Ammonium iron(III) phosphate(V) fluoride, (NH4)0.5[(NH4)0.375K0.125]FePO4F, with ammonium partially substituted by potassium

Wang, L.; Zhou, Y.; Huang, Y.-X.; Mi, J.-X.

doi:10.1107/S1600536808042499

inorganic compounds

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Volume 65| Part 1| January 2009| Pages i4-i5

doi:10.1107/S1600536808042499

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Ammonium iron(III) phosphate(V) fluoride, (NH₄)_0.5[(NH₄)_0.375K_0.125]FePO₄F, with ammonium partially substituted by potassium

Lei Wang,^a Yan Zhou,^a Ya-Xi Huang ^a and Jin-Xiao Mi ^a ^*

^aDepartment of Materials Science and Engineering, College of Materials, Xiamen University, Xiamen 361005, Fujian Province, People's Republic of China
^*Correspondence e-mail: jxmi@xmu.edu.cn

(Received 28 October 2008; accepted 13 December 2008; online 20 December 2008)

The title compound, ammonium potassium iron(III) phosphate fluoride, (NH₄)_0.875K_0.125FePO₄F, is built from zigzag chains _∞¹{[FeO₄F₂]⁷⁻}, with Fe³⁺ in a distorted octahedral coordination, extending along both the [011] and [0 $[\overline{1}]$ 1] directions. These chains are made up of alternating trans-[FeO₄F₂] and cis-[FeO₄F₂] octahedra via shared F-atom corners, and are linked by PO₄ tetrahedra, resulting in an open-framework structure with channels along the [010] and [100] directions. There are two crystallographically independent ammonium sites: one in the [010] channels and the other, partially substituted by K⁺ ions, in the [100] channels. The ammonium in the [010] channels is fixed to the framework via eight hydrogen bonds (six N—H⋯O and two N—H⋯F).

Related literature

For general background, see: Hagerman & Poeppelmeier (1995 ). For related structures, see: Loiseau et al. (1994 ) for (NH₄)Fe(PO₄)F; Loiseau et al. (2000 ) for (NH₄)Ga(PO₄)F; Alda et al. (2003 ) for (NH₄)V(PO₄)F; Slovokhotova et al. (1991 ) for KAl(PO₄)F; Harrison et al. (1995 ) for KGa(PO₄)F; Matvienko et al. (1979 ) for KFe(PO₄)F; Slobodyanik et al. (1991 ) for KCr(PO₄)F; Tordjman et al. (1974 ) for K(TiO)(PO₄).

Experimental

Crystal data

(NH₄)_0.5[(NH₄)_0.375K_0.125]FePO₄F
M_r = 190.49
Orthorhombic, P n a 2₁
a = 12.9402 (4) Å
b = 6.4382 (2) Å
c = 10.6428 (3) Å
V = 886.67 (5) Å³
Z = 8
Mo Kα radiation
μ = 3.82 mm⁻¹
T = 173 (2) K
0.12 × 0.09 × 0.09 mm

Data collection

Oxford Diffraction CCD area-detector diffractometer
Absorption correction: numerical (CrysAlis RED; Oxford Diffraction, 2005 $[Oxford Diffraction (2005). CrysAlis CCD and CrysAlis RED. Oxford Diffraction, Abingdon, England.]$ ) T_min = 0.657, T_max = 0.725
5371 measured reflections
2162 independent reflections
1636 reflections with I > 2σ(I)
R_int = 0.040

Refinement

R[F² > 2σ(F²)] = 0.031
wR(F²) = 0.054
S = 0.88
2162 reflections
155 parameters
5 restraints
H-atom parameters constrained
Δρ_max = 0.52 e Å⁻³
Δρ_min = −0.56 e Å⁻³

Table 1
Selected geometric parameters (Å, °)

Fe1—O5ⁱ	1.893 (4)
Fe1—O6	1.955 (4)
Fe1—O8ⁱⁱ	1.963 (4)
Fe1—F1ⁱ	1.988 (4)
Fe1—F2	2.010 (4)
Fe1—O7	2.088 (4)
Fe2—F2	1.936 (4)
Fe2—O3	1.944 (5)
Fe2—O1	1.986 (5)
Fe2—F1	2.001 (4)
Fe2—O2	2.003 (4)
Fe2—O4	2.055 (3)
P1—O1ⁱ	1.531 (5)
P1—O7	1.532 (4)
P1—O6ⁱⁱⁱ	1.538 (4)
P1—O3ⁱⁱⁱ	1.551 (5)
P2—O2	1.530 (4)
P2—O8	1.533 (5)
P2—O4^iv	1.539 (4)
P2—O5	1.547 (5)
Symmetry codes: (i) $[-x+{\script{1\over 2}}, y+{\script{1\over 2}}, z+{\script{1\over 2}}]$ ; (ii) $[x-{\script{1\over 2}}, -y+{\script{1\over 2}}, z]$ ; (iii) x, y+1, z; (iv) $[x+{\script{1\over 2}}, -y+{\script{1\over 2}}, z]$ .

Table 2
Hydrogen-bond geometry (Å, °)

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
N2—H1⋯F1ⁱ	0.86 (4)	2.37 (5)	3.079 (6)	140 (4)
N2—H1⋯O4ⁱ	0.86 (4)	2.39 (3)	3.124 (6)	144 (4)
N2—H1⋯O1ⁱ	0.86 (4)	2.54 (5)	3.159 (7)	130 (4)
N2—H2⋯O2	0.87 (4)	2.13 (4)	2.956 (6)	159 (4)
N2—H2⋯F2	0.87 (4)	2.22 (5)	2.744 (6)	118 (4)
N2—H3⋯O8ⁱⁱⁱ	0.85 (4)	2.29 (5)	2.775 (6)	117 (4)
N2—H3⋯O3ⁱⁱⁱ	0.85 (4)	2.39 (5)	3.088 (7)	139 (4)
N2—H4⋯O7^vii	0.84 (3)	2.06 (3)	2.823 (5)	151 (4)
Symmetry codes: (i) $[-x+{\script{1\over 2}}, y+{\script{1\over 2}}, z+{\script{1\over 2}}]$ ; (iii) x, y+1, z; (vii) $[x+{\script{1\over 2}}, -y+{\script{3\over 2}}, z]$ .

Data collection: CrysAlis CCD (Oxford Diffraction, 2005 $[Oxford Diffraction (2005). CrysAlis CCD and CrysAlis RED. Oxford Diffraction, Abingdon, England.]$ ); cell refinement: CrysAlis CCD; data reduction: CrysAlis RED (Oxford Diffraction, 2005 $[Oxford Diffraction (2005). CrysAlis CCD and CrysAlis RED. Oxford Diffraction, Abingdon, England.]$ ); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008 ); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: DIAMOND (Brandenburg, 2005 ) and ATOMS (Dowty, 2004 ); software used to prepare material for publication: SHELXL97.

Supporting information

Crystal structure: contains datablocks I, global. DOI: 10.1107/S1600536808042499/fi2066sup1.cif

Structure factors: contains datablock I. DOI: 10.1107/S1600536808042499/fi2066Isup2.hkl

checkCIF report

Comment top

Compounds of the KTiOPO₄ (KTP) group have attracted great attention in the past decades owing to their non-linear optical properties, and became a large family of compositions with formula MM'OXO₄ (M = Na, K, Rb, Cs or Tl; M' = Ti, Ge, Sn and X = P or As), where M and M' can be partially replaced by two or more different cations (Hagerman et al., 1995). Tetravalent M' ions can be replaced by trivalent ions such as Fe³⁺ and Cr³⁺ with oxygen being substituted simultaneously by fluorine for charge balance. Many examples of fluorophosphates with the KTP-type structure are known, such as (NH₄)Fe(PO₄)F, (NH₄)Ga(PO₄)F (Loiseau et al., 1994, 2000 ), and (NH₄)V(PO₄)F (Alda et al., 2003) in the ammonium series, and KAl(PO₄)F (Slovokhotova et al., 1991), KGa(PO₄)F (Harrison et al., 1995), KFe(PO₄)F (Matvienko et al., 1979), and KCr(PO₄)F (Slobodyanik et al., 1991) in the potassium series. However, to the best of our knowledge, sodium fluorophosphate compounds with the KTP-type structure have not been reported to date. Our attempt to synthesize KTP-type sodium fluorophophates failed as well, instead we obtained a solid-solution ammonium fluorophosphate, (NH₄)((NH₄)_0.75K_0.25)[Fe₂(PO₄)₂F₂], partially substituted by potassium.

The crystal structure of the title compound is built from one-dimensional zigzag ferric octahedral chains _∞¹{[FeO₄F₂]^7-} (see Fig. 1) linked by PO₄ tetrahedra via common O-corners, resulting in a three dimensional open framework structure (see Fig.2). The zigzag ferric octahedral chains are made up of alternating trans-[FeO₄F₂] and cis-[FeO₄F₂] octahedra via common fluorine-corners, and are along both [011] and [0-11] directions. Each PO₄ tetrahedron shares all oxygen corners with four neighboring [FeO₄F₂] octahedra, and each [FeO₄F₂] octahedron shares its four oxygen atoms with four PO₄ tetrahedra. The negative charge of the framework is compensated by ammonium ions and potassium cations. Two crystallographically independent ammonium sites are found. One resides in the channels along [010], linking to the framework via hydrogen bonds (N-H···O(F)). If this ammonium ion is considered as a normal cation, its coordination number is 8 with an average bond distance of 2.969Å (i.e., to neighboring oxygen and fluorine atoms). The other ammonium site, partially occupied by K⁺ ions, resides in the channels along [100]. The potassium (ammonium) has a coordination number of 8 with a mean bond distance of 2.882Å. Therefore, the ammonium site in the [010] channels is slightly larger in size than its counterpart in the [100] channels. Consequently, potassium ions preferentially substitute for the ammonium ions in the [100] channels. We suggest that the potassium-to-ammonium ratio in the title compound is controlled by the size effect. It is possible that the size effect in hydrothermally synthesized crystals at lower temperatures is more pronounced than those from a solid state reaction route.

Related literature top

For general background, see: Hagerman & Poeppelmeier (1995). For related structures, see: Loiseau et al. (1994) for (NH₄)Fe(PO₄)F; Loiseau et al. (2000) for (NH₄)Ga(PO₄)F; Alda et al. (2003) for (NH₄)V(PO₄)F; Slovokhotova et al. (1991) for KAl(PO₄)F; Harrison et al. (1995) for KGa(PO₄)F; Matvienko et al. (1979) for KFe(PO₄)F; Slobodyanik et al. (1991) for KCr(PO₄)F; Tordjman et al. (1974) for K(TiO)(PO₄).

Experimental top

Transparent, colorless single crystals of the title compound were synthesized hydrothermally. A mixture of 0.055 g NaBF₄, 1.035 g NH₄H₂PO₄, 0.342 g NH₄HF₂ and 0.048 g Fe₂O₃ in an approximate molar ratio of Na: NH₄: P: Fe = 0.5: 15: 9: 6, was dissolved in 9 ml distilled water while stirring. The prepared solution was transferred to a Teflon-lined stainless steel autoclave (internal volume 30 ml, degree of filling 33%) and held at 453 K for three days under autogenous pressure. Then the autoclave was cooled to room temperature by turning off the power. Products were filtered off, washed with distilled water and dried at room temperature. The presence of potassium in the crystal that was used for single crystal X-ray data collection, was determined by semi-quantitative chemical analysis on an Oxford Instruments Energy Dispersive Spectrometer(EDS)(calcd K: 2.56 %, Obsd K: ~3%). Sodium was not detectable in the crystal by EDS. It is supposed that potassium should be introduced into the sample as impurities in the reagents.

Computing details top

Data collection: CrysAlis CCD (Oxford Diffraction, 2005); cell refinement: CrysAlis CCD (Oxford Diffraction, 2005); data reduction: CrysAlis RED (Oxford Diffraction, 2005); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: DIAMOND (Brandenburg, 2005) and ATOMS (Dowty, 2004); software used to prepare material for publication: SHELXL97 (Sheldrick, 2008).

Figures top

	Fig. 1. Unit cell of (NH₄)((NH₄)_0.75K_0.25) [Fe₂(PO₄)₂F₂] in a view along b. Trans-[FeO₄F₂], in blue octahedra; cis-[FeO₄F₂], in pink octahedra; PO₄, in red tetrahedra; black spheres: disordered K/NH₄; green spheres: NH₄.
	Fig. 2. Left: (1). Coordination environment of eight coordinated potassium/ammonium ions(upper); (2). Coordination environment of ammonium ions via hydrogen bonds(down).Right: chains built up of alternate trans-[FeO₄F₂] and cis-[FeO₄F₂] octahedra running along [011] and [0-11] respectively;
	Fig. 3. Coordination environment of Fe and P atoms, with displacement ellipsoids drawn at the 50% probability level (symmetry codes: (i) x, 1+y, z; (ii) 1/2-x, 1/2+y, 1/2+z; (iii) -1/2+x, 1/2-y, z; (iv) 1/2+x, 1/2-y, z).

Ammonium iron(III) phosphate(V) fluoride top

Crystal data top

(NH₄)_0.875K_0.125FePO₄F	F(000) = 752
M_r = 190.49	D_x = 2.854 Mg m⁻³
Orthorhombic, Pna2₁	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: P 2c -2n	Cell parameters from 5001 reflections
a = 12.9402 (4) Å	θ = 3.0–32.5°
b = 6.4382 (2) Å	µ = 3.82 mm⁻¹
c = 10.6428 (3) Å	T = 173 K
V = 886.67 (5) Å³	Prism, colorless
Z = 8	0.12 × 0.09 × 0.09 mm

Data collection top

Oxford Diffraction CCD area-detector diffractometer	2162 independent reflections
Radiation source: fine-focus sealed tube	1636 reflections with I > 2σ(I)
Graphite monochromator	R_int = 0.040
326 images,Δω=1°, Exp time: 40 s. scans	θ_max = 32.5°, θ_min = 2.5°
Absorption correction: numerical (CrysAlis RED; Oxford Diffraction, 2005)	h = −19→16
T_min = 0.657, T_max = 0.725	k = −4→9
5371 measured reflections	l = −10→16

Refinement top

Refinement on F²	Primary atom site location: structure-invariant direct methods
Least-squares matrix: full	Secondary atom site location: difference Fourier map
R[F² > 2σ(F²)] = 0.031	Hydrogen site location: inferred from neighbouring sites
wR(F²) = 0.054	H-atom parameters constrained
S = 0.88	w = 1/[σ²(F_o²) + (0.0164P)²] where P = (F_o² + 2F_c²)/3
2162 reflections	(Δ/σ)_max < 0.001
155 parameters	Δρ_max = 0.52 e Å⁻³
5 restraints	Δρ_min = −0.56 e Å⁻³

Crystal data top

(NH₄)_0.875K_0.125FePO₄F	V = 886.67 (5) Å³
M_r = 190.49	Z = 8
Orthorhombic, Pna2₁	Mo Kα radiation
a = 12.9402 (4) Å	µ = 3.82 mm⁻¹
b = 6.4382 (2) Å	T = 173 K
c = 10.6428 (3) Å	0.12 × 0.09 × 0.09 mm

Data collection top

Oxford Diffraction CCD area-detector diffractometer	2162 independent reflections
Absorption correction: numerical (CrysAlis RED; Oxford Diffraction, 2005)	1636 reflections with I > 2σ(I)
T_min = 0.657, T_max = 0.725	R_int = 0.040
5371 measured reflections

Refinement top

R[F² > 2σ(F²)] = 0.031	5 restraints
wR(F²) = 0.054	H-atom parameters constrained
S = 0.88	Δρ_max = 0.52 e Å⁻³
2162 reflections	Δρ_min = −0.56 e Å⁻³
155 parameters

Special details top

Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds 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 > 2sigma(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. The crystal structure of the title compound was refined by a inversion twin matrix so the Flack parameter is equal to zero.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å²) top

	x	y	z	U_iso*/U_eq	Occ. (<1)
Fe1	0.11299 (4)	0.48776 (11)	0.41908 (14)	0.00427 (10)
Fe2	0.25117 (7)	0.25076 (13)	0.16711 (14)	0.00434 (9)
K1	0.1161 (2)	0.7780 (4)	0.1155 (3)	0.0243 (9)	0.249 (5)
N1	0.1161 (2)	0.7780 (4)	0.1155 (3)	0.0243 (9)	0.75
N2	0.4008 (3)	0.6749 (6)	0.3543 (4)	0.0094 (7)
P1	0.18531 (6)	0.9964 (2)	0.4152 (2)	0.00453 (15)
P2	0.49699 (14)	0.17105 (12)	0.1701 (2)	0.00426 (15)
F1	0.2694 (3)	0.0303 (7)	0.0365 (3)	0.0067 (8)
F2	0.2233 (3)	0.4707 (7)	0.2864 (3)	0.0070 (8)
O1	0.2426 (3)	0.4522 (9)	0.0261 (4)	0.0082 (9)
O2	0.4023 (3)	0.3113 (6)	0.1847 (4)	0.0075 (8)
O3	0.2540 (3)	0.0417 (9)	0.2989 (4)	0.0076 (9)
O4	0.0953 (3)	0.1996 (6)	0.1474 (4)	0.0056 (8)
O5	0.4803 (4)	0.0316 (8)	0.0535 (3)	0.0095 (9)
O6	0.1173 (3)	0.1868 (5)	0.4430 (4)	0.0069 (8)
O7	0.1172 (3)	0.8075 (5)	0.3867 (4)	0.0061 (8)
O8	0.5104 (3)	0.0264 (8)	0.2834 (3)	0.0057 (9)*
H1	0.372 (3)	0.678 (8)	0.427 (3)	0.020 (7)*
H2	0.386 (4)	0.580 (7)	0.299 (4)	0.020 (7)*
H3	0.385 (4)	0.780 (6)	0.310 (4)	0.020 (7)*
H4	0.462 (2)	0.634 (8)	0.365 (5)	0.020 (7)*

Atomic displacement parameters (Å²) top

	U¹¹	U²²	U³³	U¹²	U¹³	U²³
Fe1	0.0045 (2)	0.0046 (2)	0.00376 (18)	0.0002 (3)	−0.0004 (5)	0.0001 (2)
Fe2	0.00452 (18)	0.00472 (17)	0.00377 (17)	0.00037 (17)	0.00040 (18)	0.0003 (2)
K1	0.0311 (16)	0.0146 (14)	0.0271 (14)	−0.0069 (11)	0.0077 (11)	−0.0039 (10)
N1	0.0311 (16)	0.0146 (14)	0.0271 (14)	−0.0069 (11)	0.0077 (11)	−0.0039 (10)
N2	0.0038 (17)	0.0161 (18)	0.0083 (17)	−0.0023 (15)	0.0024 (14)	0.0011 (15)
P1	0.0048 (4)	0.0048 (3)	0.0039 (4)	−0.0008 (6)	−0.0017 (9)	0.0010 (3)
P2	0.0041 (4)	0.0046 (3)	0.0041 (3)	−0.0001 (6)	−0.0001 (3)	−0.0030 (7)
F1	0.0066 (18)	0.0067 (14)	0.0070 (16)	−0.0007 (14)	0.0021 (13)	−0.0002 (13)
F2	0.0077 (18)	0.0096 (15)	0.0037 (15)	−0.0016 (15)	0.0019 (13)	−0.0036 (13)
F1	0.0066 (18)	0.0067 (14)	0.0070 (16)	−0.0007 (14)	0.0021 (13)	−0.0002 (13)
F2	0.0077 (18)	0.0096 (15)	0.0037 (15)	−0.0016 (15)	0.0019 (13)	−0.0036 (13)
O1	0.008 (2)	0.0123 (18)	0.0045 (19)	0.0027 (19)	0.0029 (15)	0.0042 (17)
O2	0.005 (2)	0.0119 (15)	0.005 (2)	−0.0012 (15)	0.0027 (18)	0.0014 (15)
O3	0.007 (2)	0.0091 (18)	0.0067 (19)	0.0002 (18)	0.0000 (14)	0.0012 (17)
O4	0.0036 (19)	0.0049 (14)	0.008 (2)	0.0006 (13)	−0.0034 (17)	0.0000 (14)
O5	0.0102 (18)	0.0095 (15)	0.0089 (16)	0.0032 (14)	−0.0035 (12)	−0.0052 (11)
O6	0.0095 (18)	0.0063 (13)	0.005 (2)	0.0009 (17)	0.0009 (19)	0.0017 (13)
O7	0.0070 (17)	0.0053 (13)	0.006 (2)	0.0005 (16)	−0.0013 (19)	−0.0034 (12)

Geometric parameters (Å, º) top

Fe1—O5ⁱ	1.893 (4)	N2—O7^iv	2.823 (5)
Fe1—O6	1.955 (4)	N2—O2	2.956 (6)
Fe1—O8ⁱⁱ	1.963 (4)	N2—F1ⁱ	3.079 (6)
Fe1—F1ⁱ	1.988 (4)	N2—O3ⁱⁱⁱ	3.088 (7)
Fe1—F2	2.010 (4)	N2—O4ⁱ	3.124 (6)
Fe1—O7	2.088 (4)	N2—O1ⁱ	3.159 (7)
Fe2—F2	1.936 (4)	P1—O1ⁱ	1.531 (5)
Fe2—O3	1.944 (5)	P1—O7	1.532 (4)
Fe2—O1	1.986 (5)	P1—O6ⁱⁱⁱ	1.538 (4)
Fe2—F1	2.001 (4)	P1—O3ⁱⁱⁱ	1.551 (5)
Fe2—O2	2.003 (4)	P2—O2	1.530 (4)
Fe2—O4	2.055 (3)	P2—O8	1.533 (5)
K1—F1ⁱⁱⁱ	2.697 (5)	P2—O4^v	1.539 (4)
K1—O5ⁱⁱ	2.739 (6)	P2—O5	1.547 (5)
K1—O4ⁱⁱⁱ	2.749 (4)	F1—Fe1^vi	1.988 (4)
K1—O1	2.825 (6)	F1—K1^vii	2.697 (5)
K1—O7	2.893 (5)	O1—P1^vi	1.531 (5)
K1—O8ⁱⁱ	2.985 (5)	O3—P1^vii	1.551 (5)
K1—F2	3.025 (5)	O3—K1^vii	3.142 (6)
K1—O3ⁱⁱⁱ	3.142 (6)	O4—P2ⁱⁱ	1.539 (4)
N2—H1	0.86 (2)	O4—K1^vii	2.749 (4)
N2—H2	0.87 (2)	O5—Fe1^vi	1.893 (4)
N2—H3	0.85 (2)	O5—K1^v	2.739 (6)
N2—H4	0.84 (2)	O6—P1^vii	1.538 (4)
N2—F2	2.744 (6)	O8—Fe1^v	1.963 (4)
N2—O8ⁱⁱⁱ	2.775 (6)	O8—K1^v	2.985 (5)

O5ⁱ—Fe1—O6	93.9 (2)	F1ⁱⁱⁱ—K1—O3ⁱⁱⁱ	56.70 (12)
O5ⁱ—Fe1—O8ⁱⁱ	97.58 (10)	O5ⁱⁱ—K1—O3ⁱⁱⁱ	155.13 (16)
O6—Fe1—O8ⁱⁱ	94.0 (2)	O4ⁱⁱⁱ—K1—O3ⁱⁱⁱ	56.31 (13)
O5ⁱ—Fe1—F1ⁱ	89.56 (19)	O1—K1—O3ⁱⁱⁱ	106.34 (16)
O6—Fe1—F1ⁱ	91.87 (18)	O7—K1—O3ⁱⁱⁱ	48.85 (13)
O8ⁱⁱ—Fe1—F1ⁱ	170.45 (17)	O8ⁱⁱ—K1—O3ⁱⁱⁱ	104.06 (15)
O5ⁱ—Fe1—F2	172.51 (19)	F2—K1—O3ⁱⁱⁱ	73.71 (16)
O6—Fe1—F2	90.97 (18)	H1—N2—H2	122 (5)
O8ⁱⁱ—Fe1—F2	87.76 (17)	H1—N2—H3	112 (5)
F1ⁱ—Fe1—F2	84.57 (10)	H2—N2—H3	98 (5)
O5ⁱ—Fe1—O7	89.7 (2)	H1—N2—H4	107 (5)
O6—Fe1—O7	176.27 (15)	H2—N2—H4	95 (5)
O8ⁱⁱ—Fe1—O7	86.68 (19)	H3—N2—H4	124 (5)
F1ⁱ—Fe1—O7	87.03 (17)	O1ⁱ—P1—O7	110.8 (3)
F2—Fe1—O7	85.37 (17)	O1ⁱ—P1—O6ⁱⁱⁱ	110.4 (3)
F2—Fe2—O3	92.1 (2)	O7—P1—O6ⁱⁱⁱ	109.98 (13)
F2—Fe2—O1	90.43 (16)	O1ⁱ—P1—O3ⁱⁱⁱ	107.56 (14)
O3—Fe2—O1	176.3 (3)	O7—P1—O3ⁱⁱⁱ	108.7 (3)
F2—Fe2—F1	175.3 (2)	O6ⁱⁱⁱ—P1—O3ⁱⁱⁱ	109.4 (3)
O3—Fe2—F1	90.44 (16)	O2—P2—O8	111.7 (3)
O1—Fe2—F1	86.9 (2)	O2—P2—O4^v	111.00 (12)
F2—Fe2—O2	88.75 (18)	O8—P2—O4^v	111.0 (2)
O3—Fe2—O2	92.82 (18)	O2—P2—O5	108.2 (3)
O1—Fe2—O2	89.87 (19)	O8—P2—O5	107.11 (13)
F1—Fe2—O2	95.06 (17)	O4^v—P2—O5	107.7 (3)
F2—Fe2—O4	90.05 (17)	Fe1^vi—F1—Fe2	128.6 (2)
O3—Fe2—O4	88.90 (18)	Fe1^vi—F1—K1^vii	132.5 (2)
O1—Fe2—O4	88.46 (18)	Fe2—F1—K1^vii	97.14 (16)
F1—Fe2—O4	86.05 (18)	Fe2—F2—Fe1	129.3 (2)
O2—Fe2—O4	177.9 (2)	Fe2—F2—K1	99.74 (15)
F1ⁱⁱⁱ—K1—O5ⁱⁱ	146.65 (16)	Fe1—F2—K1	93.52 (16)
F1ⁱⁱⁱ—K1—O4ⁱⁱⁱ	61.07 (13)	P1^vi—O1—Fe2	132.1 (3)
O5ⁱⁱ—K1—O4ⁱⁱⁱ	133.26 (16)	P1^vi—O1—K1	118.3 (3)
F1ⁱⁱⁱ—K1—O1	85.20 (17)	Fe2—O1—K1	105.24 (19)
O5ⁱⁱ—K1—O1	75.57 (15)	P2—O2—Fe2	131.1 (2)
O4ⁱⁱⁱ—K1—O1	146.27 (16)	P1^vii—O3—Fe2	134.0 (3)
F1ⁱⁱⁱ—K1—O7	105.53 (14)	P1^vii—O3—K1^vii	94.0 (2)
O5ⁱⁱ—K1—O7	106.92 (14)	Fe2—O3—K1^vii	85.15 (16)
O4ⁱⁱⁱ—K1—O7	79.17 (13)	P2ⁱⁱ—O4—Fe2	135.1 (2)
O1—K1—O7	112.44 (15)	P2ⁱⁱ—O4—K1^vii	129.4 (2)
F1ⁱⁱⁱ—K1—O8ⁱⁱ	156.77 (16)	Fe2—O4—K1^vii	94.26 (14)
O5ⁱⁱ—K1—O8ⁱⁱ	51.09 (8)	P2—O5—Fe1^vi	141.5 (3)
O4ⁱⁱⁱ—K1—O8ⁱⁱ	121.95 (15)	P2—O5—K1^v	98.0 (2)
O1—K1—O8ⁱⁱ	88.83 (16)	Fe1^vi—O5—K1^v	118.9 (2)
O7—K1—O8ⁱⁱ	56.47 (12)	P1^vii—O6—Fe1	141.4 (3)
F1ⁱⁱⁱ—K1—F2	104.14 (16)	P1—O7—Fe1	139.9 (2)
O5ⁱⁱ—K1—F2	87.88 (16)	P1—O7—K1	104.6 (2)
O4ⁱⁱⁱ—K1—F2	128.06 (15)	Fe1—O7—K1	95.74 (14)
O1—K1—F2	56.72 (12)	P2—O8—Fe1^v	133.1 (3)
O7—K1—F2	55.97 (11)	P2—O8—K1^v	88.85 (19)
O8ⁱⁱ—K1—F2	54.57 (13)	Fe1^v—O8—K1^v	95.74 (18)

Symmetry codes: (i) −x+1/2, y+1/2, z+1/2; (ii) x−1/2, −y+1/2, z; (iii) x, y+1, z; (iv) x+1/2, −y+3/2, z; (v) x+1/2, −y+1/2, z; (vi) −x+1/2, y−1/2, z−1/2; (vii) x, y−1, z.

Hydrogen-bond geometry (Å, º) top

D—H···A	D—H	H···A	D···A	D—H···A
N2—H1···F1ⁱ	0.86 (4)	2.37 (5)	3.079 (6)	140 (4)
N2—H1···O4ⁱ	0.86 (4)	2.39 (3)	3.124 (6)	144 (4)
N2—H1···O1ⁱ	0.86 (4)	2.54 (5)	3.159 (7)	130 (4)
N2—H2···O2	0.87 (4)	2.13 (4)	2.956 (6)	159 (4)
N2—H2···F2	0.87 (4)	2.22 (5)	2.744 (6)	118 (4)
N2—H3···O8ⁱⁱⁱ	0.85 (4)	2.29 (5)	2.775 (6)	117 (4)
N2—H3···O3ⁱⁱⁱ	0.85 (4)	2.39 (5)	3.088 (7)	139 (4)
N2—H4···O7^iv	0.84 (3)	2.06 (3)	2.823 (5)	151 (4)

Symmetry codes: (i) −x+1/2, y+1/2, z+1/2; (iii) x, y+1, z; (iv) x+1/2, −y+3/2, z.

Experimental details

Crystal data
Chemical formula	(NH₄)_0.875K_0.125FePO₄F
M_r	190.49
Crystal system, space group	Orthorhombic, Pna2₁
Temperature (K)	173
a, b, c (Å)	12.9402 (4), 6.4382 (2), 10.6428 (3)
V (Å³)	886.67 (5)
Z	8
Radiation type	Mo Kα
µ (mm⁻¹)	3.82
Crystal size (mm)	0.12 × 0.09 × 0.09

Data collection
Diffractometer	Oxford Diffraction CCD area-detector diffractometer
Absorption correction	Numerical (CrysAlis RED; Oxford Diffraction, 2005)
T_min, T_max	0.657, 0.725
No. of measured, independent and observed [I > 2σ(I)] reflections	5371, 2162, 1636
R_int	0.040
(sin θ/λ)_max (Å⁻¹)	0.757

Refinement
R[F² > 2σ(F²)], wR(F²), S	0.031, 0.054, 0.88
No. of reflections	2162
No. of parameters	155
No. of restraints	5
H-atom treatment	H-atom parameters constrained
Δρ_max, Δρ_min (e Å⁻³)	0.52, −0.56

Computer programs: CrysAlis CCD (Oxford Diffraction, 2005), CrysAlis RED (Oxford Diffraction, 2005), SHELXS97 (Sheldrick, 2008), SHELXL97 (Sheldrick, 2008), DIAMOND (Brandenburg, 2005) and ATOMS (Dowty, 2004).

Selected geometric parameters (Å, º) top

Fe1—O5ⁱ	1.893 (4)	K1—O4ⁱⁱⁱ	2.749 (4)
Fe1—O6	1.955 (4)	K1—O1	2.825 (6)
Fe1—O8ⁱⁱ	1.963 (4)	K1—O7	2.893 (5)
Fe1—F1ⁱ	1.988 (4)	K1—O8ⁱⁱ	2.985 (5)
Fe1—F2	2.010 (4)	K1—F2	3.025 (5)
Fe1—O7	2.088 (4)	K1—O3ⁱⁱⁱ	3.142 (6)
Fe2—F2	1.936 (4)	P1—O1ⁱ	1.531 (5)
Fe2—O3	1.944 (5)	P1—O7	1.532 (4)
Fe2—O1	1.986 (5)	P1—O6ⁱⁱⁱ	1.538 (4)
Fe2—F1	2.001 (4)	P1—O3ⁱⁱⁱ	1.551 (5)
Fe2—O2	2.003 (4)	P2—O2	1.530 (4)
Fe2—O4	2.055 (3)	P2—O8	1.533 (5)
K1—F1ⁱⁱⁱ	2.697 (5)	P2—O4^iv	1.539 (4)
K1—O5ⁱⁱ	2.739 (6)	P2—O5	1.547 (5)

Fe1^v—F1—Fe2	128.6 (2)	P2ⁱⁱ—O4—Fe2	135.1 (2)
Fe2—F2—Fe1	129.3 (2)	P2—O5—Fe1^v	141.5 (3)
P1^v—O1—Fe2	132.1 (3)	P1^vi—O6—Fe1	141.4 (3)
P2—O2—Fe2	131.1 (2)	P1—O7—Fe1	139.9 (2)
P1^vi—O3—Fe2	134.0 (3)	P2—O8—Fe1^iv	133.1 (3)

Symmetry codes: (i) −x+1/2, y+1/2, z+1/2; (ii) x−1/2, −y+1/2, z; (iii) x, y+1, z; (iv) x+1/2, −y+1/2, z; (v) −x+1/2, y−1/2, z−1/2; (vi) x, y−1, z.

Hydrogen-bond geometry (Å, º) top

D—H···A	D—H	H···A	D···A	D—H···A
N2—H1···F1ⁱ	0.86 (4)	2.37 (5)	3.079 (6)	140 (4)
N2—H1···O4ⁱ	0.86 (4)	2.39 (3)	3.124 (6)	144 (4)
N2—H1···O1ⁱ	0.86 (4)	2.54 (5)	3.159 (7)	130 (4)
N2—H2···O2	0.87 (4)	2.13 (4)	2.956 (6)	159 (4)
N2—H2···F2	0.87 (4)	2.22 (5)	2.744 (6)	118 (4)
N2—H3···O8ⁱⁱⁱ	0.85 (4)	2.29 (5)	2.775 (6)	117 (4)
N2—H3···O3ⁱⁱⁱ	0.85 (4)	2.39 (5)	3.088 (7)	139 (4)
N2—H4···O7^vii	0.84 (3)	2.06 (3)	2.823 (5)	151 (4)

Symmetry codes: (i) −x+1/2, y+1/2, z+1/2; (iii) x, y+1, z; (vii) x+1/2, −y+3/2, z.

Acknowledgements

This project was supported by the Fund of the National Natural Science Foundation of China (No. 40472027).

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