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A rigid-ion lattice-dynamical treatment accounts reasonably well for most of the atomic displacement parameters (ADPs) reported in the literature for a synthetic sample of spessartine Mn3Al2Si3O12; the model accounts less well for the ADPs of the Mn atom. These results are similar to those obtained for the corresponding garnets pyrope Mg3Al2Si3O12 and almandine Fe3Al2Si3O12. The results are confirmed by a very good agreement of the lattice-dynamical estimates with the experimental values of the heat capacity that are currently available, as well as those of the Raman and infrared vibrational spectra. The anomalous behaviour of the Mn atom is reflected in the entropy values. As is the case for pyrope and almandine, here the agreement with the experimental results can be markedly improved if the existence of a low-temperature order-disorder transition concerning the Mn atom is considered. The lattice-dynamical estimates for all the atoms presented here do not agree with the corresponding ADPs obtained in a crystal structure refinement of a supposedly `pure' natural sample from Elba. In turn, these experimental ADPs do not agree with those observed for the synthetic sample, thereby showing a physical difference; such a possibility is in agreement with recent observations by other authors, who found an unexpected fluorine content in several natural specimens of spessartine. Therefore, theoretical estimates of ADPs are reliable enough to point out unexpected situations if disagreement with the observed values occurs.

Supporting information

cif

Crystallographic Information File (CIF) https://doi.org/10.1107/S0108768102017925/av0058sup1.cif
Contains datablock I

hkl

Structure factor file (CIF format) https://doi.org/10.1107/S0108768102017925/av0058sup2.hkl
Contains datablock I

Computing details top

Data collection: CAD4 (Enraf Nonius); cell refinement: CAD4 (Enraf Nonius); data reduction: SDP for Windows; program(s) used to refine structure: Full-matrix least-squares (SDP for Windows); molecular graphics: SDP for Windows; software used to prepare material for publication: SDP for Windows.

(I) top
Crystal data top
Al2Mn3O12Si3Dx = 4.180 Mg m3
Mr = 495.03Mo Kα radiation, λ = 0.71073 Å
Cubic, Ia3dCell parameters from 25 reflections
Hall symbol: -I 4bd 2ab 3θ = 12.2–22.1°
a = 11.630 (1) ŵ = 5.31 mm1
V = 1573.0 (2) Å3T = 293 K
Z = 8[ENTER SHAPE], orange
F(000) = 19120.13 × 0.10 × 0.10 mm
Data collection top
CAD4 (Enraf Nonius)
diffractometer
289 reflections with Fo > 2.0 * 3.00 * σ(Fo)
Graphite monochromatorθmax = 40.0°, θmin = 3.0°
ω/2θ scansh = 020
Absorption correction: empirical (using intensity measurements)
?
k = 020
Tmin = 0.703, Tmax = 1.000l = 020
2701 measured reflections1 standard reflections every 120 min
417 independent reflections
Refinement top
Refinement on F20 constraints
Least-squares matrix: full
R[F2 > 2σ(F2)] = 0.013(Δ/σ)max = 0.034
wR(F2) = 0.016Δρmax = 0.48 e Å3
S = 0.65Δρmin = 0.00 e Å3
259 reflectionsExtinction correction: secondary Zachariasen
40 parametersExtinction coefficient: 0.0000
0 restraints
Crystal data top
Al2Mn3O12Si3Z = 8
Mr = 495.03Mo Kα radiation
Cubic, Ia3dµ = 5.31 mm1
a = 11.630 (1) ÅT = 293 K
V = 1573.0 (2) Å30.13 × 0.10 × 0.10 mm
Data collection top
CAD4 (Enraf Nonius)
diffractometer
417 independent reflections
Absorption correction: empirical (using intensity measurements)
?
289 reflections with Fo > 2.0 * 3.00 * σ(Fo)
Tmin = 0.703, Tmax = 1.0001 standard reflections every 120 min
2701 measured reflections
Refinement top
R[F2 > 2σ(F2)] = 0.01340 parameters
wR(F2) = 0.0160 restraints
S = 0.65Δρmax = 0.48 e Å3
259 reflectionsΔρmin = 0.00 e Å3
Special details top

Refinement. Weight = (4*Fo2)/[σ2(Fo2)] (refinement on F) σ(Fo2) = [σ2(I) + (P*Fo2)2](1/2) P = 0.0100

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2) top
xyzUiso*/UeqOcc. (<1)
Al0.0000 (1)0.0000 (1)0.0000 (1)0.00414 (4)-.17
Mn0.1250 (1)0.0000 (1)0.2500 (1)0.00832 (3)-.26
Si0.3750 (1)0.0000 (1)0.2500 (1)0.00389 (6)0.25
O0.03473 (5)0.04789 (5)0.65210 (5)0.0052 (1)
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
AL0.00443 (8)0.0044 (1)0.0044 (1)0.0003 (1)0.0003 (1)0.0003 (1)
Mn0.00476 (8)0.00923 (5)0.0092 (1)0.0000 (1)0.0000 (1)0.00174 (8)
SI0.0035 (1)0.00407 (9)0.0041 (1)0.0000 (1)0.0000 (1)0.0000 (1)
O0.0054 (2)0.0062 (2)0.0043 (2)0.0005 (2)0.0005 (2)0.0004 (2)

Experimental details

Crystal data
Chemical formulaAl2Mn3O12Si3
Mr495.03
Crystal system, space groupCubic, Ia3d
Temperature (K)293
a (Å)11.630 (1)
V3)1573.0 (2)
Z8
Radiation typeMo Kα
µ (mm1)5.31
Crystal size (mm)0.13 × 0.10 × 0.10
Data collection
DiffractometerCAD4 (Enraf Nonius)
diffractometer
Absorption correctionEmpirical (using intensity measurements)
Tmin, Tmax0.703, 1.000
No. of measured, independent and
observed [Fo > 2.0 * 3.00 * σ(Fo)] reflections
2701, 417, 289
Rint?
(sin θ/λ)max1)0.904
Refinement
R[F2 > 2σ(F2)], wR(F2), S 0.013, 0.016, 0.65
No. of reflections259
No. of parameters40
Δρmax, Δρmin (e Å3)0.48, 0.00

Computer programs: CAD4 (Enraf Nonius), Full-matrix least-squares (SDP for Windows).

 

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