Sodium di­hydrogen tris­(cyclo­propane­carboxyl­ate)

The title acid salt, Na⁺·C₄H₅O₂^-·2C₄H₆O₂, contains finite anions in which two cyclo­propanoic acid mol­ecules are hydrogen bonded to a cyclo­propanoate residue. Each such anion interacts with four different Na⁺ cations.

S1. Comment

The title acid salt, (I), was obtained during an attempt to make a conventional acid salt of cyclopropanoic acid. Most monocarboxy acids, HX, form acid salts of the general type MHX₂, where M is any singly-charged cation. However, Speakman (1972) noted in his review of the structures of acid salts that more complex compositions are very occasionally found, citing the examples of KH₂X₃, HX = acetic acid, and RbH₂X₃, HX = monochloroacetic acid. Salt (I) belongs to this rare class of acid salts. It appears to be identical to the compound whose cell dimensions were reported by Hwang & Donohue (1971). \sch

The asymmetric unit of (I) consists of one Na⁺ cation and an XH···X···HX^- anion formed by linking two cyclopropanoic acid molecules, HX, to the same cyclopropanoate anion through moderate-to-strong (Jeffrey, 1997) O—H···O hydrogen bonds (see Table 2). The geometries of the three independent cyclopropanoic acid residues are consistent with an ordered arrangement of hydrogen bonds: the deprotonated acid contains C11—O bonds of nearly equal length [1.251 (2) and 1.254 (2) Å], whereas the C21—-O and C31–O bonds show the difference in length expected if O22 and O32 are protonated [1.214 (2) and 1.305 (2) Å, and 1.189 (2) and 1.325 (2) Å, respectively]. Disorder of the C32–C34 ring obscures some of its structural details, but the other two cyclopropane units show the expected shortening of the distal C—C bonds [1.465 (3) and 1.461 (3) Å] relative to the others [1.491 (3)–1.504 (3) Å; Allen, 1980].

The Na⁺ ions lie almost exactly on the 2₁ screw axes (Fig. 1). In consequence, the operations of the screw axes generate nearly linear chains of regularly spaced Na⁺ cations which run parallel to the b axis. The distance of 3.402 (2) Å between adjacent Na⁺ ions in these chains is only 0.014 Å greater than b/2. Each Na⁺ ion is surrounded by a distorted octahedron of O atoms (Table 1). Adjacent octahedra are linked through the O21···O31 edge and also through the η²-bridging carboxy group containing O11 and O12. Each Na⁺ ion is bonded to three different XH···X···HX^- anions and each XH···X···HX^- anion donates six electron pairs to four different Na⁺ ions. This highly stable arrangement uses all lone pairs on unprotonated O atoms O11, O12, O21 and O31 and the hydrogen-bond-donor properties of the O22 and O32 OH groups for inter-residue bonding.

Since Speakman's (1972) review two MH₂X₃ structures have been fully described and both contain the finite XH···X···HX^- anions also found in (I). The cation in KH₂(CH₃CO₂)₃ (Efremov et al., 1986) is eight-coordinate. NaH₂(CH₃CO₂)₃ more closely resembles (I), with the finite XH···X···HX^- anions stabilizing a chain of octahedrally coordinated Na⁺ cations related by a 4₁ screw axis; the Na—O distances [2.316 (4)–2.580 (4) Å] are less regular than those in (I) and the O···O distances in the hydrogen bonds [2.509 (4) and 2.503 (4) Å] are somewhat shorter (Perrotti & Tazzoli, 1981). Interestingly, acetic acid also forms a regular sodium salt, Na(CH₃CO₂), which crystallizes as a trihydrate (Doxsee & Stevens, 1990) and in two anhydrous forms (Hsu & Nordman, 1983), and a regular acid salt NaHX₂ (Barrow et al., 1975); all have been structurally characterized. Though an analysis of potassium dihydrogen tris(o-chlorobenzoate) was successful (Golic & Speakman, 1975) no structural details have been published.

S2. Experimental

Crystals were obtained from an aqueous solution of cyclopropanoic acid and sodium hydroxide in 2:1 mole ratio. Analysis found: C 50.8, H 6.05%; calculated for C₁₂H₁₇NaO₆: C 51.4, H 6.07%. IR (KBr discs): 3439, 3081, 3022, 2860, 2480, 1905, 1692, 1522, 1430, 1362, 1294, 1228 cm^-1.

S3. Refinement

The carboxy H atoms, H2 and H3, were located in a ΔF synthesis. Other H atoms were positioned using stereochemical criteria and were then constrained to ride on their parent C atoms. The C32–C34 cyclopropane ring is disordered over two sites with equal probability and the parameters of the disordered atoms are therefore subject to some systematic error.

Computing details

Data collection: CAD-4 EXPRESS (Enraf Nonius, 1992); cell refinement: CAD-4 EXPRESS; data reduction: XCAD4 (Harms & Wocadlo , 1995); program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: ORTEP-3 (Farrugia, 1997); software used to prepare material for publication: WinGX (Farrugia, 1999).

Figures

Fig. 1. (a) A view of the coordination of the Na^+ ion showing 20% displacement ellipsoids and the atom labelling. Only one component of the disordered C32–C34 ring is displayed. (b) A view of one complete anion, formed by the O11···HO32^i and O12···HO22^ii hydrogen bonds, and of the four Na^+ cations to which it bonds. These cations are part of a chain running parallel to the b axis. [Symmetry codes: (i) 1/2 - x, 1/2 + y, 3/2 - z; (ii) 1/2 - x, y - 1/2, 3/2 - z; (iii) x, -1 + y, z.]

(I)

Crystal data

NaH2(C4H5O2)3	F(000) = 592
Mr = 280.25	Dx = 1.337 Mg m^−3 Dm = 1.34 Mg m^−3 Dm measured by flotation in heptane/1,2-dichloroethane
Monoclinic, P21/n	Mo Kα radiation, λ = 0.71073 Å
a = 12.3629 (7) Å	Cell parameters from 25 reflections
b = 6.7768 (4) Å	θ = 18.3–23.8°
c = 16.9374 (12) Å	µ = 0.13 mm^−1
β = 101.151 (6)°	T = 294 K
V = 1392.24 (15) Å^3	Needle, colourless
Z = 4	0.49 × 0.21 × 0.11 mm

Data collection

Enraf Nonius CAD4 diffractometer	θmax = 27°, θmin = 2.3°
ω/2θ scans	h = −15→2
4477 measured reflections	k = −8→1
3357 independent reflections	l = −23→21
2175 reflections with I > 2σ(I)	3 standard reflections every 184 reflections
Rint = 0.018	intensity decay: none

Refinement

Refinement on F^2	0 restraints
Least-squares matrix: full	H atoms treated by a mixture of independent and constrained refinement
R[F^2 > 2σ(F^2)] = 0.042	Calculated w = 1/[σ^2(Fo^2) + (0.0556P)^2 + 0.352P] where P = (Fo^2 + 2Fc^2)/3
wR(F^2) = 0.125	(Δ/σ)max = 0.001
S = 1.02	Δρmax = 0.26 e Å^−3
3357 reflections	Δρmin = −0.24 e Å^−3
207 parameters

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.

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

	x	y	z	Uiso*/Ueq	Occ. (<1)
Na1	0.25832 (6)	0.26125 (9)	0.75806 (4)	0.0424 (2)
O11	0.43738 (10)	0.16489 (18)	0.74499 (8)	0.0480 (3)
O12	0.38710 (11)	−0.11652 (19)	0.68568 (8)	0.0549 (4)
C11	0.45721 (14)	0.0169 (2)	0.70601 (10)	0.0370 (4)
C12	0.56531 (15)	−0.0031 (3)	0.68133 (12)	0.0482 (5)
H12	0.5751	−0.1226	0.6509	0.058*
C13	0.66778 (16)	0.0764 (4)	0.73416 (15)	0.0661 (6)
H13A	0.6601	0.1396	0.7842	0.079*
H13B	0.7357	0.0029	0.7366	0.079*
C14	0.62219 (17)	0.1788 (4)	0.65887 (13)	0.0614 (6)
H14A	0.662	0.1682	0.615	0.074*
H14B	0.5864	0.3049	0.6626	0.074*
O21	0.23813 (10)	−0.00417 (17)	0.84734 (7)	0.0432 (3)
O22	0.11666 (13)	0.1073 (2)	0.91684 (9)	0.0671 (5)
H2	0.107 (2)	0.207 (5)	0.8780 (17)	0.107 (10)*
C21	0.18570 (14)	−0.0252 (2)	0.90041 (10)	0.0388 (4)
C22	0.19714 (15)	−0.2029 (3)	0.95117 (10)	0.0452 (4)
H22	0.2424	−0.3079	0.9345	0.054*
C23	0.20379 (19)	−0.1860 (3)	1.04051 (11)	0.0584 (5)
H23A	0.2538	−0.2739	1.0751	0.07*
H23B	0.1969	−0.0556	1.0626	0.07*
C24	0.10587 (18)	−0.2725 (4)	0.99023 (11)	0.0595 (6)
H24A	0.0384	−0.1956	0.9815	0.071*
H24B	0.0954	−0.4138	0.994	0.071*
O31	0.12784 (16)	0.0376 (2)	0.66665 (9)	0.0677 (4)
O32	−0.04255 (14)	−0.0599 (3)	0.66820 (13)	0.0839 (6)
H3	−0.011 (3)	−0.145 (5)	0.7033 (18)	0.121 (12)*
C31	0.0311 (3)	0.0585 (3)	0.64551 (13)	0.0683 (7)
C32	0.0045 (4)	0.2197 (7)	0.5908 (3)	0.0438 (10)	0.5
H32A	0.0645	0.2941	0.5744	0.053*	0.5
C33	−0.1061 (4)	0.1989 (8)	0.5310 (3)	0.0599 (12)	0.5
H33A	−0.1122	0.2599	0.4786	0.072*	0.5
H33B	−0.146	0.0757	0.5311	0.072*	0.5
C34	−0.1004 (4)	0.3288 (7)	0.6005 (3)	0.0556 (11)	0.5
H34A	−0.137	0.2857	0.6432	0.067*	0.5
H34B	−0.1033	0.4699	0.5907	0.067*	0.5
C32B	−0.0573 (6)	0.2146 (10)	0.5948 (4)	0.0827 (19)	0.5
H32B	−0.1349	0.2039	0.5992	0.099*	0.5
C33B	−0.0323 (8)	0.2610 (9)	0.5186 (3)	0.100 (2)	0.5
H33C	−0.0934	0.2834	0.4741	0.119*	0.5
H33D	0.0317	0.1987	0.504	0.119*	0.5
C34B	−0.0133 (5)	0.4075 (7)	0.5843 (3)	0.0745 (13)	0.5
H34C	0.0622	0.4346	0.6104	0.089*	0.5
H34D	−0.063	0.5194	0.5805	0.089*	0.5

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Na1	0.0504 (4)	0.0291 (3)	0.0528 (4)	0.0021 (3)	0.0224 (3)	0.0055 (3)
O11	0.0455 (7)	0.0366 (7)	0.0650 (8)	−0.0007 (6)	0.0180 (6)	−0.0174 (6)
O12	0.0624 (8)	0.0398 (7)	0.0701 (9)	−0.0213 (7)	0.0317 (7)	−0.0164 (7)
C11	0.0435 (9)	0.0302 (8)	0.0394 (8)	−0.0012 (7)	0.0136 (7)	−0.0009 (7)
C12	0.0481 (10)	0.0413 (10)	0.0595 (11)	−0.0009 (9)	0.0209 (9)	−0.0129 (9)
C13	0.0411 (10)	0.0747 (15)	0.0795 (15)	0.0116 (11)	0.0043 (10)	−0.0067 (12)
C14	0.0485 (11)	0.0706 (14)	0.0689 (13)	−0.0173 (11)	0.0209 (10)	−0.0040 (12)
O21	0.0553 (7)	0.0325 (6)	0.0473 (7)	0.0061 (6)	0.0238 (6)	0.0052 (5)
O22	0.0866 (11)	0.0563 (9)	0.0722 (10)	0.0322 (8)	0.0497 (9)	0.0226 (8)
C21	0.0464 (9)	0.0331 (9)	0.0383 (8)	0.0031 (8)	0.0117 (7)	0.0014 (7)
C22	0.0544 (11)	0.0392 (10)	0.0448 (9)	0.0046 (8)	0.0164 (8)	0.0088 (8)
C23	0.0751 (14)	0.0576 (12)	0.0399 (10)	−0.0075 (11)	0.0043 (9)	0.0075 (9)
C24	0.0636 (13)	0.0662 (14)	0.0492 (11)	−0.0134 (11)	0.0121 (10)	0.0140 (10)
O31	0.0902 (12)	0.0523 (9)	0.0622 (9)	−0.0228 (9)	0.0192 (9)	0.0042 (7)
O32	0.0630 (10)	0.0610 (11)	0.1165 (15)	−0.0008 (9)	−0.0106 (10)	0.0366 (11)
C31	0.115 (2)	0.0337 (10)	0.0494 (12)	−0.0105 (13)	−0.0027 (13)	0.0081 (9)
C32	0.031 (2)	0.040 (2)	0.059 (2)	0.004 (2)	0.0061 (19)	0.0160 (17)
C33	0.058 (3)	0.058 (3)	0.056 (3)	0.003 (2)	−0.009 (2)	0.018 (2)
C34	0.049 (2)	0.040 (2)	0.075 (3)	0.014 (2)	0.005 (2)	0.009 (2)
C32B	0.063 (4)	0.058 (4)	0.117 (5)	−0.005 (4)	−0.006 (4)	0.036 (3)
C33B	0.163 (7)	0.066 (4)	0.055 (3)	0.033 (4)	−0.015 (4)	−0.001 (3)
C34B	0.092 (4)	0.056 (3)	0.073 (3)	0.011 (3)	0.010 (3)	0.007 (2)

Geometric parameters (Å, º)

Na1—O12^i	2.3429 (14)	O22—C21	1.305 (2)
Na1—O11	2.3590 (14)	C21—C22	1.471 (2)
Na1—O21	2.3939 (13)	C22—C24	1.491 (3)
Na1—O21^i	2.3972 (13)	C22—C23	1.504 (2)
Na1—O31	2.5162 (18)	C23—C24	1.461 (3)
Na1—O31^i	2.534 (2)	O31—C31	1.189 (3)
Na1—Na1^ii	3.4024 (2)	O31—Na1^ii	2.534 (2)
Na1—Na1^i	3.4024 (2)	O32—C31	1.325 (3)
O11—C11	1.251 (2)	C31—C32	1.429 (5)
O12—C11	1.254 (2)	C31—C32B	1.639 (7)
O12—Na1^ii	2.3429 (14)	C32—C34	1.529 (6)
C11—C12	1.482 (2)	C32—C33	1.542 (6)
C12—C13	1.502 (3)	C33—C34	1.459 (7)
C12—C14	1.504 (3)	C32B—C33B	1.419 (10)
C13—C14	1.465 (3)	C32B—C34B	1.440 (8)
O21—C21	1.214 (2)	C33B—C34B	1.477 (8)
O21—Na1^ii	2.3972 (13)
O12^i—Na1—O11	160.70 (6)	C11—C12—C14	119.22 (17)
O12^i—Na1—O21	80.02 (5)	C13—C12—C14	58.35 (14)
O11—Na1—O21	93.77 (5)	C14—C13—C12	60.87 (14)
O12^i—Na1—O21^i	101.21 (5)	C13—C14—C12	60.78 (15)
O11—Na1—O21^i	87.77 (5)	C21—O21—Na1	133.77 (11)
O21—Na1—O21^i	171.08 (5)	C21—O21—Na1^ii	124.26 (11)
O12^i—Na1—O31	90.70 (6)	Na1—O21—Na1^ii	90.50 (4)
O11—Na1—O31	106.08 (6)	O21—C21—O22	122.81 (16)
O21—Na1—O31	78.66 (5)	O21—C21—C22	121.62 (16)
O21^i—Na1—O31	92.47 (5)	O22—C21—C22	115.57 (15)
O12^i—Na1—O31^i	85.94 (6)	C21—C22—C24	121.55 (17)
O11—Na1—O31^i	79.16 (5)	C21—C22—C23	120.41 (17)
O21—Na1—O31^i	110.67 (5)	C24—C22—C23	58.42 (13)
O21^i—Na1—O31^i	78.25 (5)	C24—C23—C22	60.34 (13)
O31—Na1—O31^i	169.29 (6)	C23—C24—C22	61.24 (13)
O12^i—Na1—Na1^ii	110.21 (5)	C31—O31—Na1	126.97 (16)
O11—Na1—Na1^ii	76.12 (4)	C31—O31—Na1^ii	131.93 (14)
O21—Na1—Na1^ii	44.79 (3)	Na1—O31—Na1^ii	84.72 (6)
O21^i—Na1—Na1^ii	127.60 (5)	O31—C31—O32	123.2 (2)
O31—Na1—Na1^ii	47.86 (5)	O31—C31—C32	112.2 (3)
O31^i—Na1—Na1^ii	142.70 (5)	O32—C31—C32	124.5 (3)
O12^i—Na1—Na1^i	68.98 (4)	O31—C31—C32B	139.8 (3)
O11—Na1—Na1^i	108.15 (4)	O32—C31—C32B	96.8 (3)
O21—Na1—Na1^i	141.90 (4)	C32—C31—C32B	28.4 (2)
O21^i—Na1—Na1^i	44.71 (3)	C31—C32—C34	113.2 (4)
O31—Na1—Na1^i	121.94 (5)	C31—C32—C33	114.8 (4)
O31^i—Na1—Na1^i	47.42 (4)	C34—C32—C33	56.7 (3)
Na1^ii—Na1—Na1^i	169.60 (5)	C34—C33—C32	61.2 (3)
C11—O11—Na1	123.69 (11)	C33—C34—C32	62.1 (3)
C11—O12—Na1^ii	133.42 (11)	C33B—C32B—C34B	62.2 (4)
O11—C11—O12	121.84 (15)	C33B—C32B—C31	112.3 (7)
O11—C11—C12	120.10 (15)	C34B—C32B—C31	114.9 (5)
O12—C11—C12	118.05 (15)	C32B—C33B—C34B	59.6 (4)
C11—C12—C13	120.14 (17)	C32B—C34B—C33B	58.2 (5)
O12^i—Na1—O11—C11	142.71 (16)	C21—C22—C23—C24	110.6 (2)
O21—Na1—O11—C11	72.43 (14)	C21—C22—C24—C23	−108.6 (2)
O21^i—Na1—O11—C11	−98.77 (14)	O12^i—Na1—O31—C31	23.32 (19)
O31—Na1—O11—C11	−6.84 (15)	O11—Na1—O31—C31	−166.32 (18)
O31^i—Na1—O11—C11	−177.23 (14)	O21—Na1—O31—C31	103.00 (18)
Na1^ii—Na1—O11—C11	30.92 (13)	O21^i—Na1—O31—C31	−77.93 (18)
Na1^i—Na1—O11—C11	−139.20 (13)	O31^i—Na1—O31—C31	−48.2 (2)
Na1—O11—C11—O12	−16.2 (2)	Na1^ii—Na1—O31—C31	140.4 (2)
Na1—O11—C11—C12	162.76 (13)	Na1^i—Na1—O31—C31	−42.2 (2)
Na1^ii—O12—C11—O11	−29.3 (3)	O12^i—Na1—O31—Na1^ii	−117.06 (5)
Na1^ii—O12—C11—C12	151.69 (14)	O11—Na1—O31—Na1^ii	53.30 (5)
O11—C11—C12—C13	33.4 (3)	O21—Na1—O31—Na1^ii	−37.38 (4)
O12—C11—C12—C13	−147.62 (19)	O21^i—Na1—O31—Na1^ii	141.69 (5)
O11—C11—C12—C14	−34.9 (3)	O31^i—Na1—O31—Na1^ii	171.39 (17)
O12—C11—C12—C14	144.12 (18)	Na1^i—Na1—O31—Na1^ii	177.47 (5)
C11—C12—C13—C14	−107.8 (2)	Na1—O31—C31—O32	−112.1 (2)
C11—C12—C14—C13	109.3 (2)	Na1^ii—O31—C31—O32	9.3 (4)
O12^i—Na1—O21—C21	−9.52 (16)	Na1—O31—C31—C32	70.3 (3)
O11—Na1—O21—C21	152.07 (16)	Na1^ii—O31—C31—C32	−168.3 (2)
O21^i—Na1—O21—C21	−108.3 (3)	Na1—O31—C31—C32B	61.9 (6)
O31—Na1—O21—C21	−102.27 (17)	Na1^ii—O31—C31—C32B	−176.7 (5)
O31^i—Na1—O21—C21	72.24 (17)	O31—C31—C32—C34	−145.5 (3)
Na1^ii—Na1—O21—C21	−141.99 (18)	O32—C31—C32—C34	37.0 (5)
Na1^i—Na1—O21—C21	25.9 (2)	C32B—C31—C32—C34	23.0 (6)
O12^i—Na1—O21—Na1^ii	132.46 (6)	O31—C31—C32—C33	151.9 (3)
O11—Na1—O21—Na1^ii	−65.95 (5)	O32—C31—C32—C33	−25.7 (5)
O21^i—Na1—O21—Na1^ii	33.7 (2)	C32B—C31—C32—C33	−39.6 (7)
O31—Na1—O21—Na1^ii	39.71 (5)	C31—C32—C33—C34	102.4 (4)
O31^i—Na1—O21—Na1^ii	−145.77 (6)	C31—C32—C34—C33	−105.3 (5)
Na1^i—Na1—O21—Na1^ii	167.92 (8)	O31—C31—C32B—C33B	51.3 (8)
Na1—O21—C21—O22	5.0 (3)	O32—C31—C32B—C33B	−133.8 (5)
Na1^ii—O21—C21—O22	−126.86 (17)	C32—C31—C32B—C33B	34.6 (7)
Na1—O21—C21—C22	−174.44 (12)	O31—C31—C32B—C34B	−17.3 (9)
Na1^ii—O21—C21—C22	53.7 (2)	O32—C31—C32B—C34B	157.6 (6)
O21—C21—C22—C24	−153.56 (18)	C32—C31—C32B—C34B	−33.9 (5)
O22—C21—C22—C24	27.0 (3)	C31—C32B—C33B—C34B	−107.4 (5)
O21—C21—C22—C23	137.05 (19)	C31—C32B—C34B—C33B	103.2 (7)
O22—C21—C22—C23	−42.4 (3)

Symmetry codes: (i) −x+1/2, y+1/2, −z+3/2; (ii) −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
O22—H2···O12^i	0.93 (3)	1.62 (3)	2.5475 (18)	171 (3)
O32—H3···O11^ii	0.86 (3)	1.72 (3)	2.567 (2)	167 (3)

Symmetry codes: (i) −x+1/2, y+1/2, −z+3/2; (ii) −x+1/2, y−1/2, −z+3/2.