Hydrogen-bonded bilayers in ­piperazinium(2+) bis(mandelate) bis(methanol) solvate

In the title compound, C₄H₁₂N₂²⁺·2C₈H₇O₃^-·2CH₄O, the cations lie across centres of inversion and are disordered over two orientations with equal occupancy; there are equal numbers of (R)- and (S)-mandelate anions present (mandelate is [alpha]-hydroxy­benzene­acetate). The anions and the neutral water mol­ecules are linked by O-H...O hydrogen bonds [O...O 2.658 (3) and 2.682 (3) Å, and O-H...O 176 and 166°] into deeply folded zigzag chains. Each orientation of the cation forms two symmetry-related two-centre N-H...O hydrogen bonds [N...O 2.588 (4) and 2.678 (4) Å, and N-H...O 177 and 171°] and two asymmetric, but planar, three-centre N-H...(O)₂ hydrogen bonds [N...O 2.686 (4)-3.137 (4) Å and N-H...O 137-147°], and by means of these the cations link the anion/water chains into bilayers.

S1. Comment

We have recently described the supramolecular structures of some adducts formed between diamines and aromatic carboxylic acids carrying hydrogen-bonding functional groups on the aryl rings (Burchell et al., 2000, 2001a,b). Developing this study to include acids where the additional functionality is distinct from the aryl ring, we have now characterized the 1:2 adduct formed between piperazine and racemic mandelic acid [2-hydroxy-2-phenylacetic acid, PhCH(OH)COOH], which crystallizes from methanol as the title solvated salt, (I), [H₂N(CH₂CH₂)₂NH₂]²⁺·2[PhCH(OH)COO]^-·2MeOH. The structures of several mandelate salts of diamines have been reported previously, but in all cases a single enantiomer of the acid was employed, as the emphasis was primarily on establishing the absolute configuration of the diamine component (De Costa et al., 1989; Acs et al., 1992; Larsen et al., 1993; Gjerlov & Larsen, 1997a,b; Barnes & Weakley, 1998). By contrast, the diamine component in compound (I) is achiral, the acid is a racemic mixture of enantiomers and the primary emphasis is on the supramolecular structure. \sch

In compound (I), the cation lies across a centre of inversion, chosen for convenience as that at (1/2,1/2,1/2), while the anion and the neutral methanol molecule lie in general positions. In space group Pbca, there are thus four cations per unit cell and equal numbers of (R)- and (S)-mandelate anions. The cations are disordered, with two orientations having equal occupancy; in both orientations, the ring adopts the usual chair conformation such that the two sets of C positions are virtually coincident (Fig. 1). Each cation, of whichever orientation, acts as a fourfold donor in N—H···O hydrogen bonds, and each anion accepts such bonds from two different cations. The methanol molecule acts as both a single donor and a single acceptor of O—H···O hydrogen bonds. The three components are linked into two-dimensional sheets, which are most simply analysed in terms of the one-dimensional chains formed by the anions and the methanol molecules, and of the linking of these chains by the disordered cations.

Within the asymmetric unit, methanol atom O4 acts as a hydrogen-bond donor to carboxylate atom O1 (Fig. 1) and hydroxyl atom O3 at (x, y, z) acts as a donor to methanol atom O4 at (5/2 - x, y - 1/2, z), while atom O3 at (5/2 - x, y - 1/2, z) acts as a donor to O4 at (x, y - 1, z). Hence, these two hydrogen bonds produce a C₂²(7) chain running parallel to [010] and generated by the glide plane at x = 5/4. There are four of these zigzag chains passing through each unit cell, and each chain contains both enantiomers of the anion. The reference chain lies in the domain 0.54 < z < 0.74, and the other three chains lie in the domains 0.04 < z < 0.24, 0.26 < z < 0.46 and 0.76 < z < 0.96. Within each domain, parallel chains are linked by the cations into sheets, and pairs of these sheets related by centres of inversion are likewise linked into bilayers; there are, however, no significant interactions between adjacent bilayers.

Each N atom, regardless of the orientation of the cation in which it lies, forms a two-centre hydrogen bond to a carboxylate O atom, O1 in the case of N1A and O2 in the case of N1B, both within the asymmetric unit, and also a planar three-centre hydrogen bond to carboxylate atom O2 and hydroxyl atom O3, both of which are at (3/2 - x, 1/2 + y, z) in the case of N1A and at (x - 1/2, 1/2 - y, 1 - z) in the case of N1B (Table 1). For the cation orientation defined by N1A, the N atom at (x, y, z) in the cation centred at (1/2,1/2,1/2) forms N—H···O hydrogen bonds to three acceptors, all in the domain 0.54 < z < 0.74, while the symmetry-related N atom in the same cation, which is at (1 - x, 1 - y, 1 - z), forms hydrogen bonds to acceptors in the domain 0.26 < z < 0.46. In these cations, the hydrogen bonds formed by each individual N atom link C₂²(7) chains into an (001) sheet (Fig. 2), while those formed by the cation as a whole link pairs of (001) sheets related by centres of inversion, forming a bilayer (Fig. 3).

The cation whose orientation is defined by N1B exhibits a different pattern of hydrogen bonds: N1B at (x, y, z) forms a two-centre hydrogen bond to an acceptor in the domain 0.54 < z < 0.74 and a three-centre hydrogen bond to an acceptor in the domain 0.26 < z < 0.46, while this pattern is reversed for the symmetry-related N1B at (1 - x, 1 - y, 1 - z). In this type of cation, the hydrogen bonds formed by N1B—H1B at (x, y, z) and by N1B—H2B at (1 - x, 1 - y, 1 - z) link C₂²(7) chains into (001) sheets (Fig. 2), while again the entire cations link pairs of sheets into bilayers (Fig. 3). Query all symops - typos!

Related literature

For related literature, see: Acs et al. (1992); Barnes & Weakley (1998); Burchell et al. (2000, 2001a, 2001b); De Costa, Bowen, Hellewell, George, Rothman, Reid, Walker, Jacobson & Rice (1989); Gjerlov & Larsen (1997a, 1997b); Larsen et al. (1993).

S2. Experimental

Stoichiometric quantities of piperazine and racemic mandelic acid were separately dissolved in methanol. The solutions were mixed and the mixture was set aside to crystallize, producing analytically pure (I). Analysis: found: C 58.8, H 7.7, N 6.4%; C₂₂H₃₄N₂O₈ requires: C 58.1, H 7.5, N 6.2%. Crystals of (I) suitable for single-crystal X-ray diffraction were selected from the analytical sample.

S3. Refinement

At an early stage in the analysis it became clear that the N atoms of the centrosymmetric cation were disordered over two sites. Refinement of the site-occupancy factors (s.o.f.s) for the two sites, denoted N1A and N1B, led to values not significantly different from 0.5. Hence, the s.o.f.s were fixed at 0.5 in the final refinements. H atoms were treated as riding, with C—H 0.95–1.00, N—H 0.92 and O—H 0.84 Å.

Computing details

Data collection: COLLECT (Nonius, 1997-2000); cell refinement: DENZO-SMN (Otwinowski & Minor, 1997); data reduction: DENZO-SMN; program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: PLATON (Spek, 2001); software used to prepare material for publication: SHELXL97 and PRPKAPPA (Ferguson, 1999).

Figures

	Fig. 1. The molecular components of compound (I), showing the atom-labelling scheme. Displacement ellipsoids are drawn at the 30% probability level and the alternative sites N1A and N1B each have 0.50 occupancy [symmetry code: (iv) 1 - x, 1 - y, 1 - z]. The 0.50 occupancy sites C2A/C2B and C3A/C3B are almost coincident; the H atoms bonded to these disordered C atoms have been omitted for clarity. Remaining H atoms are shown as small spheres of arbitrary radii.
	Fig. 2. Part of the structure of (I) showing the linking of [010] chains into an (001) sheet. For the sake of clarity, H atoms bonded to C and atoms C12 and C16 of the anion have been omitted. Symmetry codes: (i) 3/2 - x, 1/2 + y, z; (iii) 5/2 - x, y - 1/2, z; (iv) 1 - x, 1 - y, 1 - z; (v) x, y - 1, z. Query symops.
	Fig. 3. Part of the structure of (I) showing the linking of adjacent (001) sheets into a bilayer. For the sake of clarity, H atoms bonded to C and atoms C12 and C16 of the anion have been omitted. Symmetry codes: (ii) x - 1/2, 1/2 - y, 1 - z; (iii) 5/2 - x, y - 1/2, z; (iv) 1 - x, 1 - y, 1 - z; (v) x, y - 1, z. Query symops.

Piperazinium(2+) bis(mandelate) bis(methanol) solvate

Crystal data

C4H12N2^2+·2C8H7O3^−·2CH4O	Dx = 1.280 Mg m^−3
Mr = 454.51	Mo Kα radiation, λ = 0.71073 Å
Orthorhombic, Pbca	Cell parameters from 2290 reflections
a = 7.7360 (2) Å	θ = 2.7–25.0°
b = 10.2394 (4) Å	µ = 0.10 mm^−1
c = 29.7822 (11) Å	T = 150 K
V = 2359.11 (14) Å^3	Needle, colourless
Z = 4	0.28 × 0.16 × 0.12 mm
F(000) = 976

Data collection

Nonius Kappa-CCD diffractometer	2074 independent reflections
Radiation source: fine-focus sealed X-ray tube	1077 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.089
ϕ scans, and ω scans with κ offsets	θmax = 25.0°, θmin = 2.7°
Absorption correction: multi-scan (DENZO-SMN; Otwinowski & Minor, 1997)	h = −9→9
Tmin = 0.973, Tmax = 0.988	k = −12→12
11737 measured reflections	l = −35→35

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)] = 0.048	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.133	H-atom parameters constrained
S = 0.91	w = 1/[σ^2(Fo^2) + (0.0694P)^2] where P = (Fo^2 + 2Fc^2)/3
2074 reflections	(Δ/σ)max = 0.001
163 parameters	Δρmax = 0.19 e Å^−3
6 restraints	Δρmin = −0.22 e Å^−3

Special details

Experimental. The program DENZO-SMN (Otwinowski & Minor, 1997) uses a scaling algorithm [Fox, G·C. & Holmes, K·C. (1966). Acta Cryst. 20, 886–891] which effectively corrects for absorption effects. High redundancy data were used in the scaling program hence the 'multi-scan' code word was used. No transmission coefficients are available from the program (only scale factors for each frame). The scale factors in the experimental table are calculated from the 'size' command in the SHELXL97 input file.

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

	x	y	z	Uiso*/Ueq	Occ. (<1)
O1	0.8595 (2)	0.46050 (17)	0.59125 (5)	0.0443 (5)
O2	0.8795 (3)	0.28474 (17)	0.54799 (6)	0.0587 (6)
O3	1.1657 (3)	0.20571 (17)	0.58472 (5)	0.0471 (6)
H3	1.2532	0.1815	0.5992	0.071*
C11	1.0100 (3)	0.2564 (2)	0.65444 (7)	0.0352 (7)
C12	0.9594 (4)	0.1274 (3)	0.66031 (8)	0.0427 (7)
H12	0.9713	0.0672	0.6362	0.051*
C13	0.8919 (4)	0.0858 (3)	0.70081 (9)	0.0495 (8)
H13	0.8595	−0.0031	0.7045	0.059*
C14	0.8713 (4)	0.1718 (3)	0.73593 (9)	0.0481 (8)
H14	0.8242	0.1430	0.7637	0.058*
C15	0.9201 (4)	0.3004 (3)	0.73029 (8)	0.0467 (8)
H15	0.9057	0.3606	0.7543	0.056*
C16	0.9894 (4)	0.3423 (3)	0.69026 (8)	0.0423 (7)
H16	1.0237	0.4309	0.6870	0.051*
C17	1.0770 (3)	0.3043 (2)	0.60933 (7)	0.0362 (7)
H17	1.1586	0.3784	0.6148	0.043*
C18	0.9281 (4)	0.3538 (3)	0.58021 (8)	0.0366 (7)
N1A	0.6078 (5)	0.5241 (4)	0.53836 (11)	0.0366 (11)	0.50
H1A	0.5691	0.6049	0.5474	0.044*	0.50
H2A	0.6952	0.4990	0.5575	0.044*	0.50
C2A	0.4644 (14)	0.4290 (12)	0.5413 (5)	0.0369 (11)	0.50
H2A1	0.5077	0.3402	0.5345	0.044*	0.50
H2A2	0.4165	0.4286	0.5721	0.044*	0.50
C3A	0.324 (2)	0.4665 (10)	0.5079 (3)	0.0384 (10)	0.50
H3A1	0.2304	0.4003	0.5088	0.046*	0.50
H3A2	0.2731	0.5516	0.5167	0.046*	0.50
N1B	0.6120 (5)	0.3897 (4)	0.50377 (12)	0.0361 (11)	0.50
H1B	0.6984	0.3450	0.5184	0.043*	0.50
H2B	0.5766	0.3396	0.4798	0.043*	0.50
C2B	0.4650 (14)	0.4083 (13)	0.5348 (5)	0.0369 (11)	0.50
H2B1	0.4211	0.3219	0.5444	0.044*	0.50
H2B2	0.5054	0.4553	0.5619	0.044*	0.50
C3B	0.318 (2)	0.4853 (8)	0.5132 (3)	0.0384 (10)	0.50
H3B1	0.2675	0.4345	0.4881	0.046*	0.50
H3B2	0.2262	0.5021	0.5356	0.046*	0.50
O4	1.0545 (3)	0.64236 (19)	0.63172 (7)	0.0625 (6)
H31	0.9826	0.5963	0.6178	0.094*
C4	0.9711 (4)	0.7525 (3)	0.64941 (8)	0.0468 (8)
H41	0.9040	0.7272	0.6759	0.070*
H42	0.8934	0.7895	0.6267	0.070*
H43	1.0575	0.8180	0.6580	0.070*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
O1	0.0443 (13)	0.0341 (11)	0.0544 (11)	0.0059 (10)	−0.0040 (9)	−0.0032 (8)
O2	0.0784 (16)	0.0412 (12)	0.0566 (12)	0.0075 (11)	−0.0323 (11)	−0.0092 (10)
O3	0.0503 (14)	0.0470 (12)	0.0441 (10)	0.0140 (10)	−0.0044 (9)	−0.0092 (9)
C11	0.0315 (17)	0.0349 (16)	0.0392 (14)	0.0028 (13)	−0.0071 (12)	0.0007 (12)
C12	0.046 (2)	0.0350 (17)	0.0473 (17)	0.0031 (14)	−0.0044 (14)	−0.0034 (13)
C13	0.052 (2)	0.0401 (17)	0.0565 (18)	0.0001 (16)	−0.0028 (15)	0.0092 (15)
C14	0.0462 (19)	0.054 (2)	0.0438 (16)	0.0054 (16)	−0.0046 (13)	0.0100 (14)
C15	0.054 (2)	0.0503 (19)	0.0362 (16)	0.0061 (16)	−0.0046 (14)	−0.0020 (13)
C16	0.052 (2)	0.0345 (16)	0.0408 (16)	0.0011 (14)	−0.0093 (14)	−0.0024 (12)
C17	0.0360 (17)	0.0335 (15)	0.0391 (14)	−0.0004 (14)	−0.0034 (12)	−0.0057 (12)
C18	0.0438 (19)	0.0323 (15)	0.0337 (15)	−0.0032 (14)	−0.0007 (13)	0.0022 (12)
N1A	0.041 (3)	0.037 (2)	0.032 (2)	0.008 (2)	−0.0099 (19)	−0.0055 (18)
C2A	0.0422 (19)	0.040 (3)	0.029 (3)	−0.006 (2)	−0.0017 (18)	−0.0043 (19)
C3A	0.041 (2)	0.037 (3)	0.037 (2)	0.001 (2)	−0.001 (2)	−0.0002 (17)
N1B	0.039 (3)	0.035 (3)	0.034 (2)	0.007 (2)	−0.0081 (19)	−0.0022 (18)
C2B	0.0422 (19)	0.040 (3)	0.029 (3)	−0.006 (2)	−0.0017 (18)	−0.0043 (19)
C3B	0.041 (2)	0.037 (3)	0.037 (2)	0.001 (2)	−0.001 (2)	−0.0002 (17)
O4	0.0443 (14)	0.0442 (12)	0.0990 (16)	−0.0069 (10)	0.0116 (12)	−0.0199 (11)
C4	0.046 (2)	0.0452 (17)	0.0492 (15)	−0.0015 (15)	0.0054 (14)	−0.0022 (13)

Geometric parameters (Å, º)

O1—C18	1.258 (3)	C2A—C3A	1.525 (3)
O2—C18	1.250 (3)	C2A—H2A1	0.99
O3—C17	1.424 (3)	C2A—H2A2	0.99
O3—H3	0.84	C3A—N1A^i	1.479 (3)
C11—C12	1.389 (3)	C3A—H3A1	0.99
C11—C16	1.392 (3)	C3A—H3A2	0.99
C11—C17	1.521 (3)	N1B—C3B^i	1.479 (3)
C12—C13	1.382 (3)	N1B—C2B	1.478 (3)
C12—H12	0.95	N1B—H1B	0.92
C13—C14	1.377 (4)	N1B—H2B	0.92
C13—H13	0.95	C2B—C3B	1.525 (3)
C14—C15	1.380 (4)	C2B—H2B1	0.99
C14—H14	0.95	C2B—H2B2	0.99
C15—C16	1.376 (3)	C3B—N1B^i	1.478 (3)
C15—H15	0.95	C3B—H3B1	0.99
C16—H16	0.95	C3B—H3B2	0.99
C17—C18	1.528 (4)	O4—C4	1.402 (3)
C17—H17	1.00	O4—H31	0.84
N1A—C3A^i	1.479 (3)	C4—H41	0.98
N1A—C2A	1.478 (3)	C4—H42	0.98
N1A—H1A	0.92	C4—H43	0.98
N1A—H2A	0.92
C17—O3—H3	109.5	N1A—C2A—H2A1	109.8
C12—C11—C16	118.2 (2)	C3A—C2A—H2A2	109.8
C12—C11—C17	120.9 (2)	N1A—C2A—H2A2	109.8
C16—C11—C17	120.8 (2)	H2A1—C2A—H2A2	108.2
C13—C12—C11	120.6 (2)	N1A^i—C3A—C2A	111.6 (12)
C13—C12—H12	119.7	N1A^i—C3A—H3A1	109.3
C11—C12—H12	119.7	C2A—C3A—H3A1	109.3
C14—C13—C12	120.6 (3)	N1A^i—C3A—H3A2	109.3
C14—C13—H13	119.7	C2A—C3A—H3A2	109.3
C12—C13—H13	119.7	H3A1—C3A—H3A2	108.0
C13—C14—C15	119.1 (3)	C3B^i—N1B—C2B	112.6 (4)
C13—C14—H14	120.4	C3B^i—N1B—H1B	109.1
C15—C14—H14	120.4	C2B—N1B—H1B	109.1
C16—C15—C14	120.6 (3)	C3B^i—N1B—H2B	109.1
C16—C15—H15	119.7	C2B—N1B—H2B	109.1
C14—C15—H15	119.7	H1B—N1B—H2B	107.8
C15—C16—C11	120.8 (3)	C3B—C2B—N1B	112.1 (13)
C15—C16—H16	119.6	C3B—C2B—H2B1	109.2
C11—C16—H16	119.6	N1B—C2B—H2B1	109.2
O3—C17—C11	112.9 (2)	C3B—C2B—H2B2	109.2
O3—C17—C18	107.82 (18)	N1B—C2B—H2B2	109.2
C11—C17—C18	110.6 (2)	H2B1—C2B—H2B2	107.9
O3—C17—H17	108.5	N1B^i—C3B—C2B	108.6 (12)
C11—C17—H17	108.5	N1B^i—C3B—H3B1	110.0
C18—C17—H17	108.5	C2B—C3B—H3B1	110.0
O2—C18—O1	124.4 (2)	N1B^i—C3B—H3B2	110.0
O2—C18—C17	118.4 (2)	C2B—C3B—H3B2	110.0
O1—C18—C17	117.2 (2)	H3B1—C3B—H3B2	108.3
C3A^i—N1A—C2A	111.6 (4)	C4—O4—H31	109.5
C3A^i—N1A—H1A	109.3	O4—C4—H41	109.5
C2A—N1A—H1A	109.3	O4—C4—H42	109.5
C3A^i—N1A—H2A	109.3	H41—C4—H42	109.5
C2A—N1A—H2A	109.3	O4—C4—H43	109.5
H1A—N1A—H2A	108.0	H41—C4—H43	109.5
C3A—C2A—N1A	109.4 (12)	H42—C4—H43	109.5
C3A—C2A—H2A1	109.8
C16—C11—C12—C13	−0.5 (4)	C12—C11—C17—C18	89.5 (3)
C17—C11—C12—C13	−177.3 (2)	C16—C11—C17—C18	−87.1 (3)
C11—C12—C13—C14	0.9 (4)	O3—C17—C18—O2	18.0 (3)
C12—C13—C14—C15	−0.4 (4)	C11—C17—C18—O2	−106.0 (3)
C13—C14—C15—C16	−0.4 (4)	O3—C17—C18—O1	−163.9 (2)
C14—C15—C16—C11	0.8 (4)	C11—C17—C18—O1	72.2 (3)
C12—C11—C16—C15	−0.3 (4)	C3A^i—N1A—C2A—C3A	−56.1 (10)
C17—C11—C16—C15	176.5 (2)	N1A—C2A—C3A—N1A^i	56.1 (8)
C12—C11—C17—O3	−31.4 (3)	C3B^i—N1B—C2B—C3B	57.2 (10)
C16—C11—C17—O3	152.0 (2)	N1B—C2B—C3B—N1B^i	−55.0 (8)

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
N1A—H2A···O1	0.92	1.67	2.588 (4)	177
N1A—H1A···O2^ii	0.92	1.88	2.686 (4)	144
N1A—H1A···O3^ii	0.92	2.37	3.137 (4)	141
N1B—H1B···O2	0.92	1.77	2.678 (4)	171
N1B—H2B···O3^iii	0.92	2.09	2.841 (4)	137
N1B—H2B···O2^iii	0.92	2.15	2.967 (4)	147
O3—H3···O4^iv	0.84	1.82	2.658 (3)	176
O4—H31···O1	0.84	1.86	2.682 (3)	166

Symmetry codes: (ii) −x+3/2, y+1/2, z; (iii) x−1/2, −y+1/2, −z+1; (iv) −x+5/2, y−1/2, z.