The Crystal Structure of Na4(UO2)(CO3)
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Mineralogical Magazine, April 2001, Vol. 65(2), pp.297–304 Thecrystalstructure of Na 4(UO2)(CO3)3 anditsr elationshiptoschrÎckingerite YAPING LI, S. V. KRIVOVICHEVAND P. C. BURNS* Department of Civil Engineering and Geological Sciences, University of Notre Dame, 156 Fitzpatrick, Notre Dame, Indiana 46556-0767, USA ABSTR ACT Crystalsof the compound Na 4(UO2)(CO3)3 havebeen synthesized and the structure has been solved. It istrigonal with a =9.3417(6), c =12.824(1)A Ê , V = 969.2(1) AÊ 3,spacegroup P3¯c1 and Z = 4. The structurewas refined on the basis of F2 (wR2 = 4.2%)forall unique data collected using Mo- Ka X- radiationand a CCD-baseddetector. The final R1 was 2.0%,calculatedfor 534 unique observed ( Fo 5 4sF)reflections,and the goodness- of-fit( S)was0.91. The structure contains a uranyltricarbonate clustercomposed of a uranylhexagonal bipyramid that shares three equatorial edges with CO 3 triangles.The uranyl tricarbonate clusters are connected through NaO 6 and NaO5 polyhedra,forming a heteropolyhedralframework structure. This compound may be related to a uranylcarbonate phase with thesame composition which has been reported as an alteration phase on the surface of Chernobyl ‘lava’,andas a mineralin the Jachymov ore district, Czech Republic. KEY WORDS: uranylcarbonate, sodium uranyl carbonate, crystal structure, nuclear waste. Introduction [Cu2(UO2)3(CO3)2O2(OH)2](H2O)4 (Ginderow andCesbron, 1985), rutherfordine, [(UO 2)(CO3)] MORE than25 uranyl carbonate minerals are (Finch et al. ,1999),andbijvoetite, known(Mandarino, 1999), and actinide-carbonate [M8(UO2)16O8(OH)8(H2O)25](H2O)14, M = REE, complexesare important over a widevariety of Y (Li et al.,2000).Of these,roubaul tite, environmentalconditions (Clark et al., 1995). The rutherfordineand bijvoetite each contain sheets crystalstructur esof eight uranyl carbonat e ofpolyhedra, whereas the others contain the mineralshave been reported. On the basis of the uranyltricarbonate cluster. polymerizationof cation polyhedra of higher Thereare several reports of the compound bondvalence, uranyl carbonat eshave been Na4(UO2)(CO3)3 inthe literature, although the groupedinto those containing in nite sheets and structurehas not been published. Douglass (1956) thosewith an isolated uranyl tricarbonate cluster synthesizedNa 4(UO2)(CO3)3 andprovided X -ray (Burns,1999) .Thestructures have been solved powderdiffraction (XRD) data.An unnamed forliebigite, Ca 2[(UO2)(CO3)3](H2O)11 (Mereiter, mineralwith composition Na 4(UO2)(CO3)3 was 1982),schro ¨ckingerite,NaCa 3[(UO2)(CO3)3] reportedfrom the Jachymov ore district, where it (SO4)F(H2O)10 (Mereiter,1986 a),swartzit e, occursas part of the secondary uranyl mineral CaMg[(UO2)(CO3)3](H2O)12 (Mereiter,1986 b), assemblage(Ondrus et al.,1997).Acompoundof andersonite,Na 2Ca[(UO 2 )(CO 3 )3 ](H 2O)5 ] thesame composition was also reported as an (Mereiter,1986 c),bayleyite,Mg 2[(UO2)(CO3)3] alterationphase on Chernobyl ‘lava’ (Burakov et (H2O)18 (Mayerand Mereiter, 1986), roubaultite, al.,1999).Recently,a mineralwith the composi- tion Na4(UO2)(CO3)3 wasapprove dbythe Commissionon New Mineralsand New Mineral Nameso ftheInt ernationalMineralogical Association(Grice and Ferraris, 2000), but *E-mail: [email protected] detailedinformation is still unavailable. Table 1 # 2001The Mineralogical Society TABLE 1. Crystallographic information reported for Na4(UO2)(CO3)3. Sources Unit cell a (AÊ ) b (AÊ ) c (AÊ ) a (8) b (8) g (8) Refs Y Douglass trigonal 9.32(1) 12.80(1) [1] APING Unnamed mineral from Czech triclinic 16.468(2) 27.578(3) 5.222(2) 94.155(2) 100.58(1) 121.25(1) [2] 298 hexagonal 18.621(3) 12.801(4) [2] Unnamed mineral triclinic 9.280 9.295 12.864 90.293 91.124 119.548 [3] LI Current work trigonal 9.3417(6) 12.824(1) ETAL. [1] Douglass (1956), [2] Ondrus et al. (1997), [3] Grice and Ferraris (2000) CRYSTAL STRUCTURE OFN A4(UO2)(CO3)3 presentsa summaryof crystallographic informa- measured,of which 804 re ections were unique, tionreported for compounds with the composition with534 classed as observed ( Fo 5 4sF). Na4(UO2)(CO3)3.Wehave grown a singlecrystal of Na4(UO2)(CO3)3 usinghydrothermal techni- ques,and report the structure here. Structuresolution and ref inement TheBruker SHELXTL Version5 systemof programswas used for the determination and Experimental renement of the crystal structure. The structure Crystalsy nthesis wassolved by direct methods in spacegroup P3¯c1 2 Crystalsof Na 4(UO2)(CO3)3 weresynthesized by andwas re ned on the basis of F forall unique hydrothermalreaction of 4mlof a0.2 M solution data.The nalmodel included all atomic- ofuranylacetate with 0. 17g ofsodiumcarbonate. positionalparameters, anisotropic-disp lacement Thesolution was heated to 220 8C in a Te on- parametersfor a llatoms, and a renable linedParr bomb for 2 weeks.Yellowish anhedral weightingscheme of the structure factors. The crystalswere recovered by ltration,washed with renement converged to a wR2 of 4.2% for all de-ionizedwater, and dried in air. data, an R1 of 2.0%,calculatedfor the 534 unique observed (Fo5 4sF)reections, and a goodness- of- t (S)of0.91 for all data. The nalatomic Single-crystalXRD coordinatesand anisotropic-displac ementpara- Asinglecrystal of Na 4(UO2)(CO3)3 with dimen- metersare given in Table 3, with selected sions 0.1060.1060.10mm wasselected and interatomicdistances given in Table 4, and a mountedon a glass bre,and diffraction data bond-valenceanalysis given in Table 5. Observed werecollected using a Bruker1K SMART CCD andcalcul atedstructu refactors have been diffractometerby usingMo- Ka X-radiationand a depositedwiththePrincipalEditorof crystal-to-detectordistance of 5. 0cm.More than MineralogicalMagazine andare available upon ahemisphereof 3-dimensionaldata was collected request. usingframe widths of 0.3 8 in o,with10 s spent countingper frame. The unit- cellparameters (Table2) were re ned from 2210 re ections Discussion usingleast-squares techniques. The data were Cationcoo rdination integratedand corrected for Lorentz, polarization Thestructure of Na 4(UO2)(CO3)3 contains a andbackground effects using the Bruker program singlesymmetrically unique U 6+ cation,which 2+ SAINT. Asemi-empiricalabsorption correction ispartof anapproximately linear (UO 2) uranyl wasapplied on thebasis of equivalentre ections ion(designated Ur)withan averageU OUr bond bymodelling the crystal as an ellipsoid; the lengthof 1.81 A Ê (Table1) .Theuranyl ion is correctionreduced Rint of1646intense re ections furthercoordinated by six O atomsthat are from4. 9to4.1 %.Atotalof 5555re ections were arrangedat the equato rial(desig natedeq ) TABLE 2.Crystallographic information for Na 4(UO2)(CO3)3. a (AÊ ) 9.3417(6) Crystal size (mm) 0.1060.1060.10 c (AÊ ) 12.824(1) Total ref. 5555 V (AÊ 3) 969.2(1) Unique ref. 804 ¯ Space group P3c1 Rint (%) 5.35 F(000) 968 Unique FO54sF 534 m (mm 1) 16.986 Final wR2 (%) 4.2 3 Dcalc (g/cm ) 3.715 Final R1 (%) 2.0 S 0.91 Unit-cell contents: 4[Na 4(UO2)(CO3)3] R1 = S(|Fo| |Fc|)/ S |Fo| 2 1/2 S = [Sw(|Fo Fc) /(m n)] , for m =804 observations and n =60 parameters 2 2 2 2 2 w = 1/[s (FO ) + (0.02176P) ], P = (max(FO ,0) + 26FC )/3 299 YAPING LI ETAL. 4 2 3 TABLE 3.Atomic coordinates ( 610 )anddisplacement parameters (A Ê 610 ) for Na4(UO2)(CO3)3. x y z U*(eq) U11 U22 U33 U23 U13 U12 U1 6667 3333 1303(1) 11(1) 10(1) 10(1) 13(1) 0 0 5(1) Na1 0 0 2500 23(1) 22(1) 22(1) 24(2) 0 0 11(1) Na2 0 0 0 22(1) 23(1) 23(1) 20(2) 0 0 11(1) Na3 8769(3) 3076(3) 3764(2) 27(1) 13(1) 16(1) 49(1) 5(1) 1(1) 6(1) O1 6667 3333 2718(4) 20(1) 22(2) 22(2) 17(3) 0 0 11(1) O2 6667 3333 –106(4) 23(1) 30(2) 30(2) 9(3) 0 0 15(1) O3 9651(4) 7833(4) 3784(3) 21(1) 15(2) 19(2) 33(2) –3(2) –2(2) 12(2) O4 460(4) 5959(5) 3817(3) 23(1) 10(2) 10(2) 49(3) 6(2) 6(2) 5(2) O5 1471(4) 3765(5) 3563(3) 26(1) 12(2) 15(2) 55(3) –2(2) 0(2) 10(2) C1 733(7) 7444(7) 3723(4) 17(1) 11(3) 13(3) 22(3) –1(2) –4(2) 2(2) * U(eq) is dened as one third of the trace of the orthogonalized Uij tensor positionsof a hexagonalbipyramid. The average average Na2 Obondlength of 2.444(3) A Ê . The 6+ U Oeq bondlength is 2. 41A Ê (Table4), which Na3cation is coordinated by veanions with an [8] compareswell with the average U Oeq bond average Na3 Obondlength of 2.398 A Ê . lengthof 2. 47(12)A Ê derivedfrom numerous well-rened structures (Burns et al., 1997). The Structuralconnectiv ity structurecontains one symmetrically unique C 4+ cationin the usual triangular coordination, with Asis thecase with other known uranyl carbonates an average C Obondlength of 1.28A Ê (Table 4). withU:Cratioso f1:3,thestru ctureof Thereare three symmetricall ydistinctNa Na4(UO2)(CO3)3 containsthe uranyl tricarbonate cationsin the structur e.Na1 and Na2 are clustershown in Fig.1 a.Thecluster contains one octahedrallycoordinated by O atoms,with an UrO6 hexagonalbipyramid that shares three of its average Na1 Obondlength of 2.501(3)A Ê and an equatorialedges with CO 3 triangles.As for all TABLE 4.Bond lengths (A Ê )andangles ( 8) for Na4(UO2)(CO3)3. U1 O2 1.807(5) Na1 O3a,d,e,f,g,h 2.501(3)66 U1 O1 1.814(5) U1 O5a,b,c 2.385(4)63 Na2 O3h,k,a,e,l,m 2.444(3)66 U1 O4a,b,c 2.427(3)63 U1 Oeq> 2.41 Na3 O5n 2.286(4) O2 U1 O1 180 Na3 O3i 2.323(4) Na3 O4n 2.345(4) C1 O3j 1.236(7) Na3 O1 2.488(3) C1 O5f 1.310(7) Na3 O2o 2.547(4) C1 O4 1.284(6) <Na3 O> 2.398 <C1 O> 1.28 O3j C1 O4 124.2(5) O3j C1 O5f 122.6(5) O4 C1 O5f 113.2(5) <O C1 O> 120 a = x + 1, x + y, z + Ý, b = y, x, z + Ý, c = x y + 1, y + 1, z + Ý; d = y +1, x y, z; e = y 1, x 1, z + Ý; f = x + y, x +1, z; g = x 1, y 1, z; h = x y, y +1, z + Ý; i = x + y + 1, x + 1, z; j = x 1, y, z; k = x + y, y 1, z Ý; l = x 1, x y, z Ý; m = y + 1, x + 1, z Ý; n = x + 1, y, z; o = y + 1, x + 1, z + Ý 300 CRYSTAL STRUCTURE OFN A4(UO2)(CO3)3 TABLE 5.Bond valence analysis* for Na 4(UO2)(CO3)3.