Bis(4-di­methyl­amino­pyridinium) 1,2-di­fluoro­diphosphate

The title compound, 2DMAPH⁺·P₂O₅F₂²⁻, where DMAP is [(CH₃)₂NC₅H₄N] or C₇H₁₀N₂ (4-di­methyl­amino­pyridine), belongs to the class of catena-difluoro­polyphosphates of general formula [P_nO_3n−1F₂]ⁿ⁻ (n = 2,3,…), and is the second representative of this series characterized by single-crystal X-ray diffraction. Compared to K₂[P₂O₅F₂], the anion adopts a different conformation, enforced by its N—H...O bridging to the cation.

Key indicators

• Single-crystal X-ray study
• T = 120 K
• Mean [sigma](C-C) = 0.005 Å
• R factor = 0.045
• wR factor = 0.142
• Data-to-parameter ratio = 12.9

checkCIF results

No syntax errors found

ADDSYM reports no extra symmetry

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S1. Comment

Phosphorus forms two extensive series of polyphosphoric acids: the cyclic metaphosphoric and the catena-polyphosphoric acids. Replacing one or more OH groups of chain polyphosphoric acids by fluorine gives fluoropolyphosphoric acids, partially known in the form of their salts. The following of these fluoropolyphosphates have been reported: 1-monofluorodiphosphate, [P₂O₆F]³⁻ (Schülke, 1968), 1-monofluorotriphosphate, [P₃O₉F]⁴⁻ (Feldmann, 1965), 1,2-difluorodiphosphate, [P₂O₅F₂]²⁻ (Falius, 1968; Neels & Grunze, 1979) and α,ω-difluorotri(tetra,penta)phosphates, [P_nO_3n-1F₂]^n- (n = 3–5) (Grunze, 1973). Their preparations are mostly based on a nucleophilic degradation of appropriate P—O—P bridged precursors by the fluoride ion, which proceeds in aqueous solutions ([P₃O₉]³⁻) (Feldmann, 1965) or in melts (P₄O₁₀) (Falius, 1968; Grunze, 1973). The potassium difluorodiphosphate, K₂[P₂O₅F₂], was first isolated by Falius (1968) from fluorophosphate melt and its crystal structure has been determined by Durand et al. (1978).

The bond lengths and angles in the difluorodiphosphate anion in [DMAPH]₂[P₂O₅F₂], (I), are very similar to what was already observed by Durand et al. (1978). The phosphorus environment is approximately tetrahedral, with the O5—P1—F1 and O5—P2—F2 angles being the most compressed [99.0 (1) and 98.7 (1)°]·The P1—O5—P2 angle is 130.7 (1)°.

The σ-bonds of the P—O—P bridge allow rotation of the –PO₂F groups but, unlike in K₂[P₂O₅F₂], they are not related by crystallographic symmetry, thus taking arbitrary orientation in space. Nevertheless, the anion shows the approximate internal symmetry C2 and its conformation with respect to the mutual orientation of –PO₂F moieties can be described as staggered, while in K₂[P₂O₅F₂], the substituents in both groups are nearly eclipsed (Fig. 2). This is also reflected in dihedral angles F1—P1—O5—P2 [−98.2 (2)°] and F2—P2—O5—P1 [−74.4 (2)°]. Considering the `dihedral angle' F1—P1···P2—F2, both –PO<sub>2</sub>F groups are staggered by 166.0 (1)°. Analogous values calculated for K<sub>2</sub>[P<sub>2</sub>O<sub>5</sub>F<sub>2</sub>] are 178.2 (2)° for both symmetry-equivalent F—P—O—P dihedral angles, and 4.4 (3)° for F—P···P—F `dihedral angle'. Staggered conformation of the anion in (I) also results into the central O2—P1—O5—P2—O4 chain being nearly in-plane, with the r.m.s. deviation of fitted atoms being 0.0505 Å. Corresponding dihedral angles O4—P2—O5—P1 and O2—P1—O5—P2 are 173.3 (2) and 16.2 (3)°, respectively.

Different conformations were observed previously for disulfuryl difluoride, S₂O₅F₂, which is isoelectronic with difluorodiphosphate anion. The –SO₂F groups in the crystalline state at 100 K (Blake & Žák, 1993) and in the gas phase determined by electron diffraction (Hencher & Bauer, 1973) are staggered differently, with angular difference of 25.9°. The conformational flexibility of S₂O₅F₂ was additionally proven by Toužín & Černík (1993) by Raman and IR spectroscopy of its liquid phase. Unfortunately, there are no relevant ab initio conformational studies on either S₂O₅F₂ or [P₂O₅F₂]²⁻ to enable a deeper insight into their conformation transitions and corresponding torsional barriers.

The dimethylaminopyridinium cations are almost perfectly planar and are comparable in their bond parameters to other examples found in the Cambridge Structural Database (Allen, 2002). The aromatic rings are mutually inclined by 17.7 (1)°. Each of the cations is involved in N—H···O hydrogen bonding with the terminal O atoms in the anion (Fig. 1 and Table 1). A similar donor–acceptor distance [2.723 (3) Å] was found for the N—H···O hydrogen bond in 4-dimethylaminopyridinium trifluoroacetate (Dega-Szafran et al., 1992). Nearly perpendicular to the c axis, the structure consists of layers of dimethylaminopyridinium cations. The perpendicular distances between the ring centroids and parallel aromatic planes vary from 3.319 to 3.571 Å, indicating the π–π-stacking interactions between pyridine rings as previously observed by Choi & Angelici (2000).

Obviously the distinct conformations in difluorodiphosphate anion are closely related to the different cationic counterparts in the crystal structures of [DMAPH]₂[P₂O₅F₂] and K₂[P₂O₅F₂]. We assume the following three factors may be of importance: (a) DMAPH π–π stacking, which is the main driving force of the packing arrangement observed; (b) easy rotation of –PO₂F pendants connected to the bridging O atom; (c) directionality of the N—H···O bridge bonding (in contrast to non-directional attractive forces around K⁺ ions in K₂[P₂O₅F₂]), which controls the extent of –PO₂F groups rotation in the anion. However, reliable structural data of higher fluoropolyphosphates with longer chains are needed for better understanding of all factors involved.

S2. Experimental

The title compound was prepared by the reaction of betaine DMAP·PO₂F (Černík, 2000) (2 mmol) and water (2 mmol) in acetonitrile (4 ml) at room temperature. A white powder was formed in the course of the reaction (yield 0.2 g). Recrystallization from hot acetonitrile produced uniform colourless crystals of [DMAPH]₂[P₂O₅F₂].

Computing details

Data collection: Xcalibur (Oxford Diffraction Ltd, 2001); cell refinement: Xcalibur; data reduction: Xcalibur; program(s) used to solve structure: SHELXTL (Bruker, 1997); program(s) used to refine structure: SHELXTL; molecular graphics: SHELXTL; software used to prepare material for publication: PLATON (Spek, 1990).

Figures

	Fig. 1. The molecular structure of bis(4-dimethylaminopyridinium) 1,2-difluorodiphosphate, showing the atom-numbering scheme and the hydrogen bonding. Ellipsoids are drawn at the 50% probability level.
	Fig. 2. The schematic frontal projections of the [P2O5F2]^2− anions viewed along the P···P vector in (a) [DMAPH]2[P2O5F2] and (b) K2[P2O5F2].

(I)

Crystal data

2C7H11N2^+·F2O5P2^2^−	F(000) = 888
Mr = 426.30	Dx = 1.537 Mg m^−3
Monoclinic, P21/c	Mo Kα radiation, λ = 0.71073 Å
a = 8.386 (2) Å	Cell parameters from 100 reflections
b = 31.076 (6) Å	θ = 5.2–25.4°
c = 7.072 (1) Å	µ = 0.29 mm^−1
β = 92.13 (3)°	T = 120 K
V = 1841.7 (6) Å^3	Prism, colourless
Z = 4	0.10 × 0.10 × 0.05 mm

Data collection

Kuma KM-4 CCDr diffractometer	2625 reflections with I > 2σ(I)
Radiation source: fine-focus sealed tube	Rint = 0.046
Graphite monochromator	θmax = 25.0°, θmin = 2.8°
Detector resolution: 0.06 mm pixels mm^-1	h = −9→7
ω scans	k = −36→36
9769 measured reflections	l = −8→8
3200 independent reflections

Refinement

Refinement on F^2	Secondary atom site location: difference Fourier map
Least-squares matrix: full	Hydrogen site location: inferred from neighbouring sites
R[F^2 > 2σ(F^2)] = 0.046	H-atom parameters constrained
wR(F^2) = 0.142	w = 1/[σ^2(Fo^2) + (0.0728P)^2] where P = (Fo^2 + 2Fc^2)/3
S = 1.28	(Δ/σ)max < 0.001
3200 reflections	Δρmax = 0.59 e Å^−3
249 parameters	Δρmin = −0.58 e Å^−3
0 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: 0.024 (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
P1	0.50995 (9)	0.39336 (3)	0.38213 (11)	0.0174 (3)
P2	0.29290 (9)	0.36514 (3)	0.07473 (12)	0.0190 (3)
F1	0.4704 (2)	0.36060 (6)	0.5421 (3)	0.0330 (5)
F2	0.3839 (2)	0.39260 (7)	−0.0731 (3)	0.0362 (5)
O1	0.5207 (2)	0.43656 (7)	0.4706 (3)	0.0210 (5)
O2	0.6431 (2)	0.37618 (7)	0.2761 (3)	0.0260 (6)
O3	0.3633 (3)	0.32172 (7)	0.0799 (4)	0.0300 (6)
O4	0.1210 (3)	0.37169 (7)	0.0402 (3)	0.0264 (6)
O5	0.3443 (2)	0.39163 (7)	0.2633 (3)	0.0260 (6)
N3	0.7739 (3)	0.48075 (8)	0.3380 (4)	0.0196 (6)
H3	0.6853	0.4693	0.3778	0.024*
N4	1.1937 (3)	0.53510 (8)	0.1725 (4)	0.0173 (6)
C10	1.0560 (3)	0.51725 (10)	0.2224 (4)	0.0158 (7)
C11	0.9173 (3)	0.54253 (10)	0.2518 (4)	0.0180 (7)
H11	0.9193	0.5727	0.2301	0.022*
C8	0.8998 (4)	0.45539 (11)	0.3049 (4)	0.0207 (7)
H8	0.8905	0.4251	0.3207	0.025*
C12	0.7821 (4)	0.52348 (10)	0.3109 (4)	0.0188 (7)
H12	0.6914	0.5408	0.3335	0.023*
C9	1.0396 (4)	0.47221 (10)	0.2494 (4)	0.0186 (7)
H9	1.1274	0.4537	0.2284	0.022*
C14	1.2105 (4)	0.58139 (10)	0.1459 (5)	0.0240 (7)
H14A	1.1132	0.5928	0.0834	0.036*
H14B	1.3019	0.5871	0.0671	0.036*
H14C	1.2278	0.5953	0.2692	0.036*
C13	1.3379 (4)	0.50879 (11)	0.1593 (5)	0.0233 (7)
H13A	1.3621	0.4949	0.2815	0.035*
H13B	1.4276	0.5271	0.1258	0.035*
H13C	1.3204	0.4867	0.0618	0.035*
N1	0.6680 (3)	0.29100 (10)	0.0629 (4)	0.0279 (7)
H1	0.5869	0.3088	0.0712	0.033*
N2	1.0459 (3)	0.20659 (8)	0.0372 (4)	0.0221 (6)
C2	0.7634 (4)	0.21968 (11)	0.0417 (5)	0.0247 (8)
H2	0.7410	0.1897	0.0345	0.030*
C4	0.9458 (4)	0.27985 (10)	0.0512 (4)	0.0206 (7)
H4	1.0503	0.2916	0.0492	0.025*
C5	0.8176 (4)	0.30645 (11)	0.0620 (4)	0.0244 (8)
H5	0.8342	0.3367	0.0691	0.029*
C3	0.9236 (4)	0.23451 (10)	0.0429 (4)	0.0190 (7)
C1	0.6425 (4)	0.24865 (12)	0.0510 (5)	0.0285 (8)
H1A	0.5357	0.2384	0.0490	0.034*
C6	1.2130 (4)	0.21998 (12)	0.0482 (6)	0.0309 (9)
H6A	1.2189	0.2514	0.0573	0.046*
H6B	1.2660	0.2104	−0.0656	0.046*
H6C	1.2662	0.2071	0.1602	0.046*
C7	1.0196 (4)	0.16017 (10)	0.0342 (6)	0.0312 (9)
H7A	0.9854	0.1507	0.1585	0.047*
H7B	1.1190	0.1455	0.0044	0.047*
H7C	0.9368	0.1531	−0.0623	0.047*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
P1	0.0133 (4)	0.0160 (4)	0.0230 (5)	−0.0004 (3)	0.0009 (3)	−0.0009 (3)
P2	0.0151 (4)	0.0159 (4)	0.0256 (5)	−0.0001 (3)	−0.0019 (3)	−0.0003 (3)
F1	0.0377 (12)	0.0268 (11)	0.0347 (12)	−0.0080 (9)	0.0026 (9)	0.0079 (9)
F2	0.0300 (11)	0.0439 (13)	0.0351 (12)	−0.0035 (9)	0.0051 (9)	0.0121 (10)
O1	0.0179 (11)	0.0181 (11)	0.0271 (13)	−0.0020 (9)	0.0041 (9)	−0.0035 (9)
O2	0.0142 (11)	0.0270 (13)	0.0369 (14)	0.0002 (9)	0.0024 (10)	−0.0076 (11)
O3	0.0190 (12)	0.0190 (12)	0.0514 (16)	0.0034 (9)	−0.0057 (11)	−0.0072 (11)
O4	0.0170 (12)	0.0215 (12)	0.0400 (14)	0.0000 (9)	−0.0058 (10)	−0.0008 (10)
O5	0.0144 (11)	0.0299 (13)	0.0336 (13)	0.0029 (9)	−0.0023 (10)	−0.0119 (11)
N3	0.0146 (13)	0.0257 (15)	0.0187 (14)	−0.0049 (11)	0.0014 (10)	0.0005 (12)
N4	0.0141 (13)	0.0167 (13)	0.0212 (14)	0.0014 (10)	0.0004 (10)	0.0009 (11)
C10	0.0128 (15)	0.0253 (17)	0.0092 (14)	0.0007 (12)	−0.0002 (12)	−0.0007 (13)
C11	0.0177 (16)	0.0171 (16)	0.0192 (16)	0.0014 (13)	−0.0003 (13)	−0.0010 (13)
C8	0.0256 (17)	0.0183 (16)	0.0178 (16)	−0.0014 (13)	−0.0019 (13)	0.0028 (13)
C12	0.0140 (15)	0.0236 (17)	0.0187 (16)	0.0000 (13)	−0.0008 (12)	−0.0029 (13)
C9	0.0176 (16)	0.0189 (16)	0.0190 (16)	0.0053 (13)	−0.0014 (13)	−0.0016 (13)
C14	0.0192 (17)	0.0199 (17)	0.0328 (19)	−0.0015 (13)	0.0010 (14)	0.0035 (15)
C13	0.0137 (16)	0.0307 (19)	0.0255 (17)	0.0045 (13)	0.0014 (13)	−0.0034 (15)
N1	0.0218 (15)	0.0319 (17)	0.0302 (16)	0.0112 (12)	0.0043 (12)	0.0015 (13)
N2	0.0151 (13)	0.0180 (14)	0.0333 (16)	0.0019 (11)	0.0024 (12)	−0.0009 (12)
C2	0.0224 (17)	0.0185 (17)	0.0334 (19)	−0.0032 (13)	0.0010 (15)	−0.0007 (15)
C4	0.0214 (17)	0.0178 (16)	0.0226 (17)	−0.0017 (13)	0.0025 (13)	−0.0020 (13)
C5	0.0313 (19)	0.0195 (17)	0.0227 (18)	0.0044 (14)	0.0052 (15)	−0.0007 (14)
C3	0.0201 (17)	0.0199 (17)	0.0170 (15)	0.0016 (13)	0.0005 (13)	−0.0016 (13)
C1	0.0164 (17)	0.035 (2)	0.034 (2)	−0.0007 (14)	−0.0009 (14)	−0.0011 (16)
C6	0.0175 (17)	0.0285 (19)	0.047 (2)	0.0014 (14)	0.0021 (16)	−0.0038 (17)
C7	0.0281 (19)	0.0201 (18)	0.046 (2)	0.0061 (15)	0.0053 (16)	−0.0001 (16)

Geometric parameters (Å, º)

P1—O2	1.468 (2)	C14—H14C	0.9800
P1—O1	1.483 (2)	C13—H13A	0.9800
P1—F1	1.567 (2)	C13—H13B	0.9800
P1—O5	1.598 (2)	C13—H13C	0.9800
P2—O4	1.468 (2)	N1—C1	1.336 (4)
P2—O3	1.473 (2)	N1—C5	1.343 (4)
P2—F2	1.569 (2)	N1—H1	0.8800
P2—O5	1.612 (2)	N2—C3	1.345 (4)
N3—C12	1.344 (4)	N2—C7	1.459 (4)
N3—C8	1.345 (4)	N2—C6	1.461 (4)
N3—H3	0.8800	C2—C1	1.360 (5)
N4—C10	1.340 (4)	C2—C3	1.419 (4)
N4—C14	1.458 (4)	C2—H2	0.9500
N4—C13	1.465 (4)	C4—C5	1.360 (4)
C10—C9	1.420 (4)	C4—C3	1.422 (4)
C10—C11	1.426 (4)	C4—H4	0.9500
C11—C12	1.358 (4)	C5—H5	0.9500
C11—H11	0.9500	C1—H1A	0.9500
C8—C9	1.355 (4)	C6—H6A	0.9800
C8—H8	0.9500	C6—H6B	0.9800
C12—H12	0.9500	C6—H6C	0.9800
C9—H9	0.9500	C7—H7A	0.9800
C14—H14A	0.9800	C7—H7B	0.9800
C14—H14B	0.9800	C7—H7C	0.9800
O2—P1—O1	120.62 (13)	N4—C13—H13A	109.5
O2—P1—F1	108.54 (13)	N4—C13—H13B	109.5
O1—P1—F1	107.16 (12)	H13A—C13—H13B	109.5
O2—P1—O5	112.46 (13)	N4—C13—H13C	109.5
O1—P1—O5	106.87 (12)	H13A—C13—H13C	109.5
F1—P1—O5	98.90 (12)	H13B—C13—H13C	109.5
O4—P2—O3	121.44 (13)	C1—N1—C5	120.0 (3)
O4—P2—F2	108.23 (13)	C1—N1—H1	120.0
O3—P2—F2	108.09 (13)	C5—N1—H1	120.0
O4—P2—O5	107.30 (13)	C3—N2—C7	121.5 (3)
O3—P2—O5	110.66 (14)	C3—N2—C6	123.1 (3)
F2—P2—O5	98.72 (12)	C7—N2—C6	115.2 (3)
P1—O5—P2	130.74 (14)	C1—C2—C3	119.5 (3)
C12—N3—C8	120.6 (3)	C1—C2—H2	120.3
C12—N3—H3	119.7	C3—C2—H2	120.3
C8—N3—H3	119.7	C5—C4—C3	120.1 (3)
C10—N4—C14	122.1 (3)	C5—C4—H4	119.9
C10—N4—C13	120.5 (3)	C3—C4—H4	119.9
C14—N4—C13	117.3 (3)	N1—C5—C4	121.5 (3)
N4—C10—C9	122.2 (3)	N1—C5—H5	119.2
N4—C10—C11	121.7 (3)	C4—C5—H5	119.2
C9—C10—C11	116.1 (3)	N2—C3—C2	120.8 (3)
C12—C11—C10	120.0 (3)	N2—C3—C4	122.8 (3)
C12—C11—H11	120.0	C2—C3—C4	116.4 (3)
C10—C11—H11	120.0	N1—C1—C2	122.5 (3)
N3—C8—C9	121.2 (3)	N1—C1—H1A	118.7
N3—C8—H8	119.4	C2—C1—H1A	118.7
C9—C8—H8	119.4	N2—C6—H6A	109.5
N3—C12—C11	121.5 (3)	N2—C6—H6B	109.5
N3—C12—H12	119.2	H6A—C6—H6B	109.5
C11—C12—H12	119.2	N2—C6—H6C	109.5
C8—C9—C10	120.6 (3)	H6A—C6—H6C	109.5
C8—C9—H9	119.7	H6B—C6—H6C	109.5
C10—C9—H9	119.7	N2—C7—H7A	109.5
N4—C14—H14A	109.5	N2—C7—H7B	109.5
N4—C14—H14B	109.5	H7A—C7—H7B	109.5
H14A—C14—H14B	109.5	N2—C7—H7C	109.5
N4—C14—H14C	109.5	H7A—C7—H7C	109.5
H14A—C14—H14C	109.5	H7B—C7—H7C	109.5
H14B—C14—H14C	109.5
O2—P1—O5—P2	16.2 (3)	N3—C8—C9—C10	−0.8 (5)
O1—P1—O5—P2	150.69 (19)	N4—C10—C9—C8	178.2 (3)
F1—P1—O5—P2	−98.2 (2)	C11—C10—C9—C8	−1.7 (4)
O4—P2—O5—P1	173.33 (19)	C1—N1—C5—C4	−0.7 (5)
O3—P2—O5—P1	38.8 (2)	C3—C4—C5—N1	−0.8 (5)
F2—P2—O5—P1	−74.4 (2)	C7—N2—C3—C2	−1.5 (5)
C14—N4—C10—C9	−179.6 (3)	C6—N2—C3—C2	−176.7 (3)
C13—N4—C10—C9	−5.2 (4)	C7—N2—C3—C4	178.2 (3)
C14—N4—C10—C11	0.3 (4)	C6—N2—C3—C4	3.1 (5)
C13—N4—C10—C11	174.7 (3)	C1—C2—C3—N2	178.8 (3)
N4—C10—C11—C12	−176.9 (3)	C1—C2—C3—C4	−0.9 (5)
C9—C10—C11—C12	3.0 (4)	C5—C4—C3—N2	−178.2 (3)
C12—N3—C8—C9	2.1 (5)	C5—C4—C3—C2	1.6 (5)
C8—N3—C12—C11	−0.8 (4)	C5—N1—C1—C2	1.4 (5)
C10—C11—C12—N3	−1.8 (5)	C3—C2—C1—N1	−0.6 (5)

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
N3—H3···O1	0.88	1.85	2.724 (3)	170
N1—H1···O3	0.88	1.92	2.735 (3)	153