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The structure of dilanthanum ruthenium pentoxide was solved by powder neutron diffraction at room temperature and 1.5 K. High-temperature La2RuO5 crystallizes in the monoclinic space group P21/c. Upon cooling, the sample undergoes a phase transition to the triclinic low-temperature form (space group P\overline{1}). This transition leads to pronounced changes in the Ru-O-Ru bond distances, resulting in a dimerization of the ruthenium ions.

Supporting information

cif

Crystallographic Information File (CIF) https://doi.org/10.1107/S010827010501509X/ty1006sup1.cif
Contains datablocks global, HT, LT

rtv

Rietveld powder data file (CIF format) https://doi.org/10.1107/S010827010501509X/ty1006HTsup2.rtv
Contains datablock HT

rtv

Rietveld powder data file (CIF format) https://doi.org/10.1107/S010827010501509X/ty1006LTsup3.rtv
Contains datablock LT

Comment top

Among the various modifications of the perovskite structure, compounds belonging to the so-called [110] phases are quite special. In these oxides, the three-dimensional perovskite framework can be considered to be cut along the [110] direction, resulting in blocks of different possible thicknesses. Many of the [110] phases have the general composition AnBnO3n + 2, in which n represents the number of BO6-octahedra within the blocks (Lichtenberg et al., 2001). The thinnest possible blocks correspond to zigzag chains of single BO6 octahedra, which are isolated by the A-type cations. This arrangement is found, for example, in LaTaO4 (n = 2, corresponding to La2Ta2O8) (Cava and Roth, 1981).

The title compound is closely related to the AnBnO3n + 2 family of oxides. It can formally be described as an n = 2 member, in which the perovskite slabs are separated by one additional AO– unit. Fig. 1 shows the structural relationship between the cubic perovskite archetype structure, La2RuO5, and the [110] phases. La2RuO5 was discovered independently by two groups. Boullay et al. (2003) published an ab-initio structural determination based on powder X-ray diffraction data, while Khalifah et al. (2002) reported electrical and magnetic properties. In the latter paper, a structural phase transition at 160 K was also described. This transition is accompanied by strong changes in the magnetic susceptibility and electrical resistivity. Khalifah et al. (2002) used powder neutron diffraction for their investigations, but unfortunately no structural details were given and to the best of our knowledge this information has not been published. In the course of our own research on the physical properties of ruthenates, we came across the need for structural data of both the high-temperature (ht) and low-temperature (lt) modifications of La2RuO5. As a starting model for ht-La2RuO5, the atomic coordinates given by Boullay et al. (2003) were used. For the triclinic lt-phase, possible new positions were generated using the program PowderCell (Kraus & Nolze, 1996). Figs. 2 and 3 show the results of the refinements. A graphical presentation of the crystal structures at 293 and 1.5 K is given in Fig. 4, while Fig. 5 shows the local Ru—O—Ru bonding arrangement within the zigzag chains.

In the high-temperature modification, the La1 ions are coordinated by nine oxygen ions, with bond distances ranging from 2.325 (6) to 2.968 (6) Å. The coordination geometry is rather irregular and cannot be described in terms of a simple polyhedron. For the La2 ions, an irregular ninefold O-atom coordination is observed, with bond distances ranging from 2.342 (7) to 2.836 (6) Å. It is noteworthy that the shortest La—O distances are found for atom O5, i.e. the oxygen ions in between the perovskite blocks. The Ru/O moieties can be described as slightly distorted octahedra. The difference between the longest and shortest bonds is 0.13 (1) Å. The O—Ru—O bond angles range from 82.5 (4) to 95.2 (4)°. The Ru—Ru distances in the zigzag chains are, within experimental error, identical to the Ru—Ru distances along the crystallographic c axis. Additionally, the Ru1—O3—Ru1 (zigzag chain) and Ru1—O4—Ru1 (along c) bond angles are very similar [155.4 (5) and 152.8 (4)°, respectively].

For the low-temperature modification, the coordination geometries change significantly, although the dimension of the unit cell remains very similar. For atoms La1 and La1A the bond lengths lie in the ranges 2.320 (7)–3.054 (6) Å and 2.352 (6)–3.000 (6) Å, respectively. Interestingly, the La1—O1A bond becomes rather short [2.381 (7) Å]. The interatomic distances for atoms La2 and La2A are 2.332 (6)–2.820 (7) and 2.346 (7)–2.834 (7) Å, respectively. The most interesting changes concern the ruthenium–oxygen coordination. Within the zigzag chains, the Ru1—O3A—Ru1A distance was found to be 0.23 (2) Å shorter than the Ru1—O3–Ru1A distance. A similar, although less pronounced, effect was found for the distances parallel to the c direction; here, the Ru1—O4—Ru1A distance is 0.12 (2) Å shorter than the Ru1–O4A–Ru1A distance. These changes in the interatomic distances can be described as a dimerization of the ruthenium ions, which apparently occurs both within the zigzag chains and along c. In addition, the bond angles differ significantly in the ht and lt modifications. The Ru—O–Ru angles within the zigzag chains are 153.2 (5)° for Ru1—O3—Ru1A and 160.2 (6)° for Ru1—O3A—Ru1A, respectively. The corresponding angles along the c axis (Ru1—O4—Ru1A and Ru1—O4A—Ru1A), on the other hand, are almost identical (151°). It is worth noting that within the zigzag chains the shorter Ru—Ru distance is accompanied by a bond angle closer to 180°. Both effects are expected to increase the superexchange interaction between these neighbouring ruthenium ions. Calculations of the electronic band structure based on our Rietveld results are currently under progress and results will be reported elsewhere. N·B. Should the bond lengths/angles involving La atoms have been included in cif?

Experimental top

Polycrystalline La2RuO5 was prepared from La2O3 and RuO2. La2O3 was dried at 1173 K for 6 h prior to use. The thoroughly ground stoichiometric mixture was heated in an alumina crucible at 1423 K for 48 h with one intermediate grinding. Phase purity was checked by preliminary X-ray diffraction measurements.

Refinement top

To reduce the number of free parameters, isotropic displacement parameters were used for all atoms. Attempts to refine the displacement parameters for the various O-atom positions independently led to unreasonable values for some of the atoms (especially for the lt phase) and only slightly reduced the residual parameters. We therefore decided to use one common displacement parameter for all O atoms. Becuase there was a strong correlation between refinement parameters, it was furthermore necessary to use a common displacement parameter for the La atoms in the lt phase.

Computing details top

For both compounds, data collection: SINQ Instrument Control System (SICS) (reference?); cell refinement: Fullprof2000 (Rodríguez-Carvajal, 1990); data reduction: SINQ Instrument Control System (SICS); program(s) used to solve structure: program (reference?); program(s) used to refine structure: Fullprof2000; molecular graphics: ATOMS for Windows (Dowty, 1995); software used to prepare material for publication: program (reference?).

Figures top
[Figure 1]
[Figure 2]
[Figure 3]
[Figure 4]
Fig. 1: Structural similarities between the [110] phases and La2RuO5. The cubic perovskite (top left) can be considered the member of the AnBnO3n + 2 series. The representatives for n = 4 and n = 2 compounds are SrTaO3.5 and LaTaO4, respectively.

Fig. 2: A Rietveld refinement plot of La2RuO5 at 293 K.

Fig. 3: A Rietveld refinement plot of La2RuO5 at 1.5 K.

Fig. 4: The structure of ht- (left) and lt-La2RuO5 (right), viewed along [001].

Fig. 5: A view of the RuO6 zigzag chains for ht- (top) and lt- (bottom) La2RuO5 including Ru—O and Ru—Ru distances.
(HT) dilanthanum ruthenium pentoxide top
Crystal data top
La2RuO5Z = 4
Mr = 458.89Dx = 7.285 Mg m3
Monoclinic, P21/cNeutron radiation, λ = 1.4935 Å
Hall symbol: -P 2ybcµ = 0.29 mm1
a = 9.1850 (4) ÅT = 293 K
b = 5.8294 (2) ÅParticle morphology: irregular powder
c = 7.9552 (3) Åblack
β = 100.79 (2)°cylinder, 35 × 8 mm
V = 418.42 (4) Å3
Data collection top
SINQ HRPT
diffractometer
Scan method: Stationary detector
Ge (533) monochromatorAbsorption correction: for a cylinder mounted on the ϕ axis
(Rodríguez-Carvajal, 1990)
Specimen mounting: vanadium canTmin = ?, Tmax = ?
Data collection mode: transmission
Refinement top
Refinement on Inet1604 data points
Least-squares matrix: full with fixed elements per cycleProfile function: Thompson-Cox-Hastings pseudo-Voigt
Rp = 0.02346 parameters
Rwp = 0.029Weighting scheme based on measured s.u.'s
Rexp = 0.018(Δ/σ)max = 0.0001
R(F) = 0.026Background function: 5th order polynomial.
χ2 = 2.592Preferred orientation correction: none
Crystal data top
La2RuO5V = 418.42 (4) Å3
Mr = 458.89Z = 4
Monoclinic, P21/cNeutron radiation, λ = 1.4935 Å
a = 9.1850 (4) ŵ = 0.29 mm1
b = 5.8294 (2) ÅT = 293 K
c = 7.9552 (3) Åcylinder, 35 × 8 mm
β = 100.79 (2)°
Data collection top
SINQ HRPT
diffractometer
Scan method: Stationary detector
Specimen mounting: vanadium canAbsorption correction: for a cylinder mounted on the ϕ axis
(Rodríguez-Carvajal, 1990)
Data collection mode: transmissionTmin = ?, Tmax = ?
Refinement top
Rp = 0.023χ2 = 2.592
Rwp = 0.0291604 data points
Rexp = 0.01846 parameters
R(F) = 0.026
Special details top

Geometry. Bond distances, angles etc. have been calculated using the rounded fractional coordinates. All su's are estimated from the variances of the (full) variance-covariance matrix. The cell e.s.d.'s are taken into account in the estimation of distances, angles and torsion angles

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2) top
xyzUiso*/Ueq
La10.1709 (3)0.2512 (7)0.5383 (4)0.0048 (5)*
La20.4466 (3)0.7638 (8)0.1197 (3)0.0056 (6)*
Ru10.1497 (4)0.7522 (11)0.2878 (6)0.0049 (5)*
O10.2767 (5)0.4881 (7)0.2803 (6)0.0096 (3)*
O20.3114 (5)0.0349 (9)0.3713 (6)0.0096 (3)*
O30.0225 (5)0.0433 (10)0.2925 (8)0.0096 (3)*
O40.1482 (6)0.3324 (7)0.4632 (8)0.0096 (3)*
O50.4225 (6)0.3365 (8)0.6024 (7)0.0096 (3)*
Geometric parameters (Å, º) top
Ru1—O11.939 (7)Ru1—O4ii2.048 (8)
Ru1—O2i1.954 (7)Ru1—O4iii2.044 (8)
Ru1—O3i2.065 (8)Ru1iv—Ru1v3.975 (8)
Ru1—O3ii2.004 (7)Ru1v—Ru1iii3.978 (7)
O1—Ru1—O2i95.2 (4)O3i—Ru1—O3ii95.1 (5)
O1—Ru1—O3i177.2 (5)O3i—Ru1—O4ii86.0 (4)
O1—Ru1—O3ii87.2 (4)O3i—Ru1—O4iii94.2 (4)
O1—Ru1—O4ii92.6 (4)O3ii—Ru1—O4ii88.1 (4)
O1—Ru1—O4iii87.2 (4)O3ii—Ru1—O4iii90.8 (5)
O2i—Ru1—O3i82.5 (4)O4ii—Ru1—O4iii178.9 (6)
O2i—Ru1—O3ii177.3 (5)Ru1iv—O3—Ru1v155.4 (5)
O2i—Ru1—O4ii93.0 (4)Ru1v—O4—Ru1iii152.8 (4)
O2i—Ru1—O4iii88.1 (4)
Symmetry codes: (i) x, y+1, z; (ii) x, y+1/2, z+1/2; (iii) x, y+1, z+1; (iv) x, y1, z; (v) x, y1/2, z+1/2.
(LT) dilanthanum ruthenium pentoxide top
Crystal data top
La4Ru2O10V = 415.45 (13) Å3
Mr = 917.78Z = 2
Triclinic, P1Dx = 7.337 Mg m3
Hall symbol: -P 1Neutron radiation, λ = 1.4935 Å
a = 9.1614 (8) ŵ = 0.30 mm1
b = 5.8075 (5) ÅT = 2 K
c = 7.9584 (8) ÅParticle morphology: irregular powder
α = 89.78 (8)°black
β = 101.00 (8)°cylinder, 35 × 8 mm
γ = 91.76 (8)°
Data collection top
SINQ HRPT
diffractometer
Scan method: Stationary detector
Ge (533) monochromatorAbsorption correction: for a cylinder mounted on the ϕ axis
(Rodríguez-Carvajal, 1990)
Specimen mounting: vanadium canTmin = ?, Tmax = ?
Data collection mode: transmission
Refinement top
Refinement on Inet3208 data points
Least-squares matrix: full with fixed elements per cycleProfile function: Thompson-Cox-Hastings pseudo-Voigt
Rp = 0.01968 parameters
Rwp = 0.023Weighting scheme based on measured s.u.'s
Rexp = 0.014(Δ/σ)max = 0.0001
R(F) = 0.018Background function: 5th order polynomial.
χ2 = 2.624Preferred orientation correction: none
Crystal data top
La4Ru2O10γ = 91.76 (8)°
Mr = 917.78V = 415.45 (13) Å3
Triclinic, P1Z = 2
a = 9.1614 (8) ÅNeutron radiation, λ = 1.4935 Å
b = 5.8075 (5) ŵ = 0.30 mm1
c = 7.9584 (8) ÅT = 2 K
α = 89.78 (8)°cylinder, 35 × 8 mm
β = 101.00 (8)°
Data collection top
SINQ HRPT
diffractometer
Scan method: Stationary detector
Specimen mounting: vanadium canAbsorption correction: for a cylinder mounted on the ϕ axis
(Rodríguez-Carvajal, 1990)
Data collection mode: transmissionTmin = ?, Tmax = ?
Refinement top
Rp = 0.019χ2 = 2.624
Rwp = 0.0233208 data points
Rexp = 0.01468 parameters
R(F) = 0.018
Special details top

Geometry. Bond distances, angles etc. have been calculated using the rounded fractional coordinates. All su's are estimated from the variances of the (full) variance-covariance matrix. The cell e.s.d.'s are taken into account in the estimation of distances, angles and torsion angles

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2) top
xyzUiso*/Ueq
La10.1721 (5)0.2469 (6)1.0389 (5)0.0010 (2)*
La1A0.1682 (4)0.2441 (6)0.5386 (5)0.0010 (2)*
La20.4476 (4)0.2691 (7)0.6212 (5)0.0010 (2)*
La2A0.5538 (4)0.2417 (7)0.8825 (5)0.0010 (2)*
Ru10.1474 (6)0.2549 (10)0.7935 (7)0.0022 (4)*
Ru1A0.1511 (6)0.7481 (9)1.2872 (7)0.0022 (4)*
O10.2803 (6)0.0041 (8)0.7786 (7)0.0027 (2)*
O1A0.2797 (6)0.4827 (9)1.2773 (7)0.0027 (2)*
O20.3084 (6)0.0424 (9)0.3668 (7)0.0027 (2)*
O2A0.3141 (6)0.5214 (9)0.8734 (6)0.0027 (2)*
O30.0136 (5)0.0251 (10)0.6940 (7)0.0027 (2)*
O3A0.0156 (6)0.4727 (9)0.7892 (7)0.0027 (2)*
O40.1364 (6)0.1678 (10)0.9656 (7)0.0027 (2)*
O4A0.1574 (6)0.6582 (9)0.5378 (7)0.0027 (2)*
O50.4219 (6)0.1592 (10)1.1031 (7)0.0027 (2)*
O5A0.4262 (5)0.3232 (9)0.6031 (6)0.0027 (2)*
Geometric parameters (Å, º) top
Ru1—O11.888 (8)Ru1A—O3iv2.097 (8)
Ru1—O2Ai2.042 (8)Ru1A—O3Aiv1.969 (8)
Ru1—O32.062 (8)Ru1A—O4iv2.049 (8)
Ru1—O3Ai1.957 (8)Ru1A—O4Av2.050 (8)
Ru1—O4ii2.007 (8)Ru1—Ru1Aiv4.045 (8)
Ru1—O4Ai2.118 (8)Ru1vi—Ru1Aiv3.868 (8)
Ru1A—O1A1.979 (8)Ru1ii—Ru1Aiv3.923 (8)
Ru1A—O2iii1.873 (8)Ru1vi—Ru1Avii4.036 (8)
O1—Ru1—O384.1 (4)O1A—Ru1A—O3iv178.0 (5)
O1—Ru1—O2Ai93.5 (4)O1A—Ru1A—O3Aiv85.3 (4)
O1—Ru1—O3Ai174.4 (6)O1A—Ru1A—O4iv94.4 (4)
O1—Ru1—O4Ai88.6 (4)O2iii—Ru1A—O4Av87.2 (4)
O1—Ru1—O4ii91.0 (5)O3iv—Ru1A—O4Av92.0 (4)
O2Ai—Ru1—O3175.1 (5)O3Aiv—Ru1A—O4Av91.1 (4)
O3—Ru1—O3Ai97.3 (5)O4iv—Ru1A—O4Av177.7 (5)
O3—Ru1—O4Ai87.3 (4)O2iii—Ru1A—O3iv85.2 (4)
O3—Ru1—O4ii91.9 (4)O2iii—Ru1A—O3Aiv178.2 (6)
O2Ai—Ru1—O3Ai84.7 (4)O2iii—Ru1A—O4iv94.9 (5)
O2Ai—Ru1—O4Ai88.4 (4)O3iv—Ru1A—O3Aiv94.3 (5)
O2Ai—Ru1—O4ii92.4 (4)O3iv—Ru1A—O4iv87.5 (4)
O3Ai—Ru1—O4Ai86.0 (4)O3Aiv—Ru1A—O4iv86.8 (4)
O3Ai—Ru1—O4ii94.4 (5)Ru1—O3—Ru1Aiv153.2 (5)
O4ii—Ru1—O4Ai179.1 (5)Ru1vi—O3A—Ru1Aiv160.2 (6)
O1A—Ru1A—O4Av86.1 (4)Ru1ii—O4—Ru1Aiv150.6 (5)
O1A—Ru1A—O2iii95.1 (4)Ru1vi—O4A—Ru1Avii151.0 (5)
Symmetry codes: (i) x, y1, z; (ii) x, y, z+2; (iii) x, y+1, z+1; (iv) x, y+1, z+2; (v) x, y, z+1; (vi) x, y+1, z; (vii) x, y, z1.

Experimental details

(HT)(LT)
Crystal data
Chemical formulaLa2RuO5La4Ru2O10
Mr458.89917.78
Crystal system, space groupMonoclinic, P21/cTriclinic, P1
Temperature (K)2932
a, b, c (Å)9.1850 (4), 5.8294 (2), 7.9552 (3)9.1614 (8), 5.8075 (5), 7.9584 (8)
α, β, γ (°)90, 100.79 (2), 9089.78 (8), 101.00 (8), 91.76 (8)
V3)418.42 (4)415.45 (13)
Z42
Radiation typeNeutron, λ = 1.4935 ÅNeutron, λ = 1.4935 Å
µ (mm1)0.290.30
Specimen shape, size (mm)Cylinder, 35 × 8Cylinder, 35 × 8
Data collection
DiffractometerSINQ HRPT
diffractometer
SINQ HRPT
diffractometer
Specimen mountingVanadium canVanadium can
Data collection modeTransmissionTransmission
Scan methodStationary detectorStationary detector
Absorption correctionFor a cylinder mounted on the ϕ axis
(Rodríguez-Carvajal, 1990)
2θ values (°)2θfixed = ?2θfixed = ?
Refinement
R factors and goodness of fitRp = 0.023, Rwp = 0.029, Rexp = 0.018, R(F) = 0.026, χ2 = 2.592Rp = 0.019, Rwp = 0.023, Rexp = 0.014, R(F) = 0.018, χ2 = 2.624
No. of data points16043208
No. of parameters4668
No. of restraints??

Computer programs: SINQ Instrument Control System (SICS) (reference?), Fullprof2000 (Rodríguez-Carvajal, 1990), SINQ Instrument Control System (SICS), program (reference?), Fullprof2000, ATOMS for Windows (Dowty, 1995).

Selected geometric parameters (Å, º) for (HT) top
Ru1—O11.939 (7)Ru1—O4ii2.048 (8)
Ru1—O2i1.954 (7)Ru1—O4iii2.044 (8)
Ru1—O3i2.065 (8)Ru1iv—Ru1v3.975 (8)
Ru1—O3ii2.004 (7)Ru1v—Ru1iii3.978 (7)
O1—Ru1—O2i95.2 (4)O3i—Ru1—O3ii95.1 (5)
O1—Ru1—O3i177.2 (5)O3i—Ru1—O4ii86.0 (4)
O1—Ru1—O3ii87.2 (4)O3i—Ru1—O4iii94.2 (4)
O1—Ru1—O4ii92.6 (4)O3ii—Ru1—O4ii88.1 (4)
O1—Ru1—O4iii87.2 (4)O3ii—Ru1—O4iii90.8 (5)
O2i—Ru1—O3i82.5 (4)O4ii—Ru1—O4iii178.9 (6)
O2i—Ru1—O3ii177.3 (5)Ru1iv—O3—Ru1v155.4 (5)
O2i—Ru1—O4ii93.0 (4)Ru1v—O4—Ru1iii152.8 (4)
O2i—Ru1—O4iii88.1 (4)
Symmetry codes: (i) x, y+1, z; (ii) x, y+1/2, z+1/2; (iii) x, y+1, z+1; (iv) x, y1, z; (v) x, y1/2, z+1/2.
Selected geometric parameters (Å, º) for (LT) top
Ru1—O11.888 (8)Ru1A—O3iv2.097 (8)
Ru1—O2Ai2.042 (8)Ru1A—O3Aiv1.969 (8)
Ru1—O32.062 (8)Ru1A—O4iv2.049 (8)
Ru1—O3Ai1.957 (8)Ru1A—O4Av2.050 (8)
Ru1—O4ii2.007 (8)Ru1—Ru1Aiv4.045 (8)
Ru1—O4Ai2.118 (8)Ru1vi—Ru1Aiv3.868 (8)
Ru1A—O1A1.979 (8)Ru1ii—Ru1Aiv3.923 (8)
Ru1A—O2iii1.873 (8)Ru1vi—Ru1Avii4.036 (8)
O1—Ru1—O384.1 (4)O1A—Ru1A—O3iv178.0 (5)
O1—Ru1—O2Ai93.5 (4)O1A—Ru1A—O3Aiv85.3 (4)
O1—Ru1—O3Ai174.4 (6)O1A—Ru1A—O4iv94.4 (4)
O1—Ru1—O4Ai88.6 (4)O2iii—Ru1A—O4Av87.2 (4)
O1—Ru1—O4ii91.0 (5)O3iv—Ru1A—O4Av92.0 (4)
O2Ai—Ru1—O3175.1 (5)O3Aiv—Ru1A—O4Av91.1 (4)
O3—Ru1—O3Ai97.3 (5)O4iv—Ru1A—O4Av177.7 (5)
O3—Ru1—O4Ai87.3 (4)O2iii—Ru1A—O3iv85.2 (4)
O3—Ru1—O4ii91.9 (4)O2iii—Ru1A—O3Aiv178.2 (6)
O2Ai—Ru1—O3Ai84.7 (4)O2iii—Ru1A—O4iv94.9 (5)
O2Ai—Ru1—O4Ai88.4 (4)O3iv—Ru1A—O3Aiv94.3 (5)
O2Ai—Ru1—O4ii92.4 (4)O3iv—Ru1A—O4iv87.5 (4)
O3Ai—Ru1—O4Ai86.0 (4)O3Aiv—Ru1A—O4iv86.8 (4)
O3Ai—Ru1—O4ii94.4 (5)Ru1—O3—Ru1Aiv153.2 (5)
O4ii—Ru1—O4Ai179.1 (5)Ru1vi—O3A—Ru1Aiv160.2 (6)
O1A—Ru1A—O4Av86.1 (4)Ru1ii—O4—Ru1Aiv150.6 (5)
O1A—Ru1A—O2iii95.1 (4)Ru1vi—O4A—Ru1Avii151.0 (5)
Symmetry codes: (i) x, y1, z; (ii) x, y, z+2; (iii) x, y+1, z+1; (iv) x, y+1, z+2; (v) x, y, z+1; (vi) x, y+1, z; (vii) x, y, z1.
 

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