Sodium scandium diphosphate, NaScP₂O₇, isotypic with α-NaTi(III)P₂O₇

Abstract

Crystals of the title compound, NaScP₂O₇, were grown by a flux method. The crystal structure is isotypic with those of α-NaTiP₂O₇, NaYbP₂O₇ and NaLuP₂O₇, and is closely related to that of NaYP₂O₇. The structural set-up consists of a three-dimensional framework of P₂O₇ units that are corner-shared by ScO₆ octa­hedra, forming tunnels running parallel to [010]. The Na atoms are situated in the tunnels and are surrounded by nine O atoms in a distorted environment.

Related literature

Previous X-ray powder data of NaScP₂O₇ were reported by Vitins et al. (2000 ▶). NaScP₂O₇ is isotypic with α-NaTiP₂O₇ (Leclaire et al., 1988 ▶), NaYbP₂O₇ (Férid et al., 2004 ▶) and NaLuP₂O₇ (Yuan et al., 2007 ▶) and shows similar structural features as NaYP₂O₇ (Hamady & Jouini, 1996 ▶). Both structure types are topologically related to β-cristobalite (Leclaire et al., 1988 ▶). For a detailed review on the structures of A ^I M ^IIIP₂O₇-type diphosphates, see: Li et al. (2005 ▶); Schwendtner & Kolitsch (2004 ▶). For possible applications as scintillators or phosphor materials based on A ^I M ^IIIP₂O₇-type diphosphates, see: Hizhnyi et al. (2007 ▶, 2008 ▶). For background to structural parameters, see: Brese & O’Keeffe (1991 ▶); Robinson et al. (1971 ▶).

Experimental

Crystal data

• NaScP₂O₇

• M _r = 241.89

• Monoclinic,

• a = 8.9044 (18) Å

• b = 5.3300 (11) Å

• c = 12.516 (3) Å

• β = 104.11 (3)°

• V = 576.1 (2) ų

• Z = 4

• Mo Kα radiation

• μ = 1.89 mm⁻¹

• T = 293 K

• 0.40 × 0.15 × 0.05 mm

Data collection

• Kuma KM-4-CCD diffractometer

• Absorption correction: multi-scan (CrysAlis CCD; Oxford Diffraction, 2003 ▶) T _min = 0.067, T _max = 0.093

• 5082 measured reflections

• 1018 independent reflections

• 932 reflections with I > 2σ(I)

• R _int = 0.028

Refinement

• R[F ² > 2σ(F ²)] = 0.025

• wR(F ²) = 0.082

• S = 1.18

• 1018 reflections

• 101 parameters

• Δρ_max = 0.46 e Å⁻³

• Δρ_min = −0.46 e Å⁻³

Data collection: CrysAlis CCD (Oxford Diffraction, 2003 ▶); cell refinement: CrysAlis CCD; data reduction: CrysAlis RED (Oxford Diffraction, 2003 ▶); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008 ▶); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008 ▶); molecular graphics: ATOMS (Dowty, 2003 ▶); software used to prepare material for publication: SHELXL97.

Supplementary Material

Additional supplementary materials: crystallographic information; 3D view; checkCIF report

Table 1. Selected geometric parameters (Å, °).

Sc—O3	2.0217 (19)
Sc—O6i	2.0770 (17)
Sc—O7ii	2.1112 (17)
Sc—O1	2.1220 (16)
Sc—O2	2.1220 (16)
Sc—O4	2.1506 (18)
P1—O6	1.5088 (17)
P1—O7	1.5254 (17)
P1—O4	1.5313 (18)
P1—O5iii	1.6114 (17)
P2—O3	1.5013 (19)
P2—O1iv	1.5278 (16)
P2—O2v	1.5332 (16)
P2—O5	1.6151 (17)

P1vi—O5—P2

125.47 (10)

Symmetry codes: (i) ; (ii) ; (iii) ; (iv) ; (v) ; (vi) .

supplementary crystallographic information

Comment

A^IM^IIIT^V₂O₇-type compounds recently have received an increased attention, partly due to their possible applications as scintillators or phosphor materials (Hizhnyi et al., 2007; Hizhnyi et al., 2008). So far, the A^IM^IIIP₂O₇-type diphosphates are known to adopt eight different structure types which depends on the ratio of ionic radii of the alkali metal and the rare earth element or the three-valent metal M^III. Among the eight different structure types, the KAlP₂O₇-type structures are most common. For a detailed review including also diarsenates, see: Schwendtner & Kolitsch (2004); Li et al. (2005). In this article we present the structure of NaScP₂O₇ determined from single-crystal x-ray diffaction data. Previous X-ray powder data of NaScP₂O₇ were reported by Vitins et al. (2000). However, authors could not index all reflections at that time, probably because of by-products. The crystal structure of the title compound is isotypic with α-NaTiP₂O₇ (Leclaire et al., 1988), NaYbP₂O₇ (Férid et al., 2004) and NaLuP₂O₇ (Yuan et al., 2007). It is also closely related to that of NaYP₂O₇ (Hamady and Jouini, 1996) and β-cristobalite (Leclaire et al., 1988).

All atoms in the crystal structure occupy general positions. The structure is characterized by a three-dimensional framework of PO₄ tetrahedra (forming P₂O₇ groups via corner-sharing) and ScO₆ octahedra leading to narrow tunnels parallel to [010] which are occupied by Na atoms (Fig. 1). One ScO₆ octahedron is corner-linked to six tetrahedra of six different diphosphate groups, which are all oriented approximately perpendicular to (001) (Fig. 2). Tunnels are formed by stacking pseudohexagonal rings of [Sc₂P₄O₂₂] units. A cage enclosing one Na atom is formed by three P₂O₇ groups, connected to four ScO₆ octahedra (Fig. 3).

The P—O bond-lengths range between 1.5088 (17) Å and 1.5332 (16) Å for terminal O of the diphosphate group that are connected to octahedra. The P1—O5_bridge—P2 angle is 125.47 (10) °, and corresponding bond lengths to the bridging O atom are 1.6114 (17) Å and 1.6151 (17) Å for <P1—O5> and <P2—O5>, respectively. The average Sc—O bond length is 2.101 Å, corresponding well with the average value for oxide compounds (2.105 Å; Brese & O'Keeffe, 1991). The ScO₆ octahedron is significantly less distorted (in terms of quadatic elongation; Robinson et al., 1971) in comparison with the equivalent polyhedra in α-NaTi³⁺P₂O₇, NaLuP₂O₇ and NaYP₂O₇; the polyhedral distortion is the lowest in NaYbP₂O₇ structure.

Experimental

NaScP₂O₇ crystals were grown by the flux-growth technique. The flux, sodium hexametaphosphate (NaPO₃)₆ (purity 3 N) was mixed together with Sc₂O₃ (purity 4 N) at a molar ratio of 6:1. The mixture was filled into a platinum crucible, covered by a loose fitting lid, and heated up to 1593 K within 3 h. The temperature was held for 24 h and afterwards slowly cooled down to 1503 K in the course of 72 h. The solidified flux was dissolved in hot water and crystals of NaScP₂O₇ were mechanically separated. The procedure produced transparent to translucent, colorless skeletal aggregates of tabular to acicular crystals, up to 23 mm in lengths. A fragment of a crystal was used for single-crystal structure determination.

Figures

Fig. 1.

Perspective view of the NaScP2O7 framework structure projected down [010]. Diphosphate groups are corner-linked to the deformed ScO6 octahedra. Tunnels parallel to [010] are occupied by nine-coordinated atoms of Na. Displacement ellipsoids are drawn at the 50% probability level.

Fig. 2.

View on six P2O7 groups corner-linked to the ScO6 polyhedron.

Fig. 3.

Cage formed by three diphosphate groups and four ScO6 polyhedra enclosing the Na cation.

Crystal data

NaScP2O7	F(000) = 472
Mr = 241.89	Dx = 2.789 Mg m−3
Monoclinic, P21/n	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2yn	Cell parameters from 5348 reflections
a = 8.9044 (18) Å	θ = 4.2–27.2°
b = 5.3300 (11) Å	µ = 1.89 mm−1
c = 12.516 (3) Å	T = 293 K
β = 104.11 (3)°	Platy to fibrous fragment, colourless
V = 576.1 (2) Å3	0.40 × 0.15 × 0.05 mm
Z = 4

Data collection

Kuma KM-4-CCD diffractometer	1018 independent reflections
Radiation source: fine-focus sealed tube	932 reflections with I > 2σ(I)
graphite	Rint = 0.028
Detector resolution: 0.06 pixels mm-1	θmax = 25.0°, θmin = 4.2°
ω scans	h = −10→10
Absorption correction: multi-scan (CrysAlis CCD; Oxford Diffraction, 2003)	k = −4→6
Tmin = 0.067, Tmax = 0.093	l = −14→14
5082 measured reflections

Refinement

Refinement on F2	Primary atom site location: structure-invariant direct methods
Least-squares matrix: full	Secondary atom site location: difference Fourier map
R[F2 > 2σ(F2)] = 0.025	w = 1/[σ2(Fo2) + (0.0535P)2 + 0.089P] where P = (Fo2 + 2Fc2)/3
wR(F2) = 0.082	(Δ/σ)max < 0.001
S = 1.18	Δρmax = 0.46 e Å−3
1018 reflections	Δρmin = −0.46 e Å−3
101 parameters	Extinction correction: SHELXL97 (Sheldrick, 2008), Fc*=kFc[1+0.001xFc2λ3/sin(2θ)]-1/4
0 restraints	Extinction coefficient: 0.080 (5)

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
Sc	0.26720 (5)	0.26098 (7)	0.52783 (4)	0.0137 (2)
P1	−0.06473 (7)	0.22372 (11)	0.61678 (5)	0.0140 (2)
P2	0.52089 (7)	0.25413 (10)	0.35283 (5)	0.0139 (2)
Na	0.35939 (11)	0.23101 (18)	0.81018 (9)	0.0278 (3)
O1	0.39845 (17)	0.4953 (3)	0.65350 (12)	0.0177 (4)
O2	0.36250 (17)	−0.0381 (3)	0.63494 (13)	0.0182 (4)
O3	0.4256 (2)	0.2456 (3)	0.43658 (14)	0.0210 (4)
O4	0.10881 (19)	0.2727 (3)	0.63286 (14)	0.0187 (4)
O5	0.39984 (18)	0.2187 (3)	0.23463 (13)	0.0175 (4)
O6	−0.16444 (17)	0.4047 (3)	0.53739 (12)	0.0220 (4)
O7	−0.10300 (18)	−0.0507 (3)	0.58783 (12)	0.0190 (4)

Atomic displacement parameters (Ų)

	U11	U22	U33	U12	U13	U23
Sc	0.0124 (3)	0.0152 (3)	0.0135 (3)	0.00023 (15)	0.0032 (2)	0.00014 (16)
P1	0.0126 (4)	0.0155 (4)	0.0136 (4)	−0.0001 (2)	0.0025 (3)	−0.0002 (2)
P2	0.0127 (4)	0.0156 (4)	0.0134 (4)	0.0001 (2)	0.0033 (3)	0.0003 (2)
Na	0.0270 (7)	0.0245 (7)	0.0318 (7)	−0.0010 (4)	0.0069 (5)	0.0003 (4)
O1	0.0189 (8)	0.0161 (9)	0.0173 (8)	−0.0021 (6)	0.0028 (6)	0.0000 (6)
O2	0.0190 (8)	0.0172 (9)	0.0190 (8)	0.0026 (6)	0.0055 (6)	0.0014 (7)
O3	0.0208 (8)	0.0240 (11)	0.0196 (10)	0.0009 (6)	0.0077 (7)	0.0001 (6)
O4	0.0160 (8)	0.0238 (10)	0.0175 (9)	−0.0013 (6)	0.0062 (7)	−0.0020 (6)
O5	0.0149 (9)	0.0220 (10)	0.0156 (9)	−0.0018 (6)	0.0037 (7)	0.0005 (6)
O6	0.0240 (9)	0.0188 (10)	0.0215 (8)	0.0020 (7)	0.0022 (7)	0.0026 (7)
O7	0.0205 (8)	0.0168 (9)	0.0193 (8)	−0.0009 (7)	0.0041 (6)	−0.0006 (7)

Geometric parameters (Å, °)

Sc—O3	2.0217 (19)	P2—O2v	1.5332 (16)
Sc—O6i	2.0770 (17)	P2—O5	1.6151 (17)
Sc—O7ii	2.1112 (17)	Na—O1	2.5066 (18)
Sc—O1	2.1220 (16)	Na—O7vi	2.5176 (19)
Sc—O2	2.1220 (16)	Na—O4vii	2.5410 (19)
Sc—O4	2.1506 (18)	Na—O2vi	2.5597 (19)
P1—O6	1.5088 (17)	Na—O2	2.6264 (19)
P1—O7	1.5254 (17)	Na—O4	2.746 (2)
P1—O4	1.5313 (18)	Na—O1vii	2.7505 (19)
P1—O5iii	1.6114 (17)	Na—O4vi	2.9710 (19)
P2—O3	1.5013 (19)	Na—O6viii	2.992 (2)
P2—O1iv	1.5278 (16)
O3—Sc—O6i	96.54 (6)	O4vii—Na—O2vi	115.31 (6)
O3—Sc—O7ii	93.04 (7)	O1—Na—O2	67.77 (6)
O6i—Sc—O7ii	91.19 (6)	O7vi—Na—O2	119.51 (6)
O3—Sc—O1	96.23 (7)	O4vii—Na—O2	71.71 (6)
O6i—Sc—O1	84.07 (7)	O2vi—Na—O2	130.74 (5)
O7ii—Sc—O1	170.01 (6)	O1—Na—O4	64.06 (6)
O3—Sc—O2	95.73 (6)	O7vi—Na—O4	143.35 (6)
O6i—Sc—O2	164.29 (6)	O4vii—Na—O4	108.52 (6)
O7ii—Sc—O2	97.93 (7)	O2vi—Na—O4	69.49 (6)
O1—Sc—O2	84.87 (7)	O2—Na—O4	62.69 (6)
O3—Sc—O4	176.82 (7)	O1—Na—O1vii	131.81 (5)
O6i—Sc—O4	85.62 (6)	O7vi—Na—O1vii	141.08 (7)
O7ii—Sc—O4	89.25 (6)	O4vii—Na—O1vii	63.57 (5)
O1—Sc—O4	81.63 (6)	O2vi—Na—O1vii	56.31 (6)
O2—Sc—O4	81.75 (6)	O2—Na—O1vii	93.88 (6)
O6—P1—O7	113.28 (9)	O4—Na—O1vii	67.92 (5)
O6—P1—O4	112.98 (9)	O1—Na—O4vi	67.56 (5)
O7—P1—O4	110.77 (9)	O7vi—Na—O4vi	53.79 (5)
O6—P1—O5iii	105.42 (9)	O4vii—Na—O4vi	150.38 (8)
O7—P1—O5iii	108.54 (9)	O2vi—Na—O4vi	60.19 (5)
O4—P1—O5iii	105.29 (10)	O2—Na—O4vi	135.34 (6)
O3—P2—O1iv	114.55 (9)	O4—Na—O4vi	97.26 (6)
O3—P2—O2v	113.07 (9)	O1vii—Na—O4vi	116.03 (6)
O1iv—P2—O2v	110.27 (9)	O1—Na—O6viii	159.25 (6)
O3—P2—O5	105.75 (10)	O7vi—Na—O6viii	83.21 (6)
O1iv—P2—O5	105.78 (9)	O4vii—Na—O6viii	61.94 (5)
O2v—P2—O5	106.74 (9)	O2vi—Na—O6viii	67.85 (6)
O1—Na—O7vi	82.54 (6)	O2—Na—O6viii	132.80 (6)
O1—Na—O4vii	137.09 (7)	O4—Na—O6viii	123.78 (6)
O7vi—Na—O4vii	106.18 (6)	O1vii—Na—O6viii	58.46 (5)
O1—Na—O2vi	101.72 (6)	O4vi—Na—O6viii	91.81 (5)
O7vi—Na—O2vi	105.53 (6)	P1ix—O5—P2	125.47 (10)

Symmetry codes: (i) −x, −y+1, −z+1; (ii) −x, −y, −z+1; (iii) x−1/2, −y+1/2, z+1/2; (iv) −x+1, −y+1, −z+1; (v) −x+1, −y, −z+1; (vi) −x+1/2, y+1/2, −z+3/2; (vii) −x+1/2, y−1/2, −z+3/2; (viii) x+1/2, −y+1/2, z+1/2; (ix) x+1/2, −y+1/2, z−1/2.