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1 Department of Geosciences, University of Arizona Tucson, Arizona 85719-0077 USA

Crystal structure and bonding in the new mineral AsSbO 3 . Marcus J. Origlieri 1 *, Robert T. Downs 1§ , Michael D. Carducci 1 Kevin M. Rosso 2 , G. V. Gibbs 3. 1 Department of Geosciences, University of Arizona Tucson, Arizona 85719-0077 USA 2 Pacific Northwest National Laboratory

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1 Department of Geosciences, University of Arizona Tucson, Arizona 85719-0077 USA

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  1. Crystal structure and bonding in the new mineral AsSbO3.Marcus J. Origlieri1*, Robert T. Downs1§, Michael D. Carducci1Kevin M. Rosso2, G. V. Gibbs3 1Department of Geosciences, University of Arizona Tucson, Arizona 85719-0077 USA 2Pacific Northwest National Laboratory P.O. Box 999, K8-96, Richland, WA 99352 USA 3Department of Geological Sciences, Virginia Polytechnic Institute Blacksburg, VA 24061-0420 USA *marcus@mineralzone.com; §downs@geo.arizona.edu

  2. unknown mineral • EDS indicated only major As, Sb

  3. Raman spectrum

  4. crystal morphology Palache (1934)

  5. microprobe chemical analysis Average of 10 standardized WDS analyses: Sb2O3 55.77% As2O3 45.15% total 101.92% EMPIRICAL FORMULA = As1.088Sb0.912O3 standards enargite Cu3AsS4 stibiotantalite SbTaO4

  6. X-ray diffraction • streaky data • merged well for space group P21/n (Rsym = 2.71%)

  7. crystal structure solution • Matches synthetic AsSbO3 (Bodenstein et al. 1983) • Trigonal pyramids of AsO3 and SbO3 link corners to form infinite sheets of composition AsSbO3 stacked along b

  8. crystal structure solution

  9. new mineral vs. claudetite new mineral claudetite chemistry AsSbO3 As2O3 space group P21/n P21/n a 4.5757(4) Å 4.5460(4) Å b 13.1288(13) Å 13.0012(14) Å c 5.4216(5) Å 5.3420(5) Å b 95.039(4)° 94.329(2)° V 324.44(5) Å3 314.83(5) Å3 Z 4 4 dcalc 5.009 g/cm3 4.174 g/cm3

  10. bond distances new mineral As−O1 1.773(7) Å Sb−O1 1.978(7) Å As−O2 1.781(6) Å Sb−O2 2.006(6) Å As−O3 1.792(6) Å Sb−O3 1.995(7) Å <R(As−O)> 1.782 Å <R(Sb−O)> 1.993 Å claudetite As1−O1 1.772(5) Å As2−O1 1.783(5) Å As1−O2 1.788(4) Å As2−O2 1.805(5) Å As1−O3 1.790(5) Å As2−O3 1.790(5) Å <R(As1−O)> 1.783 Å <R(As2−O)> 1.793 Å

  11. bond angles new mineral O1−As−O2 100.8(3)° O1−Sb−O2 92.2(3)° O1−As−O3 101.1(3)° O1−Sb−O3 93.0(3)° O2−As−O3 91.1(3)° O2−Sb−O3 84.8(3)° <O−As−O> 97.7° <O−Sb−O> 90.0° claudetite O1−As1−O2 100.8(2)° O1−As2−O2 95.2(2)° O1−As1−O3 102.1(2)° O1−As2−O3 97.9(2)° O2−As1−O3 91.3(2)° O2−As2−O3 91.3(2)° <O−As1−O> 98.1° <O−As2−O> 94.8°

  12. substitution of Sb into claudetite Sb in AsSbO3 structure preferentially occupies the As2 site of claudetite <R(As2−O) ~ <R(As1−O)> <O−As2−O> < <O−As1−O> 94.8° < 98.1° Sb prefers a smaller O−M−O for MO3 than As

  13. ordering of As and Sb synthetic natural Bodenstein et al. (1983)this study <R(As−O)> 1.80 Å 1.782 Å <R(Sb−O)> 1.95 Å 1.993 Å The more extreme <R(As−O)> and <R(Sb−O)> indicate a higher degree of ordering in natural AsSbO3 than synthetic material

  14. formula of new mineral • Natural AsSbO3 shows a higher degree of As/Sb ordering than synthetic material • Crystal structure refinement gives lower residual value (5.66%) with idealized chemistry than with microprobe chemistry ACTUAL CHEMISTRY = AsSbO3

  15. bonding in arsenites • Between sheets of the leiteite (ZnAs2O4) structure, Ghose (1987) argues “long As-O interactions must be considered as weak bonds, which hold the composite layers together.” • Pertlik (1975) notes that As-O distances of 3.15 Å in trippkeite result from steric effects.

  16. definition of bonding • Bader (1990) defines a bonded interaction exists when electron density shows both: • BOND PATH – a continuous path of local maxima of electron density in the perpendicular plane between two maxima of electron density (i.e. atoms) • BOND CRITICAL POINT – a (3,−1) saddle point of electron density along the bond path located between the atoms

  17. electron density distribution Sb−O1 2.947 Å (intra-layer) Sb−O2 3.237 Å (inter-layer)

  18. quantum calculations • Follow Density Function Theory • Linear combinations of numerically solved wave functions • Basis sets optimized for Crystal98 (Pisani et al. 2000) • Uses coordinates of atoms and unit cell from crystal structure refinement • Search radius 9 Å

  19. bonding topology • three groups of bonds distinguished their electron densities at the bond critical points • close contacts r(rc) = 0.984−1.012 As−O r(rc) = 0.730−0.757 Sb−O • intra-layer bonds r(rc) = 0.169−0.134 • inter-layer bonds r(rc) = 0.084−0.062

  20. intra-layer bonds responsible for the corrugation of the sheet Three separate bonds: Sb−O3 2.791 Å As−O2 2.903 Å Sb−O1 2.947 Å

  21. inter-layer bonds Two weakest bonds in the structure are between sheets: Sb−O2 3.237 Å As−O3 3.346 Å Responsible for perfect (010) cleavage of the mineral

  22. related structures • Cubic As2O3 (arsenolite) and Sb2O3 (senarmontite) have structures consisting of M4O6 molecular units. • Oxygen atoms form corners of octahedra with metal atoms centered above alternating faces of the octahedron • Cubic AsSbO3 is a solid solution between As2O3 and Sb2O3

  23. crystal structure of cubic As2O3 view down [010] view down [110]

  24. cubic As2O3 and Sb2O3 • As2O3 (Ballirano & Maras, 2002) • a = 11.074 Å • R(As−O) = 1.786(2) Å • O−As−O = 98.4(2)° • Sb2O3 (Whitten et al. 2004) • a = 11.116 Å • R(Sb−O) = 1.978(1) Å • O−Sb−O = 95.9(1)°

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