlyfrom the as- sumedone (Fig. l). The main differenceamong the threecrystal structures is in the modeof sheetstack- c ings.In the crystalstructures ofgypsum and brushitp, 6.2sOA the mode of sheetstackings is controlled by the a glidesymmetry, but in the present crystalstructure it (1) is not definedby such a symmetryoperation. This differencecauses the differentconfigurations of the water moleculesdescribed later. Z-O bond lengthsat T(l) site rangefrom 1.47to 1.54,{ with a mean of 1.50,{,and at Z(2) site from 1.47to 1.53,{with a meanof 1.49,{.There are no significantdifferences between the two. The mean distanbesare closeto an averagevalue of 1.50Abe- tweenthe meanP-O bond length,L540,4, in brushite, and the meanS-O bond length,1.459A in gypsum. Calculation of structure factor multiplicities for Z(l) and T(2) gave the valuesof 1.008and 0.984 respectively,which are near unity. Thesevalues ought to be 1.033and 0.967respectively in a structurehav- ing a completelyordered distribution of P and S atomsin the Z siteS.Qa the other hand,the isotropic temperaturefactor of f(2) is threetimes that of ( I ), asshown in Table2.The resultsuggests that thereis a Q) orderingof P and S atomsin the T sites.Refinement .. basedon the orderedstructure model did not reduce R to lessthan 0.071.These facts, with the resultof the Fourier differencesynthesis, suggest that at this stage N

Table 2. Positional and isotropic thermal atomic parametersfor CarHPO.SO..4HrO

Aton

ca(1) 0.500 0.0383 0.250 1.s(2) -/ ca(2) .590(3) ,2L20(3) .428(4) 1.1(2) !'rn)..qiz.z4 a' r(r) .999(4) .0388(4) .747(5) 0.5(2) 5.72]j. (4) r(2) .se2(4) . 2111(4) .937 L.6(2) Fig. l. Projectionof the crystalstructure onto (1) c glideplane o(1) .942(7) .0700(r0) .549(7) 1.7(6) and(2) z glideplane along the D axis. The sheet structure on c glide o(2) .038(5) .0632(11) .976(7) 1.8(5) plane(1) alsoappears in (2), asis easilyshown by selectinga'and o(3) .77L(7) .0098(10) .676(7) 2.0(5) c' axes.The dark tetrahedralie below the planes. o(4) .257(7) .0151(10) . 828(8) 2.0(6)

o(5) .4L2(6) .18s2(11) .7L4(7) 3.1( 6) o(5) .73s(7) .1809(11) .r40(7) 2.0(s) thereseems to be no orderingin the distributionof P o(7) .175(7) .2354(rr) .872(7) 2.2(s) o(8) ,432(6) .2399(10) .001(7) 1.5(s) and S atomsin the I sites. The calciumatoms at Ca(l) arid Ca(2) sitesare hr(l) .173(7) .0875(14) .493(9) 2.6(6) w(2) .614(7) .093r(12) .019(8) 2.0(6) eight-coordinated:six to the oxygensbelonging to w(3) .227(7) .1520(14) .200(9) 3.r(5) tetrahedraand two to water moleculesat the surface w(4) ,940(7) .15s4(13) .654(8) 3.1(5) of the sheet.Thus structuralenvironments of the x Estimated standard deui.ations are gixen in pa$.entheeee calcium atoms are similar to those in gypsum and and refer to the Last decdtml pLace. brushite.It is found that the Ca-W bond lengthsare 524 SAKAE ET AL.: CALCIUM PHOSPHATE-SULFATE HYDRATE

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Table4. Selectedinteratomic distances and anglesfor CarHPOoSO,.4HzO

Tetrahedral coordlnatlon Calcium coordLnation

0(1)-0(2) 2.48(6) A o(1)-r(1)-0(2) r09.7(2.r)" ca(1)-o(1) Ls6(3) A r(1)-o(I) 1.49(s)A -0 (3) 2.40(6) o(3)- -o(2) 108.3(2.3) -o(2) 2.s3(3) -o(2) 1.s4(s) -0 (4) 2.sr (s) o(4)- -o(2) 103.1(2.s) -o(3) 2.s5(4) -o(3) r.47(4) o (2)-0 (3) 2.44(4) o(1)- -0(3) 108.6(2.3) -o(3') 2.35(4) -o(4) r.s2(4) _o(4) 2.40(6) o(1)- -o(4) 113.5(3. 3) -o(4) 2.46(4) o(3)-o(4) 2.so(s) o(3)* -o(4) 113.4(1. 9) -o(4') 2.3s(4) -w(1) 2.49(6) -w(2) 2.so(s) MEAN 1.50 A MEAN 2.45A MEAN 109.4" MEAN 2.47 A

o (s) -0 (6) 2.4s(5) o(s)-r(2)-o(6) 109.1 (2.0) ' ca(2)-o(s) 2.s7(s) ^ r(2)-o(s) r.53(4) -o(7) 2.4L(5) 0(s)- -0(7) LO6.7(2.9) -0(6) 2.4e(s) -o(6) L.49(4) -0(8) 2.43(6) 0(s)- -o(8) 108.8(2.1) -o (7) 2.s8 (s) -o(7) 1.48(5) o(6)-o(7) 2.46(6) o(6)- -o(7) rr2.o(2.3) :o(7,) 2.34(4) -o(8) L.47(s) -0(8) 2.39(s) o(6)- -o(8) 108.3 (3. 0) -o(8) 2.54G) o(7)-o(8) 2.44(7) o(7)- -o(8) rlr.9(2.2) -o(8') 2.33(4) -w(3) 2.46(4) -w(4) 2.5s(4) MEAN 1.49 A MEAN 2.43 A MEAN 109.5' MEAN 2.48 A

Water molecule environment**

w(1)-o(1) 2.70(7) A w(2)-o(6) 2.83(s) A !,r(3)-w(1) 2.83(6) A w(4)-o(s) 2.7L(6) ^ -o(2) 3.00(6) -w(1) 2.93(7) -0(6) 2.736) -o(1) 2.73G) * Estinated standard deuiations az,e gioen in paz,entheses mtd z,efer to the Last deeinnl pLaee. ** The shoy,test Ano distaneea a?e eelected.

longer than the Ca-O bond lengthsin the present tallographicproperties, such as the cell dimensions crystalstructure, whereas the Ca-W bond lengthsare being similar to gypsum and brushitebut the b di- shorter than the Ca-O bond lengths in gypsum, mensionof the presentcrystal being twice as long as brushite, and its arsenateanalogue pharmacolite thoseof the two minerals,and althoughthe contrast- (Table5). ing sheetsare analogousto thosein the two minerals The W-W bond lengthsin a sheetin brushiteand the mode of sheetstacking is different.The resultof pharmacoliteare shorter than in gypsum;this bond is synthesissuggests that this compoundmay occur in termed an interwaterhydrogen bond by Curry and nature.X-ray powder diffractiondata are calculated Jones(1971). In the presentcrystal structure a short from the crystal structure,and most of the powder W(l)-W(2) bond length,2.93A,seems to be due to reflectionsagree with those of natural ardealitein the interwaterhydrogen bond. On the other hand the spacingsand intensities.But we note that several W(3)-W(4)bond length, 3.04A, is not asshort, but is principal reflectionsusually observed in the pattern still shorter than 3.09A of the interwaterhydrogen of naturalardealite are missingfrom the calculated bond length in brushite.The W-O bond lengthsin pattern. It is not certain whether these additional the present crystal structure range from 2.70 to reflectionsare due to impuritiesor to the structural 2.83A.They are shorter than those in brushite(2.74- 3.094) and in gypsum(2.816-2.8964). Note that a Table 5. Ca-O and Ca-l{l'bond lengths for Ca,HPO.SO..4HrO, short I(l)-W(3) bond length, 2.834, making a gypsum, brushite, and pharmacolite bridge betweenthe adjacentsheets, is unusualcom- paredwith similar bondsin the structuresof gypsum, Ca2HPOaSOa.4H,0 GyPs@ Bru€hite Phamacolite brushite,and pharmacolite. Cole + Lancuckl Curry + Jones Ferraris Thls atudy (1974) (1971) (r96e)

Conclusion ca(1)-o 2.46 A ca-o 2.483 A ca-o 2.508 A ca-O 2,550 A ca(2)-o 2.48 Synthetic calcium phosphate-sulfate hydrate is ca(1)-w 2,49 ca-w 2.380 Ca-ttl 2.404 Ca-rt 2,4L3 identical to ardealitein chemicalcomposition. The ca(2)-w 2.50 analyzedcrystal structure has someinteresting crys- 526 SAKAE ET AL.: CALCIUM PHOSPHATE-SULFATE HYDRATE

(l)

'r Vo2

16-

Fig. 2. Crystal structureof gypsum,brushite, and CaTHPO.SO.'4HrOprojected along the c axis; (l) gypsum (12/a, Cole and Lancucki,1914), (2) brushite(1a, Curry and Jones,l97l), (3) CazHPO.SOr.4HrO(Cc, this study).Large circles represent water mole- culesand small circlesrepresent calcium atoms. Numbers are the z coordinatesof the tetrahedra,calcium, and water sites. propertiesofardealite, because we could not obtain a References singlecrystal of ardealitefor structuralanalysis. In Atoji, M. and R. E. Rundle(1958) Neutron diffractionstudy of this respect,we take care not to concludethat the gypsum,CaSO..2H,O. J. Chem.Phys.,29, 1306-1311. presentcrystal structure is that of naturalardealite. Baynham,J. W. and B. Raistrick(1960) Structural and X-ray data on chemicalcompounds found in fertilizers.In V. Sauchelli,Ed., Acknowledgments Chemistryand Technologyof Fertilizers,p. 538-575,Reinhold, The authorsthank Dr. K. Kihara of KanazawaUniversity for New York. his helpful measurementsand advice;Professor S. Shimodaand Beevers,C. A. (1958)The crystalstructure of dicalciumphosphate the membersof the MineralogicalInstitute, Tokyo Universityof dihydrate,CaHPO..2HzO. Acta Crystallogr.,1l, 273-277. Education,for their criticaldiscussions; and ProfessorS. Sugiura Busing,W. R., K. D. Martin and H. A. Levy (1962)Onrls, a of KanazawaUniversity for the opportunityto usethe instrument, Fortran crystallographicleast-squares program. Oak RidgeNa- and Dr. N. Kohyamaof lndustrialPhysics Institution for measure- tional Laboratory,Report ORNL TM 305. mentson SEM. Computationswere carried out on Mrlcou 7500 Cole,W. F. and C. J. Lancucki(1974) A refinementof the crystal at Tokyo Universityof Educationand Htrec 8E00/8700at the structureof gypsum,CaSOr.2HzO. Acta Crystallogr.,830, 921- Universityof Tokyo. A part of the expensewas defrayedby a 929. Grant-in-Aid for ScienceResearch, Ministry of Education. Curry, N. A. and D. W. Jones( 197I ) Crystalstructure of brushite, SAKAE ET AL,: CALCIUM PHOSPHATE-SALFATE HYDRATE 527

calciumorthophosphate dihydrate: A neutrondiffraction inves- O'Daniel,H. (1939)Die Gitterbeziehungenund Mischverhaltnisse tigation.J. Chem.Soc. (A),3725-3'129. zwischenCaSOr.2HzO und Ca(POrH).2H"O.Fortschr. Min- Ferraris, G. (1969) The crystal structure of pharmacolite, eral.,23.10E-110. CaH(AsO.). 2H zQ.A cta C rystallog r., 825, l 544-15 50. Sakurai,T. (1967)Urrcs: UnruersalCrystallographic Computation Hill, W. L. and S.B. Hendricks(1936) Composition and properties Program System.Crystallographic Society, Japan. of superphosphate.Calcium phosphate and calcium sulfatp con- Schadlar,J. (1932)Ardealite, ein neuesMineral CaHPO..CaSO. stituentsas shown by chemicaland X-ray diffractionanalysis. + 4HrO. "L Centralbl.Mineral., Abt A,40-41. Ind. Eng. Chem., 28, 440-47. Jones,D. W. and J. A. S. Smith (1962)The crystalstructure of Manuscript receiued,March 14, 1977; accepted brushite,CaHPO. .2HrO . J, Chem.,Soc., part l, 1414-1420. for publication,Nouember 2E, 1977.