inorganic compounds ActaCrystallographicaSectionE al. (1998); Yang et al. (2009). For general information on Structure Reports polyhedral distortion and ionic radii, see: Robinson et al. Online (1971) and Shannon (1976), respectively. ISSN1600-5368 Experimental High-pressure synthetic (Na Mg )- 0.97 0.03 Crystaldata (Mg Fe 3+Si )Si O , with six- 0.43 0.17 0.40 2 6 (Na Mg )(Mg Fe - (cid:3)=108.003(6)(cid:2) 0.97 0.03 0.43 0.17 coordinated silicon, isostructural with Si0.40)Si2O6 V=407.95(6)A˚3 M =206.39 Z=4 r P2/n omphacite Monoclinic,P2=n MoK(cid:4)radiation a=9.4432(8)A˚ (cid:5)=1.69mm(cid:3)1 b=8.6457(7)A˚ T=293K Esther S. Posner,a* Ju¨rgen Konzett,b Daniel J. Frost,c c=5.2540(5)A˚ 0.06(cid:4)0.05(cid:4)0.05mm Robert T. Downsa and Hexiong Yanga Datacollection aDepartmentofGeosciences,UniversityofArizona,1040E.4thStreet,Tucson,AZ BrukerAPEXIICCDarea-detector 6586measuredreflections 85721-0077,USA,bInstitutfu¨rMineralogieundPetrographie,Universita¨tInnsbruck, diffractometer 1481independentreflections Absorptioncorrection:multi-scan 980reflectionswithI>2(cid:2)(I) Innsbruck,Austria,andcBayerischesGeoinstitut,Universita¨tBayreuth,Bayreuth, (SADABS;Sheldrick2005) R =0.033 Germany T =0.906,T =0.920 int min max Correspondencee-mail:[email protected] Refinement Received6January2012;accepted23January2012 R[F2>2(cid:2)(F2)]=0.036 96parameters Keyindicators:single-crystalX-raystudy;T=293K;mean(cid:2)(Si–O)=0.002A˚; wR(F2)=0.085 3restraints S=1.07 (cid:2)(cid:6) =0.51eA˚(cid:3)3 disorderinmainresidue;Rfactor=0.036;wRfactor=0.085;data-to-parameter max 1481reflections (cid:2)(cid:6) =(cid:3)0.66eA˚(cid:3)3 ratio=15.4. min Data collection: APEX2 (Bruker, 2004); cell refinement: SAINT (Bruker, 2004); data reduction: SAINT; program(s) used to solve The title compound, (sodium magnesium) [magnesium structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine iron(III) silicon]disilicate,(Na Mg )(Mg Fe 3+Si )- 0.97 0.03 0.43 0.17 0.40 structure: SHELXL97 (Sheldrick, 2008); molecular graphics: Xtal- Si O ,isisotypicwithorderedP2/nomphacite.Itsstructureis 2 6 Draw (Downs & Hall-Wallace, 2003); software used to prepare characterized by single chains of corner-sharing SiO tetra- 4 materialforpublication:publCIF(Westrip,2010). hedra, extending along the c axis, which are crosslinked by bands of edge-sharing octahedra (site symmetry 2), statisti- Theauthorsgratefullyacknowledgesupportofthisstudyby cally occupied by (Mg2+ + Fe3+ + Si4+). Between the bands theArizona Science Foundation. built up of the octahedra are two non-equivalent highly distorted six-coordinated sites (site symmetry 2), statistically Supplementary data and figures for this paper are available from the occupied by (Na + Mg). In contrast to omphacites, the great IUCrelectronicarchives(Reference:FJ2504). differencesinsizeandchargebetweenMg2+andSi4+resultin complete,rather thanpartial,orderingofMgandSiintotwo References distinct octahedral sites, whereas Fe3+ is disordered between Angel,R.J.,Gasparik,T.,Ross,N.L.,Finger,L.W.,Prewitt,C.T.&Hazen, thetwosites.Theoctahedronfilledby(Mg+Fe)islargerand R.M.(1988).Nature(London),335,156–158. markedlymoredistortedthanthatoccupiedby(Si+Fe).The Boffa Ballaran, T., Carpenter, M. A., Domeneghetti, M. C. & Tazzoli, V. average (Mg + Fe)—O and (VISi + Fe)—O bond lengths are (1998).Am.Mineral.83,434–443. Bruker(2004).APEX2andSAINT.BrukerAXSInc.,Madison,Wisconsin, 2.075 and 1.850A˚,respectively. USA. Curtis, L., Gittins, J., Kocman, V., Rucklidge, J. C., Hawthorne, F. C. & Ferguson,R.B.(1975).Can.Mineral.13,62–67. Related literature Downs,R.T.&Hall-Wallace,M.(2003).Am.Mineral.88,247–250. Finger,L.W.&Hazen,R.M.(1991).ActaCryst.B47,561–580. For structures of high-pressure synthetic clinopyroxenes with Gasparik,T.(1989).Contrib.Mineral.Petrol.102,389–405. six-coordinated Si, see: Angel et al. (1988); Yang & Konzett Konzett,J.,Yang,H.&Frost,D.J.(2005).J.Petrol.46,749–781. Matsumoto,T.,Tokonami,M.&Morimoto,N.(1975).Am.Mineral.60,634– (2005); Yang et al. (2009). For structures of ordered P2/n 641. omphacites, see: Curtis et al. (1975); Matsumoto et al. (1975); Robinson,K.,Gibbs,G.V.&Ribbe,P.H.(1971).Science,172,567–570. Rossi et al. (1983). For background on the stability of clino- Rossi, G., Smith, D. C., Ungaretti, L. & Domeneghetti, C. (1983). Contrib. Mineral.Petrol.83,247–258. pyroxenes at high pressures and temperatures, see: Gasparik Shannon,R.D.(1976).ActaCryst.A32,751–767. (1989); Konzett et al. (2005). For general background on Sheldrick,G.M.(2005).SADABS.UniversityofGo¨ttingen,Germany. materials with six-coordinated silicon, see: Finger & Hazen Sheldrick,G.M.(2008).ActaCryst.A64,112–122. Wang,W.&Sueno,S.(1996).Mineral.J.18,9–16. (1991).Forthegeologicoccurrenceofclinopyroxenewithsix- Westrip,S.P.(2010).J.Appl.Cryst.43,920–925. coordinatedSi,see: Wang &Sueno(1996). Forspectroscopic Yang,H.&Konzett,J.(2005).Am.Mineral.90,1223–1226. measurements onP2/nclinopyroxenes,see:Boffa Ballaranet Yang,H.,Konzett,J.,Frost,D.J.&Downs,R.T.(2009).Am.Mineral.94,942– 949. i18 Posneretal. doi:10.1107/S1600536812002966 ActaCryst.(2012).E68,i18 supplementary materials supplementary materials Acta Cryst. (2012). E68, i18 [ doi:10.1107/S1600536812002966 ] 3+ High-pressure synthetic (Na Mg )(Mg Fe Si )Si O , with six-coordinated silicon, 0.97 0.03 0.43 0.17 0.40 2 6 isostructural with P2/n omphacite E. S. Posner, J. Konzett, D. J. Frost, R. T. Downs and H. Yang Comment The coordination of silicon with oxygen in crystalline materials is crucial for our understanding of the structure and com- position of the Earth's interior because together they account for 63% of the atoms in the planet. In general, silicon is four- IV VI coordinated ( Si) in the Earth's crust and upper mantle, but six-coordinated ( Si) in the lower mantle (e.g., Finger & IV Hazen, 1991). In the Earth's transition zone (between depths of 410 and 670 km), minerals are found to contain both Si VI and Si. Phase transitions that involve a change in the Si coordination may affect many important physical and chemical properties of materials, such as density, bulk moduli, and elasticity, which, when coupled with seismic observations, can provide vital information on the complex constituents of the Earth's mantle. Clinopyroxenes, one of the major rock-forming minerals of the Earth's upper mantle, were long assumed to con- IV tain Si only. Studies of pyroxenes synthesized at high temperatures and pressures, however, have revealed their capa- IV VI city to accommodate both Si and Si (Angel et al. 1988; Konzett et al. 2005; Yang & Konzett 2005; Yang et al., 2009), pointing to their possible stabilities at higher pressures. In particular, Angel et al. (1988) reported a high-pressure Na(Mg Si )Si O clinopyroxene (designated as NaPx hereafter), which is isostructural with ordered P2/n omphacite, 0.5 0.5 2 6 VI with Si and Mg fully ordered into two distinct octahedral sites. Later studies of NaPx-CaMgSi O (diopside) and NaPx- 2 6 NaAlSi O (jadeite) solid solutions uncovered a symmetry transition from an ordered P2/n to a disordered C2/c structure 2 6 VI as Si content decreases (Yang & Konzett, 2005; Yang et al., 2009). The natural occurrence of a clinopyroxene contain- VI ing Si, (Na Mg )(Mg Si )Si O , was reported by Wang & Sueno (1996) as an inclusion in a diamond from 0.16 0.84 0.92 0.08 2 6 a kimberlite in China. According to the phase stability relations for the NaPx-Mg Si O (enstatite) join (Gasparik, 1989), 2 2 6 this inclusion crystallized at pressures greater than 16.5 GPa, or at a depth within the Earth's transition zone (~500 km). The foremost implications of this finding include that (1) some portions of the Earth's upper mantle may contain a greater ratio of Na/Al than previously inferred from the xenolith chemistry, and (2) clinopyroxenes may be one of potential candidates as a silica-rich phase in the Earth's mantle. To gain more insights into the systematics on the crystal chemistry and stability VI field of pyroxenes with Si, we conducted a structure refinement of a high-pressure synthetic NaPx-NaFeSi O (aegirine) 2 6 solid solution (designated as NaPxFe hereafter) based on the single-crystal X-ray diffraction data. NaPxFe is isotyic with P2/n omphacite (Matsumoto et al. 1975; Curtis et al. 1975; Rossi et al. 1983) and NaPx (Angel et al., 1988; Yang et al., 2009). Its structure is characterized by a distorted closest-packed array of oxygen atoms with a layer of single silicate chains, extending along c, formed by Si1O and Si2O tetrahedra, alternating with a layer containing 4 4 2+ 3+ 4+ two distinct, edge-sharing octahedra M1 and M1(1), occupied by (Mg + Fe + Si ). Also in the octahedral layer are two nonequivalent, considerably distorted six-coordinated sites M2 and M2(1), occupied by (Na + Mg) (Fig. 1). Note that Na in clinopyroxenes has been regarded to be eight-coordinated in all previous studies. However, our electron-density and sup-1 supplementary materials bond-valence sum calculations indicate that Na in NaPxFe is actually six-coordinated. In contrast to omphacites, the great 2+ 4+ differences in size and charge between Mg and Si result in complete, rather than partial, ordering of Mg at M1 and Si VI at M1(1), while Fe is disordered between the two sites. An inspection of structure data for pyroxenes containing Si shows that, as the respective contents of Mg and Si in the M1 and M1(1) sites decreases from NaPx to Na(Mg Al Si )Si O 0.45 0.10 0.45 2 6 (Angel et al., 1988; Yang et al., 2009) and NaPxFe, the average M1—O bond length decreases from 2.092 to 2.084 and 2.075 Å, respectively, whereas the average M1(1)-O bond distance increases from 1.807 Å to 1.813 and 1.850 Å, respectively. 2+ 3+ This observation is evidently a direct consequence of the differences in ionic radii among Mg (0.72 Å), Fe (0.645 Å), 3+ VI 4+ Al (0.535 Å), and Si (0.40 Å) (Shannon, 1976). The coupled changes in the average M1—O and M1(1)-O bond distances from NaPx to Na(Mg Al Si )Si O and NaPxFe lead to a substantial reduction in the size mismatch 0.45 0.10 0.45 2 6 between the two edge-shared octahedra, as well as the degree of distortion of the M1 octahedron in terms of the octahedral angle variance (OAV) and octahedral quadratic elongation (OQE) (Robinson et al., 1971). The OAV and OQE values are 107.2 and 1.035, respectively, for the M1 octahedron in NaPx, 101.4 and 1.033 in Na(Mg Al Si )Si O , and 88.2 0.45 0.10 0.45 2 6 and 1.029 in NaPxFe. Interestingly, as the geometric differences between the M1 and M1(1) octahedra decreases with VI decreasing Si content from NaPx to Na(Mg Al Si )Si O and NaPxFe, the difference between the mean M2—O 0.45 0.10 0.45 2 6 and M2(1)-O bond distances is also reduced, which is 0.123, 0.113, and 0.096 Å for NaPx, Na(Mg Al Si )Si O , 0.45 0.10 0.45 2 6 VI and NaPxFe, respectively. Conceivably, as the Si content is further decreased, the P2/n structure will eventually transform to the C2/c structure, in which M1 and M1(1) become identical, so do M2 and M2(1), and Si1 and Si2. Plotted in Figure 2 are Raman spectra of NaPxFe and two clinopyroxenes in the NaPx-jadeite system for comparison, one with P2/n symmetry and the other C2/c (Yang et al., 2009). The detailed assignment of Raman bands for clinopyroxenes VI containing Si has been discussed by Yang et al. (2009). Generally, the Raman spectra of pyroxenes can be classified into -1 four regions. Region 1 includes the bands between 800 and 1200 cm , which are assigned as the Si—O stretching vibrations -1 in the SiO tetrahedra. Region 2 is between 630–800 cm , which includes the bands attributable to the Si—O—Si vibrations 4 -1 within the silicate chains. Region 3, from 400 to 630 cm , includes the bands that are mainly associated with the O—Si—O -1 bending modes of SiO tetrahedra. The bands in Region 4, which spans from 50 to 400 cm , are of a complex nature, chiefly 4 due to lattice vibration modes, polyhedral librations and M—O interactions, as well as possible O—Si—O bending. As noted by Boffa Ballaran et al. (1998) and Yang et al. (2009), the C2/c-to-P2/n transformation is characterized by the splitting of many observable Raman bands in the C2/c structure into doublets in the P2/n structure, consistent with the doubled number of independent atomic sites in the P2/n structure relative to that in the C2/c structure. Compared to the Raman spectrum of P2/n Na(Mg Al Si )Si O (Sample J2, Yang et al., 2009), most Raman bands for NaPxFe are noticeably broader, 0.45 0.10 0.45 2 6 indicating the increased positional disorder of atoms in our sample, which further suggests that the chemistry of our sample is closer to the P2/n-to-C2/c transition than that of Na(Mg Al Si )Si O (Yang et al., 2009), in agreement with the 0.45 0.10 0.45 2 6 conclusion we derived above from the structure refinement. Experimental The specimen used in this study was synthesized in a multi-anvil apparatus at 15 GPa and 1500 °C for 23.2 h (run #JKB2006–12) and then rapidly quenched (< 5 s) to ambient conditions. The crystal chemistry was determined with a Jeol electron microprobe on the same single-crystal used for the X-ray intensity data collection. The average composition of nine sup-2 supplementary materials analysis points yielded a chemical formula (normalized on the basis of 6 oxygen atoms and 4 cations while maintaining charge-balance) (Na Mg )(Mg Fe Si )Si O 0.97 0.03 0.43 0.17 0.40 2 6. The Raman spectrum of (Na Mg )(Mg Fe Si )Si O was collected from a randomly oriented crystal at 0.97 0.03 0.43 0.17 0.40 2 6 100% power on a Thermo Almega microRaman system, using a 532 nm solid-state laser, and a thermoelectrically cooled -1 CCD detector. The laser is partially polarized with 4 cm resolution and a spot size of 1 µm. Refinement Throughout the structure refinements, the chemical composition of the crystal was fixed to that determined from electron VI microprobe analysis. From crystal-chemical considerations, all Mg and Si were assigned to the M1 and M1(1) sites, 3+ respectively, with the rest filled by Fe for both sites. Because the average distance of M2—O is shorter than that of M2(1)-O, we assigned 0.03 Mg apfu to the M2 site. The highest residual peak in the difference Fourier maps was located at (0.7991, 0.0789, 0.2448), 0.54 Å from M2, and the deepest hole at (0.2602, 0.1856, 0.1853), 0.48 Å from M1(1). Figures Fig. 1. Crystal structure of P2/n (Na Mg )(Mg Fe Si )Si O clinopyroxene. 0.97 0.03 0.43 0.17 0.40 2 6 Fig. 2. Raman spectra of clinopyroxenes. (a) P2/n (Na Mg )(Mg Fe Si )Si O 0.97 0.03 0.43 0.17 0.40 2 6 (this study), (b) P2/n Na(Mg Al Si )Si O (Yang et al., 2009) and (c) C2/c 0.45 0.10 0.45 2 6 (Na Mg )(Mg Al Si )Si O (Yang et al., 2009). 0.97 0.03 0.37 0.30 0.33 2 6 (sodium magnesium) [magnesium iron(III) silicon] disilicate Crystal data (Na0.97Mg0.03)(Mg0.43Fe0.17Si0.40)Si2O6 F(000) = 409 Mr = 206.39 Dx = 3.360 Mg m−3 Monoclinic, P2/n Mo Kα radiation, λ = 0.71073 Å Hall symbol: -P 2yac Cell parameters from 1071 reflections a = 9.4432 (8) Å θ = 3.3–35.6° b = 8.6457 (7) Å µ = 1.69 mm−1 c = 5.2540 (5) Å T = 293 K β = 108.003 (6)° Cube, pale gray V = 407.95 (6) Å3 0.06 × 0.05 × 0.05 mm Z = 4 sup-3 supplementary materials Data collection Bruker APEXII CCD area-detector 1481 independent reflections diffractometer Radiation source: fine-focus sealed tube 980 reflections with I > 2σ(I) graphite Rint = 0.033 φ and ω scan θmax = 32.5°, θmin = 3.3° Absorption correction: multi-scan h = −14→14 (SADABS; Sheldrick 2005) Tmin = 0.906, Tmax = 0.920 k = −13→10 6586 measured reflections l = −7→7 Refinement Primary atom site location: structure-invariant direct Refinement on F2 methods Least-squares matrix: full Secondary atom site location: difference Fourier map R[F2 > 2σ(F2)] = 0.036 w = 1/[σ2(Fo2) + (0.0264P)2 + 0.6629P] where P = (Fo2 + 2Fc2)/3 wR(F2) = 0.085 (Δ/σ)max = 0.001 S = 1.07 Δρmax = 0.51 e Å−3 1481 reflections Δρmin = −0.66 e Å−3 Extinction correction: SHELXL97 (Sheldrick, 2008), 96 parameters Fc*=kFc[1+0.001xFc2λ3/sin(2θ)]-1/4 3 restraints Extinction coefficient: 0 Special details Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance mat- rix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s. planes. Refinement. Refinement of F2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F2, convention- al R-factors R are based on F, with F set to zero for negative F2. The threshold expression of F2 > σ(F2) is used only for calculating R- factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F2 are statistically about twice as large as those based on F, and R- factors based on ALL data will be even larger. 2 Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å ) x y z Uiso*/Ueq Occ. (<1) M2 0.7500 0.04980 (16) 0.2500 0.0129 (3) 0.9400 (1) M2MG 0.7500 0.04980 (16) 0.2500 0.0129 (3) 0.0600 (1) M2(1) 0.7500 0.45601 (17) 0.7500 0.0169 (3) M1 0.7500 0.65310 (10) 0.2500 0.00495 (18) 0.8600 (1) M1Fe 0.7500 0.65310 (10) 0.2500 0.00495 (18) 0.1400 (1) M1(1) 0.7500 0.84745 (9) 0.7500 0.00855 (17) 0.8000 (1) sup-4 supplementary materials M11Fe 0.7500 0.84745 (9) 0.7500 0.00855 (17) 0.2000 (1) Si1 0.04344 (7) 0.84714 (7) 0.22988 (13) 0.00748 (14) Si2 0.03811 (7) 0.66398 (7) 0.73666 (13) 0.00731 (14) O1 0.86242 (18) 0.8417 (2) 0.1106 (4) 0.0133 (4) O2 0.85803 (18) 0.6879 (2) 0.6524 (4) 0.0129 (4) O3 0.1201 (2) 0.0136 (2) 0.3071 (4) 0.0130 (4) O4 0.1012 (2) 0.4949 (2) 0.7949 (4) 0.0141 (4) O5 0.10966 (18) 0.7652 (2) 0.0132 (3) 0.0105 (3) O6 0.09535 (18) 0.74992 (19) 0.5087 (3) 0.0112 (3) 2 Atomic displacement parameters (Å ) U11 U22 U33 U12 U13 U23 M2 0.0162 (7) 0.0106 (7) 0.0093 (7) 0.000 0.0002 (5) 0.000 M2MG 0.0162 (7) 0.0106 (7) 0.0093 (7) 0.000 0.0002 (5) 0.000 M2(1) 0.0210 (7) 0.0107 (7) 0.0128 (8) 0.000 −0.0037 (6) 0.000 M1 0.0060 (4) 0.0045 (4) 0.0037 (4) 0.000 0.0006 (3) 0.000 M1Fe 0.0060 (4) 0.0045 (4) 0.0037 (4) 0.000 0.0006 (3) 0.000 M1(1) 0.0094 (3) 0.0085 (4) 0.0073 (4) 0.000 0.0020 (3) 0.000 M11Fe 0.0094 (3) 0.0085 (4) 0.0073 (4) 0.000 0.0020 (3) 0.000 Si1 0.0081 (3) 0.0074 (3) 0.0065 (3) −0.0002 (2) 0.0016 (2) −0.0005 (2) Si2 0.0075 (3) 0.0076 (3) 0.0065 (3) 0.0000 (2) 0.0018 (2) 0.0004 (2) O1 0.0103 (7) 0.0128 (9) 0.0165 (9) 0.0007 (6) 0.0039 (7) −0.0023 (7) O2 0.0074 (7) 0.0173 (9) 0.0132 (9) −0.0013 (6) 0.0018 (6) 0.0035 (7) O3 0.0200 (9) 0.0074 (8) 0.0106 (9) −0.0014 (6) 0.0033 (7) −0.0009 (6) O4 0.0188 (9) 0.0104 (9) 0.0132 (9) 0.0006 (7) 0.0050 (7) 0.0002 (7) O5 0.0098 (7) 0.0136 (9) 0.0078 (8) 0.0009 (6) 0.0024 (6) −0.0018 (6) O6 0.0125 (8) 0.0129 (9) 0.0086 (8) −0.0017 (6) 0.0037 (6) 0.0017 (6) Geometric parameters (Å, °) M2—O1i 2.319 (2) M1—O2 2.0658 (18) M2—O1ii 2.319 (2) M1—O2xi 2.0658 (18) M2—O3iii 2.3356 (18) M1—O1xi 2.1917 (19) M2—O3iv 2.3356 (18) M1—O1 2.1917 (19) M2—O6v 2.3651 (19) M1(1)—O3v 1.8071 (19) M2—O6vi 2.3651 (19) M1(1)—O3vii 1.8071 (19) M2—O5vii 2.7127 (19) M1(1)—O1xii 1.8645 (18) M2—O5viii 2.7127 (19) M1(1)—O1xi 1.8645 (18) M2(1)—O2ix 2.376 (2) M1(1)—O2ix 1.8788 (19) M2(1)—O2 2.376 (2) M1(1)—O2 1.8788 (19) M2(1)—O4x 2.4073 (19) Si1—O3xiii 1.6058 (19) M2(1)—O4vi 2.4073 (19) Si1—O5 1.6216 (18) M2(1)—O5vii 2.438 (2) Si1—O6 1.6276 (18) M2(1)—O5v 2.438 (2) Si1—O1xiv 1.6294 (18) M2(1)—O6vii 2.8944 (19) Si2—O4 1.5725 (19) sup-5 supplementary materials M2(1)—O6v 2.8944 (19) Si2—O2xiv 1.6326 (18) M1—O4vi 1.9678 (19) Si2—O6 1.6366 (18) M1—O4v 1.9678 (19) Si2—O5xii 1.6510 (18) O4vi—M1—O4v 98.88 (11) O3v—M1(1)—O2ix 170.80 (8) O4vi—M1—O2 96.72 (7) O3vii—M1(1)—O2ix 89.37 (8) O4v—M1—O2 94.15 (7) O1xii—M1(1)—O2ix 83.67 (8) O4vi—M1—O2xi 94.15 (7) O1xi—M1(1)—O2ix 94.09 (8) O4v—M1—O2xi 96.72 (7) O3v—M1(1)—O2 89.37 (8) O2—M1—O2xi 163.26 (11) O3vii—M1(1)—O2 170.80 (8) O4vi—M1—O1xi 90.36 (7) O1xii—M1(1)—O2 94.09 (8) O4v—M1—O1xi 164.04 (7) O1xi—M1(1)—O2 83.67 (8) O2—M1—O1xi 71.74 (7) O2ix—M1(1)—O2 85.52 (11) O2xi—M1—O1xi 95.54 (7) O3xiii—Si1—O5 109.12 (10) O4vi—M1—O1 164.04 (7) O3xiii—Si1—O6 104.39 (10) O4v—M1—O1 90.36 (7) O5—Si1—O6 109.41 (9) O2—M1—O1 95.54 (7) O3xiii—Si1—O1xiv 117.40 (10) O2xi—M1—O1 71.74 (7) O5—Si1—O1xiv 107.69 (9) O1xi—M1—O1 83.83 (10) O6—Si1—O1xiv 108.64 (10) O3v—M1(1)—O3vii 96.67 (12) O4—Si2—O2xiv 118.08 (10) O3v—M1(1)—O1xii 89.08 (8) O4—Si2—O6 111.93 (10) O3vii—M1(1)—O1xii 92.94 (8) O2xiv—Si2—O6 107.21 (9) O3v—M1(1)—O1xi 92.94 (8) O4—Si2—O5xii 107.11 (10) O3vii—M1(1)—O1xi 89.08 (8) O2xiv—Si2—O5xii 106.27 (9) O1xii—M1(1)—O1xi 176.97 (12) O6—Si2—O5xii 105.39 (9) Symmetry codes: (i) −x+3/2, y−1, −z+1/2; (ii) x, y−1, z; (iii) x+1/2, −y, z−1/2; (iv) −x+1, −y, −z+1; (v) −x+1, −y+1, −z+1; (vi) x+1/2, −y+1, z−1/2; (vii) x+1/2, −y+1, z+1/2; (viii) −x+1, −y+1, −z; (ix) −x+3/2, y, −z+3/2; (x) −x+1, −y+1, −z+2; (xi) −x+3/2, y, −z+1/2; (xii) x, y, z+1; (xiii) x, y+1, z; (xiv) x−1, y, z. sup-6 supplementary materials Fig. 1 sup-7 supplementary materials Fig. 2 sup-8