9L The CanadianMineralo gist Vol. 34, pp. 91,-97(1996) THE CRYSTALSTRUCTURE OF SHIGAITE, lAlMne*(oH)ele(so+lzNa(H2o)6{H2o}6, A HYDROTALCITE.GROUPMINERAL MARK A. COOPERand FRANK C. HAWTHORNE Deparnnewof GeolagicalSciences, University of Manitoba"Winnipeg, Manitoba, R3T 2N2 ABSTRACT The cryslal strucbre of shigaite, tAMnA+(OlD6l3(SOfrNa(H2O)6{HzO}0,rhombohedral, a 9.512(l), c 33.074$) 4,, y 2591.0(8) Ar, Z = 3, R3, hasbeen solved by direct nethods and refined to an R ndex of 4.2Vousing 979 observedreflections measuredwith MoKcl X-radiation.The structuralunit of shigaiteis a planar sheetof edge-sharingoctahedra [AlMna+(OID6]1+. These oxycation sheetsare intercalatedwith oxyanion she€tsof chemical composition Na(H2O)6{H2O}6(SOf2;hydrogen bonding plays a major role in linkage both within the oxyanionsheet and betweenthe structuraluoit and the oxyanionsheet of interstitial species.This work showsshigaite to containessential Na andresults in a significantrevision ofthe chemicalformula- Shigaiteis a hydrotalcite-goup mineral, the Mn2+analogue of motukoreaite. Keywords:shigaite, crystal structure,chemical formul4 hydrogenbonding, hydrotalcite group. Somaanr Nous avons affin6 la stucture de la shigarte, IA1MnS+(OII)613(SO)2Na(H2O)6{HzO}0,rhombo6drique, a 9.512(l), c 33.074(0A, V259L.09)N,z= 3, Rl parm6thoaes directeijusqu'lirnreiiiu n a6l.Z%6nuinsnt979 r6flexionsobserv6es avecun rayonnementMorcr. L'unit6 structuraleest un feuillet d'octabdrese a€tes partag6es,de composition[AlMn3+(OI{)6]11 Ces couchesoxy-cationiques sont intercal6esavec des couchesoxy-anioniques de composition Na(H2O)6{H2O}6(SO)2; les liaisons hydrogdnejouent un role imporanq aussi bien dsns les couchesoxy-anioniques qu'enhe I'unit6 structuraleet la coucheoxy-anionique de I'espbceinterstitielle. Nos rdsulas montrentque la shigaltecontient un atomede sodium,essentiel, ce qui mbne d une revision de la formule chimique. l,a shigaite fait putie du groupe de la hydrotalcite, et est I'analoguee Mn2+de la motukorealte. (Traduit par la Rddaction) Mots-clAs:shigaite, structure sistalline, formule chimique,liaison hydrogbne,groupe de la hydrotalcite. Inrnooucnox district), Cape Province, South Africa, and was generouslyprovided by Mr. William M. Pinch. The Shigaite is a sulfate mineral describedfrom Shiga crystal usedin the measurementof the X-ray intensity hefecture, Japan,by Peasoret al. (1985).The orieinal data a niangular {001} plate -0.28 mm on an edge formul4 AI4M&(OII)22(SO/2.8H2O,the tabular habit and 0.04 mm tlick, was mounted on a SiemensP4 atrd perfect {001} cleavageindicate a sheetstructure, automatedfour-circle diffractometer.Cell dimensions and Peacor et aL (L985) suggestedthat shigaite has (Iable l) were derived from the setting anglesof 37 sfructural affinities with lawsonbauerite,(Mn,Mg)e automatically aligned reflections. Intensities were ZnIOI{)22(SO)2.8H2O(Treiman & Peacor1982). As measuredfrom 4 to 60'20 (0 < h < 11, 0 < k < LI, part of our interestin [MQr]-derivativesheet structures 46 < I < 46) with scanspeeds varying between 1.78 (M: octahedrally coordinated divalent or trivalent ard 29.3"201min: a total of 1988 reflections was cation, 0: unspecified anion), we have solved and measuredover one asyrnmetric unit. Psi-scan data refined the structureof shigaiteand presentthe results were measnredon 12 reflectionsbetween 9 and59'20 here. at incremetrts of 5o, and a thin-plate absorption correctionreduced R(azimuthal) from 3.3 to 2.0Vofor a Enpm.nm.rrat glancing angle of 2o. Intensities were correctedfor absorption, Lorentzo polarization and background The material used in this work is from the effects, and then reduced to strucfure factors; N'Chyaning mine, Kuruman (Kalahad manganese 979 reflectionswere classedas observed(lF"l > 5olFl). 92 TTIE CANADIAN MINERALOGIST TAELE 1. MIgCE.I-ANEOUS INFORMATION FOR SHIGAM identified via the relative scatteringpowers at the atom a (A 9.612(1) Ctystsl dzo (mml O.3Or 0.30 r 0.25 x 0.04 positions,together with the local tetrahedralgeomery. c 33.074(51 Radiation Mor(d/GGphho Tbree atom positions were located with scattering vA1 269r.0(a) Tdd No. of r 1988 powers approximately equal to that of oxygen. One 3p. Gr. R3 'No. ot r 1855 atomis at the origin andis octahedrallycoordinated by P (mmn) 2.4e No. of lR 1699 Do(9.@1 2.21 No. of lF.l>soF 979 one of the other atomswith an interatomicdistance of R(uimdhaf) % 3,?-2,O 2.47 L The central atom was assignedas Na, and the A(obs) % 4.2 coordinating anion was assignedas an oxygen atom larR(obs, % 4.8 group. Call @ntenr: 3lNaAlsMn6(SO.l,(OHlBt2H,Ol of an H2O The third interstitial atom is not a - :(lr.l-lr.llElF.l directly bondedto any cation andwas assignedas HrO. Subsequentleast-squares refinement confirmed a fully occupiedNa site at the origin. Difference-Fouriermaps ' altgr removd ot glgncing reflsctiono following fuIl-matrix least-squaresrefinement showe{ all H atomsin the structurebetween 0.88 and 0.95 A from their associateddonor oxygenatoms. All H atoms were input into the least-squaresrefinement with the soft constraint that all O-H distances are approxi- mately equal to 0.98 A, and all H-H distancesin H2O groupsare approximatelyequal to 1.55 A. Full-matrix Srnuctunr Sonrnou eNn Rmnwvmnr least-squares refinement of all variables with anisotopic displacement parametersfor all non-H All calculationswere done with the SHELXTL PC atomsconverged to an R rndex of 4.2Vo.Final atomic (Plus) systemof programs;R indices are of the form positionsand displacement factors are given in Table 2, given in Table 1 and areexpressed as percentages.The selectedinteratomic distancesand angles for non-H E statisticsindicate a centrosymmetic stucture, and a atomsare given in Table 3, interatomic distancesand solutionwas found in the spacegroup R3 peacor et aL angles involving H atoms are given in Table 4, 1985).Cation and anion positions eqmFatiblewith an and a bond-valencetable is given asTable 5. Observed [MQr] sheetwere locatedand refine4 and the relative and calculatedstructure.factors are availablefrom the X-ray scattering powers were used to establish the Depository of Unpublished Data CISTI, National cation identiti"r. q interstitial (SO/ group was ReseaxchCouncil, Ottaw4 Ontario KlA 0S2. TABLE2. FINALATOMIC PARAMETERS FOR SHIGA]TE tUn uf u2 us u6 ur Utz trrn -0.0011(11 0.3336(11 0.16671(2) 130(3) 66(4) 62(4t 261(3) 8(41 3(4) 31(3) At(l\ 0 0 0.16476(8) 75(6) 5rt{6) 54(61 118112) 0 0 2743't A^2t 1t3 2t3 1t6 82(9) 60(101 60(10) 1zt6(18) o 0 25(5) NaO0 o 332117t 336(201 336(20) 324(33) 0 0 168(10) s 2t3 1t3 o.o3822(7',t 182(6t 181(6) 181(6) 184(11) o o 9r(3) o(1) 1t3 2t3 0,0063(21 267(19't 3421221 342t22t 118(33) 0 0 171111',t otzt 0.6144(6) O.1690(5) 0.0535(1I 296(181 373(241 189(191 3221211 28(18) 23(20't 138(20) oH(1) 0,5705(4) O.1373(4i 0.1374(1) 100(13) 114(171 72(16t 112(151 -8(141 9(14) 46(14't oH(2) 0.1979(4) 0.O984(4i 0.1346(1) ro9(13) 72(161 101(16) 146(16) 14(14t 21(16) 37(13' oH(3) 0.2336(4) O.4698(4i o.1361 (1) 113(14) 1261171 92117t. 125(16' -2(15) 2(15) 671141 ow(1) 0.1180(5) O.4236t6t o.o556(1) 321(19) 2801221 381(25) 302(211 77120t 34(191 166(21) ow(z) 0.2036(5) 0.1794(5) 0.0601(11 315(181 245l23l 297(221 384(23) -13(21) 18(20) 122118) H(1) 0.684(6) 0.166(7) o.1082(3) r200 Hlz) 0.193(7) 0.109(6) o.1062(2:l .200 H(3) 0.197(6) 0.475(6) 0.1087(61 r200 H{4) 0.172161 O.sO7(6) 0.035(11 t700 H(5) 0.00[(2] 0.394(8] o.064(2' r700 H(6) 0.172(6) O.262(5't 0.055(2) .700 o.242Gl 0.045(2) .700 I Uvalussx 10{; r fixed in rofinemem TIIE CRYSTAL STRUCTTJREOF SHIGAITE 93 (4, ') TABLE3. SELECTEDINTEFATOMIC DISTANCES (A) & ANGLEITI N SHIGAITE TABLE4. DETAILSOF H.BONDING IN SHTGAITE x3 Mn-OH(1)d 2,171141 Al(1)-OH(1)d,l,s 1.915{3) oH(1)-H(1) 0.98(1) H(r)-o(2) 1.83(1) Al(1)-OH(2),e,h x3 Mn-OH{llo 2,17714t l=912G!L oH(2)-H(2) 0.98(t) H(2)€W(2) 1.9SQl Mn-OH(2)o 2,211131 <A(1)-OH> JE34__ oH(3)-H(3) 0.98(3) H(3)-OW(1) 1.88(2) Mn-OH(2)t 2.205(31 Mn-OH(3) 2.190(3) Ar(2)-OHl3)ti,j,kr r.912(3) x6 oH(1)-O(2) 2.800(5) OH(1)-H(1)-O(2) 173171 Mn-OHl3)l 2.199(31 oH(21-ow(2) 2.891(5) OH(21-Ht2)-Ow(2) 167(6) < Mn-OH> 2.142 Ns-Ow(2),a.e,h,m,n 2.470141to oH(3)-OW{1) 2.829(5} OH(3}-H(3}-OW(1) 163(6) S-O(1)a 1.472181 1.79(4) s-o(2),b,c L4Z3IlL x3 ow(1)-H(4) 0.98(6) H(4)-O(1) < > J.473- Ow(1)-H(6) 0.S8(3) H(6)-O(2)e 1.93(6) Mo ocbhedron ow(2)-H(6) 0.98(6) H(6)-OW(1) 1.86(6) OH(1)e-OH(2)t 2.61016) OH(1)e-Mn-oH(2)t 73.1(1) ow(2)-H(7) 0.98(2) H(7)-O(2)c 1.9712].