Crystal structure and bonding in the new mineral AsSbO3. Marcus J. Origlieri1, Robert T. Downs1, Mic

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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_at_mineralzone.com downs_at_geo.arizona.ed
u
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unknown mineral

• EDS indicated only major As, Sb

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Raman spectrum
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crystal morphology
Palache (1934)
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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

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X-ray diffraction

• streaky data
• merged well for space group P21/n (Rsym 2.71)

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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

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crystal structure solution
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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

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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
• ltR(As-O)gt 1.782 Å ltR(Sb-O)gt 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
• ltR(As1-O)gt 1.783 Å ltR(As2-O)gt 1.793 Å

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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)
• lt?O-As-Ogt 97.7 lt?O-Sb-Ogt 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)
• lt?O-As1-Ogt 98.1 lt?O-As2-Ogt 94.8

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substitution of Sb into claudetite

• Sb in AsSbO3 structure preferentially occupies
  the As2 site of claudetite
• ltR(As2-O) ltR(As1-O)gt
• lt?O-As2-Ogt lt lt?O-As1-Ogt
• 94.8 lt 98.1
• Sb prefers a smaller ?O-M-O for MO3 than As

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

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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.

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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

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electron density distribution

• Sb-O1
• 2.947 Å
• (intra-layer)
• Sb-O2
• 3.237 Å
• (inter-layer)

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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

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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

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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
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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
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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

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crystal structure of cubic As2O3
view down 110
view down 010
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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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