Hydrogen bonding and short contacts in [2,4,6-tris­(trifluoro­meth­yl)phenyl]­phosphinic acid

In the title compound, C₉H₄F₉O₂P, mol­ecules are linked by a single O—H...O hydrogen bond into chains related to those in phenyl­phosphinic acid. There are short intra­molecular F...P contacts.

S1. Comment

Several group 15 halides containing the tris(2,4,6-trifluoromethyl)phenyl (Ar) ligand have been described, some of which have been characterized crystallographically, including phosphorus, arsenic, antimony and bismuth compounds (Batsanov et al., 2002; Burford et al., 2000; Whitmire et al., 1991). Although the compound ArPCl₂ has been synthesized and characterized by ³¹P and ¹⁹F NMR spectroscopy (Dillon et al., 1988; Scholz et al., 1989), single crystals have not been isolated so far; however, the hydrolysis product tris(2,4,6-trifluoromethyl)phenylphosphinic acid, ArP(O)H(OH), (I), has now been crystallized. This compound is believed to be formed by rearrangement of the initial phosphorus(III) hydrolysis product ArP(OH)₂ to the more stable phosphorus(V) form, with a P═O double bond and a P—H bond as, for example, in phosphorous acid H₃PO₃, which has the structure P(O)H(OH)₂ in solution and which behaves as a dibasic rather than as a tribasic acid.

Compound (I) (Fig. 1) crystallizes in the noncentrysymmetric space group P2₁ and shows signs of inversion twinning: the Flack x parameter (Flack, 1983) refined to 0.24 (16), although analysis of the Bijvoet differences using PLATON (Spek, 2009) gave the Hooft y parameter as 0.08 (7), indicating that the probability that the configuration is correct is greater than 0.999% and the probability of an inversion twin is 0.3 × 10^-8 (Hooft et al., 2008). Each P—OH group is hydrogen bonded to the O═ P group of an adjacent molecule (Table 1), forming a chain along [010] (Fig. 2). This hydrogen-bonding motif is similar to that seen in phenylphosphinic acid (Burrow et al., 2000), although the chains in (I) propagate along a 2₁ screw axis, whereas in phenylphosphinic acid the chains are propagated along the a axis by glide planes. The chains in (I) pack together to form a herring-bone-type motif around the 2₁ axes, which leads to short intermolecular F···F contacts (2.87–2.926Å) and may perhaps explain why the p-CF₃ group, although displaying slightly elevated anisotropic displacement parameters, appears to be less mobile than observed in many related materials (Batsanov et al., 2002, 2003; Cornet et al., 2003).

The hydrogen-bonded O···O distance in (I) is comparable with those in phenylphosphinic acid, ethylenebis(phosphinic acid), methylenebis(phosphinic acid) and in the 1:1 mixture of 2-diphenylphosphinophenylphosphinic acid and its dimethylammonium salt (Table 2; Burrow et al., 2000; Bruckmann et al., 1999; King et al., 1986; Kottsieper et al., 2001), and corresponds to a strong hydrogen bond. Slightly longer O···O contacts, between 2.62 and 2.69Å, were found in {[C₅H₅NH]⁺[PhP(O)(H)O]^-}₂.3F₃CC(OH)₂CF₃ (Goerlich et al., 1995). The P═O and P—O bond lengths are also comparable with those in these phosphinic acids (Table 2).

Another interesting feature of the structure is the existence of short intramolecular contacts between two F atoms, in particular (F2 and F7) of the o-CF₃ groups and the P atom, at distances of 2.922 (2) and 2.915 (2)Å, respectively (Fig. 3). This is appreciably shorter than the sum of the empirical van der Waals radii of P (1.91Å) and F (1.40Å) (Zefirov & Zorkii, 1989), as well as the theoretical ones, estimated as 2.05 and 1.42Å, respectively (Franck et al., 1984). The next nearest F atoms, F1 and F8, are at 3.356 (2) and 3.5341 (2)Å, respectively, from P atom and would thus not appear to have significant interactions. Short P—F contacts between 2.843 and 3.25Å have been found previously in other arylphosphorus compounds with one or two o-CF₃ groups on the aromatic ring, as shown in Table 3.

Similar short E—F distances have been reported in the 2,4,6-(CF₃)₃C₆H₂ (Ar), 2,6-(CF₃)₂C₆H₃ (Ar') and 2,4-(CF₃)₂C₆H₃ [Ar''; o-(CF₃) group only] derivatives of elements in group 14 (Si, Ge, Sn and Pb; Grützmacher et al., 1991, 1992, 1994; Brooker et al., 1991 [Please provide reference]; Lay et al., 1992; Buijink et al., 1993; Grützmacher & Pritzkow, 1993; Vij et al., 1994; Van der Maelen Uría et al., 1994; Braddock-Wilking et al., 1995; Freitag et al., 1995; Bender et al., 1997, 1998, 1999; Klinkhammer et al., 1998), group 15 (As and Sb, as well as P; Burford et al., 2000; Batsanov et al., 2002; Cornet et al., 2004), group 16 [Se and Te (Voelker et al., 1999); Zn, Cd and Hg (Brooker et al., 1992 [Please provide reference]), Li (Stalke & Whitmire, 1990) and B (Toyota et al., 2000; Cornet et al., 2003).

They have also been reported for similar derivatives of V (Gibson et al., 1996), Cr (Batsanov, Cornet et al., 2001 or Batsanov, Dillon et al., 2001) and Mo (Dillon et al., 1997; Batsanov, Cornet et al., 2001 or Batsanov, Dillon et al., 2001) and Ni (Benedikt et al., 2001),although the M—F distances in Pd^II derivatives (Bartolomé et al., 1996), and Au^I and Au^III compounds (Espinet et al., 2000) were considered to be essentially nonbonding. In systems where such short contacts have been found, they have generally been regarded as contributing to the overall stabilities of the species concerned, and that is expected to be true for the title compound. There are also the short contacts F1···H1 [2.46 (4)Å], F2···H1 [2.44 (3)Å], F2···O2 [2.944 (3)Å], F7···O1 [2.766 (3)Å] and F7···O2 [2.978 (4)Å].

S2. Experimental

Crystals of the title compound were obtained by slow hydrolysis of a solution of ArPCl₂ (Dillon et al., 1988; Scholz et al., 1989) in a CH₂Cl₂/CDCl₃ mixture in an NMR tube. NMR: δ(H) 8.21 (s, aromatic C—H), 8.06 (d, ¹J_PH = 618 Hz, H—P), 5.90 (s, br, HO—P); δ(F) -55.9 (d, ⁴J_PF = 6.4 Hz, o-CF₃), -64.1 (s, p-CF₃); δ(P) 14.0 (d, ¹J_PH = 625 Hz). The ³¹P NMR data are very similar to those recorded for 2,6-(CF₃)₂C₆H₃PH(O)OH [δ(P): 9.50 (d, ¹J_PH = 600 Hz); Karlstédt et al., 1992]; comparable values have also been reported for MePH(O)OH [δ(P): 35.0 (d, ¹J_PH = 557 Hz); Gallagher, 1991], PhPH(O)OH [δ(P): 20 (d, ¹J_PH = 560 Hz); Gallagher, 1991] and 2,4,6-tBu₃C₆H₂PH(O)OH [δ(P): 25.7 (d, ¹J_PH = 576 Hz); Yoshifuji et al., 1983].

S3. Refinement

H atoms bonded to C atoms were treated as riding atoms, with C—H distances of 0.93Å and U_iso(H) = 1.2U_eq(C). The two other H atoms were freely refined, giving distances O—H = 0.84 (5)Å and P—H = 1.28 (4)Å.

Computing details

Data collection: SMART-NT (Bruker, 2000); cell refinement: SMART-NT (Bruker, 2000); data reduction: SAINT-NT (Bruker, 2000); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: SHELXTL (Sheldrick, 2008); software used to prepare material for publication: SHELXTL (Sheldrick, 2008).

Figures

	Fig. 1. The molecular structure of (I), showing the atom-labelling scheme. Displacement ellipsoids are drawn at the 50% probability level.
	Fig. 2. A hydrogen-bonded chain in (I). For the sake of clarity, H atoms bonded to C atoms have been omitted, but the H atom bonded to P is included. [Symmetry codes: (i) 1-x, -0.5+y, 1-z; (ii) 1-x, 0.5+y, 1-z.]
	Fig. 3. The intramolecular F···F interactions in (I). The strongest interactions are shown with a broken line and the longer distances are shown with a dotted line.

tris(2,4,6-trifluoromethyl)phenylphosphinic acid

Crystal data

C9H4F9O2P	F(000) = 340
Mr = 346.09	Dx = 1.973 Mg m^−3
Monoclinic, P21	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: P 2yb	Cell parameters from 2981 reflections
a = 8.324 (1) Å	θ = 2.5–28.1°
b = 6.3744 (8) Å	µ = 0.36 mm^−1
c = 11.0384 (13) Å	T = 120 K
β = 95.898 (2)°	Needle, colourless
V = 582.60 (12) Å^3	0.49 × 0.12 × 0.06 mm
Z = 2

Data collection

Bruker SMART CCD 1K area-detector diffractometer	2828 independent reflections
Radiation source: fine-focus sealed tube	2293 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.041
Detector resolution: 8 pixels mm^-1	θmax = 28.3°, θmin = 1.9°
ω scans	h = −11→11
Absorption correction: integration (XPREP in SHELXTL; Sheldrick, 2008)	k = −8→8
Tmin = 0.874, Tmax = 0.978	l = −14→14
6410 measured 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)] = 0.051	H atoms treated by a mixture of independent and constrained refinement
wR(F^2) = 0.107	w = 1/[σ^2(Fo^2) + (0.0491P)^2 + 0.2812P] where P = (Fo^2 + 2Fc^2)/3
S = 1.05	(Δ/σ)max < 0.001
2828 reflections	Δρmax = 0.48 e Å^−3
199 parameters	Δρmin = −0.54 e Å^−3
1 restraint	Absolute structure: Flack (1983), 1258 Friedel pairs
Primary atom site location: structure-invariant direct methods	Absolute structure parameter: 0.24 (16)

Special details

Experimental. ¹H NMR spectra were recorded on a Varian Mercury 200 instrument at 199.99 MHz, or on a Varian Unity 300 spectrometer at 299.95 MHz; ¹⁹F spectra were similarly recorded on the Varian Mercury 200 at 188.18 MHz, and ³¹P spectra on Varian Mercury 200 or Unity 300 instruments at 80.96 or 121.4 MHz respectively.

A single-crystal (approximately 0.49 x 0.12 x 0.06 mm) was mounted on a glass fibre using perfluoropolyether oil and quench-cooled to 150 K in a stream of cold N₂ using an Oxford Cryosystems Cryostream unit (Cosier and Glazer, 1986). Diffraction data were measured using an Bruker SMART CCD 1 K area detector diffractometer.

The data collection nominally covered a full sphere of reciprocal space, by a combination of 4 sets of ω scans each set at different ϕ and/or 2θ angles and each scan (10 s exposure) covering 0.3° in ω. Crystal to detector distance 4.51 cm.

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	0.50478 (10)	−0.02178 (14)	0.39056 (8)	0.01692 (19)
O1	0.4772 (3)	−0.0291 (5)	0.52100 (19)	0.0208 (5)
O2	0.4921 (3)	−0.2366 (4)	0.3262 (2)	0.0237 (6)
C1	0.3648 (4)	0.1520 (5)	0.3008 (3)	0.0170 (7)
C2	0.4171 (4)	0.2773 (5)	0.2068 (3)	0.0162 (7)
C3	0.3191 (4)	0.4302 (5)	0.1493 (3)	0.0200 (8)
H3	0.3560	0.5107	0.0876	0.024*
C4	0.1670 (4)	0.4627 (7)	0.1836 (3)	0.0214 (7)
C5	0.1088 (4)	0.3389 (6)	0.2707 (3)	0.0210 (7)
H5	0.0045	0.3594	0.2915	0.025*
C6	0.2054 (4)	0.1823 (6)	0.3282 (3)	0.0186 (7)
C7	0.5833 (5)	0.2557 (6)	0.1655 (3)	0.0233 (8)
C8	0.0679 (5)	0.6377 (7)	0.1230 (4)	0.0312 (9)
C9	0.1285 (5)	0.0513 (6)	0.4200 (4)	0.0253 (8)
F1	0.6968 (2)	0.3465 (4)	0.2427 (2)	0.0295 (5)
F2	0.6265 (3)	0.0537 (4)	0.15541 (19)	0.0300 (5)
F3	0.5926 (3)	0.3421 (4)	0.0574 (2)	0.0362 (6)
F4	0.0532 (4)	0.6200 (5)	0.0033 (3)	0.0700 (11)
F5	0.1387 (4)	0.8224 (4)	0.1433 (2)	0.0476 (7)
F6	−0.0759 (4)	0.6502 (6)	0.1581 (5)	0.1145 (19)
F7	0.1745 (3)	−0.1508 (3)	0.4183 (2)	0.0286 (5)
F8	0.1598 (3)	0.1201 (4)	0.53368 (19)	0.0316 (6)
F9	−0.0323 (3)	0.0502 (4)	0.3957 (2)	0.0365 (6)
H1	0.645 (4)	0.052 (6)	0.377 (3)	0.018 (10)*
H2	0.516 (5)	−0.333 (8)	0.377 (4)	0.039 (13)*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
P1	0.0188 (4)	0.0136 (4)	0.0181 (4)	0.0018 (4)	0.0006 (3)	0.0007 (4)
O1	0.0297 (12)	0.0148 (11)	0.0176 (11)	−0.0001 (12)	0.0007 (9)	0.0001 (12)
O2	0.0403 (17)	0.0126 (13)	0.0183 (13)	0.0015 (12)	0.0042 (11)	−0.0004 (10)
C1	0.0183 (17)	0.0131 (17)	0.0192 (16)	−0.0021 (14)	−0.0002 (13)	−0.0012 (14)
C2	0.0182 (17)	0.0144 (17)	0.0156 (16)	−0.0020 (13)	−0.0003 (13)	0.0012 (13)
C3	0.0252 (18)	0.0133 (18)	0.0210 (17)	−0.0028 (13)	−0.0005 (14)	0.0059 (13)
C4	0.0190 (16)	0.0178 (18)	0.0259 (16)	−0.0034 (16)	−0.0048 (13)	0.0019 (17)
C5	0.0155 (16)	0.0172 (17)	0.0292 (19)	−0.0009 (14)	−0.0028 (14)	−0.0019 (16)
C6	0.0169 (17)	0.0140 (18)	0.0244 (18)	0.0001 (14)	−0.0001 (14)	0.0001 (14)
C7	0.025 (2)	0.0185 (18)	0.0257 (19)	0.0024 (15)	0.0013 (15)	0.0010 (16)
C8	0.029 (2)	0.020 (2)	0.043 (2)	−0.0028 (17)	−0.0059 (18)	0.0109 (18)
C9	0.0209 (19)	0.0195 (18)	0.037 (2)	0.0006 (15)	0.0078 (16)	0.0035 (16)
F1	0.0199 (11)	0.0302 (13)	0.0390 (13)	−0.0060 (10)	0.0068 (9)	−0.0033 (11)
F2	0.0352 (12)	0.0241 (12)	0.0323 (12)	0.0080 (10)	0.0117 (10)	−0.0020 (9)
F3	0.0394 (13)	0.0432 (14)	0.0287 (12)	0.0046 (12)	0.0170 (10)	0.0123 (11)
F4	0.115 (3)	0.0333 (17)	0.0493 (17)	0.0175 (17)	−0.0514 (18)	−0.0015 (14)
F5	0.0683 (19)	0.0144 (12)	0.0532 (16)	0.0050 (12)	−0.0267 (13)	0.0010 (11)
F6	0.0351 (18)	0.103 (3)	0.212 (5)	0.041 (2)	0.045 (2)	0.120 (3)
F7	0.0306 (12)	0.0164 (11)	0.0398 (13)	−0.0036 (10)	0.0078 (10)	0.0088 (10)
F8	0.0404 (14)	0.0303 (13)	0.0259 (12)	0.0046 (11)	0.0127 (10)	0.0029 (10)
F9	0.0190 (11)	0.0367 (14)	0.0553 (15)	−0.0026 (9)	0.0110 (10)	0.0143 (12)

Geometric parameters (Å, º)

P1—O1	1.482 (2)	C5—C6	1.393 (5)
P1—O2	1.541 (3)	C5—H5	0.9300
P1—C1	1.824 (4)	C6—C9	1.505 (5)
P1—H1	1.28 (4)	C7—F3	1.324 (4)
O2—H2	0.84 (5)	C7—F1	1.337 (4)
C1—C6	1.405 (5)	C7—F2	1.345 (4)
C1—C2	1.413 (5)	C8—F6	1.298 (5)
C2—C3	1.383 (5)	C8—F4	1.319 (5)
C2—C7	1.507 (5)	C8—F5	1.325 (5)
C3—C4	1.374 (5)	C9—F8	1.330 (5)
C3—H3	0.9300	C9—F9	1.337 (4)
C4—C5	1.370 (5)	C9—F7	1.345 (5)
C4—C8	1.503 (5)
O1—P1—O2	114.17 (16)	C5—C6—C1	120.9 (3)
O1—P1—C1	113.14 (15)	C5—C6—C9	116.0 (3)
O2—P1—C1	106.22 (16)	C1—C6—C9	123.0 (3)
O1—P1—H1	110.9 (15)	F3—C7—F1	107.0 (3)
O2—P1—H1	107.0 (16)	F3—C7—F2	106.4 (3)
C1—P1—H1	104.8 (16)	F1—C7—F2	106.9 (3)
P1—O2—H2	110 (3)	F3—C7—C2	112.0 (3)
C6—C1—C2	116.7 (3)	F1—C7—C2	112.2 (3)
C6—C1—P1	122.1 (3)	F2—C7—C2	112.0 (3)
C2—C1—P1	120.9 (2)	F6—C8—F4	108.1 (4)
C3—C2—C1	121.6 (3)	F6—C8—F5	107.6 (4)
C3—C2—C7	116.2 (3)	F4—C8—F5	103.8 (3)
C1—C2—C7	122.2 (3)	F6—C8—C4	113.2 (3)
C4—C3—C2	119.8 (3)	F4—C8—C4	111.9 (4)
C4—C3—H3	120.1	F5—C8—C4	111.7 (3)
C2—C3—H3	120.1	F8—C9—F9	106.6 (3)
C5—C4—C3	120.5 (3)	F8—C9—F7	107.5 (3)
C5—C4—C8	121.5 (3)	F9—C9—F7	105.8 (3)
C3—C4—C8	118.0 (3)	F8—C9—C6	113.3 (3)
C4—C5—C6	120.2 (3)	F9—C9—C6	110.7 (3)
C4—C5—H5	119.9	F7—C9—C6	112.4 (3)
C6—C5—H5	119.9
O1—P1—C1—C6	−32.4 (3)	P1—C1—C6—C9	−9.8 (5)
O2—P1—C1—C6	93.6 (3)	C3—C2—C7—F3	−18.9 (5)
O1—P1—C1—C2	141.7 (3)	C1—C2—C7—F3	162.4 (3)
O2—P1—C1—C2	−92.2 (3)	C3—C2—C7—F1	101.5 (4)
C6—C1—C2—C3	3.4 (5)	C1—C2—C7—F1	−77.2 (4)
P1—C1—C2—C3	−171.0 (3)	C3—C2—C7—F2	−138.4 (3)
C6—C1—C2—C7	−178.0 (3)	C1—C2—C7—F2	43.0 (4)
P1—C1—C2—C7	7.6 (5)	C5—C4—C8—F6	−2.7 (6)
C1—C2—C3—C4	0.1 (5)	C3—C4—C8—F6	177.4 (4)
C7—C2—C3—C4	−178.6 (3)	C5—C4—C8—F4	−125.2 (4)
C2—C3—C4—C5	−2.9 (5)	C3—C4—C8—F4	55.0 (5)
C2—C3—C4—C8	177.0 (3)	C5—C4—C8—F5	118.9 (4)
C3—C4—C5—C6	2.0 (5)	C3—C4—C8—F5	−60.9 (5)
C8—C4—C5—C6	−177.9 (3)	C5—C6—C9—F8	−94.8 (4)
C4—C5—C6—C1	1.7 (5)	C1—C6—C9—F8	85.1 (4)
C4—C5—C6—C9	−178.4 (3)	C5—C6—C9—F9	25.0 (5)
C2—C1—C6—C5	−4.3 (5)	C1—C6—C9—F9	−155.1 (3)
P1—C1—C6—C5	170.0 (3)	C5—C6—C9—F7	143.2 (3)
C2—C1—C6—C9	175.8 (3)	C1—C6—C9—F7	−36.9 (5)

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
O2—H2···O1^i	0.84 (5)	1.68 (5)	2.509 (4)	168 (5)

Symmetry code: (i) −x+1, y−1/2, −z+1.