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Acta Crystallogr Sect E Struct Rep Online. 2010 December 1; 66(Pt 12): i84.
Published online 2010 November 24. doi:  10.1107/S1600536810043527
PMCID: PMC3011656

Hydro­thermally synthesized α-Ba2P2O7


Single crystals of α-Ba2P2O7, dibarium diphosphate, were obtained under hydro­thermal conditions. The structure belongs to the diphosphate A 2P2O7 series with A being an alkaline earth cation. α-Ba2P2O7 crystallizes isotypically with α-Sr2P2O7. All atomic sites have site symmetry m with the exception of two O atoms which reside on general positions. Both Ba2+ cations are coordinated by nine terminal O atoms from eclipsed diphosphate P2O7 anions to form a three-dimensional network throughout the structure.

Related literature

For general background, see: Brown & Calvo (1970 [triangle]); ElBelghitti et al. (1995 [triangle]); Mehdi et al. (1977 [triangle]); Mohri (2000 [triangle]). For the uses of alkaline earth diphosphates, see: McKeag & Steward (1955 [triangle]); Ranby et al. (1955 [triangle]); Ropp & Mooney (1960 [triangle]); Srivastava et al. (2003 [triangle]). For structurally related compounds, see: Calvo (1968 [triangle]); Barbier & Echard (1998 [triangle]). For an independent refinement of the α-Ba2P2O7 structure based on data from a crystal grown by solid-state reactions, see: Zakaria et al. (2010 [triangle]).


Crystal data

  • Ba2P2O7
  • M r = 448.62
  • Orthorhombic, An external file that holds a picture, illustration, etc.
Object name is e-66-00i84-efi2.jpg
  • a = 9.2842 (19) Å
  • b = 5.6113 (11) Å
  • c = 13.796 (3) Å
  • V = 718.7 (3) Å3
  • Z = 4
  • Mo Kα radiation
  • μ = 11.32 mm−1
  • T = 298 K
  • 0.45 × 0.15 × 0.15 mm

Data collection

  • Rigaku AFC-8S Mercury CCD diffractometer
  • Absorption correction: multi-scan (REQAB; Jacobson, 1998 [triangle]) T min = 0.080, T max = 0.281
  • 7205 measured reflections
  • 1854 independent reflections
  • 1510 reflections with I > 2σ(I)
  • R int = 0.042


  • R[F 2 > 2σ(F 2)] = 0.047
  • wR(F 2) = 0.127
  • S = 1.11
  • 1854 reflections
  • 58 parameters
  • Δρmax = 6.71 e Å−3
  • Δρmin = −3.53 e Å−3

Data collection: CrystalClear (Rigaku/MSC, 2001 [triangle]); cell refinement: CrystalClear; data reduction: CrystalClear; program(s) used to solve structure: SHELXTL (Sheldrick, 2008 [triangle]); program(s) used to refine structure: SHELXTL; molecular graphics: DIAMOND (Brandenburg, 1999 [triangle]); software used to prepare material for publication: SHELXTL.

Table 1
Selected geometric parameters (Å, °)

Supplementary Material

Crystal structure: contains datablocks I, global. DOI: 10.1107/S1600536810043527/wm2406sup1.cif

Structure factors: contains datablocks I. DOI: 10.1107/S1600536810043527/wm2406Isup2.hkl

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


This work was supported by the National Science Foundation (grant No. DMR 0907395). The authors would also like to thank Dr Colin McMillen and Don VanDerveer for their help.

supplementary crystallographic information


Traditionally, alkaline earth diphosphates (or pyrophosphates) have been of interest as phosphor matrices in fluorescent lamps, among other applications (McKeag & Steward, 1955; Ranby et al., 1955; Ropp & Mooney, 1960). More recently, research is focused on using these phosphor materials for multi-colored white LED devices (Srivastava et al., 2003) to eliminate the use of mercury in fluorescent lamps. The activators ranged from metals such as manganese and tin to rare-earth elements like europium.

In the diphosphate A2P2O7 series (A = alkaline earth metal), when the ionic radius of A is greater than 0.97 Å, the structure is of the dichromate type and the P2O7 anion is in the eclipsed conformation as shown in Fig. 1 (Brown & Calvo, 1970). These structures include α-Ca2P2O7 which crystallizes in the monoclinic space group P21/n (Calvo, 1968) and α-Sr2P2O7 in the orthorhombic space group Pnma (Barbier & Echard, 1998). In the case of barium, a hexagonal high-temperature form σ and an orthorhombic low-temperature form α are known to exist (ElBelghitti et al., 1995). The structure of σ-Ba2P2O7 has been previously characterized from single crystal data in space group P62m and reported to have a very different structure from other known alkaline earth A2P2O7 diphosphates (ElBelghitti et al., 1995). The more stable and common form α-Ba2P2O7 has been characterized by X-ray powder diffraction (Mehdi et al., 1977), but there has been no previous report of the crystal structure determined from single-crystal data therefore, it is presented here. The cell parameters from our single-crystal data are in agreement with those of the previous powder diffraction study. The α nomenclature has been used for the orthorhombic Ba2P2O7 structure in previous reports (Mehdi et al., 1977; Ranby et al., 1955), consistent with being isostructural with α-Sr2P2O7 (Barbier & Echard, 1998).

The α-Ba2P2O7 structure contains two unique Ba atoms each surrounded by nine terminal oxygen atoms from diphosphate groups. The Ba1—O bond lengths range from 2.564 (6) - 2.9272 (18) Å and Ba2—O range from 2.765 (4) - 3.084 (3) Å. The Ba2 atoms connect to O4 along the a-axis to give a layered pattern. Ba1 atoms lie in between the layers and connect to O1 along the c axis resembling a ladder housing two eclipsed P2O7 groups in each section. Additional criss-cross action takes place with Ba1 connected to a terminal O5 atom and Ba2 connected to a terminal O2 atom of the diphosphate anion (Fig. 1). As mentioned before, α-Ba2P2O7 is isostructural with α-Sr2P2O7, whereas the α-Ca2P2O7 structure differs slightly. In this structure, the eight-coordinate Ca2+ cation is edge-sharing three O atoms and corner-sharing two O atoms with the P2O7 groups (Calvo, 1968). In the α-Ba2P2O7 and α-Sr2P2O7 structures, the nine-coordinate cations are edge-sharing four O atoms and corner-sharing one oxygen with the P2O7 groups (Barbier & Echard, 1998). The diphosphate group consists of two tetrahedral PO4 groups sharing O3 to form the P2O7 moiety (Fig. 2). A typical P—O bond length for the tetrahedral PO4 group is reported as 1.538 Å (Mohri, 2000) and the average terminal P—O bond distance in the title structure is 1.516 Å which is comparable to the average of 1.521 Å observed in both α-Sr2P2O7 (Barbier & Echard, 1998) and α-Ca2P2O7 (Calvo, 1968). In diphosphate groups, the bridging P—O bonds are characteristically longer. In the titled structure, the bridging P1—O3 and P2—O3 bonds are 1.588 (6) Å and 1.598 (5) Å which is in comparison to 1.579 (8) and 1.616 (8) Å reported for α-Ca2P2O7 (Calvo, 1968) and 1.599 (2) and 1.615 (2) Å observed in α-Sr2P2O7 (Barbier & Echard, 1998). The bridging O3 atom has longer bonds to P1 and P2. The P1—O3—P2 angle of 134.7 (4)° is wider than 130 (4)° reported for both α-Sr2P2O7 (Barbier & Echard, 1998) and α-Ca2P2O7 (Calvo, 1968) to help reduce structural strain resulting from the larger Ba2+ cation.

An independent refinement of the α-Ba2P2O7 structure based on data from a crystal grown by solid state reactions has been reported by Zakaria et al. (2010). The results of both refinements in terms of geometric parameters are the same within the threefold standard deviation.


The crystals were synthesized by combining 0.17 g of BaHPO4 and 0.05 g of NH4H2PO4 with 0.4 mL of 1M Ba(OH)2 solution in a sealed silver ampoule for 7–10 days at 773 K with a counter pressure of 19000 psi (131 MPa). The contents of the ampoule were washed with deionized water. Colorless needle shaped single crystals of α-Ba2P2O7 were the minor product and colorless polyhedrally shaped crystals of BaHPO4 were the major product.


Despite multiple data collections to high 2θ angles, the bridging oxygen atom O3 of the diphosphate group always appeared as non-positive definite when refined anisotropically. Therefore, we have refined this atom isotropically. The highest remaining peak is located 0.37 Å away from O3 and the deepest hole is 0.58 Å away from Ba1. The large density arises from O3 being defined as isotropically. The xyz coordinates for Q1 are 1.34 0.25 0.41 and for Q2 are 1.43 0.25 0.42 which are close to O3 at 1.38 0.25 0.42. The Q peaks are 0.37 and 0.54 Å away from O3 instead of the heavier atom Ba.


Fig. 1.
A view of the α-Ba2P2O7 structure along the b axis. Some Ba—O bonds are omitted for clarity. The purple polyhedra represent the diphosphate P2O7 groups.
Fig. 2.
A view of the asymmetric unit of α-Ba2P2O7 with additional symmetry-related atoms displayed to show the tetrahedral environment around phosphorus. The Ba—O bonds were left out for clarity. Displacement ellipsoids are drawn at the 50% probability ...

Crystal data

Ba2P2O7F(000) = 792
Mr = 448.62Dx = 4.146 Mg m3
Orthorhombic, PnmaMo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2ac 2nCell parameters from 3690 reflections
a = 9.2842 (19) Åθ = 2.7–36.3°
b = 5.6113 (11) ŵ = 11.32 mm1
c = 13.796 (3) ÅT = 298 K
V = 718.7 (3) Å3Needle, colorless
Z = 40.45 × 0.15 × 0.15 mm

Data collection

Rigaku AFC-8S Mercury CCD diffractometer1854 independent reflections
Radiation source: sealed tube1510 reflections with I > 2σ(I)
graphiteRint = 0.042
Detector resolution: 14.6306 pixels mm-1θmax = 36.3°, θmin = 2.6°
ω scansh = −8→15
Absorption correction: multi-scan (REQAB; Jacobson, 1998)k = −7→9
Tmin = 0.080, Tmax = 0.281l = −21→22
7205 measured reflections


Refinement on F20 restraints
Least-squares matrix: fullPrimary atom site location: structure-invariant direct methods
R[F2 > 2σ(F2)] = 0.047Secondary atom site location: difference Fourier map
wR(F2) = 0.127w = 1/[σ2(Fo2) + (0.0617P)2 + 4.9464P] where P = (Fo2 + 2Fc2)/3
S = 1.11(Δ/σ)max = 0.001
1854 reflectionsΔρmax = 6.71 e Å3
58 parametersΔρmin = −3.53 e Å3

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 (Å2)

Ba10.86006 (5)0.25000.41750 (3)0.01365 (12)
Ba20.84160 (5)0.25000.74453 (3)0.01249 (12)
P11.2179 (2)0.25000.45777 (12)0.0120 (3)
P21.4529 (2)0.25000.31494 (13)0.0120 (3)
O11.1427 (4)0.0289 (8)0.4204 (3)0.0163 (8)
O21.2271 (6)0.25000.5677 (4)0.0164 (10)
O31.3792 (6)0.25000.4196 (3)0.0118 (9)*
O41.4045 (4)0.0278 (7)0.2617 (3)0.0154 (7)
O51.6144 (7)0.25000.3326 (4)0.0230 (12)

Atomic displacement parameters (Å2)

Ba10.0139 (2)0.0148 (2)0.0122 (2)0.000−0.00132 (12)0.000
Ba20.01179 (19)0.0128 (2)0.01293 (18)0.0000.00048 (12)0.000
P10.0126 (7)0.0131 (8)0.0103 (6)0.0000.0008 (5)0.000
P20.0105 (7)0.0119 (7)0.0138 (7)0.0000.0002 (5)0.000
O10.0170 (18)0.0134 (19)0.0187 (18)−0.0009 (14)0.0018 (12)0.0001 (13)
O20.018 (2)0.018 (3)0.013 (2)0.000−0.0009 (17)0.000
O40.0149 (17)0.0108 (17)0.0205 (15)−0.0033 (13)0.0000 (13)−0.0010 (13)
O50.011 (2)0.037 (3)0.022 (2)0.0000.001 (2)0.000

Geometric parameters (Å, °)

Ba1—O5i2.564 (6)Ba2—O2viii2.800 (5)
Ba1—O1ii2.730 (4)Ba2—O4ix2.836 (4)
Ba1—O1iii2.730 (4)Ba2—O4x2.836 (4)
Ba1—O4iv2.799 (4)Ba2—O5xi3.084 (3)
Ba1—O4v2.799 (4)Ba2—O5x3.084 (3)
Ba1—O1vi2.903 (4)P1—O11.514 (5)
Ba1—O12.903 (4)P1—O1vi1.514 (5)
Ba1—O2iii2.9272 (18)P1—O21.519 (6)
Ba1—O2vii2.9272 (18)P1—O31.588 (6)
Ba1—P2iv3.320 (2)P1—Ba1vii3.3700 (11)
Ba1—P13.369 (2)P1—Ba1iii3.3700 (11)
Ba1—P1vii3.3700 (11)P2—O41.515 (4)
Ba2—O1iii2.765 (4)P2—O4vi1.515 (4)
Ba2—O1ii2.765 (4)P2—O51.519 (6)
Ba2—O4iii2.767 (4)P2—O31.598 (5)
Ba2—O4ii2.767 (4)
O5i—Ba1—O1ii111.47 (14)O2viii—Ba2—O4x103.79 (13)
O5i—Ba1—O1iii111.47 (14)O4ix—Ba2—O4x66.70 (16)
O1ii—Ba1—O1iii69.95 (18)O1iii—Ba2—O5xi146.29 (14)
O5i—Ba1—O4iv74.19 (15)O1ii—Ba2—O5xi78.59 (14)
O1ii—Ba1—O4iv168.60 (12)O4iii—Ba2—O5xi129.35 (14)
O1iii—Ba1—O4iv118.01 (12)O4ii—Ba2—O5xi66.99 (14)
O5i—Ba1—O4v74.19 (15)O2viii—Ba2—O5xi71.70 (11)
O1ii—Ba1—O4v118.01 (13)O4ix—Ba2—O5xi49.98 (14)
O1iii—Ba1—O4v168.60 (12)O4x—Ba2—O5xi110.92 (14)
O4iv—Ba1—O4v52.90 (17)O1iii—Ba2—O5x78.59 (14)
O5i—Ba1—O1vi144.13 (12)O1ii—Ba2—O5x146.29 (14)
O1ii—Ba1—O1vi75.66 (12)O4iii—Ba2—O5x66.99 (14)
O1iii—Ba1—O1vi104.02 (8)O4ii—Ba2—O5x129.35 (14)
O4iv—Ba1—O1vi93.97 (11)O2viii—Ba2—O5x71.70 (11)
O4v—Ba1—O1vi71.85 (11)O4ix—Ba2—O5x110.92 (14)
O5i—Ba1—O1144.13 (12)O4x—Ba2—O5x49.98 (14)
O1ii—Ba1—O1104.02 (8)O5xi—Ba2—O5x130.9 (2)
O1iii—Ba1—O175.66 (12)O1—P1—O1vi110.0 (3)
O4iv—Ba1—O171.85 (11)O1—P1—O2111.48 (19)
O4v—Ba1—O193.97 (11)O1vi—P1—O2111.48 (19)
O1vi—Ba1—O150.61 (18)O1—P1—O3108.79 (19)
O5i—Ba1—O2iii77.64 (11)O1vi—P1—O3108.79 (19)
O1ii—Ba1—O2iii119.32 (14)O2—P1—O3106.1 (3)
O1iii—Ba1—O2iii52.47 (14)O4—P2—O4vi110.7 (3)
O4iv—Ba1—O2iii71.07 (13)O4—P2—O5111.7 (2)
O4v—Ba1—O2iii121.96 (13)O4vi—P2—O5111.7 (2)
O1vi—Ba1—O2iii131.20 (15)O4—P2—O3108.14 (19)
O1—Ba1—O2iii80.75 (14)O4vi—P2—O3108.14 (19)
O5i—Ba1—O2vii77.64 (11)O5—P2—O3106.1 (3)
O1ii—Ba1—O2vii52.47 (14)P1—O1—Ba1iii101.23 (18)
O1iii—Ba1—O2vii119.32 (14)P1—O1—Ba2iii136.0 (2)
O4iv—Ba1—O2vii121.96 (13)Ba1iii—O1—Ba2iii110.49 (16)
O4v—Ba1—O2vii71.07 (13)P1—O1—Ba194.1 (2)
O1vi—Ba1—O2vii80.75 (14)Ba1iii—O1—Ba1104.34 (12)
O1—Ba1—O2vii131.20 (15)Ba2iii—O1—Ba1106.17 (13)
O2iii—Ba1—O2vii146.9 (2)P1—O2—Ba2xii160.9 (4)
O1iii—Ba2—O1ii68.95 (18)P1—O2—Ba1iii93.11 (12)
O1iii—Ba2—O4iii72.50 (12)Ba2xii—O2—Ba1iii92.31 (11)
O1ii—Ba2—O4iii109.70 (12)P1—O2—Ba1vii93.11 (12)
O1iii—Ba2—O4ii109.70 (12)Ba2xii—O2—Ba1vii92.31 (11)
O1ii—Ba2—O4ii72.50 (12)Ba1iii—O2—Ba1vii146.9 (2)
O4iii—Ba2—O4ii68.58 (18)P1—O3—P2134.7 (4)
O1iii—Ba2—O2viii141.37 (10)P2—O4—Ba2iii136.3 (2)
O1ii—Ba2—O2viii141.37 (10)P2—O4—Ba1xiii96.06 (19)
O4iii—Ba2—O2viii73.45 (13)Ba2iii—O4—Ba1xiii95.85 (12)
O4ii—Ba2—O2viii73.45 (13)P2—O4—Ba2xiv104.2 (2)
O1iii—Ba2—O4ix109.63 (12)Ba2iii—O4—Ba2xiv111.96 (14)
O1ii—Ba2—O4ix73.36 (12)Ba1xiii—O4—Ba2xiv107.08 (13)
O4iii—Ba2—O4ix176.88 (2)P2—O5—Ba1xv162.0 (4)
O4ii—Ba2—O4ix112.28 (14)P2—O5—Ba2xiv93.88 (15)
O2viii—Ba2—O4ix103.79 (13)Ba1xv—O5—Ba2xiv93.56 (13)
O1iii—Ba2—O4x73.36 (12)P2—O5—Ba2xvi93.88 (15)
O1ii—Ba2—O4x109.63 (12)Ba1xv—O5—Ba2xvi93.56 (13)
O4iii—Ba2—O4x112.28 (14)Ba2xiv—O5—Ba2xvi130.9 (2)
O4ii—Ba2—O4x176.88 (2)

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


Supplementary data and figures for this paper are available from the IUCr electronic archives (Reference: WM2406).


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