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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.

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Presentation on theme: "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."— Presentation transcript:

1 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 USA 2 Pacific Northwest National Laboratory P.O. Box 999, K8-96, Richland, WA USA 3 Department of Geological Sciences, Virginia Polytechnic Institute Blacksburg, VA USA

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: Sb 2 O % As 2 O % total101.92% EMPIRICAL FORMULA = As Sb O 3 standardsenargite Cu 3 AsS 4 stibiotantalite SbTaO 4

6 X-ray diffraction streaky data merged well for space group P2 1 /n (R sym = 2.71%)

7 crystal structure solution Matches synthetic AsSbO 3 (Bodenstein et al. 1983) Trigonal pyramids of AsO 3 and SbO 3 link corners to form infinite sheets of composition AsSbO 3 stacked along b

8 crystal structure solution

9 new mineral vs. claudetite new mineralclaudetite chemistryAsSbO 3 As 2 O 3 space groupP2 1 /nP2 1 /n a4.5757(4) Å4.5460(4) Å b (13) Å (14) Å c5.4216(5) Å5.3420(5) Å b95.039(4)°94.329(2)° V324.44(5) Å (5) Å 3 Z44 d calc g/cm g/cm 3

10 bond distances new mineral As − O11.773(7) ÅSb − O11.978(7) Å As − O21.781(6) ÅSb − O22.006(6) Å As − O31.792(6) ÅSb − O31.995(7) Å Å Å claudetite As1 − O11.772(5) ÅAs2 − O11.783(5) Å As1 − O21.788(4) ÅAs2 − O21.805(5) Å As1 − O31.790(5) ÅAs2 − O31.790(5) Å Å Å

11 bond angles new mineral  O1−As−O2100.8(3)°  O1−Sb−O292.2(3)°  O1−As−O3101.1(3)°  O1−Sb−O393.0(3)°  O2−As−O391.1(3)°  O2−Sb−O384.8(3)° 97.7° 90.0° claudetite  O1−As1−O2100.8(2)°  O1−As2−O295.2(2)°  O1−As1−O3102.1(2)°  O1−As2−O397.9(2)°  O2−As1−O391.3(2)°  O2−As2−O391.3(2)° 98.1° 94.8°

12 substitution of Sb into claudetite Sb in AsSbO 3 structure preferentially occupies the As2 site of claudetite 94.8° < 98.1° Sb prefers a smaller  O−M−O for MO 3 than As

13 ordering of As and Sb syntheticnatural Bodenstein et al. (1983)this study 1.80 Å1.782 Å 1.95 Å1.993 Å The more extreme and indicate a higher degree of ordering in natural AsSbO 3 than synthetic material

14 formula of new mineral Natural AsSbO 3 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 = AsSbO 3

15 bonding in arsenites Between sheets of the leiteite (ZnAs 2 O 4 ) 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−O Å (intra- layer) Sb−O 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 c ) = 0.984−1.012 As−O  (r c ) = 0.730−0.757 Sb−O –intra-layer bonds  (r c ) = 0.169−0.134 –inter-layer bonds  (r c ) = 0.084−0.062

20 intra-layer bonds responsible for the corrugation of the sheet Three separate bonds: Sb−O Å As−O Å Sb−O Å

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

22 related structures Cubic As 2 O 3 (arsenolite) and Sb 2 O 3 (senarmontite) have structures consisting of M 4 O 6 molecular units. Oxygen atoms form corners of octahedra with metal atoms centered above alternating faces of the octahedron Cubic AsSbO 3 is a solid solution between As 2 O 3 and Sb 2 O 3

23 crystal structure of cubic As 2 O 3 view down [110]view down [010]

24 cubic As 2 O 3 and Sb 2 O 3 As 2 O 3 (Ballirano & Maras, 2002) –a = Å –R(As−O) = 1.786(2) Å –  O−As−O = 98.4(2)° Sb 2 O 3 (Whitten et al. 2004) –a = Å –R(Sb−O) = 1.978(1) Å –  O−Sb−O = 95.9(1)°

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