Crystal structure and bonding
in the new mineral AsSbO3.
Marcus J. Origlieri1*, Robert T. Downs1§, Michael D. Carducci1
Kevin 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
unknown
mineral
• EDS
indicated
only major
As, Sb
Intensity (arbitrary units)
Raman spectrum
new mineral
leiteite
100
200
300
400
500
600
-1
Raman shift (rel. cm )
700
800
900
crystal morphology
Palache (1934)
microprobe chemical analysis
Average of 10 standardized WDS analyses:
Sb2O3
As2O3
total
55.77%
45.15%
101.92%
EMPIRICAL FORMULA = As1.088Sb0.912O3
standards
enargite
stibiotantalite
Cu3AsS4
SbTaO4
X-ray diffraction
• streaky data
• merged well
for space
group P21/n
(Rsym =
2.71%)
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
crystal structure solution
new mineral vs. claudetite
new mineral
chemistry
AsSbO3
space group P21/n
a
4.5757(4) Å
b
13.1288(13) Å
c
5.4216(5) Å
b
95.039(4)°
V
324.44(5) Å3
Z
4
dcalc
5.009 g/cm3
claudetite
As2O3
P21/n
4.5460(4) Å
13.0012(14) Å
5.3420(5) Å
94.329(2)°
314.83(5) Å3
4
4.174 g/cm3
bond distances
new mineral
As−O11.773(7) Å
As−O21.781(6) Å
As−O31.792(6) Å
<R(As−O)> 1.782 Å
claudetite
As1−O1
As1−O2
As1−O3
<R(As1−O)>
1.772(5) Å
1.788(4) Å
1.790(5) Å
1.783 Å
Sb−O11.978(7) Å
Sb−O22.006(6) Å
Sb−O31.995(7) Å
<R(Sb−O)>
As2−O1
As2−O2
As2−O3
<R(As2−O)>
1.993 Å
1.783(5) Å
1.805(5) Å
1.790(5) Å
1.793 Å
bond angles
new mineral
O1−As−O2
92.2(3)°
O1−As−O3
93.0(3)°
O2−As−O3
84.8(3)°
<O−As−O>
claudetite
O1−As1−O2
95.2(2)°
O1−As1−O3
97.9(2)°
100.8(3)°
O1−Sb−O2
101.1(3)°
O1−Sb−O3
91.1(3)°
O2−Sb−O3
97.7°
<O−Sb−O>
100.8(2)°
O1−As2−O2
102.1(2)°
O1−As2−O3
90.0°
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
ordering of As and Sb
synthetic
natural
Bodenstein et al. (1983)
this study
<R(As−O)>1.80 Å
<R(Sb−O)>
1.95 Å
1.782 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
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
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.
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
electron density distribution
Sb−O1
2.947 Å
(intralayer)
Sb−O2
3.237 Å
(interlayer)
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
bonding topology
• three groups of bonds distinguished their
electron densities at the bond critical points
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
– close contacts
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
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
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
crystal structure of cubic As2O3
view down [010]
view down [110]
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)°