Supporting information
Crystallographic Information File (CIF) https://doi.org/10.1107/S1600536807046727/wm2146sup1.cif | |
Structure factor file (CIF format) https://doi.org/10.1107/S1600536807046727/wm2146Isup2.hkl |
Key indicators
- Single-crystal X-ray study
- T = 120 K
- Mean (r-Pr) = 0.001 Å
- R factor = 0.023
- wR factor = 0.057
- Data-to-parameter ratio = 8.3
checkCIF/PLATON results
No syntax errors found
Alert level C PLAT088_ALERT_3_C Poor Data / Parameter Ratio .................... 8.33
Alert level G PLAT794_ALERT_5_G Check Predicted Bond Valency for Pr (3) 0.77
0 ALERT level A = In general: serious problem 0 ALERT level B = Potentially serious problem 1 ALERT level C = Check and explain 1 ALERT level G = General alerts; check 0 ALERT type 1 CIF construction/syntax error, inconsistent or missing data 0 ALERT type 2 Indicator that the structure model may be wrong or deficient 1 ALERT type 3 Indicator that the structure quality may be low 0 ALERT type 4 Improvement, methodology, query or suggestion 1 ALERT type 5 Informative message, check
For the previous model of Pr3In, reported to adopt the AuCu3 structure type (Villars & Calvert, 1991), see: Delfino et al. (1979). For re-determinations of other intermetallic phases where light elements such as N, C and O were found to occupy the interstices, see: Eisenmann et al. (1980); Gesing et al. (1995); Haschke et al. (1966); Leon-Escamilla & Corbett (2001); Röhr (1995); Schuster (1985); Widera & Schäfer (1980); Xia & Bobev (2007). For characterization of polycrystalline `Pr3In' samples, see: Christianson et al. (2005, 2007). Ionic radii were taken from Shannon (1976).
The reaction was carried out in an alumina crucible. The metallic elements, Pr (Alfa, ingot, 99.9%), In (Alfa, shot, 99.99%), and Cu (Alfa, shot, 99.99%) were loaded in a ratio of 7:1:2. The eutectic Pr–Cu (m.p. 715 K) mixture was intended to serve as a metal flux. The crucible with the reaction mixture was then flame sealed under vacuum in a silica ampoule, which was then placed in a furnace and heated to 1373 K at a rate of 300 K/h. The reaction proceeded at this temperature for 4 h before being cooled to 973 K at a rate of 4 K/h. At 973 K the ampoule was removed from the furnace and the flux was decanted. The main product of the reaction consisted of dark to black crystals with irregular shapes, which were later determined to be the title compound. The source of oxygen is unknown. Most likely a small, inadvertent crack in the fused silica ampoule is the cause for the partial oxidation of the molten intermetallic mixture during the reaction. However, we note that although the crystals were handled with care due to their air-sensitivity, diffusion of atmospheric oxygen through them cannot be ruled out.
Structure refinements using the old Pr3In model (Delfino et al., 1979) proved a large residual peak in the difference Fourier map. The peak was located approximately 2.5 Å away from Pr. Such an interatomic distance is too short for a metal–metal bond and this ruled out the possibility for partially occupied In and/or Cu to be at that site. Since there were precedents in the literature for C, N, and O-atoms occupying this site, test refinements were performed with C, N, and O at the 1b site (hydrogen is too light to be even considered) and the results were as follows: 1) Pr3InC (R1 = 0.0338, wR2 = 14.21); 2) Pr3InN (R1 = 0.0284, wR2 = 0.0867); and 3) Pr3InO (R1 = 0.0230, wR2 = 0.0590). The overall improvement in the refinement parameters, as well as the improved anisotropic displacement parameters confirmed that this octahedral site is indeed occupied by oxygen atoms. The full occupancies for all three crystallographic positions were verified by freeing the site occupation factor for an individual atom, while other remaining occupation parameters were kept fixed. This proved that all positions are fully occupied with corresponding deviations from full occupancy within 3σ. The maximum peak and deepest hole are located 0.90 Å away and 0.27 Å away from In, respectively.
"Pr3In" has been known since 1979 (Delfino et al., 1979) to crystallize in the AuCu3 structure type (Villars & Calvert, 1991). A wide variety of other isotypic gallides, indides, germanides, stannides, and plumbides of the alkaline-earth and rare-earth metals are also known to crystallize with this cubic type (Villars & Calvert, 1991).
For many of these phases, subsequent structure re-determinations have proven that they are not true binary compounds and that light non-metallic elements such as carbon (Haschke et al., 1966; Gesing et al., 1995), nitrogen (Schuster, 1985), and oxygen (Widera & Schäfer, 1980; Röhr, 1995) fill the octahedral holes. Stabilization of the parent structures by utilizing well characterized interstitial holes is observed not only for the above-named cubic compounds with the inverse perovskite structure. Similar interstitial stabilization by oxygen for example is also reported for the layered pnictides of the alkaline-earth metals, such as Ca4Sb2O (Eisenmann et al., 1980) and Ca4Bi2O (Xia & Bobev, 2007). Corbett's group has documented numerous examples of hydrogen impurity effects in A5B3-phases (A = alkaline-earth metals; B = Ge, Sn, Pb, Sb) with the Cr5B3 or Mn5Si3 structure types (Leon-Escamilla & Corbett, 2001).
In our previous studies of "Pr3In" (Christianson et al., 2005; Christianson et al., 2007), we noticed that polycrystalline samples of this compound indicated the existence of an antiferromagnetic transition in the range 10–20 K. These results based on neutron diffraction, magnetic susceptibility and specific heat for a single-crystal of "Pr3In" confirmed that antiferromagnetic order occurs in this material below TN = 12 K with propagation vector 0, 0, 0.5 ± δ, where δ = 1/12 (Christianson et al., 2005). Even though these studies were carried out using single crystals grown by the Bridgeman method, we noticed a subtle sample-dependence of the results, which pointed our attention at the possibility for an unrecognized impurity.
To study this in greater detail, we undertook a different synthetic approach (flux growth) and synthesized good quality crystals of the desired material, suitable for singe-crystal X-ray diffraction. This work confirmed that the product of the latter reaction crystallizes in the primitive cubic space group Pm3m with a cell parameter in excellent agreement with the previously reported value of 4.99 Å (Delfino et al., 1979). Based on this information and surveying the Pearson's handbook (Villars & Calvert, 1991) one might conclude that "Pr3In" is indeed a member of the cubic AuCu3 structure type (Pearson's code cP4), in which the Pr atoms occupy the 3c Wyckoff site ((4/mm.m symmetry) and the In atoms are at the 1a Wyckoff site (m3m symmetry).
The presented structure refinements and the corresponding analyses of the Fourier and difference Fourier maps clearly indicate that the crystals we grew are not "Pr3In" but its "stuffed" ternary variant Pr3InO. A view of this structure, which is best described as an inverse cubic perovskite type (aka CaTiO3), is shown in Figure 1. As can be seen, the interstitial oxygen atoms are found at Wyckoff site 1b (m3m symmetry). The resultant [OPr6] octahedron is shown in Figure 2. The Pr—O distance of 2.4911 (4) Å is well within the expected range for trivalent Pr, according to the sum of the ionic radii (0.99 + 1.40 Å; Shannon, 1976).
Although the herein presented results are just a limiting case, this study calls the attention to the fact that many of recurring problems with "sample-dependence" in the literature on related intermetallic phases are most likely due to different types and amounts of interstitials occupying the octahedral holes in these structures.
For the previous model of Pr3In, reported to adopt the AuCu3 structure type (Villars & Calvert, 1991), see: Delfino et al. (1979). For re-determinations of other intermetallic phases where light elements such as N, C and O were found to occupy the interstices, see: Eisenmann et al. (1980); Gesing et al. (1995); Haschke et al. (1966); Leon-Escamilla & Corbett (2001); Röhr (1995); Schuster (1985); Widera & Schäfer (1980); Xia & Bobev (2007). For characterization of polycrystalline `Pr3In' samples, see: Christianson et al. (2005, 2007). Ionic radii were taken from Shannon (1976).
Data collection: SMART (Bruker, 2002); cell refinement: SAINT (Bruker, 2002); data reduction: SAINT (Bruker, 2002); program(s) used to solve structure: SHELXTL (Bruker, 2002); program(s) used to refine structure: SHELXTL (Bruker, 2002); molecular graphics: XP in SHELXTL (Bruker, 2002); software used to prepare material for publication: SHELXTL (Bruker, 2002).
Pr3InO | Dx = 7.433 Mg m−3 |
Mr = 553.55 | Mo Kα radiation, λ = 0.71073 Å |
Cubic, Pm3m | Cell parameters from 1353 reflections |
Hall symbol: -P 4 2 3 | θ = 4.1–27.9° |
a = 4.9822 (7) Å | µ = 33.45 mm−1 |
V = 123.67 (3) Å3 | T = 120 K |
Z = 1 | Irregular, black |
F(000) = 234 | 0.08 × 0.04 × 0.03 mm |
Bruker SMART APEX diffractometer | 50 independent reflections |
Radiation source: fine-focus sealed tube | 47 reflections with I > 2σ(I) |
Graphite monochromator | Rint = 0.016 |
ω scans | θmax = 27.9°, θmin = 4.1° |
Absorption correction: multi-scan (SADABS; Sheldrick, 2003) | h = −6→6 |
Tmin = 0.188, Tmax = 0.368 | k = −6→6 |
1353 measured reflections | l = −6→6 |
Refinement on F2 | 0 restraints |
Least-squares matrix: full | w = 1/[σ2(Fo2) + (0.031P)2] where P = (Fo2 + 2Fc2)/3 |
R[F2 > 2σ(F2)] = 0.023 | (Δ/σ)max < 0.001 |
wR(F2) = 0.057 | Δρmax = 1.43 e Å−3 |
S = 1.29 | Δρmin = −1.21 e Å−3 |
50 reflections | Extinction correction: SHELXTL (Bruker, 2002), Fc*=kFc[1+0.001xFc2λ3/sin(2θ)]-1/4 |
6 parameters | Extinction coefficient: 0.0026 (3) |
Pr3InO | Z = 1 |
Mr = 553.55 | Mo Kα radiation |
Cubic, Pm3m | µ = 33.45 mm−1 |
a = 4.9822 (7) Å | T = 120 K |
V = 123.67 (3) Å3 | 0.08 × 0.04 × 0.03 mm |
Bruker SMART APEX diffractometer | 50 independent reflections |
Absorption correction: multi-scan (SADABS; Sheldrick, 2003) | 47 reflections with I > 2σ(I) |
Tmin = 0.188, Tmax = 0.368 | Rint = 0.016 |
1353 measured reflections |
R[F2 > 2σ(F2)] = 0.023 | 6 parameters |
wR(F2) = 0.057 | 0 restraints |
S = 1.29 | Δρmax = 1.43 e Å−3 |
50 reflections | Δρmin = −1.21 e Å−3 |
Experimental. Crystals were selected from the reaction and cut in a Paratone N oil bath to the desired dimensions. A suitable crystal was then chosen mounted on the tip of a glass fiber and quickly placed under the cold nitrogen stream (ca 120 K) in a Bruker SMART CCD-based diffractometer. Data collection was performed with four batch runs at φ = 0.00 ° (450 frames), at φ = 90.00 ° (450 frames), at φ = 180.00 ° (450 frames), and at φ = 270.00 (450 frames). Frame width was = 0.40 ° in ω. Data were merged, corrected for decay, and treated with multi-scan absorption corrections. |
Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s. planes. |
Refinement. Refinement of F2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F2, conventional R-factors R are based on F, with F set to zero for negative F2. The threshold expression of F2 > 2σ(F2) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F2 are statistically about twice as large as those based on F, and R- factors based on ALL data will be even larger. |
x | y | z | Uiso*/Ueq | ||
Pr | 0.0000 | 0.5000 | 0.5000 | 0.0090 (6) | |
In | 0.0000 | 0.0000 | 0.0000 | 0.0129 (6) | |
O | 0.5000 | 0.5000 | 0.5000 | 0.010 (3) |
U11 | U22 | U33 | U12 | U13 | U23 | |
Pr | 0.0078 (7) | 0.0097 (7) | 0.0097 (7) | 0.000 | 0.000 | 0.000 |
In | 0.0129 (6) | 0.0129 (6) | 0.0129 (6) | 0.000 | 0.000 | 0.000 |
O | 0.010 (3) | 0.010 (3) | 0.010 (3) | 0.000 | 0.000 | 0.000 |
In—Pri | 3.5229 (5) | Pr—Prxiii | 3.5229 (5) |
In—Pr | 3.5229 (5) | Pr—Prxi | 3.5229 (5) |
In—Prii | 3.5229 (5) | Pr—Inxiv | 3.5229 (5) |
In—Priii | 3.5229 (5) | Pr—Prvii | 3.5229 (5) |
In—Priv | 3.5229 (5) | Pr—Prxv | 3.5229 (5) |
In—Prv | 3.5229 (5) | Pr—Inxvi | 3.5229 (5) |
In—Prvi | 3.5229 (5) | Pr—Prxvii | 3.5229 (5) |
In—Prvii | 3.5229 (5) | Pr—Priv | 3.5229 (5) |
In—Prviii | 3.5229 (5) | Pr—Pri | 3.5229 (5) |
In—Prix | 3.5229 (5) | O—Prxiii | 2.4911 (4) |
In—Prx | 3.5229 (5) | O—Prxviii | 2.4911 (4) |
In—Prxi | 3.5229 (5) | O—Priv | 2.4911 (4) |
Pr—Oxii | 2.4911 (4) | O—Prxv | 2.4911 (4) |
Pr—O | 2.4911 (4) | O—Pri | 2.4911 (4) |
Pri—In—Pr | 60.0 | In—Pr—Prxi | 60.0 |
Pri—In—Prii | 120.0 | Prxiii—Pr—Prxi | 180.0 |
Pr—In—Prii | 180.0 | Oxii—Pr—Inxiv | 90.0 |
Pri—In—Priii | 180.0 | O—Pr—Inxiv | 90.0 |
Pr—In—Priii | 120.0 | In—Pr—Inxiv | 180.0 |
Prii—In—Priii | 60.0 | Prxiii—Pr—Inxiv | 60.0 |
Pri—In—Priv | 60.0 | Prxi—Pr—Inxiv | 120.0 |
Pr—In—Priv | 60.0 | Oxii—Pr—Prvii | 45.0 |
Prii—In—Priv | 120.0 | O—Pr—Prvii | 135.0 |
Priii—In—Priv | 120.0 | In—Pr—Prvii | 60.0 |
Pri—In—Prv | 120.0 | Prxiii—Pr—Prvii | 120.0 |
Pr—In—Prv | 120.0 | Prxi—Pr—Prvii | 60.0 |
Prii—In—Prv | 60.0 | Inxiv—Pr—Prvii | 120.0 |
Priii—In—Prv | 60.0 | Oxii—Pr—Prxv | 135.0 |
Priv—In—Prv | 180.0 | O—Pr—Prxv | 45.0 |
Pri—In—Prvi | 60.0 | In—Pr—Prxv | 120.0 |
Pr—In—Prvi | 90.0 | Prxiii—Pr—Prxv | 60.0 |
Prii—In—Prvi | 90.0 | Prxi—Pr—Prxv | 120.0 |
Priii—In—Prvi | 120.0 | Inxiv—Pr—Prxv | 60.0 |
Priv—In—Prvi | 120.0 | Prvii—Pr—Prxv | 180.0 |
Prv—In—Prvi | 60.0 | Oxii—Pr—Inxvi | 90.0 |
Pri—In—Prvii | 120.0 | O—Pr—Inxvi | 90.0 |
Pr—In—Prvii | 60.0 | In—Pr—Inxvi | 90.0 |
Prii—In—Prvii | 120.0 | Prxiii—Pr—Inxvi | 120.0 |
Priii—In—Prvii | 60.0 | Prxi—Pr—Inxvi | 60.0 |
Priv—In—Prvii | 90.0 | Inxiv—Pr—Inxvi | 90.0 |
Prv—In—Prvii | 90.0 | Prvii—Pr—Inxvi | 120.0 |
Prvi—In—Prvii | 120.0 | Prxv—Pr—Inxvi | 60.0 |
Pri—In—Prviii | 60.0 | Oxii—Pr—Prxvii | 45.0 |
Pr—In—Prviii | 120.0 | O—Pr—Prxvii | 135.0 |
Prii—In—Prviii | 60.0 | In—Pr—Prxvii | 120.0 |
Priii—In—Prviii | 120.0 | Prxiii—Pr—Prxvii | 120.0 |
Priv—In—Prviii | 90.0 | Prxi—Pr—Prxvii | 60.0 |
Prv—In—Prviii | 90.0 | Inxiv—Pr—Prxvii | 60.0 |
Prvi—In—Prviii | 60.0 | Prvii—Pr—Prxvii | 90.0 |
Prvii—In—Prviii | 180.0 | Prxv—Pr—Prxvii | 90.0 |
Pri—In—Prix | 120.0 | Inxvi—Pr—Prxvii | 60.0 |
Pr—In—Prix | 90.0 | Oxii—Pr—Priv | 135.0 |
Prii—In—Prix | 90.0 | O—Pr—Priv | 45.0 |
Priii—In—Prix | 60.0 | In—Pr—Priv | 60.0 |
Priv—In—Prix | 60.0 | Prxiii—Pr—Priv | 60.0 |
Prv—In—Prix | 120.0 | Prxi—Pr—Priv | 120.0 |
Prvi—In—Prix | 180.0 | Inxiv—Pr—Priv | 120.0 |
Prvii—In—Prix | 60.0 | Prvii—Pr—Priv | 90.0 |
Prviii—In—Prix | 120.0 | Prxv—Pr—Priv | 90.0 |
Pri—In—Prx | 90.0 | Inxvi—Pr—Priv | 120.0 |
Pr—In—Prx | 120.0 | Prxvii—Pr—Priv | 180.0 |
Prii—In—Prx | 60.0 | Oxii—Pr—Pri | 135.0 |
Priii—In—Prx | 90.0 | O—Pr—Pri | 45.0 |
Priv—In—Prx | 60.0 | In—Pr—Pri | 60.0 |
Prv—In—Prx | 120.0 | Prxiii—Pr—Pri | 90.0 |
Prvi—In—Prx | 120.0 | Prxi—Pr—Pri | 90.0 |
Prvii—In—Prx | 120.0 | Inxiv—Pr—Pri | 120.0 |
Prviii—In—Prx | 60.0 | Prvii—Pr—Pri | 120.0 |
Prix—In—Prx | 60.0 | Prxv—Pr—Pri | 60.0 |
Pri—In—Prxi | 90.0 | Inxvi—Pr—Pri | 60.0 |
Pr—In—Prxi | 60.0 | Prxvii—Pr—Pri | 120.0 |
Prii—In—Prxi | 120.0 | Priv—Pr—Pri | 60.0 |
Priii—In—Prxi | 90.0 | Prxiii—O—Pr | 90.0 |
Priv—In—Prxi | 120.0 | Prxiii—O—Prxviii | 90.0 |
Prv—In—Prxi | 60.0 | Pr—O—Prxviii | 180.0 |
Prvi—In—Prxi | 60.0 | Prxiii—O—Priv | 90.0 |
Prvii—In—Prxi | 60.0 | Pr—O—Priv | 90.0 |
Prviii—In—Prxi | 120.0 | Prxviii—O—Priv | 90.0 |
Prix—In—Prxi | 120.0 | Prxiii—O—Prxv | 90.0 |
Prx—In—Prxi | 180.0 | Pr—O—Prxv | 90.0 |
Oxii—Pr—O | 180.0 | Prxviii—O—Prxv | 90.0 |
Oxii—Pr—In | 90.0 | Priv—O—Prxv | 180.0 |
O—Pr—In | 90.0 | Prxiii—O—Pri | 180.0 |
Oxii—Pr—Prxiii | 135.0 | Pr—O—Pri | 90.0 |
O—Pr—Prxiii | 45.0 | Prxviii—O—Pri | 90.0 |
In—Pr—Prxiii | 120.0 | Priv—O—Pri | 90.0 |
Oxii—Pr—Prxi | 45.0 | Prxv—O—Pri | 90.0 |
O—Pr—Prxi | 135.0 |
Symmetry codes: (i) y, z, x; (ii) x, y−1, z−1; (iii) y−1, z−1, x; (iv) z, x, y; (v) z−1, x, y−1; (vi) x, y, z−1; (vii) z−1, x, y; (viii) z, x, y−1; (ix) x, y−1, z; (x) y, z−1, x; (xi) y−1, z, x; (xii) x−1, y, z; (xiii) y, z, x+1; (xiv) x, y+1, z+1; (xv) z, x+1, y; (xvi) x, y+1, z; (xvii) z−1, x+1, y; (xviii) x+1, y, z. |
Experimental details
Crystal data | |
Chemical formula | Pr3InO |
Mr | 553.55 |
Crystal system, space group | Cubic, Pm3m |
Temperature (K) | 120 |
a (Å) | 4.9822 (7) |
V (Å3) | 123.67 (3) |
Z | 1 |
Radiation type | Mo Kα |
µ (mm−1) | 33.45 |
Crystal size (mm) | 0.08 × 0.04 × 0.03 |
Data collection | |
Diffractometer | Bruker SMART APEX |
Absorption correction | Multi-scan (SADABS; Sheldrick, 2003) |
Tmin, Tmax | 0.188, 0.368 |
No. of measured, independent and observed [I > 2σ(I)] reflections | 1353, 50, 47 |
Rint | 0.016 |
(sin θ/λ)max (Å−1) | 0.658 |
Refinement | |
R[F2 > 2σ(F2)], wR(F2), S | 0.023, 0.057, 1.29 |
No. of reflections | 50 |
No. of parameters | 6 |
Δρmax, Δρmin (e Å−3) | 1.43, −1.21 |
Computer programs: SMART (Bruker, 2002), SAINT (Bruker, 2002), XP in SHELXTL (Bruker, 2002).
In—Pr | 3.5229 (5) | Pr—Pri | 3.5229 (5) |
Pr—O | 2.4911 (4) |
Symmetry code: (i) y, z, x+1. |
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"Pr3In" has been known since 1979 (Delfino et al., 1979) to crystallize in the AuCu3 structure type (Villars & Calvert, 1991). A wide variety of other isotypic gallides, indides, germanides, stannides, and plumbides of the alkaline-earth and rare-earth metals are also known to crystallize with this cubic type (Villars & Calvert, 1991).
For many of these phases, subsequent structure re-determinations have proven that they are not true binary compounds and that light non-metallic elements such as carbon (Haschke et al., 1966; Gesing et al., 1995), nitrogen (Schuster, 1985), and oxygen (Widera & Schäfer, 1980; Röhr, 1995) fill the octahedral holes. Stabilization of the parent structures by utilizing well characterized interstitial holes is observed not only for the above-named cubic compounds with the inverse perovskite structure. Similar interstitial stabilization by oxygen for example is also reported for the layered pnictides of the alkaline-earth metals, such as Ca4Sb2O (Eisenmann et al., 1980) and Ca4Bi2O (Xia & Bobev, 2007). Corbett's group has documented numerous examples of hydrogen impurity effects in A5B3-phases (A = alkaline-earth metals; B = Ge, Sn, Pb, Sb) with the Cr5B3 or Mn5Si3 structure types (Leon-Escamilla & Corbett, 2001).
In our previous studies of "Pr3In" (Christianson et al., 2005; Christianson et al., 2007), we noticed that polycrystalline samples of this compound indicated the existence of an antiferromagnetic transition in the range 10–20 K. These results based on neutron diffraction, magnetic susceptibility and specific heat for a single-crystal of "Pr3In" confirmed that antiferromagnetic order occurs in this material below TN = 12 K with propagation vector 0, 0, 0.5 ± δ, where δ = 1/12 (Christianson et al., 2005). Even though these studies were carried out using single crystals grown by the Bridgeman method, we noticed a subtle sample-dependence of the results, which pointed our attention at the possibility for an unrecognized impurity.
To study this in greater detail, we undertook a different synthetic approach (flux growth) and synthesized good quality crystals of the desired material, suitable for singe-crystal X-ray diffraction. This work confirmed that the product of the latter reaction crystallizes in the primitive cubic space group Pm3m with a cell parameter in excellent agreement with the previously reported value of 4.99 Å (Delfino et al., 1979). Based on this information and surveying the Pearson's handbook (Villars & Calvert, 1991) one might conclude that "Pr3In" is indeed a member of the cubic AuCu3 structure type (Pearson's code cP4), in which the Pr atoms occupy the 3c Wyckoff site ((4/mm.m symmetry) and the In atoms are at the 1a Wyckoff site (m3m symmetry).
The presented structure refinements and the corresponding analyses of the Fourier and difference Fourier maps clearly indicate that the crystals we grew are not "Pr3In" but its "stuffed" ternary variant Pr3InO. A view of this structure, which is best described as an inverse cubic perovskite type (aka CaTiO3), is shown in Figure 1. As can be seen, the interstitial oxygen atoms are found at Wyckoff site 1b (m3m symmetry). The resultant [OPr6] octahedron is shown in Figure 2. The Pr—O distance of 2.4911 (4) Å is well within the expected range for trivalent Pr, according to the sum of the ionic radii (0.99 + 1.40 Å; Shannon, 1976).
Although the herein presented results are just a limiting case, this study calls the attention to the fact that many of recurring problems with "sample-dependence" in the literature on related intermetallic phases are most likely due to different types and amounts of interstitials occupying the octahedral holes in these structures.