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The structure of rhombohedral (R\overline{3}) iron(III) tris­[di­hydrogen­phosphate(I)] or iron(III) hypophosphite, Fe(H2PO2)3, has been determined by single-crystal X-ray diffraction. The structure consists of [001] chains of Fe3+ cations in octa­hedral sites with \overline{3} symmetry bridged by bidentate hypophosphite anions.

Supporting information

cif

Crystallographic Information File (CIF) https://doi.org/10.1107/S0108270105038035/bc1084sup1.cif
Contains datablocks I, global

hkl

Structure factor file (CIF format) https://doi.org/10.1107/S0108270105038035/bc1084Isup2.hkl
Contains datablock I

Comment top

Previous crystal structure investigations of anhydrous salts of hypophosphoric acid include NH4H2PO2 (Zachariasen & Mooney, 1934), Ca(H2PO2)2 (GoedkooP1 & Loopstra, 1959), CaNa(H2PO2)3 (Matsuzaki & Iitaka, 1969), Zn(H2PO2)2 (Weakley, 1979; Tanner et al., 1997), La(H2PO2)3 (Tanner et al., 1999), Er(H2PO2)3 (Aslanov et al., 1975), Ge2(H2PO2)6 (Weakley, 1983) and U(H2PO2)4 (Tanner et al., 1992). It is evident that the investigation of this type of compound is incomplete and the limited number of studies is probably a result of the difficulty of preparation and crystal growth. Our own crystallographic studies on anhydrous hypophosphites include Cu(H2PO2)2 (Naumov et al., 2002), MH2PO2 (M = K, Rb and Cs; Naumova et al., 2004), LiH2PO2 and Be(H2PO2)2 (Naumov et al., 2004), and M(H2PO2)2 (M = Sr, Ba and Pb; Kuratieva et al., 2005).

All bivalent metal hypophosphites adopt layered structures. Rare-earth hypophosphites adopt layered structures, as in Er(H2PO2)3 (Aslanov et al., 1975), or three-dimentional network structures, as in La(H2PO2)3 (Tanner et al., 1999). In contrast, the structure of Fe(H2PO2)3 consists of chains formed by hypophosphite anions and iron cations, the latter being coordinated by six hypophosphite O atoms forming a nearly ideal octahedral environment for both Fe3+ cations (Fig. 1). The structure is isotypical to that of the GeIIGeIV hypophosphite in which, however, the two Ge atoms have different coordination spheres (Weakley, 1983). The chains are parallel to the c axis and linked together via van der Waals interactions, with short H···H contacts of 2.35 (2) and 2.56 (2) Å.

Experimental top

Iron(III) hypophosphite was synthesized by the reaction of equimolar quantities of iron powder and 100% hypophosphoric acid in air at room temperature. A precipitate formed when about 70% of the iron powder was taken into the reaction (about 2 days). The mixture was filtered and left to stand in air. Powder formed at the bottom of the beaker and crystals appeared in the meniscus. The powder X-ray pattern of the bulk product is in good agreement with the calculated pattern. Iron(III) hypophosphite is almost insoluble in water.

Refinement top

H atoms were located in difference electron density maps and included in the refinement without any constraints.

Structure description top

Previous crystal structure investigations of anhydrous salts of hypophosphoric acid include NH4H2PO2 (Zachariasen & Mooney, 1934), Ca(H2PO2)2 (GoedkooP1 & Loopstra, 1959), CaNa(H2PO2)3 (Matsuzaki & Iitaka, 1969), Zn(H2PO2)2 (Weakley, 1979; Tanner et al., 1997), La(H2PO2)3 (Tanner et al., 1999), Er(H2PO2)3 (Aslanov et al., 1975), Ge2(H2PO2)6 (Weakley, 1983) and U(H2PO2)4 (Tanner et al., 1992). It is evident that the investigation of this type of compound is incomplete and the limited number of studies is probably a result of the difficulty of preparation and crystal growth. Our own crystallographic studies on anhydrous hypophosphites include Cu(H2PO2)2 (Naumov et al., 2002), MH2PO2 (M = K, Rb and Cs; Naumova et al., 2004), LiH2PO2 and Be(H2PO2)2 (Naumov et al., 2004), and M(H2PO2)2 (M = Sr, Ba and Pb; Kuratieva et al., 2005).

All bivalent metal hypophosphites adopt layered structures. Rare-earth hypophosphites adopt layered structures, as in Er(H2PO2)3 (Aslanov et al., 1975), or three-dimentional network structures, as in La(H2PO2)3 (Tanner et al., 1999). In contrast, the structure of Fe(H2PO2)3 consists of chains formed by hypophosphite anions and iron cations, the latter being coordinated by six hypophosphite O atoms forming a nearly ideal octahedral environment for both Fe3+ cations (Fig. 1). The structure is isotypical to that of the GeIIGeIV hypophosphite in which, however, the two Ge atoms have different coordination spheres (Weakley, 1983). The chains are parallel to the c axis and linked together via van der Waals interactions, with short H···H contacts of 2.35 (2) and 2.56 (2) Å.

Computing details top

Data collection: APEX2 (Bruker, 2004); cell refinement: SAINT (Bruker, 2004); data reduction: SAINT; program(s) used to solve structure: SHELXTL (Bruker, 2004); program(s) used to refine structure: SHELXTL; molecular graphics: SHELXTL and BS (Ozawa & Kang, 2004); software used to prepare material for publication: SHELXTL.

Figures top
[Figure 1] Fig. 1. A [001] chain in the structure of Fe(H2PO2)3. Displacement ellipsoids are plotted at the 50% probability level and H atoms are drawn as small spheres of arbitrary radii.
Iron(III) tris[dihydrogenphosphate(I)] top
Crystal data top
Fe(H2PO2)3Dx = 2.353 Mg m3
Mr = 250.81Mo Kα radiation, λ = 0.71073 Å
Hexagonal, R3Cell parameters from 521 reflections
Hall symbol: -R 3θ = 3.6–28.2°
a = 11.2800 (11) ŵ = 2.78 mm1
c = 9.6375 (11) ÅT = 293 K
V = 1061.97 (19) Å3Prism, colourless
Z = 60.08 × 0.04 × 0.02 mm
F(000) = 750
Data collection top
Bruker–Nonius X8 APEX CCD area-detector
diffractometer
430 independent reflections
Radiation source: fine-focus sealed tube361 reflections with I > 2σ(I)
Graphite monochromatorRint = 0.034
Detector resolution: 25 pixels mm-1θmax = 25.3°, θmin = 3.6°
φ scansh = 137
Absorption correction: multi-scan
(SADABS; Bruker, 2004)
k = 513
Tmin = 0.808, Tmax = 0.947l = 1111
1147 measured reflections
Refinement top
Refinement on F2Primary atom site location: structure-invariant direct methods
Least-squares matrix: fullSecondary atom site location: difference Fourier map
R[F2 > 2σ(F2)] = 0.030Hydrogen site location: difference Fourier map
wR(F2) = 0.073All H-atom parameters refined
S = 1.03 w = 1/[σ2(Fo2) + (0.0377P)2]
where P = (Fo2 + 2Fc2)/3
430 reflections(Δ/σ)max < 0.001
40 parametersΔρmax = 0.46 e Å3
2 restraintsΔρmin = 0.39 e Å3
Crystal data top
Fe(H2PO2)3Z = 6
Mr = 250.81Mo Kα radiation
Hexagonal, R3µ = 2.78 mm1
a = 11.2800 (11) ÅT = 293 K
c = 9.6375 (11) Å0.08 × 0.04 × 0.02 mm
V = 1061.97 (19) Å3
Data collection top
Bruker–Nonius X8 APEX CCD area-detector
diffractometer
430 independent reflections
Absorption correction: multi-scan
(SADABS; Bruker, 2004)
361 reflections with I > 2σ(I)
Tmin = 0.808, Tmax = 0.947Rint = 0.034
1147 measured reflections
Refinement top
R[F2 > 2σ(F2)] = 0.0302 restraints
wR(F2) = 0.073All H-atom parameters refined
S = 1.03Δρmax = 0.46 e Å3
430 reflectionsΔρmin = 0.39 e Å3
40 parameters
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
Fe10.00000.00000.00000.0184 (3)
Fe20.00000.00000.50000.0204 (4)
P10.18791 (9)0.20062 (9)0.24457 (9)0.0190 (3)
O10.1648 (2)0.1143 (2)0.1173 (2)0.0249 (6)
O20.1596 (2)0.1276 (3)0.3822 (2)0.0285 (6)
H10.322 (2)0.305 (2)0.247 (3)0.020 (9)*
H20.106 (3)0.258 (3)0.227 (3)0.015 (8)*
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
Fe10.0242 (5)0.0242 (5)0.0067 (6)0.0121 (2)0.0000.000
Fe20.0278 (5)0.0278 (5)0.0055 (6)0.0139 (2)0.0000.000
P10.0219 (5)0.0206 (5)0.0124 (5)0.0090 (4)0.0011 (4)0.0012 (4)
O10.0289 (13)0.0339 (15)0.0128 (13)0.0164 (12)0.0045 (10)0.0069 (11)
O20.0307 (14)0.0354 (16)0.0143 (14)0.0126 (12)0.0022 (10)0.0031 (11)
Geometric parameters (Å, º) top
Fe1—O12.000 (2)Fe2—O2v2.003 (2)
Fe1—O1i2.000 (2)Fe2—O2vii2.003 (2)
Fe1—O1ii2.000 (2)Fe2—O2iii2.003 (2)
Fe1—O1iii2.000 (2)Fe2—O2viii2.003 (2)
Fe1—O1iv2.000 (2)P1—O11.506 (2)
Fe1—O1v2.000 (2)P1—O21.509 (2)
Fe2—O22.003 (2)P1—H11.38 (4)
Fe2—O2vi2.003 (2)P1—H21.38 (4)
O1—Fe1—O1i180O2v—Fe2—O2iii91.04 (9)
O1i—Fe1—O1ii91.17 (9)O2vii—Fe2—O2iii180
O1—Fe1—O1ii88.83 (9)O2vi—Fe2—O288.96 (9)
O1i—Fe1—O1iii88.83 (9)O2v—Fe2—O291.04 (9)
O1—Fe1—O1iii91.17 (9)O2vii—Fe2—O288.96 (9)
O1ii—Fe1—O1iii180O2iii—Fe2—O291.04 (9)
O1i—Fe1—O1iv91.17 (9)O2vi—Fe2—O2viii91.04 (9)
O1—Fe1—O1iv88.83 (9)O2v—Fe2—O2viii88.96 (9)
O1ii—Fe1—O1iv91.17 (9)O2vii—Fe2—O2viii91.04 (9)
O1iii—Fe1—O1iv88.83 (9)O2iii—Fe2—O2viii88.96 (9)
O1i—Fe1—O1v88.83 (9)O2—Fe2—O2viii180
O1—Fe1—O1v91.17 (9)O1—P1—O2116.25 (15)
O1ii—Fe1—O1v88.83 (9)O1—P1—H1109.0 (13)
O1iii—Fe1—O1v91.17 (9)O2—P1—H1107.1 (14)
O1iv—Fe1—O1v180O1—P1—H2105.2 (13)
O2vi—Fe2—O2v180O2—P1—H2111.0 (12)
O2vi—Fe2—O2vii91.04 (9)H1—P1—H2108 (2)
O2v—Fe2—O2vii88.96 (9)P1—O1—Fe1133.01 (15)
O2vi—Fe2—O2iii88.96 (9)P1—O2—Fe2139.42 (15)
Symmetry codes: (i) x, y, z; (ii) y, x+y, z; (iii) y, xy, z; (iv) xy, x, z; (v) x+y, x, z; (vi) xy, x, z+1; (vii) y, x+y, z+1; (viii) x, y, z+1.

Experimental details

Crystal data
Chemical formulaFe(H2PO2)3
Mr250.81
Crystal system, space groupHexagonal, R3
Temperature (K)293
a, c (Å)11.2800 (11), 9.6375 (11)
V3)1061.97 (19)
Z6
Radiation typeMo Kα
µ (mm1)2.78
Crystal size (mm)0.08 × 0.04 × 0.02
Data collection
DiffractometerBruker–Nonius X8 APEX CCD area-detector
Absorption correctionMulti-scan
(SADABS; Bruker, 2004)
Tmin, Tmax0.808, 0.947
No. of measured, independent and
observed [I > 2σ(I)] reflections
1147, 430, 361
Rint0.034
(sin θ/λ)max1)0.602
Refinement
R[F2 > 2σ(F2)], wR(F2), S 0.030, 0.073, 1.03
No. of reflections430
No. of parameters40
No. of restraints2
H-atom treatmentAll H-atom parameters refined
Δρmax, Δρmin (e Å3)0.46, 0.39

Computer programs: APEX2 (Bruker, 2004), SAINT (Bruker, 2004), SAINT, SHELXTL (Bruker, 2004), SHELXTL and BS (Ozawa & Kang, 2004).

Selected geometric parameters (Å, º) top
Fe1—O12.000 (2)P1—O21.509 (2)
Fe2—O22.003 (2)P1—H11.38 (4)
P1—O11.506 (2)P1—H21.38 (4)
O1—Fe1—O1i180O1—P1—O2116.25 (15)
O1—Fe1—O1ii91.17 (9)H1—P1—H2108 (2)
Symmetry codes: (i) x, y, z; (ii) y, xy, z.
 

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