Pr₃MoO₇

Tripraseodymium molybdenum heptaoxide, Pr₃MoO₇, is isostructural with La₃MoO₇. Its crystal structure consists of chains of corner-linked MoO₆ octahedra that are parallel with the b axis and separated from each other by seven-coordinate Pr-O polyhedra.

Key indicators

• Single-crystal X-ray study
• T = 293 K
• Mean [sigma](Mo-O) = 0.004 Å
• R factor = 0.029
• wR factor = 0.067
• Data-to-parameter ratio = 33.1

checkCIF results

No syntax errors found


 Alert Level B:



PLAT_111  Alert B ADDSYM Detects (Pseudo) Centre of Symmetry ...         81 Perc Fit

PLAT_112  Alert B ADDSYM Detects Additional (Pseudo) Symm. Elem.          b

PLAT_112  Alert B ADDSYM Detects Additional (Pseudo) Symm. Elem.          n

PLAT_112  Alert B ADDSYM Detects Additional (Pseudo) Symm. Elem.          m

PLAT_113  Alert B ADDSYM Suggests Possible Pseudo/New Spacegroup       Pnma


 Alert Level C:



STRVAL_01
         From the CIF: _refine_ls_abs_structure_Flack    0.490
         From the CIF: _refine_ls_abs_structure_Flack_su    0.030
           Alert C Flack test results are ambiguous.

PLAT_741  Alert C Bond    Calc   3.7752(3), Rep     3.77520 ....    Missing s.u.
                     PR3  -PR3     1.555   2.565

PLAT_741  Alert C Bond    Calc   3.7752(3), Rep     3.77520 ....    Missing s.u.
                     PR3  -PR3     1.555   2.465

General Notes



ABSTM_02  When printed, the submitted absorption T values will be replaced
          by the scaled T values. Since the ratio of scaled T's is
          identical to the ratio of reported T values, the scaling does
          not imply a change to the absorption corrections used in the
          study.
          Ratio of Tmax expected/reported      1.189
          Tmax scaled      0.267 Tmin scaled      0.165

REFLT_03
         From the CIF: _diffrn_reflns_theta_max           37.79
         From the CIF: _reflns_number_total               3345
         Count of symmetry unique reflns         1923
         Completeness (_total/calc)            173.95%
         TEST3: Check Friedels for noncentro structure
         Estimate of Friedel pairs measured      1422
         Fraction of Friedel pairs measured     0.739
         Are heavy atom types Z>Si present          yes
          Please check that the estimate of the number of Friedel pairs is
          correct. If it is not, please give the correct count in the
          _publ_section_exptl_refinement section of the submitted CIF.


 0 Alert Level A = Potentially serious problem

 5 Alert Level B = Potential problem

 3 Alert Level C = Please check

---

S1. Comment

The Ln₃MO₇ compounds, where M is a pentavalent 4 d or 5 d transition element such as Nb, Mo, Ru, Ir, Os or Ta, and Ln is a 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 Ln₃MoO₇ compounds is the occurrence of zigzag chains of trans-corner-sharing MO₆ octahedra that are separated by seven or eight-coordinate Ln–O polyhedra. Because of this quasi-one-dimensionality, La₃RuO₇, La₃OsO₇ (Lam et al., 2002), Ln₃OsO₇ (Ln = Pr, Nd, Sm; Plaisier et al., 2002), La₃MoO₇ (Greedan et al., 1997), Ln₃RuO₇ (Ln = Sm, Eu; Harada & Hinatsu, 2001) and Pr₃MO₇ (M = Nb, Ta; Vente et al., 1994) have been extensively studied for their physical properties.

We present here the crystal structure of Pr₃MoO₇. 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 Pr₃MoO₇ crystallizes in the space group P2₁2₁2₁ and is isostructural with La₃MoO₇ (Greedan et al., 1997). Perspective views of Pr₃MoO₇ along the b and c axes are shown in Figs. 1 and 2, respectively. The Mo—O distances within the MoO₆ octahedra range from 1.854 (4) to 2.088 (5) Å [1.861 (3)–2.098 (4) Å in La₃MoO₇], with an average value of 1.974 Å compared to 1.981 Å in La₃MoO₇. The three crystallographically independent Pr³⁺ ions are each surrounded by seven O atoms. The oxygen environment of Pr1 can be viewed as a highly distorted cube, with one apex missing and those of Pr2 and Pr3 as distorted pentagonal bipyramids. The Pr—O distances are in the ranges 2.382 (4)–2.690 (5), 2.302 (3)–2.658 (3) and 2.280 (4)–2.581 (3) Å for the Pr1, Pr2 and Pr3 sites, respectively. As mentioned in the Experimental, the structure presents a Pbnm pseudosymmetry. The non-centrosymmetric nature of the structure arises probably from the Pr1 ion that does not reside at an inversion center as revealed by the refinement made in the space group Pbnm.

S2. Experimental

Single crystals of Pr₃MoO₇ were prepared from a stoichiometric amount of Pr₆O₁₁, MoO₃ and Mo. 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, held at this temperature for 10 min, then cooled at a rate of 100 K h⁻¹ to 1373 K and finally furnace-cooled.

S3. Refinement

Systematic absences were only consistent with the acentric space group P2₁2₁2₁. The atomic coordinates of La, Mo and O from La₃MoO₇ (Greedan et al., 1997) were used as starting positions in the first stages of the refinement in the present study. Attempts to refine the structure in the space group Pbnm, as suggested by PLATON (Spek, 1998), were unsuccessful and led to an R factor of about 0.10. Refinement of the Flack (1983) parameter gave a value of 0.49 (3), indicating that the crystal studied is a racemic twin.

Computing details

Data collection: COLLECT (Nonius, 1998); cell refinement: COLLECT; data reduction: DENZO and SCALEPACK (Otwinowski & Minor, 1997); program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: DIAMOND(Bergerhoff, 1996); software used to prepare material for publication: SHELXL97.

Figures

	Fig. 1. Perspective view of Pr3MoO7 along the b axis. Displacement ellipsoids are drawn at the 97% probability level.
	Fig. 2. Perspective view of Pr3MoO7 along the c axis.

Triprasepdymium molybdenum heptaoxide

Crystal data

Pr3MoO7	F(000) = 1100
Mr = 630.67	Dx = 6.701 Mg m^−3
Orthorhombic, P212121	Mo Kα radiation, λ = 0.71070 Å
Hall symbol: P 2ac 2ab	Cell parameters from 11425 reflections
a = 7.5087 (1) Å	θ = 1–37.8°
b = 7.6412 (2) Å	µ = 24.91 mm^−1
c = 10.8952 (2) Å	T = 293 K
V = 625.12 (2) Å^3	Irregular block, black
Z = 4	0.09 × 0.06 × 0.05 mm

Data collection

Nonius KappaCCD diffractometer	3345 independent reflections
Radiation source: fine-focus sealed tube	3222 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.058
ϕ scans (κ = 0) + additional ω scans	θmax = 37.8°, θmin = 3.3°
Absorption correction: multi-scan (Blessing, 1995)	h = −12→12
Tmin = 0.139, Tmax = 0.225	k = −13→12
16521 measured reflections	l = −16→18

Refinement

Refinement on F^2	w = 1/[σ^2(Fo^2) + (0.0091P)^2 + 7.1924P] where P = (Fo^2 + 2Fc^2)/3
Least-squares matrix: full	(Δ/σ)max = 0.001
R[F^2 > 2σ(F^2)] = 0.029	Δρmax = 4.07 e Å^−3
wR(F^2) = 0.067	Δρmin = −4.05 e Å^−3
S = 1.05	Extinction correction: SHELXL97, Fc^*=kFc[1+0.001xFc^2λ^3/sin(2θ)]^-1/4
3345 reflections	Extinction coefficient: 0.0110 (3)
101 parameters	Absolute structure: Flack (1983)
0 restraints	Absolute structure parameter: 0.49 (3)
Primary atom site location: isomorphous structure methods

Special details

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.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Ų)

	x	y	z	Uiso*/Ueq
Mo	0.49773 (5)	1.00093 (5)	0.74955 (5)	0.00537 (7)
Pr1	0.98074 (4)	1.00637 (3)	0.75374 (3)	0.01071 (7)
Pr2	0.70257 (3)	0.75417 (4)	0.53386 (2)	0.00700 (6)
Pr3	0.69200 (3)	0.74788 (4)	−0.01812 (2)	0.00686 (6)
O1	1.2042 (7)	1.0298 (5)	1.3685 (4)	0.0126 (8)
O2	1.1372 (7)	1.0505 (5)	1.1117 (4)	0.0161 (9)
O3	0.9590 (5)	0.7487 (7)	−0.1179 (3)	0.0092 (5)
O4	0.7888 (7)	0.9639 (5)	0.1292 (4)	0.0119 (8)
O5	0.5707 (5)	0.7473 (4)	−0.2398 (3)	0.0095 (5)
O6	0.8275 (7)	0.9616 (5)	0.3754 (4)	0.0116 (8)
O7	0.9904 (5)	0.7577 (6)	0.6184 (3)	0.0088 (6)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Mo	0.00628 (14)	0.00418 (14)	0.00564 (13)	0.00035 (10)	−0.00025 (8)	−0.00016 (11)
Pr1	0.01858 (13)	0.00594 (10)	0.00763 (10)	−0.00259 (9)	−0.00359 (9)	0.00055 (8)
Pr2	0.00728 (10)	0.00670 (11)	0.00702 (9)	−0.00024 (11)	−0.00112 (7)	0.00025 (9)
Pr3	0.00684 (10)	0.00639 (11)	0.00736 (9)	−0.00004 (11)	0.00108 (7)	−0.00012 (9)
O1	0.015 (2)	0.0111 (16)	0.0122 (15)	−0.0014 (15)	−0.0070 (16)	0.0011 (13)
O2	0.027 (3)	0.0101 (16)	0.0113 (16)	−0.0038 (15)	0.0107 (16)	−0.0008 (13)
O3	0.0061 (13)	0.0118 (15)	0.0099 (12)	−0.0009 (15)	−0.0013 (11)	0.0003 (14)
O4	0.017 (2)	0.0078 (15)	0.0107 (14)	−0.0015 (14)	−0.0037 (16)	−0.0005 (12)
O5	0.0112 (13)	0.0049 (12)	0.0124 (12)	0.0004 (11)	−0.0004 (11)	−0.0001 (16)
O6	0.016 (2)	0.0078 (15)	0.0112 (15)	−0.0014 (13)	0.0047 (14)	−0.0016 (12)
O7	0.0086 (15)	0.0109 (15)	0.0070 (12)	0.0038 (15)	0.0002 (9)	0.0013 (14)

Geometric parameters (Å, º)

Mo—O2^i	1.854 (4)	Pr2—O7^x	2.302 (3)
Mo—O6^ii	1.920 (5)	Pr2—O7	2.349 (3)
Mo—O5^iii	1.954 (3)	Pr2—O4^ii	2.392 (4)
Mo—O1^i	2.008 (5)	Pr2—O1^xi	2.416 (4)
Mo—O5^iv	2.018 (3)	Pr2—O6	2.524 (4)
Mo—O4^ii	2.088 (5)	Pr2—O2^xii	2.527 (4)
Mo—Pr2	3.3828 (6)	Pr2—O5^iv	2.658 (3)
Mo—Pr2^v	3.4021 (5)	Pr2—Mo^xiii	3.4021 (5)
Mo—Pr3^iii	3.4566 (6)	Pr2—Pr1^i	3.8154 (4)
Mo—Pr3^iv	3.5034 (6)	Pr2—Pr1^xii	3.8203 (4)
Mo—Pr1	3.6273 (4)	Pr3—O3	2.280 (4)
Pr1—O7^vi	2.382 (4)	Pr3—O3^xiv	2.293 (4)
Pr1—O7	2.406 (4)	Pr3—O4	2.414 (4)
Pr1—O3^vii	2.414 (5)	Pr3—O1^xii	2.458 (4)
Pr1—O3^iv	2.420 (5)	Pr3—O6^i	2.509 (4)
Pr1—O4^ii	2.447 (5)	Pr3—O2^x	2.531 (4)
Pr1—O6^ii	2.678 (5)	Pr3—O5	2.581 (3)
Pr1—O1^viii	2.690 (5)	Pr3—Mo^xv	3.4566 (6)
Pr1—Pr2	3.7169 (4)	Pr3—Mo^xvi	3.5034 (6)
Pr1—Pr3^ii	3.7393 (4)	Pr3—Pr1^i	3.7393 (4)
Pr1—Pr2^ii	3.8154 (4)	Pr3—Pr3^xvii	3.7752
Pr1—Pr3^ix	3.8194 (4)	Pr3—Pr3^xiv	3.7752
O2^i—Mo—O6^ii	169.7 (2)	O7—Pr2—O1^xi	80.39 (16)
O2^i—Mo—O5^iii	90.94 (17)	O4^ii—Pr2—O1^xi	128.12 (12)
O6^ii—Mo—O5^iii	94.31 (16)	O7^x—Pr2—O6	77.82 (15)
O2^i—Mo—O1^i	94.9 (2)	O7—Pr2—O6	85.36 (15)
O6^ii—Mo—O1^i	94.2 (2)	O4^ii—Pr2—O6	73.82 (13)
O5^iii—Mo—O1^i	87.10 (16)	O1^xi—Pr2—O6	149.65 (13)
O2^i—Mo—O5^iv	89.50 (16)	O7^x—Pr2—O2^xii	81.55 (16)
O6^ii—Mo—O5^iv	85.20 (16)	O7—Pr2—O2^xii	79.35 (16)
O5^iii—Mo—O5^iv	179.46 (6)	O4^ii—Pr2—O2^xii	144.50 (17)
O1^i—Mo—O5^iv	93.18 (15)	O1^xi—Pr2—O2^xii	73.79 (14)
O2^i—Mo—O4^ii	86.5 (2)	O6—Pr2—O2^xii	77.32 (13)
O6^ii—Mo—O4^ii	84.52 (18)	O7^x—Pr2—O5^iv	114.20 (12)
O5^iii—Mo—O4^ii	92.49 (15)	O7—Pr2—O5^iv	88.81 (11)
O1^i—Mo—O4^ii	178.6 (2)	O4^ii—Pr2—O5^iv	67.99 (12)
O5^iv—Mo—O4^ii	87.22 (15)	O1^xi—Pr2—O5^iv	64.89 (12)
O7^vi—Pr1—O7	172.81 (4)	O6—Pr2—O5^iv	141.76 (11)
O7^vi—Pr1—O3^vii	73.92 (12)	O2^xii—Pr2—O5^iv	138.38 (12)
O7—Pr1—O3^vii	102.97 (15)	O3—Pr3—O3^xiv	168.18 (11)
O7^vi—Pr1—O3^iv	108.90 (15)	O3—Pr3—O4	92.88 (16)
O7—Pr1—O3^iv	73.38 (12)	O3^xiv—Pr3—O4	78.02 (16)
O3^vii—Pr1—O3^iv	172.36 (9)	O3—Pr3—O1^xii	92.25 (16)
O7^vi—Pr1—O4^ii	108.95 (12)	O3^xiv—Pr3—O1^xii	79.70 (15)
O7—Pr1—O4^ii	76.01 (13)	O4—Pr3—O1^xii	85.83 (12)
O3^vii—Pr1—O4^ii	75.16 (13)	O3—Pr3—O6^i	80.11 (17)
O3^iv—Pr1—O4^ii	109.88 (13)	O3^xiv—Pr3—O6^i	104.14 (17)
O7^vi—Pr1—O6^ii	73.48 (12)	O4—Pr3—O6^i	73.74 (13)
O7—Pr1—O6^ii	113.66 (13)	O1^xii—Pr3—O6^i	157.67 (13)
O3^vii—Pr1—O6^ii	113.30 (13)	O3—Pr3—O2^x	87.33 (17)
O3^iv—Pr1—O6^ii	74.33 (13)	O3^xiv—Pr3—O2^x	98.42 (17)
O4^ii—Pr1—O6^ii	63.35 (13)	O4—Pr3—O2^x	158.83 (13)
O7^vi—Pr1—O1^viii	74.38 (13)	O1^xii—Pr3—O2^x	73.01 (13)
O7—Pr1—O1^viii	100.22 (12)	O6^i—Pr3—O2^x	126.96 (12)
O3^vii—Pr1—O1^viii	101.47 (12)	O3—Pr3—O5	82.20 (11)
O3^iv—Pr1—O1^viii	72.98 (12)	O3^xiv—Pr3—O5	109.59 (12)
O4^ii—Pr1—O1^viii	174.02 (15)	O4—Pr3—O5	136.84 (12)
O6^ii—Pr1—O1^viii	122.63 (14)	O1^xii—Pr3—O5	136.98 (12)
O7^x—Pr2—O7	156.88 (10)	O6^i—Pr3—O5	63.16 (12)
O7^x—Pr2—O4^ii	111.54 (16)	O2^x—Pr3—O5	64.16 (12)
O7—Pr2—O4^ii	78.14 (17)	Mo^xv—O5—Mo^xvi	148.3 (2)
O7^x—Pr2—O1^xi	106.58 (16)

Symmetry codes: (i) −x+3/2, −y+2, z−1/2; (ii) −x+3/2, −y+2, z+1/2; (iii) −x+1, y+1/2, −z+1/2; (iv) x, y, z+1; (v) −x+1, y+1/2, −z+3/2; (vi) −x+2, y+1/2, −z+3/2; (vii) −x+2, y+1/2, −z+1/2; (viii) −x+5/2, −y+2, z−1/2; (ix) x+1/2, −y+3/2, −z+1; (x) x−1/2, −y+3/2, −z+1; (xi) x−1/2, −y+3/2, −z+2; (xii) −x+2, y−1/2, −z+3/2; (xiii) −x+1, y−1/2, −z+3/2; (xiv) x−1/2, −y+3/2, −z; (xv) −x+1, y−1/2, −z+1/2; (xvi) x, y, z−1; (xvii) x+1/2, −y+3/2, −z.