Ammonium dipotassium hydrogen di­fluoro­phosphate at room temperature

(NH₄)_0.926K_2.074[H(PO₃F)₂] crystallized from aqueous solution after mixing stoichiometric amounts of (NH₄)₂PO₃F and K₂PO₃F in a 1:1 ratio. The structure contains two sites that are occupied by symmetry-independent cations; one site is occupied by potassium and ammonium in an approximate 1:1 ratio, while the other cation site is occupied exclusively by K. The anions are connected by a very short symmetry-restricted O...H...O hydrogen bond (∼2.47 Å) into pairs [H(PO₃F)₂]³⁻. Ammonium is connected to anion O atoms by two- and three-centred N—H...O hydrogen bonds. Fluorines do not take part in the hydrogen-bond pattern.

Key indicators

• Single-crystal X-ray study
• T = 293 K
• Mean [sigma](P-O) = 0.001 Å
• Disorder in solvent or counterion
• R factor = 0.021
• wR factor = 0.054
• Data-to-parameter ratio = 11.9

checkCIF results

No syntax errors found

ADDSYM reports no extra symmetry


 Alert Level B:



CHEMS_01  Alert B The sum formula contains elements in the wrong order.
          H  precedes F
          Sequence must be C, H, then alphabetical.

Author response: The structure does not contain carbon. The sum formula was created according to the CIF rules.

 Alert Level C:



ABSTM_02  Alert C The ratio of expected to reported Tmax/Tmin(RR) is > 1.10
          Tmin and Tmax reported:      0.715     0.796
          Tmin and Tmax expected:      0.626     0.786
          RR =      1.129
          Please check that your absorption correction is appropriate.

PLAT_302  Alert C Anion/Solvent Disorder .......................      33.00 Perc.

General Notes



FORMU_01  There is a discrepancy between the atom counts in the
          _chemical_formula_sum and _chemical_formula_moiety. This is
          usually due to the moiety formula being in the wrong format.
          Atom count from _chemical_formula_sum:   H4.704 F2 K2.074 N0.926 O6 P
          Atom count from _chemical_formula_moiety:N0.926 P1.852


 0 Alert Level A = Potentially serious problem

 1 Alert Level B = Potential problem

 2 Alert Level C = Please check

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S1. Comment

Though the structures of K₂PO₃F (Robinson, 1958; Harrison et al., 1966; Payen et al., 1979) and (NH₄)₂PO₃F (Krupková et al., 2002) are known, no structure determination of the trioxofluorophosphate with mixed potassium and ammonium cations has been reported. The structure of (NH₄)_{2 − x}K_xPO₃F can be inferred by analogy to existing series of (NH₄)_{2 − x}K_xSO₄. On the other hand, the space groups of potassium and ammonium dihydrogensulfates at room temperature are the same (Pnam), while the space group of K₂PO₃F (Pnam) at room temperature differs from that of (NH₄)₂PO₃F (Pna2₁). The original aim of this study was the preparation and structural characterization of (NH₄)_{2 − x}K_xPO₃F. However, the compound that we isolated and studied had a different composition than we expected.

The main features of the title structure are described in the Abstract. All the H atoms could be distinguished on the difference Fourier map. Atom H1 of the symmetry-restricted O1···H1···O1 hydrogen bond was found to reside on the centre of symmetry. The hydrogen bonds are listed in Table 2. A view of the unit-cell content is given in Fig. 1.

An interesting point regards the fact that ammonium shares the same site with K2. On the other hand, the refinement showed that ammonium does not enter into the site occupied by K1. (The occupancies of K2 and ammonium are given in the CIF.) The qualitative reason is expressed by the bond-valence sums (Brese & O'Keeffe, 1991; García-Rodríguez et al., 2000). The K1 site would be too overbonded [1.453 (2)] if ammonium entered into this site exclusively; for the bond-valence sum of K1 see Table 3. On the other hand, if the site K2/N2 is assumed to be occupied by potassium only then this site would be underbonded [0.8813 (9)] in contrast to the overbonding [1.142 (1)] that is pertinent to the full occupancy of this site by ammonium. In other words, the K1 site is too small to permit ammonium to enter into this site in contrast to the site K2/N2 where optimal bonding is achieved by appropriate mixing of ammonium and potassium cations (see Table 3). The bond-valence sums were calculated using JANA2000 (Pet\vrí\vcek & Du\vsek, 2000).

We are still trying to synthesize the crystalsof (NH₄)_{2 − x}K_xPO₃F.

S2. Experimental

The title compound was prepared from the solution from which (NH₄)_{2 − x}K_xPO₃F was intended to be prepared. Stoichiometric amounts of K₂CO₃·1.5H₂O (2.13 g) and (NH₄)₂CO₃ (1.24 g) in a 1:1 ratio were neutralized with H₂PO₃F. The latter compound was prepared just before the neutralization by elution of (NH₄)₂PO₃F·H₂O (3.92 g) through the ionex amberlite-IR-120 (35 ml of the wet form). The resulting volume of the solution before crystallization was ~120 ml. The solution in a polypropylene crucible was put into the desiccator over P₄O₁₀ and within two months almost all water was removed. More phases were probably present than the phase that was studied. Plate-like crystals of the title structure were under the upper crust. The crystals were fragile and the chips had a typical triangular form. The composition determined by X-ray structure determination indicates that most probably a phase that was more rich in potassium had precipitated before the title crystals were formed.

S3. Refinement

A search in the Cambridge Structural Database (Allen, 2002) returned 348 hits of ammonium containing structures with R factors ≤ 0.05. The average ammonium N—H bond length and its s.u. given in parenthesis was thus established as 0.91 (1) Å. Assuming an ideal tetrahedral H—N—H angle, the corresponding H···H distances are 1.486 Å in the ammonium molecule. These values were applied in the SHELXL97 restraints (Sheldrick, 1997) by the instructions DFIX 0.91 0.01 N2 H2··· for N—H bond lengths and DANG 1.486 0.04 H2 H3 ···. (The value 0.04 corresponds to the assessed standard uncertainty of the pertinent distances.)

Computing details

Data collection: COLLECT (Nonius, 1997-2000); cell refinement: HKL SCALEPACK (Otwinowski & Minor, 1997); data reduction: HKL DENZO (Otwinowski & Minor, 1997) and SCALEPACK; program(s) used to solve structure: SIR97 (Cascarano et al., 1996); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: ORTEPIII (Burnett & Johnson, 1996); software used to prepare material for publication: SHELXL97.

Figures

Fig. 1. View of the title structure. Displacement ellipsoids are shown at the 30% probability level.

dipotassium ammonium hydrogen difluorophosphate

Crystal data

(H4N)0.926K2.074(HF2O6P2)	F(000) = 586.368
Mr = 294.75	Dx = 2.365 Mg m^−3
Monoclinic, C2/c	Mo Kα radiation, λ = 0.71070 Å
Hall symbol: -C 2yc	Cell parameters from 4538 reflections
a = 7.9470 (3) Å	θ = 1–27.5°
b = 11.6800 (4) Å	µ = 1.60 mm^−1
c = 9.7290 (3) Å	T = 293 K
β = 113.570 (3)°	Triangular plate, colourless
V = 827.71 (5) Å^3	0.5 × 0.25 × 0.15 mm
Z = 4

Data collection

Nonius KappaCCD diffractometer	942 independent reflections
Radiation source: fine-focus sealed tube	908 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.030
Detector resolution: 9.091 pixels mm^-1	θmax = 27.5°, θmin = 3.3°
ω scans	h = −10→10
Absorption correction: multi-scan (SORTAV; Blessing, 1997)	k = −15→15
Tmin = 0.715, Tmax = 0.796	l = −12→12
5391 measured reflections

Refinement

Refinement on F^2	Secondary atom site location: difference Fourier map
Least-squares matrix: full	Hydrogen site location: difference Fourier map
R[F^2 > 2σ(F^2)] = 0.021	H atoms treated by a mixture of independent and constrained refinement
wR(F^2) = 0.054	w = 1/[σ^2(Fo^2) + (0.0222P)^2 + 0.6144P] where P = (Fo^2 + 2Fc^2)/3
S = 1.11	(Δ/σ)max = 0.001
942 reflections	Δρmax = 0.25 e Å^−3
79 parameters	Δρmin = −0.30 e Å^−3
10 restraints	Extinction correction: SHELXL97, Fc^*=kFc[1+0.001xFc^2λ^3/sin(2θ)]^-1/4
Primary atom site location: structure-invariant direct methods	Extinction coefficient: 0.0124 (18)

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. If the most disagreeable diffractions 1 1 0; −1 1 1; 0 2 1 were omitted the occupancy of K2 was little affected: the value resulted in 0.530 (3).

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Ų)

	x	y	z	Uiso*/Ueq	Occ. (<1)
P1	0.20952 (4)	0.11763 (3)	0.67774 (4)	0.01911 (14)
K1	0.5000	0.36364 (3)	0.7500	0.02554 (15)
K2	0.40575 (7)	0.86732 (4)	0.56294 (6)	0.0315 (2)	0.537 (3)
N2	0.40575 (7)	0.86732 (4)	0.56294 (6)	0.0315 (2)	0.463 (3)
H2	0.328 (5)	0.876 (3)	0.610 (4)	0.058 (14)*	0.463 (3)
H3	0.460 (7)	0.798 (2)	0.584 (7)	0.16 (3)*	0.463 (3)
H4	0.355 (6)	0.887 (4)	0.4646 (17)	0.083 (19)*	0.463 (3)
H5	0.495 (5)	0.922 (3)	0.607 (5)	0.080 (17)*	0.463 (3)
F1	0.33434 (12)	0.13492 (8)	0.58546 (11)	0.0361 (2)
O1	0.01999 (13)	0.09842 (9)	0.55062 (12)	0.0312 (3)
O2	0.28305 (13)	0.01327 (8)	0.77045 (12)	0.0296 (3)
O3	0.22155 (13)	0.22794 (8)	0.75689 (12)	0.0295 (2)
H1	0.0000	0.0000	0.5000	0.099 (13)*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
P1	0.0187 (2)	0.0185 (2)	0.0197 (2)	−0.00152 (10)	0.00721 (14)	−0.00072 (11)
K1	0.0247 (2)	0.0241 (2)	0.0320 (3)	0.000	0.01575 (18)	0.000
K2	0.0333 (4)	0.0368 (4)	0.0242 (3)	0.00133 (19)	0.0113 (2)	0.00219 (18)
N2	0.0333 (4)	0.0368 (4)	0.0242 (3)	0.00133 (19)	0.0113 (2)	0.00219 (18)
F1	0.0367 (5)	0.0437 (5)	0.0375 (5)	0.0036 (4)	0.0249 (4)	0.0049 (4)
O1	0.0233 (5)	0.0323 (5)	0.0282 (5)	0.0010 (4)	0.0001 (4)	−0.0032 (4)
O2	0.0270 (5)	0.0242 (5)	0.0311 (5)	−0.0012 (4)	0.0049 (4)	0.0067 (4)
O3	0.0321 (5)	0.0233 (5)	0.0352 (5)	−0.0050 (4)	0.0157 (4)	−0.0078 (4)

Geometric parameters (Å, º)

P1—O3	1.4843 (10)	K2—O2^viii	2.9622 (12)
P1—O2	1.4897 (10)	K2—O2^ix	3.0834 (12)
P1—O1	1.5358 (10)	K2—O1^x	3.1366 (11)
P1—F1	1.5947 (9)	K2—F1^ix	3.1999 (10)
K1—O3^i	2.7445 (10)	K2—O1^iii	3.2848 (11)
K1—O3	2.7445 (10)	F1—K2^vii	2.9558 (10)
K1—O2^ii	2.7921 (10)	F1—K2^xi	3.1998 (10)
K1—O2^iii	2.7921 (10)	F1—K1^iv	3.2827 (10)
K1—O1^iv	2.8990 (11)	O1—K1^iv	2.8990 (11)
K1—O1^v	2.8990 (11)	O1—K2^x	3.1367 (11)
K1—F1	3.1220 (10)	O1—K2^xii	3.2848 (11)
K1—F1^i	3.1221 (10)	O1—K1^xii	3.3991 (11)
K1—F1^iv	3.2827 (10)	O1—H1	1.2356 (10)
K1—F1^v	3.2827 (10)	O2—K1^xii	2.7921 (10)
K1—O1^iii	3.3991 (11)	O2—K2^xiii	2.9058 (11)
K1—O1^ii	3.3991 (11)	O2—K2^xiv	2.9623 (12)
K2—O3^ii	2.8573 (11)	O2—K2^xi	3.0833 (12)
K2—O2^vi	2.9058 (11)	O3—K2^xv	2.8573 (11)
K2—O3^iii	2.9532 (11)	O3—K2^xii	2.9532 (11)
K2—F1^vii	2.9557 (10)	O3—K2^xiv	2.9599 (12)
K2—O3^viii	2.9599 (12)
O3—P1—O2	117.90 (6)	F1^vii—K2—O3^viii	70.51 (3)
O3—P1—O1	112.56 (6)	O3^ii—K2—O2^viii	142.78 (3)
O2—P1—O1	112.89 (6)	O2^vi—K2—O2^viii	98.02 (3)
O3—P1—F1	104.87 (5)	O3^iii—K2—O2^viii	137.95 (3)
O2—P1—F1	105.23 (5)	F1^vii—K2—O2^viii	63.95 (3)
O1—P1—F1	101.28 (6)	O3^viii—K2—O2^viii	50.96 (3)
H2—N2—H3	110 (3)	O3^ii—K2—O2^ix	68.35 (3)
H2—N2—H4	113 (3)	O2^vi—K2—O2^ix	74.45 (4)
H2—N2—H5	104 (3)	O3^iii—K2—O2^ix	107.27 (3)
H3—N2—H4	116 (4)	F1^vii—K2—O2^ix	142.23 (3)
H3—N2—H5	108 (4)	O3^viii—K2—O2^ix	135.06 (3)
H4—N2—H5	104 (3)	O2^viii—K2—O2^ix	107.45 (2)
O3^i—K1—O3	109.45 (4)	O3^ii—K2—O1^x	72.07 (3)
O3^i—K1—O2^ii	173.84 (3)	O2^vi—K2—O1^x	132.78 (3)
O3—K1—O2^ii	74.26 (3)	O3^iii—K2—O1^x	144.76 (3)
O3^i—K1—O2^iii	74.26 (3)	F1^vii—K2—O1^x	134.04 (3)
O3—K1—O2^iii	173.84 (3)	O3^viii—K2—O1^x	70.35 (3)
O3^i—K1—O1^v	113.17 (3)	O2^viii—K2—O1^x	72.97 (3)
O3—K1—O1^v	77.47 (3)	O2^ix—K2—O1^x	65.23 (3)
O3^i—K1—O1^iv	77.47 (3)	O3^ii—K2—F1^ix	113.49 (3)
O3—K1—O1^iv	113.17 (3)	O2^vi—K2—F1^ix	61.54 (3)
O2^ii—K1—O2^iii	102.50 (4)	O3^iii—K2—F1^ix	128.56 (3)
O2^ii—K1—O1^iv	96.60 (3)	F1^vii—K2—F1^ix	102.70 (2)
O2^iii—K1—O1^iv	72.17 (3)	O3^viii—K2—F1^ix	113.96 (3)
O2^ii—K1—O1^v	72.17 (3)	O2^viii—K2—F1^ix	66.83 (3)
O2^iii—K1—O1^v	96.60 (3)	O2^ix—K2—F1^ix	45.89 (2)
O1^iv—K1—O1^v	162.41 (4)	O1^x—K2—F1^ix	72.76 (3)
O3^ii—K2—O2^vi	115.03 (4)	O3^ii—K2—O1^iii	69.42 (3)
O3^ii—K2—O3^iii	73.31 (4)	O2^vi—K2—O1^iii	113.28 (3)
O2^vi—K2—O3^iii	69.56 (3)	O3^iii—K2—O1^iii	47.13 (3)
O3^ii—K2—F1^vii	141.50 (3)	F1^vii—K2—O1^iii	73.53 (3)
O2^vi—K2—F1^vii	70.89 (3)	O3^viii—K2—O1^iii	68.69 (3)
O3^iii—K2—F1^vii	74.09 (3)	O2^viii—K2—O1^iii	113.88 (3)
O3^ii—K2—O3^viii	104.42 (3)	O2^ix—K2—O1^iii	135.80 (3)
O2^vi—K2—O3^viii	138.58 (3)	O1^x—K2—O1^iii	112.59 (2)
O3^iii—K2—O3^viii	112.81 (2)	F1^ix—K2—O1^iii	174.65 (3)

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

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
N2—H2···O2^ix	0.91 (1)	2.36 (3)	3.0834 (12)	136 (3)
N2—H2···O3^ii	0.91 (1)	2.29 (4)	2.8573 (11)	120 (3)
N2—H3···O1^iii	0.90 (1)	2.43 (2)	3.2848 (11)	159 (5)
N2—H3···O3^iii	0.90 (1)	2.24 (4)	2.9532 (11)	136 (5)
N2—H4···F1^vii	0.91 (1)	2.71 (5)	2.9557 (10)	97 (3)
N2—H4···O2^viii	0.91 (1)	2.09 (2)	2.9622 (12)	160 (4)
N2—H4···O3^viii	0.91 (1)	2.30 (4)	2.9599 (12)	129 (4)
N2—H5···O2^vi	0.92 (1)	2.00 (1)	2.9058 (11)	168 (4)
N2—H5···F1^ix	0.92 (1)	2.77 (5)	3.1999 (10)	110 (3)
O1—H1···O1^xvi	1.24	1.24	2.471 (2)	180

Symmetry codes: (ii) −x+1/2, y+1/2, −z+3/2; (iii) x+1/2, y+1/2, z; (vi) −x+1, y+1, −z+3/2; (vii) −x+1, −y+1, −z+1; (viii) x, −y+1, z−1/2; (ix) x, y+1, z; (xvi) −x, −y, −z+1.