Amertcan Mineralogist, Volume 62, pages 142-146, 1977

Thecrystal structure of lanthanite

At-snnroDll Nscno, GrusEplrRossl nNn VrrroRlo T xzzort C.N.R. Centrodi Studioper la CristallografiaStrutturale c/ o Istituto di Mineralogiadell' Uniuersitd,Pauia, Italy

Abstract

The structureof lanthanite,(La,Ce)r(COs)s.8HrO, a:9.504(4), b:16.943(6\, c=8.937(5)A; space group Pbnb, Z=4, has been determinedby pattersonand Fourier methodsusing 1022intensities measured with an automaticdiffractometer. The hydrogen atomsbelonging to threeof the four independentwater moleculeshave been located in the differenceFourier map. The least-squaresrefinement led to a final R index of 0.025.The principal structuralfeature of lanthaniteconsists of infinite layersof RE-O coordination polyhedraand COr2-groups. These layers are parallelto theac planeand are connectedto oneanother only by hydrogenbonds. This featureaccounts for themicaceous {010} .

Introduction reflectionswith k:2n* I werevery weakbecause the Lanthaniteis a hydratedcarbonate of lanthanum heavy cationsand some light atoms do not con- and cerium, originally found coating cerite at the tributeto theirstructure factors (see Table l). Owing Bastndsmine, Vdstmanland,. A sampleof to the smallcrystal size no absorptioncorrection was lanthanitefrom this localitywas kindly providedby applied. the SmithsonianInstitution, Washington,D. C. (NM NH 810530)through John S. White,Jr., of Crystalstructure analysis the Departmentof Sciences. The coordinatesof the heavyatoms RE(l) and RE(2) wereobtained from a three-dimensional - Experimental Pat- tersonsynthesis. A subsequentelectron density map The lattice parameterswere determinedat room computedwith the phasesgiven by the heavycations temperaturewith a PhilipsPW ll00 singlecrystal revealedall the remainingnon-hydrogen atoms. The automatic diffractometer. They are: a:9.504(4'1, isotropicleast-squares refinement, carried out on the b:16.943(6),c:8.937(5) A, V:1439.1 A', Z:4; structureamplitudes with theprogram ORFLS (Bus- spacegroup Pbnb; specificgravity, calculatedfor ing et al., 1962),reduced the conventionalR index formula LaCe(COg)s.8H2O,is 2.78. The X-ray dif- from 0.085to 0.047.Three successive anisotropic cy- fraction data were collectedfrom a small fragment cles loweredthe R index to 0.026.At this stagea (dimensions:0.13X0.1 I X0.05 mm) using MoKa radi- differenceFourier synthesisshowed several maxima, ation monochromatizedby a flat graphitecrystal. A six of which were assigned,on the basisof bond uniqueset of intensitieswas collected up to N:600 lengthsand angles,to the hydrogenatoms belonging by the 0-20 scanmode with a symmetricalscan range to the threewater moleculeslZ(l), W(2), and W(3). of 1.5' ?i from the calculatedscattering angles and a It has not beenpossible to locatethe hydrogenbe- scan rate of 0.05"/sec.Three standard reflections longingto the watermolecule W(4). The positional monitoredat three-hourintervals show no variation parametersof the hydrogenatoms, refined isotrop- greaterthan 4 percent.Processing of the data was ically in one least-squarescycle, were held fixedin the carriedout as describedby Daviesand Gatehouse last cycles at the differenceFourier values as the (1973)to yieldthe valuesof Fo and oFq.Of the 2104 atomicshifts were physically meaningless. The refine- measuredreflections, 1022were found to haveI ) oI ment was stoppedwhen the atomic shifts were less andwere used in thecalculations; the remaining1082 than the estimatedstandard deviations. The final R werediscarded because they did not fulfil the condi- index was0.025 for the 1022observed reflections. - tion 1o* 2tE. ) Iur.g.It must be noted that the The scdtteringcurves of the atoms RE(l) and t42 DAL NEGRO ET AL.: CRYSTAL STRUCTUREOF LANTHANITE 143

Trsle l. Atomic coordinatesand equivalentisbtropic factors of RE(2) have beencomputed taking into accountthe lanthanitet chemicalanalysis assuming that La and Ce weredis- orderedover the two sites'The scatteringcurves of Atcn x/a s.(A2) tu z/s. n Hansonet al. (1964)were used' The populationpa- rametersof RE(l) and RE(2)and thoseof the water (2) 0.84 RE(1) O.2s o.25037 0.75 were allowedto vary during the isotropic FE(2) 0.25 o.28122(2) U.ZJ 0.79 molecules refinement,but they did not showany changegreater o(1) 0.2s 0.0340 (4) 0.25 5.44 than one standarddeviation. The final atomicpara- (4) (2) 0.3232(4) 1.40 o(2) 0.3423 o.1469 I and 2; bond distances o(3) 0.5072(4) 0.7948(2) 0.187s(4) 1.56 metersare given in Tables o(4) 0.6164(4) 0.7620(3) 0.979'l(s) 1.72 and anglesare listedin Table 3. The observedand o(s) 0.384s(4) 0.7919(3) 0.9770(s) 1.65 calculatedstructure factors are compared in Table4.1 (3) (s) w(1) 0.1478(6) 0.40s9 0.3781 2.61 of the structure w(2) 0.6713$) 0.3784(3) 0.11 40 (s) 2.16 Descriptionand discussion (5) w(3) 0.8837(4) 0.1209(2) 0.'1844 1.88 The principalstructural feature of lanthanitecon- w(4) 0.6089(B) 0.4e57(4) 0.3874 (e) 5.3't sistsof infinite layersof RE-O coordinationpoly' c(1) 0.25 0.1 066 (4) 0.25 1.82 hedra.These layers are parallelto the ac plane(Fig' (3) (6) ce) 0.4975(5) 0.716s 0.s428 1.23 l) and areconnected to one anotheronly by hydro- mi- H(11) 0.586(8) 0.044(s) 0.6s3(8) 6.4e gen bonds (Fig. 2): this fact accountsfor the H(1D 0.641(8) 0.096(4) 0.s12(9) 6.05 caceous{010} cleavage.The two independentRE (4) (9) H(2't) o. 334(8) 0.1 34 0.506 4.04 atoms have a ten-foldcoordination: RE(l) is sur- H(22) 0.2s2(12) 0.081(4) 0.618(8) 8.09 H(31) 0.379(7) o.423(4) 0.145(2) 4.5s H(.32) 0. s15(9) 0.1 34 (4) 0.324(8) s.54 I To obtaina copyof Table6, orderDocument AM-76-025 from The MineralogicalSociety of America,Business Office, 1909 K St', xstardard deviations in parenthesest equivalent 1000,lower level,Washington, D. C. 20006.Please isotropic tsq)erature factors after Handlton (1959). N.W., Suite remit in advance$1.00 for a copy of the microfiche.

Tlnu 2. Anisotropicthermal parameters for lanthanite*

r.m.s. u,a u.b u.c ui3 ui!' ui9

re(1) 0.07e(2) 161 90 71 w(1) 0.131(8) 76 104 159 0.099 (2) 71 90 18 0.1 60 (7) 76 17 101 0.,t26() 90 180 90 o.237(7) 150 80 107 '175 FE(2) 0.079(1) 't73 90 84 w(2) 0.123(8) 87 93 0.101(1) 83905 0.173Q) 90393 0.116(1) 90 180 90 0.192(7) 177 90 93

o(1) 0.'141(11',) 90 180 90 w(3) 0.11e(8) 166 89 16 0.200(1 s) 50 90 39 0.1s7(7) 88783 0.381(15) 140 90 51 0.1 81 (6) 103 83 16s

o(2) 0.116(8) 1't2 103 153 w(4) 0.166(11) 70 149 67 0.133(7) 32 72 115 0.227(10) 42 90 132 0. '148(7) 67 157 85 0.350(10) 125 121 129 't o(3) 0.108(e) 137 104 129 c(1) 0.117(14) 90 80 90 0.127 (8) 47 108 132 0.142Q4) s7 90 32 0.177(7) 91 156 66 0.188(23) 147 90 57 't54 o(4) 0.112(8) 72 72 cQl 0.11s(10) 150 ?8 53 0. 13s (9) 58 82 22 0.123 (10) 64 98 27 0.1 85 (7) 103 161 77 0.135(12) 104 165 92

o(s) 0.091(10) 140 96 129 0.146 (8) 127 99 39 0.182(7) 79 168 94

* rcot nean square tter:na] vibrations alorg the euiPsoid axes (A) arli algles (") betHeen (Ur) of the vlbration ellipsold. ttre crystallographic axes ad lFe pnillcipal a

roundedby six oxygenatoms belonging to the car- Tnslr 3. Interatomic distances(A) and angle (.) in lanthanite bonategroups and by four watermolecules; RE(2) is bondedto eight carbonateoxygens and two water RE(1)-o(3) 2.495(4)x2 FE(2){(4) 2.518(4)x2 F€(1)-o(5) 2.499(41x2 RE(2) -O (3) 2.518(4) x2 molecules(Table 3). Thecorresponding coordination RE(1)-w(3) 2.59j(4) xZ RE(2)-O(2) 2.52s(4)x2 polyhedraare similar and cannot be describedin RE(1)-w(2) 2.592(5)x2 RE(2)-w(1) 2.s91(5) x2 RE(1)-o(4) 2.742(4)x2 RE(2) -o (s) 2.760(4) x2 termsof regulargeometric solids. Theirshape can be M(il value 2.584 Mean value 2.582 approximately -o(1) describedas that of distortedArchi- c (1) 1.232(9t c (2)-o (5) 1.2'74 (1) medeanantiprisms whose square faces are replaced c(1)-o(2) 1.290(s)x2 c (2)-o (4) 1.271(7) c (2)-o (3) 1.309 (6) by pyramids(Fig. 3). The oxygenatoms O(4) are M€n value 1.2'11 at M{m value 1.287 the apices of the pyramids. These polyhedra are o(1){(1)-o(2) 121.9(31 x2 o(3)-c (2)-o(4) 117.0(5) linkedparallel to the c axisby sharingthe O(a)-O(s) o(2){(1)-o(2)'t16.1(6) o (3)-c (2)-o (5) 11 8. 0 (s) edgesand alongthe a directionby sharingthe O(3) o(4){(2)-o(s) 125.0(s) cornersto form the infinite layersparallel to the ac plane.Each O(l ) atom of onelayer is bondedto two ---o W(l) water moleculesof the adjacentlayer; fhe W(4) w(1)----+t(11) (1) 2.639('7) 0.97 (8) 1. 6e(8) w(1 ) -----fi (1 2) ---w (3) 2.791(7',) water moleculesact as bridgesbetween two layers 0.e8(8) 1.83(8) w(2) -----+r (21 \ ---o (2) 2.640(6) (8) (8) ---w(4) 1.00 1.65 being bondedto W(3) and W(2) water molecules.w(2)----4(22) 2.842(8) 0.96(7) 1.89(9) ----+r ---w(4) Besidesthe hydrogenbonds which connectadjacent w(3) (31) 2.792(8) 0.97(9' 1-82(9) w(3)---rl (32)---o (2) layers,hydrogen bonds are also presentwithin each 2.64't(6\ 0.99 (8) 1.56 (8) layer (Table 3). The water molecule W(4) has H(11)-w(1)-H(12) -H(11) an 109 w(1) -o(1) too approach H(211-w (2) -H(22) 105 w(1)-H(12) -w(3) of 2.891A to a W(4) relatedby a centerof -w -H 167 H(3'1) (3) (32) 106 w(2)-H(21){ (2) 174 symmetry.This could mean that thereis a disordered w(2t -H (22t-w (4) 175 W() - VzH-YzH- W(4) bond. w(3)-H(31) -w(4) 174 w(3)-H(32) -o (2) 173 The bonddistances and angles within the two inde-

Ftc. l. ORTEP (johnson 1965) plot of the of lanthanite. DAL NEGRO ET AL: CRYSTAL STRUCTUREOF LANTHANITE 145

H3l H3l

RE2

ttt\b n\n,, n,

Frc. 2. ORTEP plot of the crystal structure of lanthanite showing the connection among adjacent layers of RE-O polyhedra.

pendentcarbonate groups deserve some comment. In oxygenatom in that carbonategroups which has two theC(l)-O' trianglethe C(l)-O(l) bondlength (1.23 short contactsto RE. The O(4)-C(2)-O(5)angle A) is remarkablyshorter than the averageC-O dis- (125') is notablylarger than the expectedvalue of tance(1.28 A). It mustbe pointed out that O(l) isnot 120': O(4) and O(5), which form one side of the bondedto RE, but it is only involvedin hydrogen C(2)-Oa triangle, are bonded to two different RE bondswith W(l). The C(l)-O bond lengthscalcu- atoms.On the other hand,the sidesof the triangle latedfollowing the methodsuggested by Baur(1970), formedby the oxygenatoms bonded to the sameRE C(l)-O(l): r.n7 A andC(1)-O(2):1.288 A, arein cationsubtend O-C-O anglessmaller than 120". good agreementwith thosegiven in Table 4. The The deviationof the C(2) atom from the plane distortionsin C(2)-O3groups are smaller and, also in passingthrough the oxygensO(3), O(4), and O(5)is this case,correlated with the environmentof the oxy- -0.017 A (e.s.d.0.007 A). No deviationcan be ob- genatoms. The long C(2)-O(3)distance (1.309 A) is servedin the C(l)-O' trianglebecause C(l) andO(1) possibly related to the fact that O(3) is the only occuron a diad axis. 146 DAL NEGRO ET AL. CRYSTAL STRUCTUREOF LANTHANITE

Flc. 3. The coordinationpolyhedra of RE(l) andRE(2) atoms.

References Heurr-roN, W. C. (1959) On the isotropictemperature factor equivalentto a givenanisotropic temperature factor. Blun, W. H. (1970)Bond length variation and distorted coordina- Acta Crys- tallogr.12,609-610. tion polyhedrain inorganiccrystals. Trans. Am. Crystallogr. Assoc.6,129-155. HANsoN,H. P., F. HnnnalN,J. D. Lel ANDS. SKTLMANN(1964) HFS atomicscattering factors. Acla Crystallogr.11, 1040-1044. BusrNc,W. R., K. O. M,rrnrrrqnNo H. A. Lrvv (1962)ORFLS, a JoHNsott,C. K. (1965)ORTEP, a Fortran plot Fortran crystallographicleast-squares program. U. S. Natt. thermalellipsoid Tech.Inf. Seru.ORNL-TM-305. programfor crystalstructure illustrations. U. S. Tech.Inf. Sero. oRNL 3794. DAvrEs,J. E. ruo B. M. Grrrsouse (1973)The Crystaland molecular structure of unsolved a-oxo-bis N,N,- ethylenebis-(salicylaldiminato)iron(III). Acta Crystallogr.B,29, Manuscripl receiued, January 8, 1976; accepted 1934-1942. Jbr publication, May 5, 1976.