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The compound diiron diphosphate dihydrate, Fe2P2O7(H2O)2, was synthesized hydro­thermally and crystallizes in the monoclinic space group P21/n. The compound has a somewhat open framework made up of edge-sharing iron(II) octahedra that form chains connected by five bridging diphosphates. The remaining octahedral site of each iron is occupied by coordinated water. The H atoms of the water molecules all point into a common channel.

Supporting information

cif

Crystallographic Information File (CIF) https://doi.org/10.1107/S0108270199014407/br1253sup1.cif
Contains datablocks FD0991, I

hkl

Structure factor file (CIF format) https://doi.org/10.1107/S0108270199014407/br1253Isup2.sft
Contains datablock I

Comment top

We have been interested in making low-density iron phosphates for the last few years (Korzenski et al., 1998). They exhibit interesting magnetic and structural properties, and can possibly form large microporous frameworks under appropriate conditions. Herein we report a new FeII diphosphate synthesized hydrothermally. The title compound crystallizes in the monoclinic space group P21/n. There are two crystallographically unique iron sites. Both have octahedral coordination with five diphosphate O atoms and one water oxygen. Two oxygen atoms are bridging, forming edge sharing iron octahedra. The Fe—O distances for both Fe(1) and Fe(2) range from 2.022 (2) to 2.197 (2) Å [average 2.14 (5) Å], in good agreement with those reported in a series of iron(II) phosphate hydrates (Moore & Araki, 1975; Warner et al., 1992), and iron diphosphates (Le Meins & Courbion, 1999). There are also two unique phosphorus sites. Both are tetrahedrally bound to four O atoms atoms and share a common vertex at O4 to form the diphosphate group. The average P—O distance for the terminal oxygen atoms is 1.518 Å (standard deviation 0.007 Å), those to the bridging oxygen atom are longer [1.608 (1) and 1.614 (1) Å], and the average O—P—O angle is 109° (standard deviation 4°), comparable to other iron phosphates (Warner et al., 1992; Stefanidis & Nord, 1982).

All of the atoms in the unit cell sit on general positions. The asymmetric unit (Fig. 1) shows the connectivity of the atoms and how they bond to symmetry-related units. The compound comprises edge-sharing iron octahedra that are linked by bridging diphosphates. This connectivity forms a cavity that houses the hydrogen atoms of the two water molecules (Fig. 2). Like most hydrated iron(II) phosphates the water molecules are coordinated to the iron (Mori & Ito, 1950; Eversheim & Kleber, 1953; Moore & Araki, 1976). One of the hydrogen atoms on each water is hydrogen-bonded to an oxygen of another iron. The remaining hydrogen atoms have no obvious interactions. The synthesis of this compound requires titanium oxide (TiO) to be present although it does not become incorporated into the compound, as confirmed by EDAX. Attempts to synthesize this compound in the absence of titanium oxide have not been successful.

Experimental top

Colorless single crystals of Fe2PO7(H2O)2 were obtained from a reaction mixture of iron metal (42 mg, 752 mmol), TiO (48 mg, 752 mmol) and 25% H3PO4(aq) (0.7 ml) which was placed into a quartz tube. The tube was then put into an autoclave with a counter pressure of 18.62 MPa of argon gas. The reaction was heated for 3 d at 648 K and cooled in air to room temperature. Upon visual inspection of the quartz tube, the only crystalline material present were colorless truncated diamond-shaped crystals of the title compound and black polyhedral shaped crystals precipitated from a clear solution. The yield for the colorless crystals was approximately 5–7%. The black polyhedral crystals are currently being characterized.

Refinement top

All atoms except the H atoms were refined with anisotropic displacement parameters.

Computing details top

Data collection: P3 Software (Siemens, 1989); cell refinement: P3 Software; data reduction: SHELXTL-Plus (Sheldrick, 1990); program(s) used to solve structure: SHELXTL-Plus); program(s) used to refine structure: SHELXTL-Plus; software used to prepare material for publication: SHELXTL-Plus.

Figures top
[Figure 1] Fig. 1. Asymmetric view of the Fe2P2O7(H2O)2 unit showing 70% probability displacement ellipsoids.
[Figure 2] Fig. 2. Packing of Fe2P2O7(H2O)2 diagram viewed down the a axis with positive z toward the right and positive y down.
Iron(II) Diphosphate Dihydrate top
Crystal data top
Fe2P2O7(H2O)2F(000) = 632.00
Mr = 321.7Dx = 3.188 Mg m3
Monoclinic, P21/nMo Kα radiation, λ = 0.71073 Å
a = 6.400 (2) ÅCell parameters from 50 reflections
b = 14.181 (3) Åθ = 25.1–27.5°
c = 7.416 (1) ŵ = 4.83 mm1
β = 95.43 (2)°T = 297 K
V = 670.1 (2) Å3Truncated diamonds, colorless
Z = 40.48 × 0.24 × 0.17 mm
Data collection top
Nicolet R 3m/V
diffractometer
1454 reflections with (F) > 4σ(F)
Radiation source: Sealed tubeRint = 0.016
Graphite monochromatorθmax = 27.5°, θmin = 1.8°
ω/2–θ scansh = 08
Absorption correction: ψ scan
(North et al., 1968)
k = 018
Tmin = 0.185, Tmax = 0.416l = 99
1754 measured reflections3 standard reflections every 97 reflections
1547 independent reflections intensity decay: 1.0%
Refinement top
Refinement on FPrimary atom site location: Direct Methods
Least-squares matrix: fullHydrogen site location: Difference Fourier
R[F2 > 2σ(F2)] = 0.019Isotropic
wR(F2) = 0.0301/(σ2(F) + 0.0005F2)
S = 1.18(Δ/σ)max = 0.042
1454 reflectionsΔρmax = 0.55 e Å3
135 parametersΔρmin = 0.58 e Å3
0 restraintsExtinction correction: (Larson, 1970)
0 constraintsExtinction coefficient: 0.0000004861 (3)
Crystal data top
Fe2P2O7(H2O)2V = 670.1 (2) Å3
Mr = 321.7Z = 4
Monoclinic, P21/nMo Kα radiation
a = 6.400 (2) ŵ = 4.83 mm1
b = 14.181 (3) ÅT = 297 K
c = 7.416 (1) Å0.48 × 0.24 × 0.17 mm
β = 95.43 (2)°
Data collection top
Nicolet R 3m/V
diffractometer
1454 reflections with (F) > 4σ(F)
Absorption correction: ψ scan
(North et al., 1968)
Rint = 0.016
Tmin = 0.185, Tmax = 0.4163 standard reflections every 97 reflections
1754 measured reflections intensity decay: 1.0%
1547 independent reflections
Refinement top
R[F2 > 2σ(F2)] = 0.0190 restraints
wR(F2) = 0.030Isotropic
S = 1.18Δρmax = 0.55 e Å3
1454 reflectionsΔρmin = 0.58 e Å3
135 parameters
Special details top

Refinement. The structure was solved using direct methods and refined by full matrix, least squares techniques.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2) top
xyzUiso*/Ueq
Fe(1)0.7374 (1)0.6099 (1)0.0801 (1)0.008 (1)
Fe(2)0.0490 (1)0.2474 (1)0.3470 (1)0.008 (1)
P(1)0.7572 (1)0.4148 (1)0.1499 (1)0.006 (1)
P(2)0.5658 (1)0.3124 (1)0.4248 (1)0.006 (1)
O(1)0.7956 (2)0.5187 (1)0.1281 (2)0.011 (1)
O(2)0.9588 (2)0.3580 (1)0.1585 (2)0.010 (1)
O(3)0.5863 (2)0.3726 (1)0.0171 (2)0.010 (1)
O(4)0.6691 (2)0.4053 (1)0.3460 (2)0.008 (1)
O(5)0.7231 (2)0.2325 (1)0.4057 (2)0.010 (1)
O(6)0.3627 (2)0.2950 (1)0.3057 (2)0.010 (1)
O(7)0.5343 (2)0.3382 (1)0.6181 (2)0.011 (1)
O(8)0.7500 (3)0.5021 (1)0.2811 (2)0.018 (1)
O(9)0.0693 (2)0.3502 (1)0.5611 (2)017 (1)
H(1)0.662 (6)0.458 (3)0.303 (5)0.062 (12)
H(2)0.878 (9)0.475 (4)0.290 (7)0.12 (2)
H(3)0.163 (8)0.389 (3)0.536 (6)0.088 (17)
H(4)0.085 (7)0.330 (3)0.684 (6)0.083 (15)
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
Fe(1)0.008 (1)0.006 (1)0.008 (1)0.000 (1)0.001 (1)0.001 (1)
Fe(2)0.009 (1)0.007 (1)0.008 (1)0.000 (1)0.001 (1)0.001 (1)
P(1)0.007 (1)0.005 (1)0.007 (1)0.000 (1)0.001 (1)0.001 (1)
P(2)0.007 (1)0.006 (1)0.006 (1)0.000 (1)0.001 (1)0.000 (1)
O(1)0.014 (1)0.006 (1)0.012 (1)0.002 (1)0.000 (1)0.002 (1)
O(2)0.008 (1)0.008 (1)0.014 (1)0.002 (1)0.002 (1)0.003 (1)
O(3)0.009 (1)0.010 (1)0.010 (1)0.001 (1)0.001 (1)0.002 (1)
O(4)0.010 (1)0.006 (1)0.007 (1)0.002 (1)0.002 (1)0.000 (1)
O(5)0.009 (1)0.007 (1)0.013 (1)0.002 (1)0.003 (1)0.002 (1)
O(6)0.009 (1)0.011 (1)0.009 (1)0.002 (1)0.000 (1)0.002 (1)
O(7)0.015 (1)0.010 (1)0.007 (1)0.001 (1)0.002 (1)0.000 (1)
O(8)0.020 (1)0.012 (1)0.022 (1)0.003 (1)0.002 (1)0.007 (1)
O(9)0.017 (1)0.022 (1)0.014 (1)0.001 (1)0.001 (1)0.003 (1)
Geometric parameters (Å, º) top
Fe(1)—O(1)2.022 (2)P(1)—O(1)1.505 (2)
Fe(1)—O(8)2.142 (2)P(1)—O(2)1.517 (1)
Fe(1)—O(2)i2.130 (2)P(1)—O(3)1.524 (1)
Fe(1)—O(3)ii2.181 (2)P(1)—O(4)1.614 (1)
Fe(1)—O(5)iii2.166 (2)P(2)—O(4)1.608 (1)
Fe(1)—O(6)ii2.197 (1)P(2)—O(5)1.532 (2)
Fe(2)—O(6)2.167 (2)P(2)—O(6)1.521 (1)
Fe(2)—O(9)2.151 (2)P(2)—O(7)1.511 (1)
Fe(2)—O(2)iv2.144 (2)O(8)—H(1)0.85 (4)
Fe(2)—O(3)v2.118 (2)O(8)—H(2)0.92 (6)
Fe(2)—O(5)iv2.181 (2)O(9)—H(3)0.85 (5)
Fe(2)—O(7)vi2.081 (2)O(9)—H(4)0.95 (4)
O(1)—Fe(1)—O(8)93.3 (1)O(2)—P(1)—O(3)112.0 (1)
O(1)—Fe(1)—O(2)i103.8 (1)O(1)—P(1)—O(4)104.6 (1)
O(8)—Fe(1)—O(2)i82.4 (1)O(2)—P(1)—O(4)106.7 (1)
O(1)—Fe(1)—O(3)ii91.1 (1)O(3)—P(1)—O(4)105.0 (1)
O(8)—Fe(1)—O(3)ii109.2 (1)O(4)—P(2)—O(5)106.0 (1)
O(2)i—Fe(1)—O(3)ii160.8 (1)O(4)—P(2)—O(6)106.3 (1)
O(1)—Fe(1)—O(5)iii93.1 (1)O(5)—P(2)—O(6)111.1 (1)
O(8)—Fe(1)—O(5)iii167.9 (1)O(4)—P(2)—O(7)104.0 (1)
O(2)i—Fe(1)—O(5)iii86.2 (1)O(5)—P(2)—O(7)114.5 (1)
O(3)ii—Fe(1)—O(5)iii80.8 (1)O(6)—P(2)—O(7)114.0 (1)
O(1)—Fe(1)—O(6)ii173.6 (1)Fe(1)—O(1)—P(1)133.5 (1)
O(8)—Fe(1)—O(6)ii86.3 (1)P(1)—O(2)—Fe(1)i132.1 (1)
O(2)i—Fe(1)—O(6)ii82.5 (1)P(1)—O(2)—Fe(2)vii126.2 (1)
O(3)ii—Fe(1)—O(6)ii83.0 (1)Fe(1)i—O(2)—Fe(2)vii97.9 (1)
O(5)iii—Fe(1)—O(6)ii88.3 (1)P(1)—O(3)—Fe(1)ii117.1 (1)
O(6)—Fe(2)—O(9)84.3 (1)P(1)—O(3)—Fe(2)viii137.2 (1)
O(6)—Fe(2)—O(2)iv82.9 (1)Fe(1)ii—O(3)—Fe(2)viii99.4 (1)
O(9)—Fe(2)—O(2)iv88.8 (1)P(1)—O(4)—P(2)125.9 (1)
O(6)—Fe(2)—O(3)v106.3 (1)P(2)—O(5)—Fe(1)ix125.4 (1)
O(9)—Fe(2)—O(3)v96.3 (1)P(2)—O(5)—Fe(2)vii126.6 (1)
O(2)iv—Fe(2)—O(3)v169.9 (1)Fe(1)ix—O(5)—Fe(2)vii97.9 (1)
O(6)—Fe(2)—O(5)iv167.1 (1)Fe(2)—O(6)—P(2)136.1 (1)
O(9)—Fe(2)—O(5)iv84.8 (1)Fe(2)—O(6)—Fe(1)ii95.3 (1)
O(2)iv—Fe(2)—O(5)iv89.9 (1)P(2)—O(6)—Fe(1)ii120.9 (1)
O(3)v—Fe(2)—O(5)iv81.9 (1)P(2)—O(7)—Fe(2)x129.3 (1)
O(6)—Fe(2)—O(7)vi92.1 (1)Fe(1)—O(8)—H(1)126 (3)
O(9)—Fe(2)—O(7)vi172.9 (1)Fe(1)—O(8)—H(2)116 (3)
O(2)iv—Fe(2)—O(7)vi84.6 (1)H(1)—O(8)—H(2)105 (5)
O(3)v—Fe(2)—O(7)vi90.7 (1)Fe(2)—O(9)—H(3)106 (3)
O(5)iv—Fe(2)—O(7)vi97.8 (1)Fe(2)—O(9)—H(4)120 (3)
O(1)—P(1)—O(2)112.2 (1)H(3)—O(9)—H(4)113 (4)
O(1)—P(1)—O(3)115.4 (1)
Symmetry codes: (i) x+2, y+1, z; (ii) x+1, y+1, z; (iii) x+3/2, y+1/2, z+1/2; (iv) x1, y, z; (v) x1/2, y+1/2, z+1/2; (vi) x1/2, y+1/2, z1/2; (vii) x+1, y, z; (viii) x+1/2, y+1/2, z1/2; (ix) x+3/2, y1/2, z+1/2; (x) x+1/2, y+1/2, z+1/2.
Hydrogen-bond geometry (Å, º) top
D—H···AD—HH···AD···AD—H···A
O(8)—H(1)···O(7)0.85 (4)1.95 (4)2.770 (4)162 (4)
O(8)—H(2)0.92 (6)
O(9)—H(3)0.85 (2)
O(9)—H(4)···O(5)0.95 (4)2.00 (4)2.898 (4)157 (4)

Experimental details

Crystal data
Chemical formulaFe2P2O7(H2O)2
Mr321.7
Crystal system, space groupMonoclinic, P21/n
Temperature (K)297
a, b, c (Å)6.400 (2), 14.181 (3), 7.416 (1)
β (°) 95.43 (2)
V3)670.1 (2)
Z4
Radiation typeMo Kα
µ (mm1)4.83
Crystal size (mm)0.48 × 0.24 × 0.17
Data collection
DiffractometerNicolet R 3m/V
diffractometer
Absorption correctionψ scan
(North et al., 1968)
Tmin, Tmax0.185, 0.416
No. of measured, independent and
observed [(F) > 4σ(F)] reflections
1754, 1547, 1454
Rint0.016
(sin θ/λ)max1)0.650
Refinement
R[F2 > 2σ(F2)], wR(F2), S 0.019, 0.030, 1.18
No. of reflections1454
No. of parameters135
H-atom treatmentIsotropic
Δρmax, Δρmin (e Å3)0.55, 0.58

Computer programs: P3 Software (Siemens, 1989), P3 Software, SHELXTL-Plus (Sheldrick, 1990), SHELXTL-Plus), SHELXTL-Plus.

Selected geometric parameters (Å, º) top
Fe(1)—O(1)2.022 (2)P(1)—O(1)1.505 (2)
Fe(1)—O(8)2.142 (2)P(1)—O(2)1.517 (1)
Fe(1)—O(2)i2.130 (2)P(1)—O(3)1.524 (1)
Fe(1)—O(3)ii2.181 (2)P(1)—O(4)1.614 (1)
Fe(1)—O(5)iii2.166 (2)P(2)—O(4)1.608 (1)
Fe(1)—O(6)ii2.197 (1)P(2)—O(5)1.532 (2)
Fe(2)—O(6)2.167 (2)P(2)—O(6)1.521 (1)
Fe(2)—O(9)2.151 (2)P(2)—O(7)1.511 (1)
Fe(2)—O(2)iv2.144 (2)O(8)—H(1)0.85 (4)
Fe(2)—O(3)v2.118 (2)O(8)—H(2)0.92 (6)
Fe(2)—O(5)iv2.181 (2)O(9)—H(3)0.85 (5)
Fe(2)—O(7)vi2.081 (2)O(9)—H(4)0.95 (4)
P(1)—O(4)—P(2)125.9 (1)
Symmetry codes: (i) x+2, y+1, z; (ii) x+1, y+1, z; (iii) x+3/2, y+1/2, z+1/2; (iv) x1, y, z; (v) x1/2, y+1/2, z+1/2; (vi) x1/2, y+1/2, z1/2.
Hydrogen-bond geometry (Å, º) top
D—H···AD—HH···AD···AD—H···A
O(8)—H(1)···O(7)0.85 (4)1.95 (4)2.770 (4)162 (4)
O(9)—H(4)···O(5)0.95 (4)2.00 (4)2.898 (4)157 (4)
 

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