Supporting information
Crystallographic Information File (CIF) https://doi.org/10.1107/S0108270107045416/fa3110sup1.cif | |
Structure factor file (CIF format) https://doi.org/10.1107/S0108270107045416/fa3110Isup2.hkl |
Single crystals of Sm3MoO7 were prepared from a stoichiometric amount of Sm2O3, MoO3 and Mo. Before use, the Mo powder was reduced under a hydrogen flow at 1273 K for 6 h and the rare-earth oxide was prefired at 1273 K overnight and left at 873 K. The initial mixture (ca 5 g) was cold pressed and loaded into a molybdenum crucible, which was sealed under a low argon pressure using an arc welding system. The charge was heated at a rate of 300 K h−1 to 1973 K, at which it was held for 10 min, then cooled at 100 K h−1 to 1373 K and finally furnace cooled.
Systematic absences were only consistent with the noncentrosymmetric space group P212121. The atomic coordinates of Pr, Mo and O from Pr3MoO7 (Barrier & Gougeon, 2003) were used as starting positions in the first stages of the refinement in the present study. The least-squares refinement with anisotropic atomic displacement parameters for all atoms yielded an R factor of 0.027 for 3438 reflections. At this stage, however, a relatively large residual electron-density peak of 8.1 e Å−3 was found at about 0.58 Å from atom Sm1. To model the electron density of the Sm1 site, it was necessary to split it into two independent sites, Sm1 and Sm1', separated by 0.58 Å. The split pair Sm1 and Sm1' was constrained to have the same anisotropic atomic displacement parameters in the further refinements. The site occupation factors of Sm1 and Sm1' were first refined freely, leading to a sum of 1.001 (3). Consequently, the sum was constrained to be 1 in the final cycles of refinement. This split-atom model decreased the R factor to 0.022 and the residual electron density near the Sm1 and Sm1' sites to 1.79 e Å−3. An attempt to refine the structure in the space group Pnma as suggested by PLATON (Spek, 2003) were unsuccessful and led to an R factor of about 0.10. The Flack (1983) parameter refined to 0.491 (17), indicating that the crystal contained a mixture of the two absolute structures. The highest peak and the deepest hole in the final Fourier map are located 0.59 and 0.52 Å from Sm2.
Data collection: COLLECT (Nonius, 1998); cell refinement: COLLECT (Nonius, 1998); data reduction: EVALCCD (Duisenberg, 1998); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: DIAMOND (Brandenburg, 2001); software used to prepare material for publication: SHELXL97 (Sheldrick, 1997).
Sm3MoO7 | Dx = 7.293 Mg m−3 |
Mr = 658.99 | Mo Kα radiation, λ = 0.71069 Å |
Orthorhombic, P212121 | Cell parameters from 9716 reflections |
a = 7.4500 (1) Å | θ = 3.3–40.0° |
b = 7.5460 (1) Å | µ = 30.94 mm−1 |
c = 10.6766 (2) Å | T = 293 K |
V = 600.21 (2) Å3 | Irregular block, black |
Z = 4 | 0.19 × 0.09 × 0.04 mm |
F(000) = 1136 |
Nonius KappaCCD diffractometer | 3719 independent reflections |
Radiation source: fine-focus sealed tube | 3438 reflections with I > 2σ(I) |
Horizontally mounted graphite crystal monochromator | Rint = 0.034 |
Detector resolution: 9 pixels mm-1 | θmax = 40.0°, θmin = 3.3° |
ϕ scans (κ = 0) + additional ω scans | h = −13→13 |
Absorption correction: analytical (de Meulenaer & Tompa, 1965) | k = −13→13 |
Tmin = 0.037, Tmax = 0.367 | l = −18→19 |
17049 measured reflections |
Refinement on F2 | Secondary atom site location: difference Fourier map |
Least-squares matrix: full | w = 1/[σ2(Fo2) + (0.014P)2 + 1.4858P] where P = (Fo2 + 2Fc2)/3 |
R[F2 > 2σ(F2)] = 0.022 | (Δ/σ)max = 0.001 |
wR(F2) = 0.042 | Δρmax = 1.94 e Å−3 |
S = 1.05 | Δρmin = −3.05 e Å−3 |
3719 reflections | Extinction correction: SHELXL97 (Sheldrick, 1997), Fc*=kFc[1+0.001xFc2λ3/sin(2θ)]-1/4 |
107 parameters | Extinction coefficient: 0.00317 (8) |
1 restraint | Absolute structure: Flack (1983), 1593 Friedel pairs |
Primary atom site location: isomorphous structure methods | Absolute structure parameter: 0.491 (17) |
Sm3MoO7 | V = 600.21 (2) Å3 |
Mr = 658.99 | Z = 4 |
Orthorhombic, P212121 | Mo Kα radiation |
a = 7.4500 (1) Å | µ = 30.94 mm−1 |
b = 7.5460 (1) Å | T = 293 K |
c = 10.6766 (2) Å | 0.19 × 0.09 × 0.04 mm |
Nonius KappaCCD diffractometer | 3719 independent reflections |
Absorption correction: analytical (de Meulenaer & Tompa, 1965) | 3438 reflections with I > 2σ(I) |
Tmin = 0.037, Tmax = 0.367 | Rint = 0.034 |
17049 measured reflections |
R[F2 > 2σ(F2)] = 0.022 | 1 restraint |
wR(F2) = 0.042 | Δρmax = 1.94 e Å−3 |
S = 1.05 | Δρmin = −3.05 e Å−3 |
3719 reflections | Absolute structure: Flack (1983), 1593 Friedel pairs |
107 parameters | Absolute structure parameter: 0.491 (17) |
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 > σ(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 | Occ. (<1) | |
Mo1 | 0.50271 (3) | 0.50106 (4) | 0.75048 (5) | 0.00388 (4) | |
Sm1 | 0.02321 (9) | 0.50748 (4) | 0.74465 (4) | 0.00694 (6) | 0.920 (3) |
Sm1' | −0.0186 (8) | 0.5008 (6) | 0.7555 (5) | 0.00694 (6) | 0.080 (3) |
Sm2 | 0.71075 (2) | 0.75466 (2) | 0.533348 (15) | 0.00584 (3) | |
Sm3 | 0.69558 (2) | 0.74782 (2) | 0.984121 (14) | 0.00574 (4) | |
O1 | 0.7098 (5) | 0.4716 (3) | 0.6328 (3) | 0.0099 (5) | |
O2 | 0.6345 (5) | 0.4491 (3) | 0.8928 (3) | 0.0141 (6) | |
O3 | 0.9587 (4) | 0.7479 (4) | 0.8819 (2) | 0.0071 (4) | |
O4 | 0.2845 (5) | 0.5364 (3) | 0.8706 (2) | 0.0091 (5) | |
O5 | 0.5741 (3) | 0.7476 (3) | 0.7617 (2) | 0.0090 (4) | |
O6 | 0.3285 (5) | 0.5374 (4) | 0.6214 (3) | 0.0111 (6) | |
O7 | 0.9965 (3) | 0.7603 (4) | 0.6178 (2) | 0.0074 (4) |
U11 | U22 | U33 | U12 | U13 | U23 | |
Mo1 | 0.00462 (9) | 0.00333 (8) | 0.00369 (9) | −0.00009 (7) | −0.00027 (7) | 0.00000 (8) |
Sm1 | 0.01039 (16) | 0.00518 (7) | 0.00524 (9) | 0.00118 (11) | −0.00164 (11) | −0.00018 (7) |
Sm1' | 0.01039 (16) | 0.00518 (7) | 0.00524 (9) | 0.00118 (11) | −0.00164 (11) | −0.00018 (7) |
Sm2 | 0.00628 (7) | 0.00599 (7) | 0.00525 (6) | −0.00020 (7) | −0.00116 (5) | 0.00022 (6) |
Sm3 | 0.00555 (7) | 0.00599 (7) | 0.00567 (6) | −0.00004 (7) | 0.00100 (5) | −0.00014 (7) |
O1 | 0.0120 (14) | 0.0066 (10) | 0.0111 (11) | 0.0012 (9) | 0.0055 (12) | 0.0008 (8) |
O2 | 0.0235 (18) | 0.0097 (11) | 0.0090 (12) | 0.0038 (10) | −0.0096 (12) | −0.0007 (9) |
O3 | 0.0037 (9) | 0.0104 (10) | 0.0072 (9) | −0.0005 (10) | −0.0005 (8) | 0.0006 (10) |
O4 | 0.0116 (15) | 0.0095 (11) | 0.0063 (10) | 0.0006 (9) | 0.0032 (11) | −0.0012 (8) |
O5 | 0.0133 (11) | 0.0043 (8) | 0.0095 (9) | 0.0000 (8) | −0.0019 (8) | 0.0026 (11) |
O6 | 0.0153 (16) | 0.0077 (11) | 0.0103 (12) | 0.0021 (9) | −0.0047 (11) | 0.0003 (8) |
O7 | 0.0064 (11) | 0.0083 (10) | 0.0075 (9) | 0.0019 (10) | 0.0007 (7) | 0.0019 (10) |
Mo1—O2 | 1.851 (3) | Sm1'—O4 | 2.585 (6) |
Mo1—O6 | 1.913 (3) | Sm1'—O6 | 2.969 (8) |
Mo1—O5 | 1.939 (2) | Sm1'—O2ii | 2.997 (8) |
Mo1—O5i | 2.000 (2) | Sm2—O7iii | 2.273 (2) |
Mo1—O1 | 2.002 (3) | Sm2—O7 | 2.313 (2) |
Mo1—O4 | 2.088 (3) | Sm2—O4iv | 2.361 (3) |
Sm1—O7ii | 2.348 (3) | Sm2—O1 | 2.385 (3) |
Sm1—O4 | 2.376 (3) | Sm2—O2v | 2.438 (3) |
Sm1—O7i | 2.378 (3) | Sm2—O6vi | 2.442 (3) |
Sm1—O3ii | 2.382 (3) | Sm2—O5 | 2.642 (2) |
Sm1—O3i | 2.383 (3) | Sm3—O3 | 2.243 (3) |
Sm1—O1ii | 2.637 (3) | Sm3—O3vii | 2.272 (3) |
Sm1—O6 | 2.637 (4) | Sm3—O4viii | 2.344 (3) |
Sm1'—O7i | 2.269 (6) | Sm3—O1ix | 2.399 (3) |
Sm1'—O3ii | 2.308 (6) | Sm3—O6iv | 2.465 (3) |
Sm1'—O1ii | 2.420 (6) | Sm3—O2 | 2.498 (3) |
Sm1'—O3i | 2.448 (6) | Sm3—O5 | 2.542 (2) |
Sm1'—O7ii | 2.451 (6) | ||
O2—Mo1—O6 | 169.01 (15) | O2v—Sm2—O5 | 137.52 (8) |
O2—Mo1—O5 | 90.43 (11) | O6vi—Sm2—O5 | 140.85 (8) |
O6—Mo1—O5 | 95.34 (11) | O3—Sm3—O3vii | 170.04 (8) |
O2—Mo1—O5i | 90.13 (11) | O3—Sm3—O4viii | 94.27 (11) |
O6—Mo1—O5i | 84.04 (11) | O3vii—Sm3—O4viii | 78.08 (11) |
O5—Mo1—O5i | 179.27 (4) | O3—Sm3—O1ix | 93.74 (11) |
O2—Mo1—O1 | 94.75 (15) | O3vii—Sm3—O1ix | 79.73 (10) |
O6—Mo1—O1 | 94.96 (15) | O4viii—Sm3—O1ix | 87.62 (8) |
O5—Mo1—O1 | 86.21 (10) | O3—Sm3—O6iv | 80.85 (11) |
O5i—Mo1—O1 | 94.21 (10) | O3vii—Sm3—O6iv | 102.63 (11) |
O2—Mo1—O4 | 86.32 (13) | O4viii—Sm3—O6iv | 72.98 (9) |
O6—Mo1—O4 | 84.04 (12) | O1ix—Sm3—O6iv | 159.29 (9) |
O5—Mo1—O4 | 93.04 (10) | O3—Sm3—O2 | 88.26 (12) |
O5i—Mo1—O4 | 86.53 (10) | O3vii—Sm3—O2 | 96.72 (12) |
O1—Mo1—O4 | 178.69 (12) | O4viii—Sm3—O2 | 159.48 (9) |
O7ii—Sm1—O4 | 108.72 (9) | O1ix—Sm3—O2 | 71.88 (9) |
O7ii—Sm1—O7i | 171.13 (5) | O6iv—Sm3—O2 | 127.47 (8) |
O4—Sm1—O7i | 76.90 (9) | O3—Sm3—O5 | 81.77 (8) |
O7ii—Sm1—O3ii | 73.66 (8) | O3vii—Sm3—O5 | 108.15 (8) |
O4—Sm1—O3ii | 75.34 (9) | O4viii—Sm3—O5 | 136.00 (8) |
O7i—Sm1—O3ii | 101.83 (10) | O1ix—Sm3—O5 | 136.25 (8) |
O7ii—Sm1—O3i | 110.21 (10) | O6iv—Sm3—O5 | 63.10 (8) |
O4—Sm1—O3i | 110.50 (9) | O2—Sm3—O5 | 64.52 (8) |
O7i—Sm1—O3i | 73.09 (8) | Mo1—O1—Sm2 | 100.49 (12) |
O3ii—Sm1—O3i | 170.57 (7) | Mo1—O1—Sm3v | 135.91 (14) |
O7ii—Sm1—O1ii | 75.35 (9) | Sm2—O1—Sm3v | 108.83 (11) |
O4—Sm1—O1ii | 172.47 (11) | Mo1—O1—Sm1'x | 107.11 (19) |
O7i—Sm1—O1ii | 98.31 (9) | Sm2—O1—Sm1'x | 99.02 (16) |
O3ii—Sm1—O1ii | 100.28 (9) | Sm3v—O1—Sm1'x | 100.10 (17) |
O3i—Sm1—O1ii | 73.07 (9) | Mo1—O1—Sm1x | 112.74 (12) |
O7ii—Sm1—O6 | 73.49 (8) | Sm2—O1—Sm1x | 96.14 (10) |
O4—Sm1—O6 | 64.41 (9) | Sm3v—O1—Sm1x | 96.34 (11) |
O7i—Sm1—O6 | 115.37 (9) | Mo1—O2—Sm2ix | 152.85 (14) |
O3ii—Sm1—O6 | 114.59 (9) | Mo1—O2—Sm3 | 103.05 (11) |
O3i—Sm1—O6 | 74.84 (9) | Sm2ix—O2—Sm3 | 104.03 (11) |
O1ii—Sm1—O6 | 123.11 (10) | Mo1—O2—Sm1'x | 91.63 (15) |
O7i—Sm1'—O3ii | 107.6 (2) | Sm2ix—O2—Sm1'x | 88.60 (13) |
O7i—Sm1'—O1ii | 108.1 (2) | Sm3—O2—Sm1'x | 85.20 (13) |
O3ii—Sm1'—O1ii | 109.2 (2) | Sm3—O3—Sm3viii | 111.89 (9) |
O7i—Sm1'—O3i | 73.78 (15) | Sm3—O3—Sm1'x | 110.4 (2) |
O3ii—Sm1'—O3i | 173.5 (3) | Sm3viii—O3—Sm1'x | 108.83 (17) |
O1ii—Sm1'—O3i | 75.94 (15) | Sm3—O3—Sm1x | 118.38 (13) |
O7i—Sm1'—O7ii | 173.2 (3) | Sm3viii—O3—Sm1x | 103.97 (11) |
O3ii—Sm1'—O7ii | 73.06 (15) | Sm3—O3—Sm1iv | 109.00 (12) |
O1ii—Sm1'—O7ii | 77.68 (15) | Sm3viii—O3—Sm1iv | 107.54 (12) |
O3i—Sm1'—O7ii | 104.8 (2) | Sm1x—O3—Sm1iv | 105.40 (9) |
O7i—Sm1'—O4 | 74.71 (15) | Sm3—O3—Sm1'iv | 116.8 (2) |
O3ii—Sm1'—O4 | 72.65 (15) | Sm3viii—O3—Sm1'iv | 102.98 (16) |
O1ii—Sm1'—O4 | 175.6 (3) | Mo1—O4—Sm3vii | 135.68 (14) |
O3i—Sm1'—O4 | 101.9 (2) | Mo1—O4—Sm2i | 98.05 (11) |
O7ii—Sm1'—O4 | 99.3 (2) | Sm3vii—O4—Sm2i | 110.02 (10) |
O7i—Sm1'—O6 | 107.4 (2) | Mo1—O4—Sm1 | 106.17 (11) |
O3ii—Sm1'—O6 | 105.7 (2) | Sm3vii—O4—Sm1 | 101.93 (12) |
O1ii—Sm1'—O6 | 118.4 (2) | Sm2i—O4—Sm1 | 100.09 (11) |
O3i—Sm1'—O6 | 67.95 (17) | Mo1—O4—Sm1' | 112.01 (17) |
O7ii—Sm1'—O6 | 66.21 (17) | Sm3vii—O4—Sm1' | 98.03 (16) |
O4—Sm1'—O6 | 57.23 (15) | Sm2i—O4—Sm1' | 97.23 (15) |
O7i—Sm1'—O2ii | 70.54 (19) | Mo1—O5—Mo1iv | 146.62 (14) |
O3ii—Sm1'—O2ii | 75.88 (19) | Mo1—O5—Sm3 | 98.96 (9) |
O1ii—Sm1'—O2ii | 62.10 (16) | Mo1iv—O5—Sm3 | 99.32 (9) |
O3i—Sm1'—O2ii | 110.4 (2) | Mo1—O5—Sm2 | 93.91 (8) |
O7ii—Sm1'—O2ii | 115.9 (2) | Mo1iv—O5—Sm2 | 91.79 (8) |
O4—Sm1'—O2ii | 122.3 (2) | Sm3—O5—Sm2 | 136.46 (10) |
O6—Sm1'—O2ii | 177.76 (18) | Mo1—O6—Sm2iii | 145.41 (15) |
O7iii—Sm2—O7 | 157.58 (7) | Mo1—O6—Sm3i | 104.58 (12) |
O7iii—Sm2—O4iv | 111.33 (11) | Sm2iii—O6—Sm3i | 103.56 (11) |
O7—Sm2—O4iv | 78.48 (11) | Mo1—O6—Sm1 | 102.32 (12) |
O7iii—Sm2—O1 | 105.63 (11) | Sm2iii—O6—Sm1 | 94.75 (11) |
O7—Sm2—O1 | 81.12 (11) | Sm3i—O6—Sm1 | 95.14 (11) |
O4iv—Sm2—O1 | 127.83 (8) | Mo1—O6—Sm1' | 103.31 (14) |
O7iii—Sm2—O2v | 82.15 (11) | Sm2iii—O6—Sm1' | 94.19 (14) |
O7—Sm2—O2v | 79.43 (11) | Sm3i—O6—Sm1' | 94.28 (13) |
O4iv—Sm2—O2v | 145.91 (12) | Sm1'iv—O7—Sm2vi | 114.3 (2) |
O1—Sm2—O2v | 73.19 (9) | Sm1'iv—O7—Sm2 | 108.31 (18) |
O7iii—Sm2—O6vi | 78.68 (10) | Sm2vi—O7—Sm2 | 111.63 (10) |
O7—Sm2—O6vi | 85.49 (11) | Sm2vi—O7—Sm1x | 108.04 (12) |
O4iv—Sm2—O6vi | 73.12 (9) | Sm2—O7—Sm1x | 106.73 (11) |
O1—Sm2—O6vi | 151.37 (9) | Sm2vi—O7—Sm1iv | 121.39 (12) |
O2v—Sm2—O6vi | 79.56 (9) | Sm2—O7—Sm1iv | 101.44 (10) |
O7iii—Sm2—O5 | 112.56 (8) | Sm1x—O7—Sm1iv | 106.65 (10) |
O7—Sm2—O5 | 89.73 (8) | Sm2vi—O7—Sm1'x | 114.73 (18) |
O4iv—Sm2—O5 | 67.86 (8) | Sm2—O7—Sm1'x | 100.18 (16) |
O1—Sm2—O5 | 64.56 (8) |
Symmetry codes: (i) −x+1, y−1/2, −z+3/2; (ii) x−1, y, z; (iii) x−1/2, −y+3/2, −z+1; (iv) −x+1, y+1/2, −z+3/2; (v) −x+3/2, −y+1, z−1/2; (vi) x+1/2, −y+3/2, −z+1; (vii) x−1/2, −y+3/2, −z+2; (viii) x+1/2, −y+3/2, −z+2; (ix) −x+3/2, −y+1, z+1/2; (x) x+1, y, z. |
Experimental details
Crystal data | |
Chemical formula | Sm3MoO7 |
Mr | 658.99 |
Crystal system, space group | Orthorhombic, P212121 |
Temperature (K) | 293 |
a, b, c (Å) | 7.4500 (1), 7.5460 (1), 10.6766 (2) |
V (Å3) | 600.21 (2) |
Z | 4 |
Radiation type | Mo Kα |
µ (mm−1) | 30.94 |
Crystal size (mm) | 0.19 × 0.09 × 0.04 |
Data collection | |
Diffractometer | Nonius KappaCCD diffractometer |
Absorption correction | Analytical (de Meulenaer & Tompa, 1965) |
Tmin, Tmax | 0.037, 0.367 |
No. of measured, independent and observed [I > 2σ(I)] reflections | 17049, 3719, 3438 |
Rint | 0.034 |
(sin θ/λ)max (Å−1) | 0.904 |
Refinement | |
R[F2 > 2σ(F2)], wR(F2), S | 0.022, 0.042, 1.05 |
No. of reflections | 3719 |
No. of parameters | 107 |
No. of restraints | 1 |
Δρmax, Δρmin (e Å−3) | 1.94, −3.05 |
Absolute structure | Flack (1983), 1593 Friedel pairs |
Absolute structure parameter | 0.491 (17) |
Computer programs: COLLECT (Nonius, 1998), EVALCCD (Duisenberg, 1998), SHELXL97 (Sheldrick, 1997), DIAMOND (Brandenburg, 2001).
Mo1—O2 | 1.851 (3) | Sm1'—O4 | 2.585 (6) |
Mo1—O6 | 1.913 (3) | Sm1'—O6 | 2.969 (8) |
Mo1—O5 | 1.939 (2) | Sm1'—O2ii | 2.997 (8) |
Mo1—O5i | 2.000 (2) | Sm2—O7iii | 2.273 (2) |
Mo1—O1 | 2.002 (3) | Sm2—O7 | 2.313 (2) |
Mo1—O4 | 2.088 (3) | Sm2—O4iv | 2.361 (3) |
Sm1—O7ii | 2.348 (3) | Sm2—O1 | 2.385 (3) |
Sm1—O4 | 2.376 (3) | Sm2—O2v | 2.438 (3) |
Sm1—O7i | 2.378 (3) | Sm2—O6vi | 2.442 (3) |
Sm1—O3ii | 2.382 (3) | Sm2—O5 | 2.642 (2) |
Sm1—O3i | 2.383 (3) | Sm3—O3 | 2.243 (3) |
Sm1—O1ii | 2.637 (3) | Sm3—O3vii | 2.272 (3) |
Sm1—O6 | 2.637 (4) | Sm3—O4viii | 2.344 (3) |
Sm1'—O7i | 2.269 (6) | Sm3—O1ix | 2.399 (3) |
Sm1'—O3ii | 2.308 (6) | Sm3—O6iv | 2.465 (3) |
Sm1'—O1ii | 2.420 (6) | Sm3—O2 | 2.498 (3) |
Sm1'—O3i | 2.448 (6) | Sm3—O5 | 2.542 (2) |
Sm1'—O7ii | 2.451 (6) |
Symmetry codes: (i) −x+1, y−1/2, −z+3/2; (ii) x−1, y, z; (iii) x−1/2, −y+3/2, −z+1; (iv) −x+1, y+1/2, −z+3/2; (v) −x+3/2, −y+1, z−1/2; (vi) x+1/2, −y+3/2, −z+1; (vii) x−1/2, −y+3/2, −z+2; (viii) x+1/2, −y+3/2, −z+2; (ix) −x+3/2, −y+1, z+1/2. |
Metal oxides of general formula Ln3MO7, where M is a pentavalent 4d or 5d transition metal such as Nb, Mo, Ru, Ta, Re, Os or Ir, and Ln is a trivalent rare earth, present an ordered double fluorite structure and crystallize in various orthorhombic space groups, such as Pnma, Cmcm, C2221 or P212121. The main structural feature of the Ln3MO7 compounds is the presence of isolated zigzag chains of trans-corner-linked MO6 octahedra that are separated by seven- or eightfold coordinate Ln–O polyhedra. Because of this quasi-one-dimensionality, La3RuO7, Ln3OsO7 (Ln = La, Pr, Nd, Sm, Eu and Gd; Lam et al., 2002; Plaisier et al., 2002; Gemmill et al., 2005), Ln3MoO7 (Greedan et al., 1997; Nishimine et al. 2005), Ln3RuO7 (Ln = La, Pr, Sm and Eu; Khalifah et al., 2000; Wiss et al., 2000; Harada & Hinatsu, 2001; Gemmill et al., 2004), Ln3ReO7 (Ln = Pr, Nd, Sm, Gd, Tb and Dy; Wltschek et al., 1996; Lam et al., 2003; Hinatsu et al., 2004) and Pr3MO7 (M = Nb and Ta; Vente et al., 1994) have been extensively studied for their physical properties since peculiar magnetic and electronic properties are expected. We present here the crystal structure of Sm3MoO7. This compound was first synthesized as a powder sample by Prévost-Czeskleba (1987) and found to crystallize in the orthorhombic space group Cmcm as Nd3NbO7 (Rossel, 1979). Our investigation on a single-crystal indicates that Sm3MoO7 crystallizes in the noncentrosymmetric space group P212121 as La3MoO7 (Greedan et al., 1997) and Pr3MoO7 (Barrier & Gougeon, 2003). However, a partial disorder is observed at one rare-earth site, i.e. Sm1, in the title compound.
Perspective views of Sm3MoO7 along the b and c axes are shown in Figs. 1 and 2, respectively. The main structural feature of Sm3MoO7 is the occurrence of infinite single chains of tilted corner-linked MoO6 octahedra running parallel to the b axis. These chains alternate with rows of edge-shared Sm1O7 or Sm1'O8 polyhedra to form slabs parallel to the ab plane. The slabs are separated by the Sm2 and Sm3 cations, which are both seven coordinated by O atoms. The Mo—O distances within the MoO6 octahedra (Fig. 3) range from 1.851 (3) to 2.088 (3) Å [1.861 (3)–2.098 (4) Å and 1.852 (4)–2.088 (5) Å in La3MoO7 and Pr3MoO7, respectively], with an average value of 1.966 Å compared with 1.981 and 1.974 Å in La3MoO7 and Pr3MoO7. Because of the octahedral tilt, the Mo—O5—Movi angle [symmetry code: (vi) −x + 1, y + 1/2, −z + 3/2] along the chain differs significantlyly from 180°, with a value of 146.62 (14)°. The main difference with La3MoO7 and Pr3MoO7 concerns the Sm1 site, which has been split into two independent parts, Sm1 and Sm1'. Atom Sm1, with 92.0 (3)% occupancy, has a coordination number of 7, with five short Sm—O bonds in the 2.348 (3)–2.383 (3) Å range and two long Sm—O bonds of 2.637 (3) and 2.637 (4) Å. This 7-coordination may be described as a bicapped square-based pyramid and corresponds to the rare-earth site 1 in La3MoO7 and Pr3MoO7. In contrast, atom Sm1', with site occupancy of 0.080 (3), has a coordination number of 8, with six Sm—O bonds distributed in the 2.269 (6)–2.585 (6) Å range and two others of length 2.969 (8) and 2.997 (8) Å. The six nearest O atoms form a highly distorted octahedron and the other two cap two faces. Atoms Sm2 and Sm3 are in distorted pentagonal bipyramidal configurations, with Sm—O distances in the ranges 2.273 (2)–2.642 (2) and 2.243 (3) − 2.542 (2) Å, respectively.
The phenomenon of rare-earth site splitting has recently been observed for the related compounds Tb3RuO7 and Dy3RuO7 (Ishizawa, Suwa & Tateishi, 2007; Ishizawa, Suwa, Tateishi & Hester, 2007). Indeed, these compounds, which crystallize in the noncentrosymmetric space group P21nb with a double b axis (a axis in Sm3MoO7), present two rare-earth atom sites (out of six crystallographically independent ones) that are split into two positions. As in the ruthenium compounds, the rare-earth sites that are split in the title compound are those which alternate with the MoO6 chains. Our study shows clearly that such a partial disorder can exist with transition metals other than ruthenium in the Ln3MO7 series. Examination of various structures of the Ln3MO7 type shows that, in a number of them, the rare-earth metals that alternate with the MoO6 chains present either equivalent isotropic displacement parameters that are, at least, double those of the other rare-earth atoms (Wltschek et al., 1996; Khalifah et al., 2000; Lam et al., 2003; Hinatsu et al., 2004; Gemmill et al., 2005) or large prolate anisotropic atomic displacement parameters (Barrier & Gougeon, 2003; Ishizawa et al., 2006). Finally, one can note that the rare-earth disorder seems to occur not only in the noncentrosymmetric space groups but also in the centrosymmetric ones, and it would be interesting to see if this partial structural disorder depends on the rare-earth atom size.