Synchrotron powder study of Na₃V(PO₃)₃N

Polycrystalline tris­odium vanadium(III) nitridotriphosphate, Na₃V(PO₃)₃N, was prepared by thermal nitridation of a mixture of NaPO₃ and V₂O₅. The title compound is isotypic with Na₃Al(PO₃)₃N. In the crystal, the P-atom and the three O-atom sites are on general positions, whereas the Na-, V- and N-atom sites are located on threefold rotation axes. The P atom is coordinated by three O atoms and one N atom in form of a slightly distorted tetra­hedron. Three PO₃N tetra­hedra build up a nitridotriphosphate group, (PO₃)₃N, by sharing a common N atom. The V atom is coordinated by six O atoms in form of a slightly distorted octa­hedron. The Na⁺ ions occupy three crystallographically distinct sites. One Na⁺ ion is situated in an irregular polyhedral coordination environment composed of six O atoms and one N atom, while the other two Na⁺ cations are surrounded by six and nine O atoms, respectively.

Related literature

For structure determination of the isotypic Na₃Al(PO₃)₃N, see: Conanec et al. (1994). For the preparation of various related materials, A₃B(PO₃)₃N (A = Na, K; B = Al, Ga, Cr, Mn, Fe) and A₂B₂(PO₃)₃N (A = Na; B = Mg, Mn, Fe, Co), see: Conanec et al. (1996); Feldmann (1987a,b). For studies focused on the ionic conductivity of Na₂Mg₂(PO₃)₃N, see: Lee et al. (2012). For a review of structural features of metal nitridophosphate compounds, see: Marchand & Laurent (1991); Marchand et al. (2000). For bond-valence-sum calculations, see: Brese & O'Keeffe (1991). For comparison of bond lengths in related structures, see: Conanec et al. (1994); Jacobs & Nymwegen (1997); Lee et al. (2012); Shannon (1976); Zatovsky (2010).

Experimental

Crystal data

• Na₃V(PO₃)₃N

• M_r = 370.83

• Cubic, P 2₁ 3

• a = 9.44783 (5) Å

• V = 843.33 (1) ų

• Z = 4

• Synchrotron radiation, λ = 1.547400 Å

• T = 298 K

• Flat sheet, 20 × 20 mm

Data collection

• Pohang Light Source 9B HRPD Beamline diffractometer

• Specimen mounting: packed powder pellet

• Data collection mode: reflection

• Scan method: step

• 2θ_min = 10.060°, 2θ_max = 130.500°, 2θ_step = 0.010°

Refinement

• R_p = 0.091

• R_wp = 0.119

• R_exp = 0.075

• R_Bragg = 0.056

• χ² = 2.519

• 12045 data points

• 288 parameters

Data collection: local software at 9B HRPD beamline; cell refinement: DICVOL (Boultif & Louër, 2004); data reduction: local software at 9B HRPD beamline; method used to solve structure: coordinates taken from an isotypic compound; program(s) used to refine structure: FULLPROF (Rodriguez-Carvajal, 2001); molecular graphics: DIAMOND (Brandenburg, 1999); software used to prepare material for publication: FULLPROF.

Supporting information

S1. Comment

There has been growing interest in the area of mixed anionic systems for exploration of new functional materials. Synthesis in the area of mixed anionic systems allows for the tuning of numerous properties, including energy storage, photocatalytic, and dielectric properties. More than two decades ago, the synthesis of several isotypic compounds with the chemical formulae of A₃B(PO₃)₃N (A = Na, K; B = Al, Ga, Cr, Mn, Fe) and A₂B₂(PO₃)₃N (A = Na; B = Mg, Mn, Fe, Co) by versatile nitridation reactions have been reported (Conanec et al., 1996; Feldmann, 1987a,b; Marchand & Laurent, 1991, Marchand et al., 2000) The crystal structure of Na₃Al(PO₃)₃N has been determined by X-ray diffraction from a single-crystal (Conanec et al., 1994). For the other compounds, however, no information except their unit cell parameters are known. In this work, we report the synthesis of the new nitridophosphate compound, Na₃V(PO₃)₃N, and its crystal structure refined on baisi of the Rietveld method from synchrotron powder X-ray diffraction data.

The crystal structure of Na₃V(PO₃)₃N is isotypic with that of Na₃Al(PO₃)₃N (Conanec et al., 1994). The lattice parameter of Na₃V(PO₃)₃N (a = 9.44783 (5) Å) is slighty larger than that of Na₃Al(PO₃)₃N (a = 9.274 (1) Å), which is attributed to the different sizes of the V(III) and Al(III) ions. In this structure, the P and the three O atoms lie on general positions (12b) while the other atoms lie on special positions related to threefold rotation axes (4a).

The P atom is coordinated by three O atoms and one N atom to form a PO₃N tetrahedron. The (PO₃)₃N entity is formed by three PO₃N tetrahedra sharing the corner occupied by the nitrogen atom (Fig. 1). The range of P—O bond lengths (1.538 (6) - 1.541 (6) Å) in Na₃V(PO₃)₃N is close to that found in compositionally related compounds such as Na₃Al(PO₃)₃N (~1.50 - 1.53 Å); Na₂Mg₂(PO₃)₃N (~1.53 - 1.55 Å); Na₃V₂(PO₄)₃ (~1.52 1.54 Å) (Conanec et al., 1994; Lee et al., 2012; Zatovsky, 2010). The P—N bond length (1.738 (7) Å) is similar to those observed for tricoordinating nitrogen atoms in nitrido-compounds such as K₃P₆N₁₁ (1.71 Å) (Jacobs & Nymwegen, 1997). Na, V and N atoms are arranged along the [111] direction in the sequence of Na2—V—Na3—Na1—N—Na2—V-··· (Fig. 2). The V atom is connected to six oxygen atoms located at the vertices of PO₃N tetrahedra, forming a slightly distorted octahedron. The average V—O distance is 2.005 (11) Å which is close to the sum of the ionic radii (2.02 Å) of V³⁺ and O^2- (Shannon, 1976). The Na atoms occupy three crystallographically distinct sites. Na1 is coordinated to six O atoms (mean Na—O is 2.58 Å) and one N atom (Na—N is 2.947 (7) Å) to form an irregular NaO₆N polyhedron. Na2 and Na3 are 6- and 9-coordinated, respectively, within distorted polyhedra elongated along the threefold axis. The bond valence sums (Brese & O'Keeffe, 1991) calculated from the bond lengths (valence units; Na1: 0.80, Na2: 1.29, Na3: 0.96, V: 2.96, P: 4.61, O1: 1.90, O2: 1.92, O3: 1.85, N: 2.80) are close to the expected valence states of respective atoms.

Related literature

For structure determinations of isotypic Na₃Al(PO₃)₃N, see: Conanec et al. (1994). For the preparation of various related materials, A₃B(PO₃)₃N (A = Na, K; B = Al, Ga, Cr, Mn, Fe) and A₂B₂(PO₃)₃N (A = Na; B = Mg, Mn, Fe, Co), see: Conanec et al. (1996); Feldmann (1987a,b). For studies focused on the ionic conductivity of Na₂Mg₂(PO₃)₃N, see: Lee et al. (2012). For a review of structural features of metal nitridophosphate compounds, see: Marchand & Laurent (1991); Marchand et al. (2000). For bond-valence-sum calculations, see: Brese & O'Keeffe (1991). For comparison bond lengths in related structures, see: Conanec et al. (1994); Jacobs & Nymwegen (1997); Lee et al. (2012); Shannon (1976); Zatovsky (2010).

S2. Experimental

An appropriate amount of NaPO₃ and V₂O₅ was mixed thoroughly in an agate mortar and placed in an alumina crucible. The mixture was initially heated at 523 K for 6 h. The product was reground and heated again at 973 K for 8 h and furnace-cooled to room temperature. All the heat treatments were carried out in continuous flowing anhydrous ammonia gas (flow rate = 30 ml/min) in a tube furnace. The resultant powder sample was characterized by synchrotron X-ray diffraction (sXRD). The measurement was performed on beamline 9B-HRPD at Pohang Accelerator Laboratory, Pohang, Korea. The incident X-rays were vertically collimated by a mirror, and monochromated to the wavelength of 1.5474 Å by a double-crystal Si (111) monochromator. The datasets were collected in the range of 10°≤ 2θ ≤ 130° with a step size of 0.01° (2θ range).

S3. Refinement

Reflections were indexed using DICVOL (Boultif & Louër, 2004). The cubic symmetry was obviously obtained from sXRD data. Any additional peaks were not detected. The figures of merit were M(20) = 277.6 (19), F(20) = 378 (3). Systematic absences, h = 2n + 1 for h00 observed in the intensity data, suggested the space group P2₁3. As an initial model for the Rietveld refinements, the structural parameters of Na₃Al(PO₃)N from single crystal data (Conanec et al., 1994) were used. Refinements of structural parameters were carried out using the Fullprof program package (Rodriguez-Carvajal, 2001). The shape of the diffraction peaks was modelled with the Thompson-Cox-Hastings pseudo-Voigt function. A manual background correction was used in the refinements; preferred orientation and absorption effects were not considered. In the final refinement run, the following parameters were refined: zero shift, peak width/shape/asymmetry, scale factor, and crystal structure parameters (lattice parameter, atomic positions, isotropic atomic displacement parameters). The final refinement plot is shown in Fig. 3.

Computing details

Data collection: local software at 9B HRPD beamline; cell refinement: DICVOL (Boultif & Louër, 2004); data reduction: local software at 9B HRPD beamline; program(s) used to solve structure: coordinates taken from an isotypic compound; program(s) used to refine structure: FULLPROF (Rodriguez-Carvajal, 2001); molecular graphics: DIAMOND (Brandenburg, 1999); software used to prepare material for publication: FULLPROF (Rodriguez-Carvajal, 2001).

Figures

	Fig. 1. The crystal structure of Na3V(PO3)3N. PO4 tetrahedra are shown with gray shading; Na atoms are orange-colored spheres and V atoms are dark green spheres.
	Fig. 2. The local environments of Na, V and N atoms arranged along [111] in the structure of Na3V(PO3)3N.
	Fig. 3. Rietveld refinement plot of Na3V(PO3)3N based on synchrotron X-ray powder diffraction data. The inset shows an enlarged section of the diffraction pattern.

Trisodium vanadium(III) nitridotriphosphate

Crystal data

Na3V(PO3)3N	Dx = 2.92 Mg m^−3
Mr = 370.83	Synchrotron radiation, λ = 1.547400 Å
Cubic, P213	T = 298 K
Hall symbol: P 2ac 2ab 3	Particle morphology: powder
a = 9.44783 (5) Å	green
V = 843.33 (1) Å^3	flat sheet, 20 × 20 mm
Z = 4

Data collection

Pohang Light Source 9B HRPD Beamline diffractometer	Data collection mode: reflection
Radiation source: synchrotron	Scan method: step
Si 111 monochromator	2θmin = 10.060°, 2θmax = 130.500°, 2θstep = 0.010°
Specimen mounting: packed powder pellet

Refinement

Rp = 0.091	12045 data points
Rwp = 0.119	35 parameters
Rexp = 0.075	0 restraints
RBragg = 0.056	(Δ/σ)max = 0.02
χ^2 = 2.519

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

	x	y	z	Uiso*/Ueq
P1	0.3326 (3)	0.0844 (3)	0.2446 (3)	0.0143 (4)*
V1	0.08073 (17)	−0.08073 (17)	0.41927 (17)	0.0144 (6)*
Na1	0.0136 (3)	0.0136 (3)	0.0136 (3)	0.0278 (18)*
Na2	0.3913 (4)	0.3913 (4)	0.3913 (4)	0.0171 (18)*
Na3	0.6989 (5)	0.1989 (5)	0.3011 (5)	0.0310 (19)*
O1	0.2722 (6)	−0.0265 (6)	0.3479 (5)	0.0130 (14)*
O2	0.3727 (5)	0.0002 (6)	0.1109 (5)	0.0073 (15)*
O3	0.4543 (6)	0.1700 (6)	0.3106 (6)	0.0160 (18)*
N1	0.1937 (7)	0.1937 (7)	0.1937 (7)	0.012 (3)*

Geometric parameters (Å, º)

P1—O3	1.538 (6)	Na1—N1	2.947 (7)
P1—O2	1.540 (6)	Na2—O3^viii	2.304 (7)
P1—O1	1.541 (6)	Na2—O3^v	2.304 (7)
P1—N1	1.738 (7)	Na2—O3	2.304 (7)
V1—O1^i	1.997 (6)	Na2—O2^ix	2.456 (6)
V1—O1^ii	1.997 (6)	Na2—O2^x	2.456 (6)
V1—O1	1.997 (6)	Na2—O2^xi	2.456 (6)
V1—O2^iii	2.013 (5)	Na3—O3	2.329 (7)
V1—O2^iv	2.013 (5)	Na3—O3^x	2.329 (7)
V1—O2^v	2.013 (5)	Na3—O3^xii	2.329 (7)
Na1—O1^vi	2.561 (6)	Na3—O1^xiii	2.964 (7)
Na1—O1^vii	2.561 (6)	Na3—O1^xiv	2.964 (7)
Na1—O1^i	2.561 (6)	Na3—O1^xi	2.964 (7)
Na1—O3^vii	2.604 (6)	N1—P1^viii	1.738 (7)
Na1—O3^i	2.604 (6)	N1—P1^v	1.738 (7)
Na1—O3^vi	2.604 (6)
O3—P1—O2	114.9 (6)	O1—V1—O2^iii	90.5 (4)
O3—P1—O1	112.2 (6)	O1^i—V1—O2^iv	92.2 (4)
O2—P1—O1	105.0 (5)	O1^ii—V1—O2^iv	90.5 (4)
O3—P1—N1	111.4 (6)	O1—V1—O2^iv	176.8 (5)
O2—P1—N1	105.4 (6)	O2^iii—V1—O2^iv	86.5 (3)
O1—P1—N1	107.4 (6)	O1^i—V1—O2^v	90.5 (4)
O1^i—V1—O1^ii	90.8 (4)	O1^ii—V1—O2^v	176.8 (5)
O1^i—V1—O1	90.8 (4)	O1—V1—O2^v	92.2 (4)
O1^ii—V1—O1	90.8 (4)	O2^iii—V1—O2^v	86.5 (3)
O1^i—V1—O2^iii	176.8 (5)	O2^iv—V1—O2^v	86.5 (3)
O1^ii—V1—O2^iii	92.2 (4)

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