Cyclohexylphosphonic acid

The title compound, C₆H₁₃O₃P, displays a crystallographic mirror plane. Bond lengths in the phosphonic acid moiety are P-O = 1.5557 (13) Å and P=O = 1.5089 (18) Å. The mol­ecules are linked via intermolecular hydrogen bonding to form a one-dimensional chain of fused rings. There are no significant contacts between planes.

S1. Comment

Cyclohexylphosphonic acid, (I), is one of the simplest phosphonic acids. These acids find increasing use in the syntheses of organophosphorus compounds, and in organometallic chemistry as stable bulky ligands. Phosphonates exhibit a rich oxo-cluster chemistry with many different structures, e.g. a tert-butylphosphonato-zinc cluster (Roesky & Walawalkar, 1999) or a methylphosphonato-gallium cluster (Mason et al., 1998). The present structure determination of (I) was undertaken firstly because there are few published structures of aliphatic phosphonic acids, and secondly to investigate the nature of the O—H···O hydrogen-bond interactions in the solid state. \sch

The molecule of (I), which displays crystallographic mirror symmetry (the mirror plane passes through atoms P1, O1 and C4), is shown in Fig. 1, with the associated dimensions given in Table 1. The P1═O1 bond length is 1.5089 (18) Å. Within experimental error, this is similar to the values in benzenephosphonic acid [1.496 (4) Å; Weakley, 1976], phosphonoacetic acid [1.494 (2) Å; Lis, 1997] and 4-methyl-2,6-bis(phosphonomethyl)phenol dihydrate [1.4981 (13) and 1.5015 (14) Å; Ferguson et al., 1993].

The other two P—O distances, which are symmetry-equivalent, are 1.5557 (13) Å. A search of the October 2001 release of the Cambridge Structural Database (CSD; Allen & Kennard, 1993) for structures containing the C—P═ O(—OH)₂ fragment revealed only a few aliphatic phosphonic acids. The P—O distances are in agreement with the reported standard bond length of 1.503 (6) Å for P═O and 1.57 (1) Å for P—O (Allen et al., 1987), e.g. 1-hydroxycyclohexanephosphonic acid (Ohms et al., 1996) shows two P—O distances of 1.548 (2) and 1.542 (2) Å, and a P═O bond length of 1.495 (2) Å.

The results of theoretical studies for free cyclohexylphosphonic acid (6–31G** using BL3YP in TITAN; Wavefunction, 1999) Query are not exactly identical with the present experimental determination of the molecular structure of (I) in the solid state. The O—P—O angle (113 and 105°), P═O distance (1.49 Å) and P—O (1.57 Å) distances are very similar, within experimental error. However, the calculations predict a value for the H8—O2—P1—O2A dihedral angle of 103.5°, significantly different from the observed H8—O2—P1—O2 dihedral angle of 151.6 (19)°. This is clearly a consequence of the molecular packing in (I).

There is one short O—H···O hydrogen bond, with O2···O1 2.5915 (17) Å, consistent with the values of 2.458 (2)–2.753 (2) Å in 4-methyl-2,6-bis(phosphonomethyl)phenol dihydrate (Ferguson et al., 1993). A search of the CSD revealed that more than 80% of phosphonic acids have P—O—H···O═P systems, with O···O distances in the range 2.5–2.6 Å. Each P═O O atom is an acceptor of two intermolecular hydrogen bonds (Table 2).

For molecules of the type R—PO(OH)₂, three-dimensional networks, planes or chains of hydrogen bonds have been observed. Examples are a chain structure for 1-(benzyloxycarbonylamino)ethylphosphonic acid (Chadha & Oesapay 1995), a double-layer structure for benzenephosphonic acid (Weakley, 1976) or a network for 2-fluorobenzylphosphonic acid (Langley et al., 1996). In the case of (I), the hydrogen bonding leads to eight-membered rings, which form a a one-dimensional chain with oppositely oriented cyclohexyl groups. No intermolecular C—H···O hydrogen bonds are observed in (I), nor are any other significant contacts between the layers.

S2. Experimental

Cyclohexylphosphonic acid was heated in tetrahydrofurane until most of the solid was dissolved. Crystals suitable for X-ray diffraction analysis were obtained by slowly cooling of the solution containing a few drops of hexane.

S3. Refinement

All H atoms were visible in difference maps. The hydroxyl H atom was refined isotropically, while those attached to C atoms were positioned geometrically, with C—H = 0.98–0.99 Å, and refined as riding atoms, with U_iso(H) = 1.2U_eq(C). Please check restraints.

Computing details

Data collection: SMART (Siemens, 1996); cell refinement: SMART Query or SAINT?; data reduction: SAINT (Siemens, 1996); program(s) used to solve structure: SHELXS97 (Sheldrick, 1990) Query or SHELXTL?; program(s) used to refine structure: SHELXL97 (Sheldrick, 1997) Query or SHELXTL?; molecular graphics: SHELXTL (Bruker, 1997); software used to prepare material for publication: SHELXL97 Query or SHELXTL?.

Figures

	Fig. 1. A view of the molecular structure of (I), showing the atom-numbering scheme. Displacement ellipsoids are drawn at the 50% probability level and H atoms are shown as small spheres of arbitrary radii. Please check labelling of H8.
	Fig. 2. The packing in the crystal of (I). Dashed lines show hydrogen bonds [symmetry code: (i) 1 - x, 1 - y, 1 - z]. Query.

Cyclohexylphosphonic acid

Crystal data

C6H13O3P	F(000) = 176
Mr = 164.13	Dx = 1.351 Mg m^−3
Monoclinic, P21/m	Mo Kα radiation, λ = 0.71073 Å
a = 6.8193 (14) Å	Cell parameters from 75 reflections
b = 6.7291 (13) Å	θ = 3.4–19.5°
c = 9.0902 (18) Å	µ = 0.29 mm^−1
β = 104.72 (3)°	T = 203 K
V = 403.43 (14) Å^3	Needle, colourless
Z = 2	0.4 × 0.1 × 0.1 mm

Data collection

Bruker SMART CCD 1000 area-detector diffractometer	762 independent reflections
Radiation source: fine-focus sealed tube	697 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.024
ω scans	θmax = 25.0°, θmin = 3.1°
Absorption correction: empirical (using intensity measurements) (blessing, 1995) ?	h = −6→8
Tmin = 0.890, Tmax = 0.971	k = −7→7
1901 measured reflections	l = −10→8

Refinement

Refinement on F^2	Primary atom site location: structure-invariant direct methods
Least-squares matrix: full	Secondary atom site location: difference Fourier map
R[F^2 > 2σ(F^2)] = 0.037	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.103	H atoms treated by a mixture of independent and constrained refinement
S = 1.16	w = 1/[σ^2(Fo^2) + (0.0556P)^2 + 0.1287P] where P = (Fo^2 + 2Fc^2)/3
762 reflections	(Δ/σ)max = 0.001
56 parameters	Δρmax = 0.58 e Å^−3
0 restraints	Δρmin = −0.35 e Å^−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	0.67983 (9)	0.7500	0.49921 (7)	0.0247 (3)
C1	0.7825 (4)	0.7500	0.3359 (3)	0.0271 (6)
H1	0.9321	0.7500	0.3728	0.033*
O1	0.4511 (3)	0.7500	0.45263 (19)	0.0284 (5)
O2	0.7690 (2)	0.5687 (2)	0.60038 (14)	0.0321 (4)
C2	0.7202 (3)	0.5615 (3)	0.2398 (2)	0.0341 (5)
H2	0.7706	0.4442	0.3017	0.041*
H3	0.5720	0.5531	0.2076	0.041*
C4	0.7431 (5)	0.7500	0.0045 (3)	0.0390 (7)
H6	0.8075	0.7500	−0.0803	0.047*
H7	0.5958	0.7500	−0.0380	0.047*
C3	0.8051 (3)	0.5631 (3)	0.0998 (2)	0.0394 (5)
H4	0.9533	0.5555	0.1322	0.047*
H5	0.7557	0.4459	0.0374	0.047*
H8	0.700 (4)	0.473 (4)	0.584 (3)	0.053 (7)*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
P1	0.0279 (4)	0.0167 (4)	0.0280 (4)	0.000	0.0042 (3)	0.000
C1	0.0294 (13)	0.0203 (13)	0.0311 (13)	0.000	0.0066 (11)	0.000
O1	0.0296 (10)	0.0181 (9)	0.0367 (10)	0.000	0.0071 (7)	0.000
O2	0.0341 (8)	0.0226 (8)	0.0359 (7)	−0.0007 (6)	0.0020 (6)	0.0064 (5)
C2	0.0465 (12)	0.0195 (10)	0.0365 (10)	0.0003 (8)	0.0108 (8)	−0.0023 (7)
C4	0.0449 (17)	0.0408 (17)	0.0321 (14)	0.000	0.0114 (12)	0.000
C3	0.0494 (12)	0.0328 (12)	0.0367 (10)	0.0050 (9)	0.0124 (9)	−0.0065 (8)

Geometric parameters (Å, º)

P1—O1	1.5089 (18)	C2—H2	0.9800
P1—O2^i	1.5557 (13)	C2—H3	0.9800
P1—O2	1.5557 (13)	C4—C3^i	1.525 (3)
P1—C1	1.795 (3)	C4—C3	1.525 (3)
C1—C2	1.537 (2)	C4—H6	0.9800
C1—C2^i	1.537 (2)	C4—H7	0.9800
C1—H1	0.9900	C3—H4	0.9800
O2—H8	0.79 (3)	C3—H5	0.9800
C2—C3	1.526 (3)
O1—P1—O2^i	112.76 (7)	C3—C2—H3	109.4
O1—P1—O2	112.76 (7)	C1—C2—H3	109.4
O2^i—P1—O2	103.32 (11)	H2—C2—H3	108.0
O1—P1—C1	111.13 (11)	C3^i—C4—C3	111.1 (2)
O2^i—P1—C1	108.23 (7)	C3^i—C4—H6	109.4
O2—P1—C1	108.23 (7)	C3—C4—H6	109.4
C2—C1—C2^i	111.2 (2)	C3^i—C4—H7	109.4
C2—C1—P1	111.14 (12)	C3—C4—H7	109.4
C2^i—C1—P1	111.14 (12)	H6—C4—H7	108.0
C2—C1—H1	107.7	C4—C3—C2	111.74 (17)
C2^i—C1—H1	107.7	C4—C3—H4	109.3
P1—C1—H1	107.7	C2—C3—H4	109.3
P1—O2—H8	113.8 (19)	C4—C3—H5	109.3
C3—C2—C1	111.08 (17)	C2—C3—H5	109.3
C3—C2—H2	109.4	H4—C3—H5	107.9
C1—C2—H2	109.4
H8—O2—P1—O2^i	151.6 (19)

Symmetry code: (i) x, −y+3/2, z.

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
O2—H8···O1^ii	0.79 (3)	1.80 (3)	2.5915 (17)	178 (3)

Symmetry code: (ii) −x+1, −y+1, −z+1.