Betaine betainium hydrogen oxalate

The title compound, C₅H₁₂NO₂⁺·C₂HO₄^-·C₅H₁₁NO₂ or HC₂O₄^-·(HBET·BET)⁺ [BET is tri­methyl­glycine (betaine); IUPAC name: 1-carboxy-N,N,N-tri­methyl­methanaminium hydro­xide inner salt], contains pairs of betaine mol­ecules bridged by an H atom, forming dimers linked by a strong hydrogen bond. The hydrogen oxalate anions have a rather unusual star conformation, with an internal torsion angle of 70.1 (4)°. The betaine-betainium dimers are anchored between two zigzag chains of hydrogen oxalate mol­ecules hydrogen bonded head-to-tail running parallel to the b axis. An extended network of C-H...O interactions links the anionic chains to the cationic dimers.

S1. Comment

Betaine compounds are of importance in biological systems as components of complex lipids and as transmethylating agents. Pure betaine is an inner salt (zwitterion) where the proton of the carboxylic group has been transferred to the amino group. It may be combined with a variety of acids and inorganic salts to form 1:1 and 2:1 betainium salts and adducts and it is also a good chelating agent, via the carboxy group, of d and f metals. Many of these salts and adducts exhibit phase transitions associated with ferroelectric, antiferroelectric and ferro-elastic behaviour as well as commensurate and incommensurate superstructures (Shildkamp & Spilker, 1984; Haussühl, 1984, 1988). The most famous betaine compound is BCCD (betaine calcium chloride dihydrate), which exhibits a series of low-temperature phase transitions in a 'devil chair' sequence (Almeida et al., 1992). Recently, the system of isostructural ferroelectric betaine phosphite and antiferroelectric betaine phosphate, which form solid solutions over the entire composition range, has been much studied (Andrade et al., 1999; Banys et al., 2000). The crystal structures of betaine mono-hydrate (Mak, 1990) and its salts of hydrogen chloride (Fisher et al., 1970; Mak & Chen, 1990), phosphoric (Shildkamp & Spilker, 1984), sulfuric (Ratajczak et al., 1994), arsenic (Shildkamp et al., 1984), boric (Zobetz & Preisinger, 1989), telluric (Ilczysczyn et al., 1992), maleic (Ilczysczyn et al., 1995), selenic (Baran, Drozd, Lis et al., 1995), nitric (Baran, Drozd, Glowiak et al., 1995) and selenious (Paixão et al., 1997) acids have already been determined. The present work represents an effort to find other betaine compounds which may have similar interesting physical properties. \sch

The title compound, (I), contains a protonated betaine molecule with a charge counterbalanced by an hydrogenoxalate anion and an additional neutral molecule of betaine (Fig 1). The ionization states of both betaine and oxalic acid molecules were determined from the objective localization on difference Fourier maps of the H atoms bonded to the carboxylic groups, but could also be inferred from an inspection of the C–O bond distances. One of the betaine molecules exists in cationic form with a mono-positively charged trimethylammonium group and a neutral carboxylic group. The other betaine molecule retains the zwitterionic form with its large internal dipole moment due to the trimethylammonium and carboxylate groups carrying a positive and negative charge, respectively. The oxalic acid molecule is found in a single-ionized state, as necessary to maintain the overall charge neutrality of the structure. The related HBET·BET.selenic acid structure was reported by Baran et al. (1997).

Previous studies have shown that the betaine molecule has some degree of conformational flexibility depending on the crystalline environment. The carboxy groups of both protonated and neutral betaine molecules are planar within 0.003 (4) Å. The main backbone of the unprotonated betaine molecule is practically planar, the N1 atom lying within one s.u. in the carboxy plane and atom C5 being displaced out of this plane by 0.050 (8) Å. These small displacements arise from a small rotation of the carboxy and trimethylammonium groups around bonds C3–C4 and C4–N1 of 0.9 (5) and 1.9 (3)°, respectively, as shown by inspection of the appropriate torsion angles. Accordingly, the methyl groups C6 and C7 are placed in almost symmetrical positions with respect to the least-squares plane passing through the molecule backbone. The geometry of the protonated betaine molecule differs slightly from that of the neutral molecule. The torsion around C9–N2 is small and comparable to that of the neutral molecule but in the protonated species there is a significant twist by 6.5 (5)° of the carboxy group around the C8–C9 bond. As result of this twist, the N2 atom is displaced out of the carboxy plane by -0.1261 (58) Å and the distances of the C10 and C12 atoms to this plane show a larger asymmetry [-1.407 (5), 1.044 (6) Å] compared to that of the neutral molecule.

The most interesting feature of the structure is the strong hydrogen bond linking together the protonated and unprotonated betaine molecules with an O7···O6 distance of 2.457 (3) Å and a rather short H2···O6 distance of 1.39 (4) Å. The O7–H2 distance [1.07 (4) Å] is, accordingly, somewhat longer than the typical O—H bond distance found in weaker O—H···O hydrogen bonds such as those inter-joining the anions in the present compound (see below). It is characteristic of betainium compounds that the proton is loosely bound to the cation and in the presence of even a moderately strong acid the proton is often found to be located in a double potential minimum between the donor and the acceptor. This feature is considered responsible for the phase transitions often occurring in these compounds and for their peculiar dielectric properties. In such cases, and when the structure crystallizes in a polar space-group, a small applied electric field may overcome the double potential barrier and switch the position of the proton between donor and acceptor. The angle defined by the planes containing the backbones of the two betaines is 11.07 (11)° but they are not facing each other in a herring-bone way, the two molecules being practically inverted with respect to the hydrogen-bond centre so that the bare O atoms not involved in the intramolecular hydrogen bonding of the dimer are positioned farther away from each other.

The hydrogenoxalate anion is a relatively weak acid and has a large range of pK_a values in solution (1.37–3.81) due to interaction between the carboxylic groups (McAuley & Nancollas, 1960). In the many reports of structures including the hydrogenoxalate ion it usually has a near planar geometry and the anions are often found to be interconnected in chains by relatively short (2.49–2.57 Å) hydrogen bonds, with a typical H···O distance of 1.63 (3) Å (Küppers, 1973). The conformation of this anion is determined by the torsion angle around the central C–C bond that connects the two carboxylic groups. This angle rarely exceeds 35°, and it can be stated that the ion has a clear preference to remain planar. However, important deviations from planarity have been reported in some hydrogenoxalate salts (Chandra et al., 1998). In the present compound the hydrogen oxalate anions assume the more rare star conformation with a O1–C1–C2–O4 torsion angle of 70.1 (4) Å. The rather long C_sp2–C_sp2 bond [1.531 (4) Å] is within the reported range of values for the hydrogenoxalate anion (1.546–1.553 Å) (Allen et al., 1987; Barnes et al., 1998) and reflects the charge withdrawing effect of the electronegative carboxy groups. There is a clear asymmetry between the C–O bond lengths of the unionized carboxylic group, which shows that the H atom is not disordered. The angle H1–O1–C1–O2 is close to 0°, corresponding to the usual syn conformation (Chandra et al., 1998). The C1–O2 and C2–O4 bonds are short and approach the typical value of a C_sp2═O bond. The C2–O3 bond is significantly larger than these two bonds, as expected from the fact that O3 is an acceptor of a relatively strong hydrogen bond (see below).

The hydrogenoxalate ions are interlinked head to tail through hydrogen bonds, forming infinite chains running along the b axis. As result of the hydrogen bonding, the O1 and O3 atoms are not able to vibrate as freely as the O2 and O4 atoms, which have slightly larger and, in the case of O2, more anisotropic, atomic displacement parameters. These latter atoms are only involved as acceptors in weaker C—H···O interactions that connect the hydrogenoxalate chains with the betaine dimers as shown in Fig. 2.

Related literature

For related literature, see: Allen et al. (1987); Almeida et al. (1992); Andrade et al. (1999); Banys et al. (2000); Baran et al. (1997); Baran, Drozd, Glowiak, Sledz & Ratajczak (1995); Baran, Drozd, Lis, Sledz, Barnes & Ratajczak (1995); Barnes et al. (1998); Chandra et al. (1998); Fisher et al. (1970); Haussühl (1984, 1988); Ilczysczyn et al. (1992, 1995); Küppers (1973); Mak (1990); Mak & Chen (1990); McAuley & Nancollas (1960); Paixão et al. (1997); Ratajczak et al. (1994); Shildkamp & Spilker (1984); Shildkamp, Spilker & Schafer (1984); Spek (1995); Zobetz & Preisinger (1989).

S2. Experimental

Small needle-shaped colourless crystals were obtained after a few weeks of slow evaporation from an aqueous solution containing betaine and oxalic acid in the ratio 2:1. A suitable crystal was cut and checked by photographic methods before the data collection.

S3. Refinement

All H atoms could be located on a difference Fourier map; those bonded to C atoms where placed at idealized positions and refined as riding using suitable AFIX instructions with SHELXL97 defaults. The H atoms attached to the O atoms and involved in hydrogen bonding were freely refined isotropically.

Examination of the crystal structure with PLATON (Spek, 1995) showed that there are no solvent-accessible voids in the crystal lattice. All calculations were performed on a Pentium 350 MHz PC running LINUX.

Computing details

Data collection: CAD-4 Software (Enraf-Nonius, 1989); cell refinement: CAD-4 Software; data reduction: HELENA (Spek, 1997); program(s) used to solve structure: SHELXS97 (Sheldrick, 1990); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: ORTEPII (Johnson, 1976); software used to prepare material for publication: SHELXL97.

Figures

	Fig. 1. ORTEPII (Johnson, 1976) plot of the title compound. Displacement ellipsoids are drawn at the 50% level.
	Fig. 2. Packing diagram viewed along the b axis showing the intermolecular hydrogen-bonding network.

N,N,N-trimethylglycine-N,N,N-trimethylglycinium-hydrogenoxalate

Crystal data

C5H12NO2^+·C2HO4^−·C5H11NO2	F(000) = 696
Mr = 324.33	Dx = 1.346 Mg m^−3
Monoclinic, P21/c	Mo Kα radiation, λ = 0.71073 Å
a = 11.7729 (7) Å	Cell parameters from 25 reflections
b = 5.5841 (4) Å	θ = 8.1–15.5°
c = 24.549 (3) Å	µ = 0.11 mm^−1
β = 97.520 (7)°	T = 293 K
V = 1600.0 (2) Å^3	Needle, clear, colourless
Z = 4	0.50 × 0.20 × 0.15 mm

Data collection

Enraf-Nonius CAD-4 diffractometer	Rint = 0.026
Radiation source: fine-focus sealed tube	θmax = 25.1°, θmin = 3.4°
Graphite monochromator	h = −14→13
profile data from ω–2θ scans	k = −7→7
3044 measured reflections	l = 0→29
2845 independent reflections	3 standard reflections every 180 reflections
1634 reflections with I > 2σ(I)	intensity decay: 3%

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)] = 0.044	H atoms treated by a mixture of independent and constrained refinement
wR(F^2) = 0.137	w = 1/[σ^2(Fo^2) + (0.0569P)^2 + 1.1216P] where P = (Fo^2 + 2Fc^2)/3
S = 1.00	(Δ/σ)max < 0.001
2844 reflections	Δρmax = 0.25 e Å^−3
214 parameters	Δρmin = −0.19 e Å^−3
0 restraints	Extinction correction: SHELXL97 (Sheldrick, 1997), Fc^*=kFc[1+0.001xFc^2λ^3/sin(2θ)]^-1/4
Primary atom site location: structure-invariant direct methods	Extinction coefficient: 0.0094 (13)

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
O1	0.31020 (18)	0.3528 (4)	0.47984 (8)	0.0433 (5)
H1	0.301 (3)	0.210 (7)	0.4930 (15)	0.084 (13)*
O2	0.2087 (2)	0.4521 (4)	0.54575 (11)	0.0736 (8)
O3	0.3141 (2)	0.9111 (3)	0.51532 (9)	0.0576 (6)
O4	0.1981 (2)	0.7976 (4)	0.44145 (10)	0.0668 (7)
C1	0.2561 (2)	0.5053 (5)	0.50741 (11)	0.0350 (7)
C2	0.2561 (2)	0.7623 (5)	0.48567 (12)	0.0375 (7)
O5	0.6043 (2)	0.5304 (4)	0.30171 (10)	0.0598 (7)
O6	0.70907 (17)	0.8411 (4)	0.28151 (9)	0.0562 (6)
N1	0.46223 (18)	0.8427 (4)	0.35789 (9)	0.0337 (5)
C3	0.6286 (2)	0.7434 (5)	0.30280 (12)	0.0412 (7)
C4	0.5612 (2)	0.9291 (5)	0.33043 (13)	0.0462 (8)
H4A	0.6140	1.0115	0.3578	0.055*
H4B	0.5322	1.0465	0.3030	0.055*
C5	0.4077 (3)	1.0579 (5)	0.38008 (14)	0.0549 (9)
H5A	0.3445	1.0081	0.3984	0.082*
H5B	0.3805	1.1637	0.3504	0.082*
H5C	0.4630	1.1399	0.4057	0.082*
C6	0.3752 (3)	0.7167 (6)	0.31872 (13)	0.0531 (8)
H6A	0.4066	0.5687	0.3076	0.080*
H6B	0.3542	0.8158	0.2871	0.080*
H6C	0.3086	0.6842	0.3363	0.080*
C7	0.5029 (3)	0.6848 (6)	0.40507 (12)	0.0539 (8)
H7A	0.4383	0.6235	0.4208	0.081*
H7B	0.5510	0.7748	0.4323	0.081*
H7C	0.5458	0.5539	0.3926	0.081*
O7	0.82646 (18)	0.6036 (4)	0.22578 (9)	0.0537 (6)
H2	0.775 (3)	0.717 (7)	0.2476 (16)	0.101 (14)*
O8	0.9044 (2)	0.9374 (4)	0.19865 (10)	0.0646 (7)
N2	1.03564 (17)	0.6585 (4)	0.12911 (8)	0.0325 (5)
C8	0.8941 (2)	0.7220 (5)	0.19835 (11)	0.0403 (7)
C9	0.9602 (2)	0.5504 (5)	0.16707 (11)	0.0391 (7)
H9A	1.0074	0.4514	0.1935	0.047*
H9B	0.9058	0.4454	0.1457	0.047*
C10	0.9672 (2)	0.8062 (6)	0.08604 (12)	0.0476 (8)
H10A	0.9092	0.7085	0.0659	0.071*
H10B	1.0167	0.8693	0.0614	0.071*
H10C	0.9317	0.9360	0.1031	0.071*
C11	1.0898 (3)	0.4580 (5)	0.10107 (13)	0.0481 (8)
H11A	1.0311	0.3637	0.0804	0.072*
H11B	1.1334	0.3590	0.1281	0.072*
H11C	1.1395	0.5230	0.0768	0.072*
C12	1.1294 (2)	0.8038 (5)	0.16031 (12)	0.0465 (7)
H12A	1.1792	0.8635	0.1354	0.070*
H12B	1.1725	0.7052	0.1876	0.070*
H12C	1.0966	0.9359	0.1779	0.070*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
O1	0.0597 (13)	0.0223 (10)	0.0502 (13)	0.0037 (10)	0.0166 (10)	0.0000 (9)
O2	0.108 (2)	0.0390 (12)	0.0881 (18)	0.0062 (13)	0.0668 (16)	0.0116 (12)
O3	0.0798 (16)	0.0252 (11)	0.0653 (15)	−0.0063 (11)	0.0004 (12)	−0.0025 (11)
O4	0.0741 (15)	0.0427 (13)	0.0759 (17)	−0.0059 (12)	−0.0194 (13)	0.0165 (13)
C1	0.0393 (15)	0.0244 (14)	0.0425 (16)	0.0001 (12)	0.0108 (13)	0.0009 (12)
C2	0.0399 (15)	0.0247 (14)	0.0498 (18)	0.0014 (13)	0.0128 (14)	0.0004 (14)
O5	0.0632 (14)	0.0375 (13)	0.0841 (17)	0.0008 (11)	0.0302 (12)	−0.0129 (12)
O6	0.0527 (13)	0.0543 (13)	0.0680 (14)	−0.0031 (11)	0.0320 (11)	−0.0036 (11)
N1	0.0393 (12)	0.0240 (11)	0.0393 (12)	0.0009 (10)	0.0105 (10)	−0.0015 (10)
C3	0.0418 (16)	0.0394 (17)	0.0436 (16)	0.0023 (14)	0.0106 (13)	−0.0037 (14)
C4	0.0491 (17)	0.0324 (15)	0.0617 (19)	−0.0037 (14)	0.0250 (15)	−0.0025 (15)
C5	0.063 (2)	0.0329 (16)	0.075 (2)	0.0028 (16)	0.0329 (18)	−0.0107 (16)
C6	0.0436 (16)	0.0496 (19)	0.064 (2)	−0.0034 (15)	−0.0013 (15)	−0.0091 (17)
C7	0.069 (2)	0.0476 (19)	0.0445 (18)	0.0081 (17)	0.0063 (15)	0.0089 (16)
O7	0.0572 (13)	0.0495 (13)	0.0598 (14)	−0.0031 (11)	0.0280 (11)	0.0016 (11)
O8	0.0754 (16)	0.0337 (13)	0.0932 (18)	−0.0006 (12)	0.0430 (14)	−0.0086 (12)
N2	0.0339 (11)	0.0261 (11)	0.0382 (13)	−0.0004 (10)	0.0076 (10)	0.0011 (10)
C8	0.0390 (15)	0.0411 (18)	0.0417 (16)	−0.0017 (14)	0.0090 (13)	−0.0002 (14)
C9	0.0458 (16)	0.0304 (14)	0.0432 (16)	−0.0009 (13)	0.0137 (13)	0.0003 (13)
C10	0.0498 (17)	0.0459 (18)	0.0463 (17)	0.0041 (15)	0.0025 (14)	0.0151 (15)
C11	0.0521 (18)	0.0389 (16)	0.0569 (19)	0.0036 (15)	0.0207 (15)	−0.0088 (15)
C12	0.0406 (15)	0.0407 (17)	0.0569 (19)	−0.0081 (14)	0.0016 (14)	−0.0100 (15)

Geometric parameters (Å, º)

O1—C1	1.304 (3)	C7—H7A	0.9600
O1—H1	0.87 (4)	C7—H7B	0.9600
O2—C1	1.193 (3)	C7—H7C	0.9600
O3—C2	1.248 (3)	O7—C8	1.290 (3)
O4—C2	1.220 (3)	O7—H2	1.07 (4)
C1—C2	1.531 (4)	O8—C8	1.209 (3)
O5—C3	1.223 (3)	N2—C10	1.491 (3)
O6—C3	1.264 (3)	N2—C9	1.497 (3)
O6—H2	1.39 (4)	N2—C12	1.497 (3)
N1—C7	1.484 (4)	N2—C11	1.499 (3)
N1—C6	1.487 (4)	C8—C9	1.507 (4)
N1—C5	1.498 (3)	C9—H9A	0.9700
N1—C4	1.500 (3)	C9—H9B	0.9700
C3—C4	1.519 (4)	C10—H10A	0.9600
C4—H4A	0.9700	C10—H10B	0.9600
C4—H4B	0.9700	C10—H10C	0.9600
C5—H5A	0.9600	C11—H11A	0.9600
C5—H5B	0.9600	C11—H11B	0.9600
C5—H5C	0.9600	C11—H11C	0.9600
C6—H6A	0.9600	C12—H12A	0.9600
C6—H6B	0.9600	C12—H12B	0.9600
C6—H6C	0.9600	C12—H12C	0.9600
C1—O1—H1	108 (3)	N1—C7—H7C	109.5
O2—C1—O1	123.8 (3)	H7A—C7—H7C	109.5
O2—C1—C2	122.0 (2)	H7B—C7—H7C	109.5
O1—C1—C2	114.1 (2)	C8—O7—H2	113 (2)
O4—C2—O3	127.7 (3)	C10—N2—C9	110.8 (2)
O4—C2—C1	115.9 (3)	C10—N2—C12	110.9 (2)
O3—C2—C1	116.5 (3)	C9—N2—C12	111.0 (2)
C3—O6—H2	122.5 (16)	C10—N2—C11	108.1 (2)
C7—N1—C6	110.4 (2)	C9—N2—C11	107.9 (2)
C7—N1—C5	107.6 (2)	C12—N2—C11	108.1 (2)
C6—N1—C5	108.8 (2)	O8—C8—O7	125.1 (3)
C7—N1—C4	110.6 (2)	O8—C8—C9	125.3 (3)
C6—N1—C4	111.8 (2)	O7—C8—C9	109.6 (3)
C5—N1—C4	107.5 (2)	N2—C9—C8	116.7 (2)
O5—C3—O6	126.6 (3)	N2—C9—H9A	108.1
O5—C3—C4	122.6 (3)	C8—C9—H9A	108.1
O6—C3—C4	110.7 (3)	N2—C9—H9B	108.1
N1—C4—C3	117.6 (2)	C8—C9—H9B	108.1
N1—C4—H4A	107.9	H9A—C9—H9B	107.3
C3—C4—H4A	107.9	N2—C10—H10A	109.5
N1—C4—H4B	107.9	N2—C10—H10B	109.5
C3—C4—H4B	107.9	H10A—C10—H10B	109.5
H4A—C4—H4B	107.2	N2—C10—H10C	109.5
N1—C5—H5A	109.5	H10A—C10—H10C	109.5
N1—C5—H5B	109.5	H10B—C10—H10C	109.5
H5A—C5—H5B	109.5	N2—C11—H11A	109.5
N1—C5—H5C	109.5	N2—C11—H11B	109.5
H5A—C5—H5C	109.5	H11A—C11—H11B	109.5
H5B—C5—H5C	109.5	N2—C11—H11C	109.5
N1—C6—H6A	109.5	H11A—C11—H11C	109.5
N1—C6—H6B	109.5	H11B—C11—H11C	109.5
H6A—C6—H6B	109.5	N2—C12—H12A	109.5
N1—C6—H6C	109.5	N2—C12—H12B	109.5
H6A—C6—H6C	109.5	H12A—C12—H12B	109.5
H6B—C6—H6C	109.5	N2—C12—H12C	109.5
N1—C7—H7A	109.5	H12A—C12—H12C	109.5
N1—C7—H7B	109.5	H12B—C12—H12C	109.5
H7A—C7—H7B	109.5
O2—C1—C2—O4	−108.8 (3)	O5—C3—C4—N1	0.9 (5)
O1—C1—C2—O4	70.1 (4)	O6—C3—C4—N1	−180.0 (3)
O2—C1—C2—O3	70.5 (4)	C10—N2—C9—C8	−60.0 (3)
O1—C1—C2—O3	−110.6 (3)	C12—N2—C9—C8	63.6 (3)
C7—N1—C4—C3	64.7 (3)	C11—N2—C9—C8	−178.2 (2)
C6—N1—C4—C3	−58.7 (3)	O8—C8—C9—N2	−6.5 (5)
C5—N1—C4—C3	−178.1 (3)	O7—C8—C9—N2	174.9 (2)

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
O1—H1···O3^i	0.87 (4)	1.76 (4)	2.614 (3)	167 (4)
O7—H2···O6	1.07 (4)	1.39 (4)	2.457 (3)	172 (4)
C5—H5A···O4	0.96	2.44	3.383 (4)	168
C6—H6A···O5	0.96	2.36	2.971 (4)	121
C6—H6B···O5^ii	0.96	2.59	3.472 (4)	153
C7—H7B···O3^iii	0.96	2.59	3.528 (4)	165
C7—H7C···O5	0.96	2.42	3.066 (4)	124
C9—H9B···O4^iv	0.97	2.46	3.356 (4)	153
C10—H10B···O2^v	0.96	2.55	3.409 (4)	150
C10—H10C···O8	0.96	2.41	3.043 (4)	123
C12—H12A···O2^v	0.96	2.50	3.366 (4)	151
C12—H12B···O6^vi	0.96	2.53	3.409 (4)	153
C12—H12C···O8	0.96	2.38	3.019 (4)	123

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