Piperazine-1,4-diium bis­(hydrogen 2-propyl-1H-imidazole-4,5-dicarbox­ylate) monohydrate

The title compound, C₄H₁₂N₂²⁺·2C₈H₉N₂O₄⁻·H₂O, is a hydrated proton-transfer compound obtained from 2-propyl-1H-imidazole-4,5-dicarb­oxy­lic acid and piperazine. The asymmetric unit contains one half-cation, one anion and half a water mol­ecule. There is a centre of inversion at the centre of the cation ring and the water molecule O atom lies on a twofold rotation axis. In the crystal, inter­molecular N—H...O and N—H...N hydrogen bonds help to construct a three-dimensional framework. Almost symmetrical, intramolecular O—H...O inter­actions are also observed.

Key indicators

• Single-crystal X-ray study
• T = 273 K
• Mean [sigma](C-C) = 0.004 Å
• R factor = 0.050
• wR factor = 0.136
• Data-to-parameter ratio = 12.5

checkCIF/PLATON results

No syntax errors found



Alert level B
PLAT220_ALERT_2_B Large Non-Solvent    C     Ueq(max)/Ueq(min) ...       4.71 Ratio
PLAT230_ALERT_2_B Hirshfeld Test Diff for    C5     --  C6      ..       7.93 su

Alert level C
THETM01_ALERT_3_C  The value of sine(theta_max)/wavelength is less than 0.590
            Calculated sin(theta_max)/wavelength =    0.5783
PLAT023_ALERT_3_C Resolution (too) Low [sin(theta)/Lambda < 0.6]..      24.27 Deg.
PLAT222_ALERT_3_C Large Non-Solvent    H    Uiso(max)/Uso(min) ...       4.18 Ratio
PLAT242_ALERT_2_C Check Low       Ueq as Compared to Neighbors for         C5
PLAT250_ALERT_2_C Large U3/U1 Ratio for Average U(i,j) Tensor ....       2.08
PLAT303_ALERT_2_C Full Occupancy H-Atom  H2     with # Connections          2
PLAT601_ALERT_2_C Structure Contains Solvent Accessible VOIDS of .      31.00 A   3 
PLAT911_ALERT_3_C Missing # FCF Refl Between THmin & STh/L=  0.578         10
PLAT042_ALERT_1_C Calc. and Reported MoietyFormula Strings  Differ          ?
PLAT125_ALERT_4_C No '_symmetry_space_group_name_Hall' Given .....          ?
PLAT195_ALERT_1_C Missing _cell_measurement_theta_max   datum ....          ?
PLAT196_ALERT_1_C Missing _cell_measurement_theta_min   datum ....          ?
PLAT234_ALERT_4_C Large Hirshfeld Difference C6     --  C7      ..       0.16 Ang.

Alert level G
PLAT860_ALERT_3_G Note: Number of Least-Squares Restraints .......         13
PLAT128_ALERT_4_G Alternate Setting of Space-group C2/c    .......      I2/a
PLAT199_ALERT_1_G Check the Reported _cell_measurement_temperature        273 K
PLAT200_ALERT_1_G Check the Reported   _diffrn_ambient_temperature        273 K

   0 ALERT level A = In general: serious problem
   2 ALERT level B = Potentially serious problem
  13 ALERT level C = Check and explain
   4 ALERT level G = General alerts; check

   5 ALERT type 1 CIF construction/syntax error, inconsistent or missing data
   6 ALERT type 2 Indicator that the structure model may be wrong or deficient
   5 ALERT type 3 Indicator that the structure quality may be low
   3 ALERT type 4 Improvement, methodology, query or suggestion
   0 ALERT type 5 Informative message, check

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S1. Comment

t;text-indent:12.0 pt;mso-char-indent-count: 1.0;line-height:200%'>In the past decades, much attention has been focused on the design and synthesis of proton-transfer compounds, owing to their importance in physics, chemistry and biochemistry (Aghabozorg et al., 2006; Allen et al., 1987). Many multi-carboxylate or heterocyclic acids and piperazine are used for this purpose (Murugavel et al., 2009; Sheshmani et al., 2006). In order to extend the investigation, we have prepared the title compound, (I), and report its crystal structure here.

As shown in Fig.1, The asymmetric unit contains one half-cation, one anion and half a water molecule. There is a centre of inversion at the centre of the cation ring and one water molecule lies on a twofold rotation axis. The organic piperazinium dication lies at an inversion centre and adopts a typical chair geometry with normal valence bond lengths (Murugavel et al., 2009) and angles, as observed in the related structures (Sheshmani et al., 2007). The anionic fragment individually has two intramolecular hydrogen bonds, a O–H···O bond between adjacent carboxylate groups and a N–H···O bond between the imidazole ring and the carboxylate group (Fig. 2 and Table 1). In the crystal structure, intermolecular N–H···O and N–H···N hydrogen bonds play an important role in the construction of the three-dimensional framework (Fig. 3).

Related literature

For the structures and properties of proton-transfer compounds, see: Aghabozorg et al. (2006). For the use of multi-carboxylate heterocyclic acids and piperazine in coordination chemistry, see: Murugavel et al. (2009); Sheshmani et al. (2006) and for piperazinium structures, see: Murugavel et al. (2009); Sheshmani et al. (2007). For bond-length data, see: Allen et al. (1987).

S2. Experimental

To a solution of 2-propyl-1H-imidazole-4,5-dicarboxylic acid (0.100 g, 0.5 mmol) in water (5 ml) was added an aqueous solution (5 ml) of piperazine (0.089 g, 0.5 mmol). The reactants were sealed in a 25-ml Teflon-lined, stainless-steel Parr bomb. The bomb was heated at 433 K for 3 days. The cool solution yielded single crystals in ca 70% yield. Anal. Calcd for C₁₀H₁₆N₃O_4.5: C, 47.99; H, 6.44; N, 16.79. Found: C, 47.61; H, 6.77; N, 16.42.

S3. Refinement

The free water H atoms attached to oxygen atoms were placed at calculated positions and refined with the riding model, considering the position of oxygen atoms and the quantity of H atoms. The H atoms were placed in geometrically idealized positions, withN–H = 0.86–0.90 Å and C–H = 0.93 Å, and constrained to ride on their respective parent atoms, with Uiso(H) = 1.2 Ueq.

Computing details

Data collection: SMART (Bruker, 1997); cell refinement: SAINT (Bruker, 1997); data reduction: SAINT (Bruker, 1997); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: SHELXTL (Sheldrick, 2008); software used to prepare material for publication: SHELXTL (Sheldrick, 2008).

Figures

	Fig. 1. A drawing of the asymmetric unit in the structure of (I), showing the atom-labeling scheme. Displacement ellipsoids are drawn at the 30% probability level.
	Fig. 2. The hydrogen bonds are shown and are depicted by blue dashed lines. Hydrogen atoms that bonded to carbon atoms were omitted for clarity. [Symmetry codes: (i) x, -y + 3/2, z - 1/2; (ii) –x + 1/2, -y + 3/2, -z + 1/2; (iii) x, -y + 3/2, z - 1/2; (iv) –x + 3/2, -y + 3/2, -z + 1/2].
	Fig. 3. A view along the a axis, showing a three-dimensional framework.

Piperazine-1,4-diium bis(hydrogen 2-propyl-1H-imidazole-4,5-dicarboxylate) monohydrate

Crystal data

C4H12N2^2+·2C8H9N2O4^−·H2O	F(000) = 1064
Mr = 500.52	Dx = 1.302 Mg m^−3
Monoclinic, I2/a	Mo Kα radiation, λ = 0.71073 Å
a = 11.288 (2) Å	Cell parameters from 1047 reflections
b = 15.965 (3) Å	θ = 0.0–0.0°
c = 14.449 (4) Å	µ = 0.10 mm^−1
β = 101.296 (12)°	T = 273 K
V = 2553.6 (10) Å^3	Block, colorless
Z = 4	0.20 × 0.18 × 0.16 mm

Data collection

Bruker SMART CCD area-detector diffractometer	2066 independent reflections
Radiation source: fine-focus sealed tube	1499 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.039
φ and ω scans	θmax = 24.3°, θmin = 1.9°
Absorption correction: multi-scan (SADABS; Bruker, 1997)	h = −10→13
Tmin = 0.980, Tmax = 0.984	k = −18→17
6239 measured reflections	l = −16→16

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)] = 0.050	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.136	H atoms treated by a mixture of independent and constrained refinement
S = 1.05	w = 1/[σ^2(Fo^2) + (0.0619P)^2 + 1.5738P] where P = (Fo^2 + 2Fc^2)/3
2066 reflections	(Δ/σ)max = 0.001
165 parameters	Δρmax = 0.43 e Å^−3
13 restraints	Δρmin = −0.21 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
C1	0.0849 (2)	0.71261 (16)	0.09103 (17)	0.0422 (6)
C2	0.1935 (2)	0.67934 (14)	0.15314 (16)	0.0364 (6)
C3	0.2144 (2)	0.64165 (14)	0.24013 (16)	0.0363 (6)
C4	0.1292 (2)	0.62027 (16)	0.30292 (18)	0.0424 (6)
C5	0.5184 (2)	0.6485 (2)	0.1969 (2)	0.0611 (8)
H5A	0.5649	0.6478	0.2609	0.073*
H5B	0.5409	0.6984	0.1661	0.073*
C6	0.5505 (3)	0.5713 (3)	0.1446 (4)	0.1233 (18)
H6A	0.5028	0.5710	0.0810	0.148*
H6B	0.5308	0.5212	0.1765	0.148*
C7	0.6847 (4)	0.5704 (3)	0.1403 (5)	0.171 (3)
H7A	0.7039	0.6195	0.1078	0.205*
H7B	0.7024	0.5213	0.1072	0.205*
H7C	0.7320	0.5699	0.2032	0.205*
C8	0.5499 (2)	0.57768 (16)	0.47554 (19)	0.0483 (7)
H8A	0.5643	0.6370	0.4872	0.058*
H8B	0.5864	0.5617	0.4227	0.058*
C9	0.3930 (2)	0.47110 (16)	0.43879 (17)	0.0456 (7)
H9A	0.4231	0.4509	0.3845	0.055*
H9B	0.3062	0.4627	0.4267	0.055*
C12	0.3877 (2)	0.65313 (16)	0.20022 (17)	0.0429 (6)
H2	−0.004 (2)	0.6647 (18)	0.195 (2)	0.103 (11)*
H1W	0.8140	0.7443	0.0209	0.31 (5)*
N1	0.30493 (17)	0.68560 (13)	0.12993 (13)	0.0410 (5)
H1	0.3196	0.7069	0.0787	0.049*
N2	0.33568 (18)	0.62552 (13)	0.26903 (14)	0.0426 (5)
N3	0.42026 (17)	0.56200 (13)	0.45216 (14)	0.0426 (5)
H3A	0.3883	0.5897	0.3989	0.051*
H3B	0.3856	0.5818	0.4988	0.051*
O1	−0.01641 (15)	0.70340 (13)	0.11795 (13)	0.0582 (6)
O2	0.09473 (15)	0.74761 (12)	0.01667 (12)	0.0510 (5)
O3	0.01637 (15)	0.63600 (13)	0.27299 (13)	0.0566 (5)
O4	0.16861 (16)	0.58907 (12)	0.38055 (12)	0.0537 (5)
O5	0.7500	0.7747 (3)	0.0000	0.170 (3)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
C1	0.0499 (16)	0.0430 (15)	0.0338 (14)	0.0040 (12)	0.0083 (12)	−0.0025 (12)
C2	0.0403 (13)	0.0379 (14)	0.0322 (13)	0.0010 (10)	0.0101 (10)	−0.0008 (10)
C3	0.0388 (13)	0.0379 (14)	0.0331 (13)	0.0015 (10)	0.0092 (10)	0.0022 (10)
C4	0.0480 (15)	0.0419 (15)	0.0390 (15)	0.0021 (11)	0.0124 (12)	0.0047 (12)
C5	0.0471 (17)	0.088 (2)	0.0514 (17)	0.0117 (15)	0.0188 (14)	0.0195 (16)
C6	0.090 (3)	0.089 (3)	0.215 (5)	0.042 (2)	0.089 (3)	0.042 (3)
C7	0.130 (4)	0.149 (5)	0.268 (7)	0.062 (4)	0.126 (5)	0.072 (5)
C8	0.0438 (15)	0.0455 (16)	0.0572 (17)	0.0039 (12)	0.0138 (13)	0.0078 (13)
C9	0.0408 (14)	0.0511 (17)	0.0438 (16)	0.0050 (12)	0.0055 (11)	−0.0065 (12)
C12	0.0437 (14)	0.0530 (16)	0.0335 (14)	0.0049 (12)	0.0110 (11)	0.0054 (12)
N1	0.0469 (12)	0.0483 (13)	0.0307 (11)	0.0027 (10)	0.0150 (9)	0.0058 (9)
N2	0.0437 (12)	0.0494 (13)	0.0366 (12)	0.0059 (9)	0.0127 (9)	0.0089 (9)
N3	0.0448 (12)	0.0479 (13)	0.0354 (11)	0.0108 (9)	0.0090 (9)	0.0058 (9)
O1	0.0429 (11)	0.0824 (15)	0.0487 (12)	0.0088 (9)	0.0075 (9)	0.0143 (10)
O2	0.0610 (12)	0.0601 (12)	0.0334 (10)	0.0150 (9)	0.0132 (9)	0.0053 (8)
O3	0.0427 (11)	0.0766 (14)	0.0527 (12)	0.0031 (9)	0.0146 (9)	0.0180 (10)
O4	0.0540 (11)	0.0682 (13)	0.0426 (11)	0.0087 (9)	0.0189 (9)	0.0200 (9)
O5	0.084 (3)	0.089 (3)	0.315 (8)	0.000	−0.015 (4)	0.000

Geometric parameters (Å, º)

C1—O2	1.235 (3)	C7—H7C	0.9600
C1—O1	1.286 (3)	C8—N3	1.458 (3)
C1—C2	1.469 (3)	C8—C9^i	1.497 (3)
C2—N1	1.368 (3)	C8—H8A	0.9700
C2—C3	1.372 (3)	C8—H8B	0.9700
C3—N2	1.375 (3)	C9—N3	1.488 (3)
C3—C4	1.486 (3)	C9—C8^i	1.497 (3)
C4—O4	1.228 (3)	C9—H9A	0.9700
C4—O3	1.287 (3)	C9—H9B	0.9700
C5—C12	1.487 (3)	C12—N2	1.325 (3)
C5—C6	1.526 (5)	C12—N1	1.342 (3)
C5—H5A	0.9700	N1—H1	0.8600
C5—H5B	0.9700	N3—H3A	0.9000
C6—C7	1.528 (5)	N3—H3B	0.9000
C6—H6A	0.9700	O1—H2	1.26 (3)
C6—H6B	0.9700	O3—H2	1.19 (3)
C7—H7A	0.9600	O5—H1W	0.8739
C7—H7B	0.9600
O2—C1—O1	123.5 (2)	H7B—C7—H7C	109.5
O2—C1—C2	119.2 (2)	N3—C8—C9^i	110.6 (2)
O1—C1—C2	117.3 (2)	N3—C8—H8A	109.5
N1—C2—C3	104.8 (2)	C9^i—C8—H8A	109.5
N1—C2—C1	121.4 (2)	N3—C8—H8B	109.5
C3—C2—C1	133.8 (2)	C9^i—C8—H8B	109.5
C2—C3—N2	110.1 (2)	H8A—C8—H8B	108.1
C2—C3—C4	130.1 (2)	N3—C9—C8^i	110.8 (2)
N2—C3—C4	119.8 (2)	N3—C9—H9A	109.5
O4—C4—O3	122.9 (2)	C8^i—C9—H9A	109.5
O4—C4—C3	119.3 (2)	N3—C9—H9B	109.5
O3—C4—C3	117.8 (2)	C8^i—C9—H9B	109.5
C12—C5—C6	112.9 (3)	H9A—C9—H9B	108.1
C12—C5—H5A	109.0	N2—C12—N1	110.5 (2)
C6—C5—H5A	109.0	N2—C12—C5	126.6 (2)
C12—C5—H5B	109.0	N1—C12—C5	122.9 (2)
C6—C5—H5B	109.0	C12—N1—C2	108.89 (19)
H5A—C5—H5B	107.8	C12—N1—H1	125.6
C5—C6—C7	111.2 (4)	C2—N1—H1	125.6
C5—C6—H6A	109.4	C12—N2—C3	105.7 (2)
C7—C6—H6A	109.4	C8—N3—C9	111.74 (18)
C5—C6—H6B	109.4	C8—N3—H3A	109.3
C7—C6—H6B	109.4	C9—N3—H3A	109.3
H6A—C6—H6B	108.0	C8—N3—H3B	109.3
C6—C7—H7A	109.5	C9—N3—H3B	109.3
C6—C7—H7B	109.5	H3A—N3—H3B	107.9
H7A—C7—H7B	109.5	C1—O1—H2	112.1 (11)
C6—C7—H7C	109.5	C4—O3—H2	112.9 (12)
H7A—C7—H7C	109.5

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
O3—H2···O1	1.19 (3)	1.26 (3)	2.447 (3)	172 (3)
O5—H1W···O1^ii	0.87	2.24	3.065 (3)	158
N1—H1···O2^iii	0.86	1.94	2.773 (3)	162
N3—H3A···N2	0.90	1.94	2.820 (3)	165
N3—H3B···O4^iv	0.90	1.96	2.826 (3)	161

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