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Crystal Structure and Bonding in the New Mineral AsSbO3

Examining the crystal structure and bonding of the newly discovered mineral AsSbO3, comparing synthetic and natural forms. The study discusses the bonding topology, substitution of Sb in the structure, and bonding in arsenites. Quantum calculations using Density Function Theory and crystal structure coordinates are analyzed, highlighting key interactions and bond critical points.

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Crystal Structure and Bonding in the New Mineral AsSbO3

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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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