Iron(III) dihydrogenphosphate(I)

The structure of rhombohedral (R) 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 symmetry bridged by bidentate hypophosphite anions.

S1. Comment

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 Ge^IIGe^IV 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.

S2. Experimental

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.

S3. Refinement

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

Computing details

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

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)]

Crystal data

Fe(H2PO2)3	Dx = 2.353 Mg m^−3
Mr = 250.81	Mo Kα radiation, λ = 0.71073 Å
Hexagonal, R3	Cell parameters from 521 reflections
Hall symbol: -R 3	θ = 3.6–28.2°
a = 11.2800 (11) Å	µ = 2.78 mm^−1
c = 9.6375 (11) Å	T = 293 K
V = 1061.97 (19) Å^3	Prism, colourless
Z = 6	0.08 × 0.04 × 0.02 mm
F(000) = 750

Data collection

Bruker–Nonius X8 APEX CCD area-detector diffractometer	430 independent reflections
Radiation source: fine-focus sealed tube	361 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.034
Detector resolution: 25 pixels mm^-1	θmax = 25.3°, θmin = 3.6°
φ scans	h = −13→7
Absorption correction: multi-scan (SADABS; Bruker, 2004)	k = −5→13
Tmin = 0.808, Tmax = 0.947	l = −11→11
1147 measured reflections

Refinement

Refinement on F^2	Primary atom site location: structure-invariant direct methods
Least-squares matrix: full	Secondary atom site location: difference Fourier map
R[F^2 > 2σ(F^2)] = 0.030	Hydrogen site location: difference Fourier map
wR(F^2) = 0.073	All H-atom parameters refined
S = 1.03	w = 1/[σ^2(Fo^2) + (0.0377P)^2] where P = (Fo^2 + 2Fc^2)/3
430 reflections	(Δ/σ)max < 0.001
40 parameters	Δρmax = 0.46 e Å^−3
2 restraints	Δρmin = −0.39 e Å^−3

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 (Ų)

	x	y	z	Uiso*/Ueq
Fe1	0.0000	0.0000	0.0000	0.0184 (3)
Fe2	0.0000	0.0000	0.5000	0.0204 (4)
P1	0.18791 (9)	0.20062 (9)	0.24457 (9)	0.0190 (3)
O1	0.1648 (2)	0.1143 (2)	0.1173 (2)	0.0249 (6)
O2	0.1596 (2)	0.1276 (3)	0.3822 (2)	0.0285 (6)
H1	0.322 (2)	0.305 (2)	0.247 (3)	0.020 (9)*
H2	0.106 (3)	0.258 (3)	0.227 (3)	0.015 (8)*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Fe1	0.0242 (5)	0.0242 (5)	0.0067 (6)	0.0121 (2)	0.000	0.000
Fe2	0.0278 (5)	0.0278 (5)	0.0055 (6)	0.0139 (2)	0.000	0.000
P1	0.0219 (5)	0.0206 (5)	0.0124 (5)	0.0090 (4)	−0.0011 (4)	−0.0012 (4)
O1	0.0289 (13)	0.0339 (15)	0.0128 (13)	0.0164 (12)	−0.0045 (10)	−0.0069 (11)
O2	0.0307 (14)	0.0354 (16)	0.0143 (14)	0.0126 (12)	0.0022 (10)	0.0031 (11)

Geometric parameters (Å, º)

Fe1—O1	2.000 (2)	Fe2—O2^v	2.003 (2)
Fe1—O1^i	2.000 (2)	Fe2—O2^vii	2.003 (2)
Fe1—O1^ii	2.000 (2)	Fe2—O2^iii	2.003 (2)
Fe1—O1^iii	2.000 (2)	Fe2—O2^viii	2.003 (2)
Fe1—O1^iv	2.000 (2)	P1—O1	1.506 (2)
Fe1—O1^v	2.000 (2)	P1—O2	1.509 (2)
Fe2—O2	2.003 (2)	P1—H1	1.38 (4)
Fe2—O2^vi	2.003 (2)	P1—H2	1.38 (4)
O1—Fe1—O1^i	180	O2^v—Fe2—O2^iii	91.04 (9)
O1^i—Fe1—O1^ii	91.17 (9)	O2^vii—Fe2—O2^iii	180
O1—Fe1—O1^ii	88.83 (9)	O2^vi—Fe2—O2	88.96 (9)
O1^i—Fe1—O1^iii	88.83 (9)	O2^v—Fe2—O2	91.04 (9)
O1—Fe1—O1^iii	91.17 (9)	O2^vii—Fe2—O2	88.96 (9)
O1^ii—Fe1—O1^iii	180	O2^iii—Fe2—O2	91.04 (9)
O1^i—Fe1—O1^iv	91.17 (9)	O2^vi—Fe2—O2^viii	91.04 (9)
O1—Fe1—O1^iv	88.83 (9)	O2^v—Fe2—O2^viii	88.96 (9)
O1^ii—Fe1—O1^iv	91.17 (9)	O2^vii—Fe2—O2^viii	91.04 (9)
O1^iii—Fe1—O1^iv	88.83 (9)	O2^iii—Fe2—O2^viii	88.96 (9)
O1^i—Fe1—O1^v	88.83 (9)	O2—Fe2—O2^viii	180
O1—Fe1—O1^v	91.17 (9)	O1—P1—O2	116.25 (15)
O1^ii—Fe1—O1^v	88.83 (9)	O1—P1—H1	109.0 (13)
O1^iii—Fe1—O1^v	91.17 (9)	O2—P1—H1	107.1 (14)
O1^iv—Fe1—O1^v	180	O1—P1—H2	105.2 (13)
O2^vi—Fe2—O2^v	180	O2—P1—H2	111.0 (12)
O2^vi—Fe2—O2^vii	91.04 (9)	H1—P1—H2	108 (2)
O2^v—Fe2—O2^vii	88.96 (9)	P1—O1—Fe1	133.01 (15)
O2^vi—Fe2—O2^iii	88.96 (9)	P1—O2—Fe2	139.42 (15)

Symmetry codes: (i) −x, −y, −z; (ii) y, −x+y, −z; (iii) −y, x−y, z; (iv) x−y, x, −z; (v) −x+y, −x, z; (vi) x−y, x, −z+1; (vii) y, −x+y, −z+1; (viii) −x, −y, −z+1.