(NH
4)
0.926K
2.074[H(PO
3F)
2] crystallized from aqueous solution after mixing stoichiometric amounts of (NH
4)
2PO
3F and K
2PO
3F 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(PO
3F)
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.
Supporting information
Key indicators
- Single-crystal X-ray study
- T = 293 K
- Mean (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
The title compound was prepared from the solution from which (NH4)2 − xKxPO3F 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.
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.)
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.
dipotassium ammonium hydrogen difluorophosphate
top
Crystal data top
(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) Å3 | 0.5 × 0.25 × 0.15 mm |
Z = 4 | |
Data collection top
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 top
Refinement on F2 | Secondary atom site location: difference Fourier map |
Least-squares matrix: full | Hydrogen site location: difference Fourier map |
R[F2 > 2σ(F2)] = 0.021 | H atoms treated by a mixture of independent and constrained refinement |
wR(F2) = 0.054 | w = 1/[σ2(Fo2) + (0.0222P)2 + 0.6144P] where P = (Fo2 + 2Fc2)/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+0.001xFc2λ3/sin(2θ)]-1/4 |
Primary atom site location: structure-invariant direct methods | Extinction coefficient: 0.0124 (18) |
Crystal data top
(H4N)0.926K2.074(HF2O6P2) | V = 827.71 (5) Å3 |
Mr = 294.75 | Z = 4 |
Monoclinic, C2/c | Mo Kα radiation |
a = 7.9470 (3) Å | µ = 1.60 mm−1 |
b = 11.6800 (4) Å | T = 293 K |
c = 9.7290 (3) Å | 0.5 × 0.25 × 0.15 mm |
β = 113.570 (3)° | |
Data collection top
Nonius KappaCCD diffractometer | 942 independent reflections |
Absorption correction: multi-scan (SORTAV; Blessing, 1997) | 908 reflections with I > 2σ(I) |
Tmin = 0.715, Tmax = 0.796 | Rint = 0.030 |
5391 measured reflections | |
Refinement top
R[F2 > 2σ(F2)] = 0.021 | 10 restraints |
wR(F2) = 0.054 | H atoms treated by a mixture of independent and constrained refinement |
S = 1.11 | Δρmax = 0.25 e Å−3 |
942 reflections | Δρmin = −0.30 e Å−3 |
79 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. 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 (Å2) top | 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 (Å2) top | U11 | U22 | U33 | U12 | U13 | U23 |
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) top
P1—O3 | 1.4843 (10) | K2—O2viii | 2.9622 (12) |
P1—O2 | 1.4897 (10) | K2—O2ix | 3.0834 (12) |
P1—O1 | 1.5358 (10) | K2—O1x | 3.1366 (11) |
P1—F1 | 1.5947 (9) | K2—F1ix | 3.1999 (10) |
K1—O3i | 2.7445 (10) | K2—O1iii | 3.2848 (11) |
K1—O3 | 2.7445 (10) | F1—K2vii | 2.9558 (10) |
K1—O2ii | 2.7921 (10) | F1—K2xi | 3.1998 (10) |
K1—O2iii | 2.7921 (10) | F1—K1iv | 3.2827 (10) |
K1—O1iv | 2.8990 (11) | O1—K1iv | 2.8990 (11) |
K1—O1v | 2.8990 (11) | O1—K2x | 3.1367 (11) |
K1—F1 | 3.1220 (10) | O1—K2xii | 3.2848 (11) |
K1—F1i | 3.1221 (10) | O1—K1xii | 3.3991 (11) |
K1—F1iv | 3.2827 (10) | O1—H1 | 1.2356 (10) |
K1—F1v | 3.2827 (10) | O2—K1xii | 2.7921 (10) |
K1—O1iii | 3.3991 (11) | O2—K2xiii | 2.9058 (11) |
K1—O1ii | 3.3991 (11) | O2—K2xiv | 2.9623 (12) |
K2—O3ii | 2.8573 (11) | O2—K2xi | 3.0833 (12) |
K2—O2vi | 2.9058 (11) | O3—K2xv | 2.8573 (11) |
K2—O3iii | 2.9532 (11) | O3—K2xii | 2.9532 (11) |
K2—F1vii | 2.9557 (10) | O3—K2xiv | 2.9599 (12) |
K2—O3viii | 2.9599 (12) | | |
| | | |
O3—P1—O2 | 117.90 (6) | F1vii—K2—O3viii | 70.51 (3) |
O3—P1—O1 | 112.56 (6) | O3ii—K2—O2viii | 142.78 (3) |
O2—P1—O1 | 112.89 (6) | O2vi—K2—O2viii | 98.02 (3) |
O3—P1—F1 | 104.87 (5) | O3iii—K2—O2viii | 137.95 (3) |
O2—P1—F1 | 105.23 (5) | F1vii—K2—O2viii | 63.95 (3) |
O1—P1—F1 | 101.28 (6) | O3viii—K2—O2viii | 50.96 (3) |
H2—N2—H3 | 110 (3) | O3ii—K2—O2ix | 68.35 (3) |
H2—N2—H4 | 113 (3) | O2vi—K2—O2ix | 74.45 (4) |
H2—N2—H5 | 104 (3) | O3iii—K2—O2ix | 107.27 (3) |
H3—N2—H4 | 116 (4) | F1vii—K2—O2ix | 142.23 (3) |
H3—N2—H5 | 108 (4) | O3viii—K2—O2ix | 135.06 (3) |
H4—N2—H5 | 104 (3) | O2viii—K2—O2ix | 107.45 (2) |
O3i—K1—O3 | 109.45 (4) | O3ii—K2—O1x | 72.07 (3) |
O3i—K1—O2ii | 173.84 (3) | O2vi—K2—O1x | 132.78 (3) |
O3—K1—O2ii | 74.26 (3) | O3iii—K2—O1x | 144.76 (3) |
O3i—K1—O2iii | 74.26 (3) | F1vii—K2—O1x | 134.04 (3) |
O3—K1—O2iii | 173.84 (3) | O3viii—K2—O1x | 70.35 (3) |
O3i—K1—O1v | 113.17 (3) | O2viii—K2—O1x | 72.97 (3) |
O3—K1—O1v | 77.47 (3) | O2ix—K2—O1x | 65.23 (3) |
O3i—K1—O1iv | 77.47 (3) | O3ii—K2—F1ix | 113.49 (3) |
O3—K1—O1iv | 113.17 (3) | O2vi—K2—F1ix | 61.54 (3) |
O2ii—K1—O2iii | 102.50 (4) | O3iii—K2—F1ix | 128.56 (3) |
O2ii—K1—O1iv | 96.60 (3) | F1vii—K2—F1ix | 102.70 (2) |
O2iii—K1—O1iv | 72.17 (3) | O3viii—K2—F1ix | 113.96 (3) |
O2ii—K1—O1v | 72.17 (3) | O2viii—K2—F1ix | 66.83 (3) |
O2iii—K1—O1v | 96.60 (3) | O2ix—K2—F1ix | 45.89 (2) |
O1iv—K1—O1v | 162.41 (4) | O1x—K2—F1ix | 72.76 (3) |
O3ii—K2—O2vi | 115.03 (4) | O3ii—K2—O1iii | 69.42 (3) |
O3ii—K2—O3iii | 73.31 (4) | O2vi—K2—O1iii | 113.28 (3) |
O2vi—K2—O3iii | 69.56 (3) | O3iii—K2—O1iii | 47.13 (3) |
O3ii—K2—F1vii | 141.50 (3) | F1vii—K2—O1iii | 73.53 (3) |
O2vi—K2—F1vii | 70.89 (3) | O3viii—K2—O1iii | 68.69 (3) |
O3iii—K2—F1vii | 74.09 (3) | O2viii—K2—O1iii | 113.88 (3) |
O3ii—K2—O3viii | 104.42 (3) | O2ix—K2—O1iii | 135.80 (3) |
O2vi—K2—O3viii | 138.58 (3) | O1x—K2—O1iii | 112.59 (2) |
O3iii—K2—O3viii | 112.81 (2) | F1ix—K2—O1iii | 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) top
D—H···A | D—H | H···A | D···A | D—H···A |
N2—H2···O2ix | 0.91 (1) | 2.36 (3) | 3.0834 (12) | 136 (3) |
N2—H2···O3ii | 0.91 (1) | 2.29 (4) | 2.8573 (11) | 120 (3) |
N2—H3···O1iii | 0.90 (1) | 2.43 (2) | 3.2848 (11) | 159 (5) |
N2—H3···O3iii | 0.90 (1) | 2.24 (4) | 2.9532 (11) | 136 (5) |
N2—H4···F1vii | 0.91 (1) | 2.71 (5) | 2.9557 (10) | 97 (3) |
N2—H4···O2viii | 0.91 (1) | 2.09 (2) | 2.9622 (12) | 160 (4) |
N2—H4···O3viii | 0.91 (1) | 2.30 (4) | 2.9599 (12) | 129 (4) |
N2—H5···O2vi | 0.92 (1) | 2.00 (1) | 2.9058 (11) | 168 (4) |
N2—H5···F1ix | 0.92 (1) | 2.77 (5) | 3.1999 (10) | 110 (3) |
O1—H1···O1xvi | 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. |
Experimental details
Crystal data |
Chemical formula | (H4N)0.926K2.074(HF2O6P2) |
Mr | 294.75 |
Crystal system, space group | Monoclinic, C2/c |
Temperature (K) | 293 |
a, b, c (Å) | 7.9470 (3), 11.6800 (4), 9.7290 (3) |
β (°) | 113.570 (3) |
V (Å3) | 827.71 (5) |
Z | 4 |
Radiation type | Mo Kα |
µ (mm−1) | 1.60 |
Crystal size (mm) | 0.5 × 0.25 × 0.15 |
|
Data collection |
Diffractometer | Nonius KappaCCD diffractometer |
Absorption correction | Multi-scan (SORTAV; Blessing, 1997) |
Tmin, Tmax | 0.715, 0.796 |
No. of measured, independent and observed [I > 2σ(I)] reflections | 5391, 942, 908 |
Rint | 0.030 |
(sin θ/λ)max (Å−1) | 0.649 |
|
Refinement |
R[F2 > 2σ(F2)], wR(F2), S | 0.021, 0.054, 1.11 |
No. of reflections | 942 |
No. of parameters | 79 |
No. of restraints | 10 |
H-atom treatment | H atoms treated by a mixture of independent and constrained refinement |
Δρmax, Δρmin (e Å−3) | 0.25, −0.30 |
Selected geometric parameters (Å, º) topP1—O3 | 1.4843 (10) | K2—O3i | 2.9532 (11) |
P1—O2 | 1.4897 (10) | K2—F1v | 2.9557 (10) |
P1—O1 | 1.5358 (10) | K2—O3vi | 2.9599 (12) |
P1—F1 | 1.5947 (9) | K2—O2vi | 2.9622 (12) |
K1—O3 | 2.7445 (10) | K2—O2vii | 3.0834 (12) |
K1—O2i | 2.7921 (10) | K2—O1viii | 3.1366 (11) |
K1—O1ii | 2.8990 (11) | K2—F1vii | 3.1999 (10) |
K2—O3iii | 2.8573 (11) | K2—O1i | 3.2848 (11) |
K2—O2iv | 2.9058 (11) | | |
| | | |
O3—P1—O2 | 117.90 (6) | O3—P1—F1 | 104.87 (5) |
O3—P1—O1 | 112.56 (6) | O2—P1—F1 | 105.23 (5) |
O2—P1—O1 | 112.89 (6) | O1—P1—F1 | 101.28 (6) |
Symmetry codes: (i) x+1/2, y+1/2, z; (ii) x+1/2, −y+1/2, z+1/2; (iii) −x+1/2, y+1/2, −z+3/2; (iv) −x+1, y+1, −z+3/2; (v) −x+1, −y+1, −z+1; (vi) x, −y+1, z−1/2; (vii) x, y+1, z; (viii) −x, −y+1, −z+1. |
Hydrogen-bond geometry (Å, º) top
D—H···A | D—H | H···A | D···A | D—H···A |
N2—H2···O2vii | 0.911 (10) | 2.36 (3) | 3.0834 (12) | 136 (3) |
N2—H2···O3iii | 0.911 (10) | 2.29 (4) | 2.8573 (11) | 120 (3) |
N2—H3···O1i | 0.903 (10) | 2.43 (2) | 3.2848 (11) | 159 (5) |
N2—H3···O3i | 0.903 (10) | 2.24 (4) | 2.9532 (11) | 136 (5) |
N2—H4···O2vi | 0.908 (10) | 2.092 (18) | 2.9622 (12) | 160 (4) |
N2—H4···O3vi | 0.908 (10) | 2.30 (4) | 2.9599 (12) | 129 (4) |
N2—H5···O2iv | 0.920 (10) | 1.999 (14) | 2.9058 (11) | 168 (4) |
O1—H1···O1ix | 1.24 | 1.24 | 2.471 (2) | 180 |
Symmetry codes: (i) x+1/2, y+1/2, z; (iii) −x+1/2, y+1/2, −z+3/2; (iv) −x+1, y+1, −z+3/2; (vi) x, −y+1, z−1/2; (vii) x, y+1, z; (ix) −x, −y, −z+1. |
Bond-valence sums for non-H atoms (Brese & O'Keffee, 1991; García-Rodríguez, 2000) for the sites in the title structure topP | K1 | K2/N2 | F1 | O1 | O2 | O3 |
4.766 (7) | 1.184 (1) | 1.002 (1) | 1.032 (3) | 1.914 (3) | 1.931 (5) | 2.010 (5) |
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 − xKxPO3F can be inferred by analogy to existing series of (NH4)2 − xKxSO4. 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 − xKxPO3F. 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 − xKxPO3F.