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The crystal structure of the novel title diphosphate, Li2BaP2O7, exists with a three-dimensional lattice composed of BaO9 polyhedra linked to corner- and edge-sharing P2O7 diphos­phate groups, forming layers parallel to the (010) plane, the layers being linked by P-O-Ba bridges. Tunnels thus created between the layers are occupied by Li+ cations, two of which lie on twofold axes.

Supporting information

cif

Crystallographic Information File (CIF) https://doi.org/10.1107/S0108270102006741/br1355sup1.cif
Contains datablocks global, I

hkl

Structure factor file (CIF format) https://doi.org/10.1107/S0108270102006741/br1355Isup2.hkl
Contains datablock I

Comment top

In recent years, structures of the formulation AI2BIIP2O7 (with AI = Li+, Na+ or K+, and where BII is a bivalent ion; Spirlet et al., 1993; Laligant, 1992a,b; Liebertz & Stahr, 1983; Huang & Hwu, 1998; Erragh et al., 1991, 1995, 1998; Belharouak et al., 2000; Dridi et al., 2000; Bennazha et al., 1999; El Maadi et al., 1994, 1995a,b; Trunov et al., 1991; Faggiani & Calvo, 1976) have been the object of structural investigation as single crystals. Except for Na2PdP2O7 (Laligant, 1992a) and β-Na2CuP2O7 (Erragh et al., 1995), which crystallize with similar cell dimensions in space group C2/c, there are no isotypical relationships within the group. However, few of these structures exist with AI = Li+. Only the structures of Li2CuP2O7 (Spirlet et al., 1993) and Li2PdP2O7 (Laligant, 1992b) have been reported in the literature with full structural details. Li2BaP2O7 was first reported by Liebertz & Stahr (1983), who described the chemical preparation of the material. From precession photographs, they observed the systematic absences hkl with h+k = 2n and h0l with l = 2n, and thus reported the cell parameters a = 7.078 (4), b = 12.164 (6) and c = 13.856 (6) Å, and space group Cmcm with Z = 8 for this compound. Neither positional parameters nor R factor were published.

In this paper, we describe the synthesis and the solid-state crystal structure redetermination of Li2BaP2O7, a member of this little-known family of lithium-containing materials. We have refined the structure in monoclinic space group C2/c with β = 90.49 (7)°. Both the previously reported orthorhombic space group and C2/c share the same absences. Accommodating Li2BaP2O7 with Z = 8 in the space group Cmcm with Z = 16 requires the placing of Ba and the P2O7 group on a mirror, twofold or 1 symmetry element. A projection view of the P2O7 group refined in C2/c shows it to be staggered, with P1—O14—P2 = 123.3 (4)° and O—P···P—O torsion angles averaging 28.97°, significantly distorted from eclipsed (O—P···P—O = 0°) or ideally staggered symmetry (O—P···P—O = 60°), and thus the phosphate O atoms are ordered in not refinable except as disordered positions in orthorhombic space group Cmcm. Please clarify this last clause.

A projection view of Li2BaP2O7 on the (100) plane is shown in Fig. 1. The structure may be regarded as a three-dimensional packing of [BaO9] polyhedra sharing edges and corners with P2O7 diphosphate groups and thus forming layers parallel to [010], which are held together by P2—O21—Ba bridges. This arrangement gives rise to tunnels within the layers. The Li+ cations are located in these tunnels.

The coordination sphere of the Ba2+ cations is formed of nine O anions in irregular geometry, located at Ba—O distances of between 2.714 (7) and 3.132 (8) Å. Each BaO9 polyhedra is surrounded by nine [PO4] tetrahedra belonging to five different P2O7 groups. These values are comparable with those observed in various barium phosphate compounds, such as CdBaP2O7, BaCuP2O7 and σ-Ba2P2O7 (Moquine et al., 1991; Alaoui El Belghiti et al., 1991, 1995). Bond-valence calculations (Brown, 1981) show a total effective cationic charge of 1.877 for Ba+2 in this environment.

The Li+ ions are seen in three different sites. Atom Li1, on a twofold axis, is surrounded by six O atoms in a distorted octahedral geometry, with an average Li1—O distance of 2.26 (2) Å. Atom Li2, also on a twofold axis, displays tetrahedral geometry, with an average Li2—O distance of 1.98 (2) Å. Atom Li3, in a general position, has five O-atom neighbours at distances in the range 1.932 (15)–2.41 (2) Å, with an average Li3—O distance of 2.10 (2) Å.

Bond-valence calculations total 0.849, 0.989 and 0.975 for Li1, Li2 and Li3, respectively. Bond-valence calculations which reveal an effective charge significantly less that the theoretical ionic charge frequently signal ion mobility in the site. Support for this point of view comes from the obvious elongation of the displacement ellipsoid of Li3 in the direction of the tunnel parallel to the (100) direction. On this basis, Li2BaP2O7 may be suspected to have potentially exploitable physical properties, such as conductivity (Ba and Li1) and luminescence (with doping of small quantities of Ln3+ into the non-centrosymmetric Ba2+ site).

Experimental top

Crystals of Li2BaP2O7 were prepared by fusion of Li2CO3, BaCO3 and NH4H2PO4 in the proportion 1:1:2. The mixture was heated slowly to the fusion temperature (1100 K) How long at 1100 K? followed by slow cooling (5 K h-1) down to 650 K; furnace power was then switched off. Parallelepiped single crystals of Li2BaP2O7 were obtained.

Computing details top

Data collection: XSCANS (Siemens, 1991); cell refinement: XSCANS; data reduction: XSCANS; program(s) used to solve structure: SHELXS97 (Sheldrick, 1990); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: Please provide missing details.

Figures top
[Figure 1] Fig. 1. A projection view of Li2BaP2O7 on the (100) plane. Displacement ellipsoids are shown at the 50% probability level.
Dilithium barium diphosphate top
Crystal data top
Li2BaP2O7F(000) = 1184
Mr = 325.16Dx = 3.511 Mg m3
Monoclinic, C2/cMo Kα radiation, λ = 0.71073 Å
a = 7.147 (8) ÅCell parameters from 25 reflections
b = 12.283 (14) Åθ = 6.4–10.5°
c = 14.016 (16) ŵ = 6.96 mm1
β = 90.49 (7)°T = 293 K
V = 1230 (2) Å3Parallelepiped, colourless
Z = 80.1 × 0.1 × 0.1 mm
Data collection top
Syntex P4 four-circle
diffractometer
1231 reflections with I > 2σ(I)
Radiation source: fine-focus sealed tubeRint = 0.091
Graphite monochromatorθmax = 30.0°, θmin = 3.5°
θ/2θ scansh = 010
Absorption correction: ψ scan
(XEMP; Siemens, 1991)
k = 014
Tmin = 0.447, Tmax = 0.499l = 1919
2324 measured reflections3 standard reflections every 97 reflections
1355 independent reflections intensity decay: none
Refinement top
Refinement on F20 restraints
Least-squares matrix: fullPrimary atom site location: structure-invariant direct methods
R[F2 > 2σ(F2)] = 0.062Secondary atom site location: difference Fourier map
wR(F2) = 0.189 w = 1/[σ2(Fo2) + (0.1P)2]
where P = (Fo2 + 2Fc2)/3
S = 1.49(Δ/σ)max = 0.002
1355 reflectionsΔρmax = 0.06 e Å3
111 parametersΔρmin = 0.09 e Å3
Crystal data top
Li2BaP2O7V = 1230 (2) Å3
Mr = 325.16Z = 8
Monoclinic, C2/cMo Kα radiation
a = 7.147 (8) ŵ = 6.96 mm1
b = 12.283 (14) ÅT = 293 K
c = 14.016 (16) Å0.1 × 0.1 × 0.1 mm
β = 90.49 (7)°
Data collection top
Syntex P4 four-circle
diffractometer
1231 reflections with I > 2σ(I)
Absorption correction: ψ scan
(XEMP; Siemens, 1991)
Rint = 0.091
Tmin = 0.447, Tmax = 0.4993 standard reflections every 97 reflections
2324 measured reflections intensity decay: none
1355 independent reflections
Refinement top
R[F2 > 2σ(F2)] = 0.062111 parameters
wR(F2) = 0.1890 restraints
S = 1.49Δρmax = 0.06 e Å3
1355 reflectionsΔρmin = 0.09 e Å3
Special details top

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 (Å2) top
xyzUiso*/Ueq
Ba10.18368 (5)0.47348 (5)0.12094 (3)0.0155 (3)
P10.6788 (2)0.3963 (2)0.11960 (12)0.0119 (5)
P20.7188 (3)0.63112 (19)0.13469 (15)0.0127 (5)
O110.5043 (8)0.3262 (6)0.1341 (4)0.0165 (12)
O120.7612 (8)0.3761 (6)0.0211 (4)0.0187 (13)
O130.8270 (7)0.3908 (6)0.1996 (4)0.0168 (12)
O140.5897 (8)0.5199 (5)0.1230 (5)0.0196 (16)
O210.5861 (7)0.7251 (6)0.1115 (4)0.0193 (13)
O220.8774 (8)0.6132 (6)0.0647 (5)0.0206 (13)
O230.7808 (8)0.6350 (6)0.2403 (4)0.0208 (14)
Li10.00000.270 (2)0.25000.025 (5)
Li20.00000.264 (2)0.75000.017 (5)
Li30.0289 (18)0.2659 (16)0.0086 (10)0.021 (3)
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
Ba10.0126 (4)0.0218 (6)0.0120 (4)0.00131 (12)0.0013 (2)0.00076 (15)
P10.0106 (9)0.0157 (15)0.0093 (10)0.0006 (5)0.0009 (6)0.0001 (7)
P20.0088 (7)0.0157 (13)0.0136 (9)0.0012 (6)0.0023 (6)0.0002 (8)
O110.016 (2)0.020 (4)0.014 (2)0.007 (2)0.0012 (17)0.003 (2)
O120.016 (2)0.020 (4)0.020 (3)0.0018 (19)0.004 (2)0.002 (3)
O130.012 (2)0.025 (4)0.013 (3)0.0017 (18)0.0070 (17)0.002 (2)
O140.009 (2)0.027 (5)0.022 (3)0.0008 (18)0.005 (2)0.015 (3)
O210.012 (2)0.027 (4)0.019 (3)0.008 (2)0.0033 (17)0.005 (3)
O220.015 (2)0.019 (4)0.028 (3)0.0020 (19)0.006 (2)0.003 (3)
O230.022 (3)0.025 (4)0.015 (3)0.002 (2)0.007 (2)0.003 (3)
Li10.034 (11)0.022 (16)0.019 (10)0.0000.000 (7)0.000
Li20.005 (6)0.023 (14)0.024 (10)0.0000.001 (6)0.000
Li30.014 (4)0.041 (11)0.009 (5)0.011 (5)0.005 (4)0.014 (6)
Geometric parameters (Å, º) top
Ba1—O13i2.714 (7)P2—O141.656 (7)
Ba1—O12ii2.747 (7)Li1—O13i2.05 (2)
Ba1—O23i2.788 (7)Li1—O13iii2.05 (2)
Ba1—O22ii2.842 (8)Li1—O21iv2.116 (10)
Ba1—O22iii2.886 (7)Li1—O21v2.116 (10)
Ba1—O112.924 (7)Li1—O23v2.61 (2)
Ba1—O142.957 (7)Li1—O23iv2.61 (2)
Ba1—O13iii2.965 (6)Li2—O11vi1.966 (15)
Ba1—O21iv3.132 (8)Li2—O11vii1.966 (15)
P1—O121.526 (7)Li2—O23viii2.002 (17)
P1—O111.530 (6)Li2—O23ix2.002 (17)
P1—O131.538 (5)Li3—O21iv1.932 (15)
P1—O141.647 (7)Li3—O22ii2.00 (2)
P2—O221.522 (6)Li3—O12iii2.066 (16)
P2—O211.527 (7)Li3—O11x2.101 (16)
P2—O231.542 (6)Li3—O12x2.41 (2)
O13i—Ba1—O12ii158.2 (2)O11—P1—O14101.5 (4)
O13i—Ba1—O23i67.8 (2)O13—P1—O14106.4 (4)
O12ii—Ba1—O23i90.8 (2)O22—P2—O21115.9 (4)
O13i—Ba1—O22ii134.7 (2)O22—P2—O23114.4 (4)
O12ii—Ba1—O22ii67.1 (2)O21—P2—O23110.8 (4)
O23i—Ba1—O22ii156.6 (2)O22—P2—O14103.6 (4)
O13i—Ba1—O22iii116.6 (2)O21—P2—O14105.0 (3)
O12ii—Ba1—O22iii61.00 (18)O23—P2—O14106.0 (4)
O23i—Ba1—O22iii80.3 (2)P1—O14—P2123.3 (4)
O22ii—Ba1—O22iii82.1 (2)O13i—Li1—O13iii87.6 (12)
O13i—Ba1—O1174.82 (18)O13i—Li1—O21iv109.0 (6)
O12ii—Ba1—O11110.17 (18)O13iii—Li1—O21iv93.0 (5)
O23i—Ba1—O11109.23 (18)O13i—Li1—O21v93.0 (5)
O22ii—Ba1—O1186.57 (19)O13iii—Li1—O21v109.0 (6)
O22iii—Ba1—O11167.78 (19)O21iv—Li1—O21v149.6 (16)
O13i—Ba1—O1495.64 (19)O13i—Li1—O23v154.6 (3)
O12ii—Ba1—O1474.39 (19)O13iii—Li1—O23v90.9 (2)
O23i—Ba1—O1476.85 (18)O21iv—Li1—O23v96.4 (8)
O22ii—Ba1—O14102.96 (19)O21v—Li1—O23v63.6 (5)
O22iii—Ba1—O14129.1 (2)O13i—Li1—O23iv90.9 (2)
O11—Ba1—O1449.47 (19)O13iii—Li1—O23iv154.6 (3)
O13i—Ba1—O13iii59.74 (18)O21iv—Li1—O23iv63.6 (5)
O12ii—Ba1—O13iii128.98 (16)O21v—Li1—O23iv96.4 (8)
O23i—Ba1—O13iii93.3 (2)O23v—Li1—O23iv100.9 (10)
O22ii—Ba1—O13iii94.95 (17)O11vi—Li2—O11vii111.4 (13)
O22iii—Ba1—O13iii69.69 (19)O11vi—Li2—O23viii112.8 (3)
O11—Ba1—O13iii116.11 (19)O11vii—Li2—O23viii108.1 (3)
O14—Ba1—O13iii155.35 (19)O11vi—Li2—O23ix108.1 (3)
O13i—Ba1—O21iv70.53 (19)O11vii—Li2—O23ix112.8 (3)
O12ii—Ba1—O21iv131.12 (18)O23viii—Li2—O23ix103.4 (12)
O23i—Ba1—O21iv137.85 (19)O21iv—Li3—O22ii107.9 (8)
O22ii—Ba1—O21iv64.13 (18)O21iv—Li3—O12iii107.4 (7)
O22iii—Ba1—O21iv113.55 (17)O22ii—Li3—O12iii89.4 (8)
O11—Ba1—O21iv64.79 (17)O21iv—Li3—O11x123.5 (9)
O14—Ba1—O21iv113.97 (16)O22ii—Li3—O11x91.2 (7)
O13iii—Ba1—O21iv59.35 (17)O12iii—Li3—O11x126.0 (7)
O12—P1—O11110.5 (4)O21iv—Li3—O12x99.4 (8)
O12—P1—O13112.6 (3)O22ii—Li3—O12x151.8 (8)
O11—P1—O13115.8 (4)O12iii—Li3—O12x89.3 (6)
O12—P1—O14109.2 (4)O11x—Li3—O12x67.2 (5)
Symmetry codes: (i) x+1, y, z+1/2; (ii) x+1, y+1, z; (iii) x1, y, z; (iv) x1/2, y1/2, z; (v) x+1/2, y1/2, z+1/2; (vi) x1/2, y+1/2, z+1/2; (vii) x+1/2, y+1/2, z+1; (viii) x+1, y+1, z+1; (ix) x1, y+1, z+1/2; (x) x+1/2, y+1/2, z.

Experimental details

Crystal data
Chemical formulaLi2BaP2O7
Mr325.16
Crystal system, space groupMonoclinic, C2/c
Temperature (K)293
a, b, c (Å)7.147 (8), 12.283 (14), 14.016 (16)
β (°) 90.49 (7)
V3)1230 (2)
Z8
Radiation typeMo Kα
µ (mm1)6.96
Crystal size (mm)0.1 × 0.1 × 0.1
Data collection
DiffractometerSyntex P4 four-circle
diffractometer
Absorption correctionψ scan
(XEMP; Siemens, 1991)
Tmin, Tmax0.447, 0.499
No. of measured, independent and
observed [I > 2σ(I)] reflections
2324, 1355, 1231
Rint0.091
(sin θ/λ)max1)0.703
Refinement
R[F2 > 2σ(F2)], wR(F2), S 0.062, 0.189, 1.49
No. of reflections1355
No. of parameters111
Δρmax, Δρmin (e Å3)0.06, 0.09

Computer programs: XSCANS (Siemens, 1991), XSCANS, SHELXS97 (Sheldrick, 1990), SHELXL97 (Sheldrick, 1997), Please provide missing details.

Selected geometric parameters (Å, º) top
Ba1—O13i2.714 (7)P2—O141.656 (7)
Ba1—O12ii2.747 (7)Li1—O13i2.05 (2)
Ba1—O23i2.788 (7)Li1—O13iii2.05 (2)
Ba1—O22ii2.842 (8)Li1—O21iv2.116 (10)
Ba1—O22iii2.886 (7)Li1—O21v2.116 (10)
Ba1—O112.924 (7)Li1—O23v2.61 (2)
Ba1—O142.957 (7)Li1—O23iv2.61 (2)
Ba1—O13iii2.965 (6)Li2—O11vi1.966 (15)
Ba1—O21iv3.132 (8)Li2—O11vii1.966 (15)
P1—O121.526 (7)Li2—O23viii2.002 (17)
P1—O111.530 (6)Li2—O23ix2.002 (17)
P1—O131.538 (5)Li3—O21iv1.932 (15)
P1—O141.647 (7)Li3—O22ii2.00 (2)
P2—O221.522 (6)Li3—O12iii2.066 (16)
P2—O211.527 (7)Li3—O11x2.101 (16)
P2—O231.542 (6)Li3—O12x2.41 (2)
O12—P1—O11110.5 (4)O22—P2—O23114.4 (4)
O12—P1—O13112.6 (3)O21—P2—O23110.8 (4)
O11—P1—O13115.8 (4)O22—P2—O14103.6 (4)
O12—P1—O14109.2 (4)O21—P2—O14105.0 (3)
O11—P1—O14101.5 (4)O23—P2—O14106.0 (4)
O13—P1—O14106.4 (4)P1—O14—P2123.3 (4)
O22—P2—O21115.9 (4)
Symmetry codes: (i) x+1, y, z+1/2; (ii) x+1, y+1, z; (iii) x1, y, z; (iv) x1/2, y1/2, z; (v) x+1/2, y1/2, z+1/2; (vi) x1/2, y+1/2, z+1/2; (vii) x+1/2, y+1/2, z+1; (viii) x+1, y+1, z+1; (ix) x1, y+1, z+1/2; (x) x+1/2, y+1/2, z.
 

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