Two new structures in the glycine–oxalic acid system

Glycinium semi-oxalate-II, C₂H₆NO₂⁺·C₂HO₄⁻, (A), and diglycin­ium oxalate methanol disolvate, 2C₂H₆NO₂⁺·C₂O₄²⁻·2CH₃OH, (B), are new examples in the glycine–oxalic acid family. (A) is a new polymorph of the known glycinium semi-oxalate salt, (C). Compounds (A) and (C) have a similar packing of the semi-oxalate monoanions with respect to the glycinium cations, but in (A) the two glycinium cations and the two semi-oxalate anions in the asymmetric unit are non-equivalent, and the binding of the glycinium cations to each other is radically different. Based on this difference, one can expect that, although the two forms grow concomitantly from the same batch, a transformation between (A) and (C) in the solid state should be difficult. In (B), two glycinium cations and an oxalate anion, which sits across a centre of inversion, are linked via strong short O—H...O hydrogen bonds to form the main structural fragment, similar to that in diglycinium oxalate, (D). Methanol solvent mol­ecules are embedded between the glycinium cations of neighbouring fragments. These fragments form a three-dimensional network via N—H...O hydrogen bonds. Salts (B) and (D) can be obtained from the same solution by, respectively, slow or rapid anti­solvent crystallization.

S1. Comment

Amino acids attract attention as drugs, biomimetics and molecular materials. They are interesting as a structural element for forming complexes with carboxylic acids: the amino and carboxylic acid groups, and in many cases also the side chains, are capable of forming hydrogen bonds with the carboxyl groups of the carboxylic acids, giving rise to a variety of crystal structures. The main structural elements, which can be found in the pure forms of amino acids (e.g. head-to-tail chains) can be preserved, or not, when introducing the additional species into the structure.

Glycine is the simplest amino acid and an optically inactive one, but it gives rise to multiple polymorphs as an individual compound, and to a rich variety of crystalline salts. Recently, the crystal structures of salts formed by glycine and oxalic acid have been described, namely glycinium semi-oxalate, (III) (Subha Nandhini et al., 2001), and diglycinium oxalate, (IV) (Chitra et al., 2006; Chitra & Choudhury, 2007). The present contribution reports the structures of two new compounds from the same family, glycinium semi-oxalate, (I), which is a new polymorph of (III), and diglycinium oxalate methanol disolvate, (II).

The asymmetric unit of (I) contains two symmetry-independent pairs of glycinium cations, NH₃⁺-CH₂—COOH, and semi-oxalate anions, HCOO-COO^- (Z' = 2) (Fig. 1), the backbone conformations of which differ significantly (compare the torsion angles in Table 2). In (I), the semi-oxalate anions are linked via O—H···O hydrogen bonds into infinite stacked chains of alternating symmetrically non-equivalent anions. Strictly speaking, these chains can be described by a C₂²(10) motif (Bernstein, 2002), since the chain has two independent oxalate ions. However, it could be approximated as C(5), if the difference between the non-equivalent oxalates is neglected. The chains are similar to the arrangement in salt (III), but, in contrast with (III), where the chains are planar, the chains in (I) have the form of a gently undulating wave which propagates in the [201] direction (Figs. 2b and 3a). The O···O distances between semi-oxalate anions in (I) are shorter than those in (III) (Table 2). The chains of semi-oxalate anions are linked to each other via glycinium bridges, forming N—H···O and O—H···O hydrogen bonds [these bonds form infinite C₂²(9) and C₂²(10) chains along the [001] direction] with semi-oxalate anions, giving a slightly folded layer which lies parallel to the (010) plane (Fig. 2a). These layers are further connected to each other via a cluster of four glycinium cations, two symmetry-independent cations from each layer, which are linked by head-to-tail N—H···O hydrogen bonds to give an R₄⁴(20) motif, thereby completing a three-dimensional network (Table 1). The glycinium cations in (I) do not form head-to-tail chains, neither planar (as in all the polymorphs of glycine) nor helical [as in (III)].

Polymorphs (I) and (III) have a similar packing of the semi-oxalate anions with respect to the glycinium cations (Fig. 3). The semi-oxalate chains are directed along [201] in (I), and along [010] in (III). The stacking directions also differ with respect to the crystallographic axes. At the same time, the distances between the molecules within a chain are similar in (I) and in (III): in (I) the period of a chain including four semi-oxalate anions is 22.033 (2) Å, whereas in (III) four periods of a chain including one semi-oxalate anion each are equal to 22.600 (6) Å. The distances between all the neighbouring chains in an undulating stack in (I) are the same (defined as d in Fig. 3a), whereas in (III) two non-equivalent distances alternate (defined as d₁ and d₂ in Fig. 3b). However, 2d in (I) is close to the sum of d₁ and d₂ in (III) [5.6481 (6) and 5.948 (2) Å, respectively]. In both (I) and (III), stacks of semi-oxalate anions alternate with columns formed by glycinium cations, and the distances between the semi-oxalate stacks, l, are very similar: 9.6000 (8) Å in (I) and 9.679 (2) Å in (III) (Fig. 3). At the same time, the binding of the glycinium cations to each other is radically different in (I) compared with (III). In (III), the infinite helical chains of glycinium cations are linked via N—H···O hydrogen bonds connecting the individual layers, and this makes d₁ shorter than d₂ and forms a structure consisting of double layers. All the glycinium cations within one individual layer have the same orientation. In (I), the orientation of the glycinium cations is different within a layer, and the layers are linked not via glycinium cations only, but via a more complex hydrogen-bond pattern involving the N—H···O hydrogen bonds between glycinium cations and semi-oxalate anions, so that a three-dimensional network is formed (Fig. 3). Based on this difference, one can expect that, although the two forms grow concomitantly from the same batch, a transformation between structures (I) and (III) in the solid state should be difficult.

Both (I) and (III) have structural elements similar to those in the structures of the individual oxalic acid and glycine. The packing of the semi-oxalate anions (hydrogen-bonded chains) is quite common for oxalate-containing crystal structures, as is the formation of stacks. The way the helical chains of glycinium cations are linked to each other in (III) can be compared with the formation of centrosymmetric dimers in α-glycine. The four-membered clusters [R₄⁴(20) hydrogen-bond motif] of glycinium cations in (I) resemble those in α-glycine (Bernstein & Davis, 1999). One can suppose that the two polymorphic structures of the same salt, (I) and (III), reflect the structures of clusters simultaneously present in aqueous solutions containing glycine and oxalic acid, and that the direction of the crystallization into different polymorphs depends on the structure of the `primary nuclei'. This hypothesis is within the approach suggested, for example, in the early work by Leonidov and co-workers (Leonidov, 1997; Leonidov et al., 1994, 1993) and presently developed by several research groups and summarized by Gavezzotti (2007).

The asymmetric unit of (II) contains a glycinium cation, half of an oxalate anion, which sits across a centre of inversion, and a methanol molecule (Fig. 4). With the exception of the methanol molecule, the chemical formula is essentially the same as in (IV). The oxalate anions are planar in both forms. The non-equivalence of the oxalate C—O bonds is apparently a consequence of the formation of a very short O—H···O hydrogen bond with the glycinium cation: the shorter C—O bond [1.2381 (14) Å] corresponds to atom O4, which accepts two longer hydrogen bonds, and the longer one [1.2684 (16) Å] corresponds to the O atom which acts as the acceptor of the short O—H···O interaction (Fig. 5). The calculated contoured difference Fourier maps in the planes of all the C—O—H groups (cations and anions) in which the H atom has been omitted from the structure factor calculation suggest that, for both structures (II) and (IV), the electron density is smeared between the oxalates. The short O—H···O bonds are not symmetric, and the values of the N—C—C—O torsion angles of the glycinium cations in (II) and (IV) differ (Table 3). Although oxalate anions are often planar in crystal structures, quantum chemical calculations have shown that a `free' oxalate anion should be twisted, and it is the interaction with the crystalline environment (the requirements of more efficient packing, chelating cations, formation of hydrogen bonds) that accounts for the planarity of the oxalate anion in a crystal structure (Naumov et al., 1997).

Salts (II) and (IV) crystallize in the same space group, P2₁/c, with similar unit-cell parameters [the values for (IV) are a = 4.9199 (18), b = 9.959 (4) and c = 11.320 (4) Å, and β = 108.010 (3)°; the choice of the unit cell is altered compared with that of Chitra et al. (2006), to obtain the standard space group setting P2₁/c]. The crystal structure of (II) is, in general, very similar to that of (IV). In both structures an oxalate anion and two glycinium cations form a similar centrosymmetric fragment via very short O—H···O hydrogen bonds. These fragments form stacks (Fig. 6). In (IV), the glycinium cations form hydrogen-bonded dimers, which link these fragments to each other. In (II), the methanol molecules are embedded between such pairs of glycinium cations via O—H···O and N—H···O hydrogen bonds, connecting fragments to each other to form infinite ribbons which run parallel to the [110] and [110] directions. Ribbons with different orientations are linked via N—H···O hydrogen bonds between the NH₃ group of the glycinium cation of one fragment and the oxalate anion of the other. Each NH₃ group is connected to two fragments, thus forming a three-dimensional hydrogen-bond network (Fig. 6, Table 3).

A comparative analysis of the graph sets describing the hydrogen-bond networks in (II) and (IV) can be significantly simplified if the short hydrogen bond O2—H2···O3 is treated as if it is intramolecular. Part of the first-level graph set of (II), which corresponds to hydrogen bonds a and b in Table 4 [C(9) a, C(9) b, C(10) a, C(10) b, R₄⁴(38) aaaa, R₄⁴(38) bbbb], is in common with the graph sets of (IV). These hydrogen bonds connect ribbons with different orientations. Other first-level graph sets present in (IV), namely C(14), R₂²(10) and C₂²(28), correspond to hydrogen bonds linking the glycinium cations into dimers. Because of the embedded methanol, in (II) these graph sets are transformed into the second-level graph sets C₂²(16) cd, R₄⁴(14) cdcd (shown in Fig. 5) and C₄⁴(32) cdcd, respectively.

The solvate (II) is metastable and when stored in air transforms into (IV), as has been confirmed by X-ray powder diffraction analysis. During this transition, a single crystal transforms into a polycrystalline pseudomorph, preserving the crystal habit.

The crystal structures of (II) and (IV) illustrate that minor modifications to the crystallization procedure from the same solution can result in a new manner of self-assembly of the same species to give a new crystalline form. The two forms can be obtained from an aqueous solution containing glycine and oxalic acid by adding methanol. If methanol is added slowly and the crystals grow on solution evaporation, methanol molecules become embedded between the glycinium cations and are preserved in the crystal structure. If the same solution is stirred to trigger a rapid antisolvent crystallization, the glycinium cations form dimers and methanol is no longer present in the final crystal structure.

Related literature

For related literature, see: Bernstein (2002); Bernstein & Davis (1999); Chitra & Choudhury (2007); Chitra et al. (2006); Gavezzotti (2007); Leonidov (1997); Leonidov et al. (1993, 1994); Naumov et al. (1997); Subha Nandhini, Krishnakumar & Natarajan (2001).

S2. Experimental

Crystals of (I) were obtained by slow evaporation of a saturated aqueous solution of glycine and oxalic acid in a 1:1 stoichiometric ratio. Colourless needle-shaped crystals of (I) were grown from the same crystallization batch as plate-shaped crystals of the known polymorph of glycine oxalate, (III). Interestingly, polymorph (I) could not be obtained on co-grinding of oxalic acid dihydrate and glycine, in contrast with polymorph (III).

Colourless needle-shaped crystals of (II) were obtained from aqueous solutions with variable ratios of the initial components (1:1 or 2:1 glycine:oxalic acid), using methanol as an antisolvent, if the solution was not stirred or disturbed in any other way. The volume of added methanol was approximately equal to the volume of the initial saturated aqueous solution. Interestingly, if the same amount of methanol was added rapidly to the same solution with energetic stirring, a powder sample of diglycinium oxalate, (IV), was formed.

S3. Refinement

All H atoms were located in difference Fourier maps. H atoms bonded to the methanol C atom in (II) were treated as riding atoms in geometrically idealized positions, with C—H = 0.96 and U_iso(H) = 1.5U_eq(C). The methyl group was permitted to rotate but not to tilt. The positions and isotropic displacement parameters of all other H atoms were refined freely.

Computing details

For both compounds, data collection: X-AREA (Stoe & Cie, 2006); cell refinement: X-AREA (Stoe & Cie, 2006); data reduction: X-RED (Stoe & Cie, 2006); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008) and X-STEP32 (Stoe & Cie, 2000); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008) and X-STEP32 (Stoe & Cie, 2000); molecular graphics: Mercury (Macrae et al., 2006); software used to prepare material for publication: Mercury (Macrae et al., 2006), PLATON (Spek, 2009), publCIF (Westrip, 2010) and enCIFer (Allen et al., 2004).

Figures

	Fig. 1. A displacement ellipsoid plot of the glycinium semi-oxalate, (I), showing the atom-numbering scheme and 50% probability displacement ellipsoids. H atoms are shown as arbitrary spheres.
	Fig. 2. (a) The structure of the (010) layer in (I). One can see chains of semi-oxalate anions along [201], and chains of alternating glycinium cations and semi-oxalate anions along [001]. (b) Undulating chains of semi-oxalate anions, viewed along [201]. Glycinium cations have been omitted for clarity. Hydrogen bonds are shown as dashed lines.
	Fig. 3. A comparison of the packing in the two semi-oxalate polymorphs, viewed along the direction of the semi-oxalate ribbons. Molecules are coloured by symmetry equivalence. (a) Compound (I) and (b) compound (III). The distances l, d, d1 and d2 are discussed in the text. Hydrogen bonds are shown as dashed lines.
	Fig. 4. A displacement ellipsoid plot of the diglycinium oxalate methanol disolvate, (III), showing the atom-numbering scheme and 50% probability displacement ellipsoids. H atoms are shown as arbitrary spheres. [Symmetry code: (i) -x + 1, -y + 1, -z + 1.]
	Fig. 5. Two fragments of the diglycinium oxalate methanol disolvate structure, showing the formation of hydrogen-bonded ribbons. Methanol molecules are embedded between glycinium cations, preventing the formation of glycinium dimers. At the centre one can see the R4^4(14) cdcd motif, which includes methanol molecules. Hydrogen bonds are shown as dashed lines.
	Fig. 6. The crystal packing in (II), viewed along the c axis. Glycinium cations and oxalate anions are coloured green (light) and methanol molecules are coloured blue (dark). Hydrogen bonds are shown as dashed lines.

(I) Glycinium semi-oxalate

Crystal data

C2H6NO2^+·C2HO4^−	F(000) = 688
Mr = 165.11	Dx = 1.686 Mg m^−3
Monoclinic, P21/c	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2ybc	Cell parameters from 14100 reflections
a = 11.8719 (8) Å	θ = 2.0–29.5°
b = 6.1493 (2) Å	µ = 0.16 mm^−1
c = 20.8247 (14) Å	T = 300 K
β = 121.180 (5)°	Prism, colourless
V = 1300.67 (15) Å^3	0.5 × 0.36 × 0.22 mm
Z = 8

Data collection

Stoe IPDSII diffractometer	3518 independent reflections
Radiation source: fine-focus sealed tube	3035 reflections with I > 2σ(I)
Plane graphite monochromator	Rint = 0.036
Detector resolution: 6.67 pixels mm^-1	θmax = 29.2°, θmin = 2.0°
ω scans	h = −15→16
Absorption correction: multi-scan (Blessing, 1995)	k = −7→8
Tmin = 0.930, Tmax = 0.965	l = −28→28
11921 measured reflections

Refinement

Refinement on F^2	0 restraints
Least-squares matrix: full	0 constraints
R[F^2 > 2σ(F^2)] = 0.047	All H-atom parameters refined
wR(F^2) = 0.119	w = 1/[σ^2(Fo^2) + (0.0773P)^2 + 0.1776P] where P = (Fo^2 + 2Fc^2)
S = 1.07	(Δ/σ)max < 0.001
3518 reflections	Δρmax = 0.31 e Å^−3
255 parameters	Δρmin = −0.36 e Å^−3

Special details

Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds 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
N1	0.89724 (12)	0.3758 (2)	0.31662 (6)	0.0291 (2)
N2	0.31663 (12)	0.1702 (2)	0.04577 (6)	0.0300 (3)
O1	0.95554 (9)	0.19671 (18)	0.60193 (5)	0.0318 (2)
O2	0.96594 (9)	0.1346 (2)	0.70932 (5)	0.0441 (3)
O3	0.70567 (9)	0.17777 (16)	0.64317 (5)	0.0290 (2)
O4	0.69147 (8)	0.20024 (18)	0.53166 (5)	0.0299 (2)
O5	0.83675 (10)	0.1903 (2)	0.45671 (6)	0.0412 (3)
O6	1.02621 (10)	0.2918 (2)	0.46706 (6)	0.0395 (3)
O7	0.44090 (11)	0.37687 (19)	0.23277 (6)	0.0370 (2)
O8	0.27592 (11)	0.14963 (19)	0.16063 (6)	0.0381 (3)
O9	0.20876 (8)	0.33454 (17)	0.27797 (4)	0.0279 (2)
O10	0.18826 (8)	0.32469 (16)	0.37893 (5)	0.0272 (2)
O11	0.44840 (8)	0.25820 (17)	0.46564 (4)	0.0286 (2)
O12	0.47180 (8)	0.32825 (17)	0.36785 (5)	0.0281 (2)
C1	0.90481 (11)	0.16919 (19)	0.64011 (6)	0.0203 (2)
C2	0.75394 (10)	0.18188 (18)	0.60417 (6)	0.0192 (2)
C3	0.83929 (12)	0.2234 (2)	0.34598 (6)	0.0247 (2)
C4	0.91232 (12)	0.2405 (2)	0.43036 (6)	0.0237 (2)
C5	0.39666 (12)	0.3123 (2)	0.11119 (7)	0.0252 (2)
C6	0.36390 (11)	0.26848 (19)	0.17084 (6)	0.0223 (2)
C7	0.25382 (10)	0.32104 (17)	0.34933 (6)	0.0180 (2)
C8	0.40540 (10)	0.30043 (18)	0.39765 (6)	0.0191 (2)
H4	0.597 (3)	0.224 (4)	0.5084 (14)	0.066 (7)*
H5	0.886 (2)	0.202 (4)	0.5084 (14)	0.061 (6)*
H7	0.428 (2)	0.335 (4)	0.2705 (15)	0.070 (7)*
H9	0.107 (3)	0.349 (5)	0.2486 (15)	0.080 (8)*
H11	0.986 (2)	0.350 (4)	0.3396 (13)	0.061 (7)*
H12	0.883 (2)	0.509 (4)	0.3244 (12)	0.062 (6)*
H13	0.864 (2)	0.358 (4)	0.2666 (13)	0.057 (6)*
H21	0.226 (2)	0.198 (3)	0.0252 (13)	0.054 (6)*
H22	0.3282 (19)	0.201 (3)	0.0077 (11)	0.041 (5)*
H23	0.343 (2)	0.031 (4)	0.0605 (11)	0.053 (6)*
H31	0.7438 (19)	0.260 (3)	0.3205 (11)	0.040 (5)*
H32	0.8499 (17)	0.077 (3)	0.3331 (9)	0.039 (5)*
H51	0.3766 (16)	0.459 (3)	0.0952 (10)	0.040 (5)*
H52	0.482 (2)	0.285 (3)	0.1293 (11)	0.038 (5)*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
N1	0.0322 (6)	0.0380 (6)	0.0263 (5)	0.0032 (5)	0.0216 (5)	0.0038 (4)
N2	0.0283 (5)	0.0443 (7)	0.0218 (5)	0.0006 (5)	0.0159 (4)	−0.0012 (4)
O1	0.0185 (4)	0.0586 (6)	0.0204 (4)	0.0014 (4)	0.0115 (3)	0.0048 (4)
O2	0.0179 (4)	0.0957 (9)	0.0148 (4)	−0.0052 (5)	0.0057 (3)	0.0043 (5)
O3	0.0220 (4)	0.0447 (5)	0.0259 (4)	−0.0005 (4)	0.0163 (4)	−0.0009 (4)
O4	0.0144 (4)	0.0544 (6)	0.0174 (4)	0.0010 (4)	0.0057 (3)	0.0028 (4)
O5	0.0296 (5)	0.0755 (8)	0.0219 (4)	−0.0103 (5)	0.0157 (4)	0.0039 (5)
O6	0.0243 (4)	0.0636 (7)	0.0293 (5)	−0.0069 (4)	0.0130 (4)	−0.0041 (4)
O7	0.0461 (6)	0.0427 (6)	0.0257 (4)	−0.0165 (5)	0.0211 (4)	−0.0078 (4)
O8	0.0405 (5)	0.0508 (6)	0.0340 (5)	−0.0189 (5)	0.0271 (4)	−0.0092 (4)
O9	0.0178 (4)	0.0496 (6)	0.0146 (4)	0.0025 (4)	0.0071 (3)	0.0025 (3)
O10	0.0172 (4)	0.0456 (5)	0.0204 (4)	0.0025 (3)	0.0109 (3)	0.0016 (3)
O11	0.0160 (4)	0.0508 (6)	0.0164 (4)	0.0025 (4)	0.0065 (3)	0.0043 (4)
O12	0.0184 (4)	0.0462 (5)	0.0216 (4)	−0.0005 (3)	0.0117 (3)	0.0023 (3)
C1	0.0139 (4)	0.0300 (6)	0.0154 (4)	−0.0026 (4)	0.0063 (4)	−0.0018 (4)
C2	0.0154 (4)	0.0240 (5)	0.0181 (5)	−0.0011 (4)	0.0085 (4)	−0.0007 (4)
C3	0.0272 (5)	0.0301 (6)	0.0200 (5)	−0.0004 (5)	0.0145 (4)	−0.0012 (4)
C4	0.0240 (5)	0.0299 (6)	0.0206 (5)	0.0013 (4)	0.0138 (4)	0.0011 (4)
C5	0.0241 (6)	0.0319 (6)	0.0250 (5)	−0.0009 (5)	0.0166 (5)	0.0019 (4)
C6	0.0242 (5)	0.0238 (5)	0.0225 (5)	0.0015 (4)	0.0147 (4)	0.0012 (4)
C7	0.0148 (4)	0.0224 (5)	0.0153 (4)	0.0002 (4)	0.0069 (4)	0.0002 (3)
C8	0.0142 (4)	0.0251 (5)	0.0167 (4)	0.0001 (4)	0.0071 (4)	−0.0007 (4)

Geometric parameters (Å, º)

C1—C2	1.5447 (15)	N1—H11	0.92 (2)
C1—O1	1.2326 (14)	N1—H12	0.87 (3)
C1—O2	1.2514 (13)	N1—H13	0.91 (2)
C2—O3	1.2128 (14)	C3—H31	0.998 (19)
C2—O4	1.2973 (13)	C3—H32	0.97 (2)
O4—H4	0.97 (3)	O5—H5	0.92 (2)
C7—C8	1.5466 (15)	N2—C5	1.4769 (17)
C7—O9	1.2955 (13)	C5—C6	1.5056 (16)
C7—O10	1.2178 (14)	C6—O7	1.3124 (15)
C8—O11	1.2587 (13)	C6—O8	1.2002 (16)
C8—O12	1.2418 (14)	N2—H21	0.95 (2)
O9—H9	1.04 (3)	N2—H22	0.89 (2)
N1—C3	1.4701 (17)	N2—H23	0.91 (2)
C3—C4	1.5078 (16)	C5—H52	0.90 (2)
C4—O5	1.3079 (15)	C5—H51	0.95 (2)
C4—O6	1.2008 (16)	O7—H7	0.91 (3)
O1—C1—O2	125.49 (10)	C4—C3—H31	114.4 (11)
O1—C1—C2	120.78 (10)	C4—C3—H32	108.0 (10)
O2—C1—C2	113.72 (10)	H31—C3—H32	109.8 (15)
C2—O4—H4	114.2 (15)	O5—C4—C3	111.53 (10)
O3—C2—O4	126.70 (10)	O6—C4—C3	122.59 (11)
O3—C2—C1	120.39 (10)	O6—C4—O5	125.87 (11)
O4—C2—C1	112.90 (9)	C4—O5—H5	108.4 (16)
O9—C7—C8	113.70 (9)	H22—N2—H23	108.2 (17)
O10—C7—O9	125.93 (10)	H22—N2—H21	103.0 (19)
O10—C7—C8	120.37 (9)	H23—N2—H21	116.1 (19)
O11—C8—C7	113.98 (10)	C5—N2—H21	110.4 (13)
O12—C8—O11	126.71 (10)	C5—N2—H22	111.9 (12)
O12—C8—C7	119.30 (9)	C5—N2—H23	107.4 (13)
C7—O9—H9	110.3 (15)	N2—C5—C6	109.74 (10)
H11—N1—H13	106 (2)	N2—C5—H51	108.3 (10)
H11—N1—H12	110 (2)	N2—C5—H52	108.9 (12)
H13—N1—H12	108 (2)	C6—C5—H51	109.5 (11)
C3—N1—H11	109.4 (14)	C6—C5—H52	109.7 (12)
C3—N1—H12	110.1 (15)	H52—C5—H51	110.6 (16)
C3—N1—H13	112.6 (14)	O7—C6—C5	111.96 (10)
N1—C3—C4	109.26 (10)	O8—C6—C5	122.38 (11)
N1—C3—H31	106.4 (11)	O8—C6—O7	125.66 (11)
N1—C3—H32	108.8 (11)	C6—O7—H7	111.1 (16)
O3—C2—C1—O1	−172.13 (12)	O10—C7—C8—O11	9.42 (16)
O3—C2—C1—O2	6.34 (17)	O10—C7—C8—O12	−169.73 (11)
O4—C2—C1—O1	6.76 (16)	O6—C4—C3—N1	−29.00 (18)
O4—C2—C1—O2	−174.77 (12)	O5—C4—C3—N1	151.84 (12)
O9—C7—C8—O11	−171.00 (11)	N2—C5—C6—O8	−6.59 (17)
O9—C7—C8—O12	9.85 (15)	N2—C5—C6—O7	174.31 (11)

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
O4—H4···O11	0.97 (3)	1.53 (3)	2.4972 (12)	175 (2)
O5—H5···O1	0.92 (2)	1.68 (2)	2.5923 (13)	171 (2)
O7—H7···O12	0.91 (3)	1.81 (3)	2.6586 (14)	153 (2)
O9—H9···O2^i	1.04 (3)	1.44 (3)	2.4744 (12)	178 (3)
N1—H11···O10^ii	0.92 (2)	2.10 (3)	3.0128 (15)	171 (2)
N1—H12···O8^iii	0.87 (3)	2.24 (2)	2.8800 (16)	131 (2)
N1—H12···O1^iv	0.87 (3)	2.50 (2)	3.1259 (17)	129.4 (18)
N1—H13···O2^v	0.91 (2)	2.09 (2)	2.7476 (14)	128.2 (19)
N1—H13···O3^v	0.91 (2)	2.28 (2)	3.1340 (15)	157 (2)
N2—H21···O6^i	0.95 (2)	2.03 (2)	2.9626 (16)	169 (2)
N2—H22···O10^v	0.89 (2)	2.32 (2)	2.9854 (14)	131.8 (16)
N2—H22···O11^v	0.89 (2)	2.04 (2)	2.8510 (14)	150.7 (17)
N2—H23···O12^vi	0.91 (2)	2.28 (2)	3.0476 (16)	141.9 (17)

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

(II) diglycinium oxalate methanol disolvate

Crystal data

2C2H6NO2^+·C2O4^2^−·2CH4O	F(000) = 324
Mr = 304.26	Dx = 1.438 Mg m^−3
Monoclinic, P21/c	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2ybc	Cell parameters from 5454 reflections
a = 5.0068 (7) Å	θ = 2.3–29.6°
b = 11.3293 (15) Å	µ = 0.13 mm^−1
c = 12.893 (2) Å	T = 295 K
β = 106.077 (12)°	Prism, colourless
V = 702.72 (17) Å^3	0.7 × 0.35 × 0.3 mm
Z = 2

Data collection

Stoe IPDSII diffractometer	1889 independent reflections
Radiation source: fine-focus sealed tube	1423 reflections with I > 2σ(I)
Plane graphite monochromator	Rint = 0.055
Detector resolution: 6.67 pixels mm^-1	θmax = 29.2°, θmin = 2.4°
ω scans	h = −6→6
Absorption correction: multi-scan (Blessing, 1995)	k = −15→15
Tmin = 0.917, Tmax = 0.962	l = −17→17
6655 measured reflections

Refinement

Refinement on F^2	0 restraints
Least-squares matrix: full	0 constraints
R[F^2 > 2σ(F^2)] = 0.042	H atoms treated by a mixture of independent and constrained refinement
wR(F^2) = 0.111	w = 1/[σ^2(Fo^2) + (0.0635P)^2] where P = (Fo^2 + 2Fc^2)/3
S = 1.06	(Δ/σ)max < 0.001
1889 reflections	Δρmax = 0.27 e Å^−3
120 parameters	Δρmin = −0.24 e Å^−3

Special details

Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds 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
N1	−0.0396 (3)	0.05018 (10)	0.75992 (9)	0.0304 (3)
O1	0.1886 (2)	0.14619 (9)	0.61386 (8)	0.0400 (3)
O2	−0.0223 (2)	0.32023 (8)	0.61376 (8)	0.0392 (3)
O3	0.2278 (2)	0.40084 (8)	0.48949 (7)	0.0336 (2)
O4	0.4573 (2)	0.51077 (9)	0.62996 (7)	0.0349 (2)
O5	0.2441 (3)	0.11246 (11)	0.40488 (9)	0.0513 (3)
C1	0.0361 (2)	0.21309 (11)	0.64474 (9)	0.0272 (3)
C2	−0.1081 (3)	0.17314 (12)	0.72752 (10)	0.0307 (3)
C3	0.4110 (2)	0.47540 (10)	0.53577 (9)	0.0253 (3)
C4	0.5073 (4)	0.14917 (18)	0.39710 (16)	0.0560 (4)
H4C	0.5180	0.1374	0.3246	0.084*
H4B	0.6496	0.1037	0.4460	0.084*
H4A	0.5331	0.2313	0.4154	0.084*
H2	0.094 (7)	0.356 (2)	0.554 (2)	0.101 (8)*
H5	0.226 (5)	0.126 (2)	0.462 (2)	0.071 (6)*
H11	−0.078 (4)	−0.0007 (16)	0.6989 (15)	0.044 (4)*
H12	0.141 (5)	0.0375 (16)	0.7930 (16)	0.054 (5)*
H13	−0.158 (4)	0.0266 (16)	0.7983 (15)	0.054 (5)*
H21	−0.053 (4)	0.2237 (15)	0.7913 (14)	0.044 (4)*
H22	−0.294 (4)	0.1818 (15)	0.6986 (15)	0.046 (5)*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
N1	0.0346 (6)	0.0345 (6)	0.0251 (5)	−0.0040 (5)	0.0134 (5)	0.0027 (4)
O1	0.0464 (6)	0.0431 (6)	0.0395 (5)	0.0071 (4)	0.0268 (5)	0.0053 (4)
O2	0.0492 (6)	0.0309 (5)	0.0463 (6)	0.0004 (4)	0.0278 (5)	0.0062 (4)
O3	0.0411 (5)	0.0357 (5)	0.0273 (4)	−0.0115 (4)	0.0147 (4)	−0.0016 (3)
O4	0.0357 (5)	0.0492 (6)	0.0247 (4)	−0.0074 (4)	0.0164 (4)	−0.0074 (4)
O5	0.0602 (8)	0.0628 (7)	0.0362 (5)	−0.0163 (6)	0.0222 (5)	−0.0150 (5)
C1	0.0254 (6)	0.0336 (6)	0.0245 (5)	−0.0040 (4)	0.0100 (4)	−0.0010 (4)
C2	0.0325 (7)	0.0341 (7)	0.0311 (6)	−0.0012 (5)	0.0178 (5)	0.0010 (5)
C3	0.0269 (6)	0.0285 (6)	0.0236 (5)	0.0018 (4)	0.0120 (5)	0.0005 (4)
C4	0.0503 (10)	0.0614 (11)	0.0575 (10)	−0.0094 (8)	0.0172 (8)	−0.0131 (8)

Geometric parameters (Å, º)

N1—C2	1.4674 (18)	O2—H2	1.16 (3)
C1—C2	1.5137 (15)	C3—C3^i	1.553 (2)
C1—O1	1.2184 (15)	C3—O3	1.2680 (15)
C1—O2	1.2860 (16)	C3—O4	1.2382 (14)
N1—H11	0.951 (18)	C4—O5	1.411 (2)
N1—H12	0.90 (2)	O5—H5	0.79 (3)
N1—H13	0.91 (2)	C4—H4C	0.9600
C2—H21	0.978 (18)	C4—H4B	0.9600
C2—H22	0.91 (2)	C4—H4A	0.9600
C2—N1—H11	111.3 (11)	O1—C1—C2	120.58 (11)
C2—N1—H12	114.4 (13)	O2—C1—C2	112.93 (10)
C2—N1—H13	107.2 (12)	C1—O2—H2	115.1 (13)
H11—N1—H12	103.9 (16)	O3—C3—C3^i	114.78 (12)
H11—N1—H13	105.1 (15)	O4—C3—C3^i	118.94 (13)
H12—N1—H13	114.6 (17)	O4—C3—O3	126.28 (10)
N1—C2—C1	111.41 (10)	C4—O5—H5	111.4 (18)
N1—C2—H21	109.1 (10)	O5—C4—H4C	109.5
N1—C2—H22	110.6 (11)	O5—C4—H4B	109.5
C1—C2—H21	109.8 (10)	H4C—C4—H4B	109.5
N1—C2—H22	110.6 (11)	O5—C4—H4A	109.5
H21—C2—H22	107.7 (16)	H4C—C4—H4A	109.5
O1—C1—O2	126.49 (11)	H4B—C4—H4A	109.5
O1—C1—C2—N1	−0.60 (18)	O2—C1—C2—N1	179.27 (11)

Symmetry code: (i) −x+1, −y+1, −z+1.

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
O2—H2···O3	1.16 (3)	1.31 (3)	2.4656 (12)	177 (3)
^dO5—H5···O1	0.79 (3)	2.03 (3)	2.8102 (15)	176 (2)
^cN1—H11···O5^ii	0.951 (18)	1.863 (19)	2.7844 (16)	162.4 (16)
^aN1—H12···O4^iii	0.90 (2)	2.01 (2)	2.9020 (17)	178.7 (18)
^bN1—H13···O4^iv	0.91 (2)	1.97 (2)	2.8695 (14)	166.8 (17)

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