Piperazine-1,4-diium–2,4-dinitrophenolate–water (1/2/2)

In the title 1/2/2 adduct, C₄H₁₂N₂²⁺·2C₆H₃N₂O₅⁻·2H₂O, the dication lies on a crystallographic inversion centre and the asymmetric unit also has one anion and one water mol­ecule in general positions. The 2,4-di­nitro­phenolate anions and the water mol­ecules are linked by two O—H...O and two C—H...O hydrogen bonds to form molecular ribbons, which extend along the b direction. The piperazine dication acts as a donor for bifurcated N—H...O hydrogen bonds with the phenolate O atom and with the O atom of the o-nitro group. Six symmetry-related molecular ribbons are linked to a piperazine dication by N—H...O and C—H...O hydrogen bonds.

S1. Comment

The crystal structures of the adducts of phenols or organic acids with diamines such as piperazine, C₄H₆N₂, in various ratios have been investigated intensively (Coupar et al., 1996a,b; Ferguson et al., 1997, 1998; Charfi et al., 1998; MacLean et al., 1999; Burchell et al., 2001). In these adducts, the two components are linked together by either intermolecular O—H···N or N—H···O hydrogen bonds, depending on the acidity of the phenols or organic acids. In the presence of weak acids such as 4,4'-thiodiphenol (Coupar et al., 1996b) or 1,1,1-tris(4-hydroxyphenyl)ethane (Ferguson et al., 1997), piperazine acts solely as an acceptor of O—H···N hydrogen bonds linking the two components into molecular chains. In contrast, with strong acids such as phenol (Loehlin et al., 1994), 4,4'sulfonyldiphenol (Coupar et al., 1996a), dihydrogenphosphate (Charfi et al., 1998), 3,4-dihydro-3-butenedione (MacLean et al., 1999) or 3,5-dinitrobenzoic acid (Burchell et al., 2001), piperazine, which is a strongly basic amine, forms a dication and acts as an N—H hydrogen-bond donor. In these cases, the strong acid transfers the H atom to a piperazine molecule, making an ionic adduct. This observation prompted us to extend the study of hydrogen-bonding motifs in the crystal structures of adducts of piperazine. In this study, we have prepared and structurally characterized the title compound, (I), as a dihydrate adduct of piperazine with 2,4-dinitrophenol (DNP), in the expectation of observing that an H atom has been transferred from the DNP to the piperazine. DNP was selected since this phenol has demonstrated the ability to transfer its H atom in its adducts with several amine bases, such as morpholine (Masjerz et al., 1996) and hexamethylenetetramine (Usman et al., 2001). \sch

The X-ray structural analysis of (I) shows unambiguously that the DNP transfers an H atom from the hydroxy group to the unique N of the centrosymmetric piperazine moiety, to form a 2,4-dinitrophenolate (DNP^-) anion and a piperazine-1,4-diium dication.

The piperazine dication N1—C1 and N1—C2 bond distances [1.496 (2) and 1.494 (2) Å, respectively] are elongated compared with those in unprotonated piperazine [1.460 (3) and 1.462 (3) Å; Coupar et al., 1996b]. The C—N and C—C bond distances of the piperazine dication are comparable with those reported for other piperazine dication adducts (Iwasaki & Mutai, 1984; Loehlin et al., 1994; Coupar et al., 1996a; MacLean et al., 1999; Burchell et al., 2001). Also similar is the chair conformation of the piperazine dication.

The H-transfer process also affects the delocalization of the π-electron in DNP^-, corresponding to an o-quinoic resonance structure, resulting in slight distortions in the N—O, C—N and C—O bond distances of the functional groups compared with the corresponding values in DNP (Iwasaki & Kawano, 1977). This is also shown by the distinct shortening of the C4—C5 and C6—C7 bonds and the lengthening of the C3—C4 and C3—C8 bonds (see Table 1). In comparison, the bond lengths and angles in DNP^- are in agreement with those in its adducts with morpholine and hexamethylenetetramine.

Within the asymmetric unit (Fig. 1), the piperazine dication and DNP^- are linked by intermolecular N1—H1N···O1 and N1—H1N···O2 hydrogen bonds, with the piperazine dication acting as a hydrogen donor in this bifurcated system. These two components are also linked by an intermolecular C2—H2A···O2 interaction. These intermolecular interactions form two closed-ring patterns, which are designated as R₁²(6) and R₂¹(5) (Bernstein et al., 1995).

The water molecule within the asymmetric unit of (I) acts as a hydrogen-bond donor via H1W to atom O1 of DNP^-, and this water molecule at (x, y, z) also acts as a hydrogen donor via H2W to atom O4 of the DNP^- anion at (2 - x, y - 1/2, 1/2 - z). These interactions involving the water molecule, along with the two linear C4—H4···O4(2 - x, y - 1/2, 1/2 - z) and C5—H5···O3(2 - x, y - 1/2, 1/2 - z) hydrogen bonds, interconnect the DNP^- and water molecules into molecular ribbons, which extend along the b direction. The DNP^-/water molecular ribbons (Fig. 2) contain two chains of rings, with the notation of these patterns being described as C(8)[R₃²(8)] and C(7)[R₂²(11)].

The packing of the structure is built from alternating layers of DNP^-/water molecular ribbons and piperazine dications, interconnected by C1—H1B···O3(1 - x, y - 1/2, 1/2 - z), N1—H2N···O1W(1 - x, 1 - y, -z), C1—H1B···O5(x - 1, y, z) and C2—H2B···O5(x - 1, y, z) hydrogen bonds along the a direction, in which six symmetry-related DNP^-/water molecular ribbons are linked to each piperazine dication (Fig. 3).

The hydrogen-bonded N···O distances in (I) are in the range 2.772 (2)–2.840 (2) Å and are comparable with those observed in other piparazine-1,4-diium adducts (Coupar et al., 1997a; MacLean et al., 1999; Burchell et al., 2001).

S2. Experimental

The title adduct, (I), was prepared by thoroughly mixing equimolar amounts of piperazine (5 mmol) and 2,4-dinitrophenol. The mixture was dissolved in ethanol (40 ml) with the addition of distilled water (3 ml), and was warmed until a clear solution was obtained. The solution was then filtered and the filtrate was left to evaporate slowly in air. Yellow single crystals of (I) suitable for X-ray diffraction studies were obtained from the solution after a few days [m.p. 515 K (decomposition)].

S3. Refinement

All H atoms were located in difference maps and were refined isotropically, with C—H = 0.94 (2)–1.02 (2) Å. 31 reflections listed as inconsistent equivalents were removed before the final refinement.

Computing details

Data collection: SMART (Siemens, 1996); cell refinement: SAINT (Siemens, 1996); data reduction: SAINT; program(s) used to solve structure: SHELXTL (Sheldrick, 1997); program(s) used to refine structure: SHELXTL; molecular graphics: SHELXTL; software used to prepare material for publication: SHELXTL, PARST (Nardelli, 1995) and PLATON (Spek, 1990).

Figures

	Fig. 1. The structure of (I) with 50% probability displacement ellipsoids and the atom-numbering scheme. H atoms are shown as small spheres of arbitrary radii.
	Fig. 2. A packing diagram for (I) viewed down the c axis, showing only the molecular ribbons of 2,4-dinitrophenolate and water molecules.
	Fig. 3. The linkage to the piperazine dication of the molecular 2,4-dinitrophenolate/water ribbons, viewed down the b axis.

Piperazine-1,4-diium–2,4-dinitrophenolate–water (1/2/2)

Crystal data

C4H12N2^2+·2C6H3N2O5^−·2H2O	Dx = 1.598 Mg m^−3
Mr = 490.40	Melting point: 515K (decompose) K
Monoclinic, P21/c	Mo Kα radiation, λ = 0.71073 Å
a = 12.1140 (6) Å	Cell parameters from 4041 reflections
b = 12.9702 (6) Å	θ = 3.1–28.3°
c = 6.5813 (3) Å	µ = 0.14 mm^−1
β = 99.646 (1)°	T = 183 K
V = 1019.44 (8) Å^3	Needle, yellow
Z = 2	0.30 × 0.14 × 0.14 mm
F(000) = 512

Data collection

Siemens SMART CCD area-detector diffractometer	2453 independent reflections
Radiation source: fine-focus sealed tube	1725 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.065
Detector resolution: 8.33 pixels mm^-1	θmax = 28.3°, θmin = 3.1°
ω scans	h = −13→16
Absorption correction: empirical (using intensity measurements) (SADABS; Sheldrick, 1996)	k = −14→17
Tmin = 0.960, Tmax = 0.981	l = −8→8
5886 measured reflections

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)] = 0.052	All H-atom parameters refined
wR(F^2) = 0.120	w = 1/[σ^2(Fo^2) + (0.0301P)^2] where P = (Fo^2 + 2Fc^2)/3
S = 0.92	(Δ/σ)max < 0.001
2453 reflections	Δρmax = 0.48 e Å^−3
199 parameters	Δρmin = −0.40 e Å^−3
0 restraints	Extinction correction: SHELXTL (Sheldrick, 1997), Fc^*=kFc[1+0.001xFc^2λ^3/sin(2θ)]^-1/4
Primary atom site location: structure-invariant direct methods	Extinction coefficient: 0.067 (6)

Special details

Experimental. The data collection covered over a hemisphere of reciprocal space by a combination of three sets of exposures; each set had a different ϕ angle (0, 88 and 180°) for the crystal and each exposure of 30 s covered 0.3° in ω. The crystal-to-detector distance was 5 cm and the detector swing angle was -35°. Crystal decay was monitored by repeating fifty initial frames at the end of data collection and analysing the intensity of duplicate reflections, and was found to be negligible.

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	0.69486 (11)	0.52605 (10)	0.2104 (2)	0.0201 (3)
O2	0.65629 (11)	0.72209 (11)	0.3258 (3)	0.0261 (4)
O3	0.78449 (12)	0.83264 (10)	0.2887 (3)	0.0274 (4)
O4	1.16477 (12)	0.73032 (11)	0.4446 (3)	0.0293 (4)
O5	1.21241 (11)	0.58732 (12)	0.3116 (3)	0.0322 (4)
N2	0.75300 (12)	0.74294 (11)	0.3032 (3)	0.0159 (4)
N3	1.14065 (13)	0.64615 (12)	0.3570 (3)	0.0196 (4)
C3	0.79589 (15)	0.55678 (14)	0.2386 (3)	0.0145 (4)
C8	0.83223 (14)	0.66063 (13)	0.2916 (3)	0.0135 (4)
C7	0.94390 (15)	0.68943 (14)	0.3278 (3)	0.0144 (4)
C6	1.02475 (14)	0.61690 (14)	0.3082 (3)	0.0145 (4)
C5	0.99577 (15)	0.51553 (14)	0.2483 (3)	0.0170 (4)
C4	0.88576 (15)	0.48688 (15)	0.2156 (3)	0.0175 (4)
H7	0.9620 (18)	0.7579 (16)	0.367 (3)	0.020 (6)*
H5	1.057 (2)	0.4637 (17)	0.235 (4)	0.030 (6)*
H4	0.8650 (18)	0.4150 (16)	0.176 (3)	0.020 (5)*
N1	0.48980 (13)	0.56797 (12)	0.3262 (3)	0.0151 (4)
C2	0.48356 (15)	0.60859 (14)	0.5364 (3)	0.0156 (4)
C1	0.44851 (15)	0.45924 (14)	0.3032 (3)	0.0161 (4)
H2A	0.5094 (17)	0.6810 (16)	0.534 (3)	0.018 (5)*
H2B	0.4035 (18)	0.6062 (16)	0.551 (3)	0.021 (5)*
H2N	0.4486 (19)	0.6086 (16)	0.219 (4)	0.026 (6)*
H1N	0.568 (2)	0.5718 (19)	0.299 (4)	0.042 (7)*
H1A	0.456 (2)	0.4356 (17)	0.171 (4)	0.027 (6)*
H1B	0.3695 (17)	0.4632 (14)	0.315 (3)	0.013 (5)*
H2W	0.675 (3)	0.304 (3)	0.020 (5)	0.067 (11)*
H1W	0.657 (2)	0.400 (2)	0.089 (4)	0.049 (8)*
O1W	0.62747 (12)	0.34292 (12)	0.0291 (2)	0.0205 (3)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
O1	0.0133 (6)	0.0191 (7)	0.0293 (9)	−0.0041 (5)	0.0078 (6)	−0.0049 (6)
O2	0.0163 (7)	0.0216 (8)	0.0441 (10)	0.0023 (6)	0.0155 (6)	0.0040 (7)
O3	0.0223 (7)	0.0102 (7)	0.0507 (11)	−0.0002 (5)	0.0085 (7)	0.0006 (6)
O4	0.0183 (7)	0.0238 (8)	0.0452 (10)	−0.0071 (6)	0.0037 (6)	−0.0062 (7)
O5	0.0127 (7)	0.0331 (9)	0.0519 (11)	0.0055 (6)	0.0087 (7)	−0.0037 (8)
N2	0.0142 (8)	0.0142 (8)	0.0201 (9)	0.0015 (6)	0.0052 (6)	0.0010 (6)
N3	0.0140 (7)	0.0198 (8)	0.0255 (9)	−0.0006 (6)	0.0043 (6)	0.0041 (7)
C3	0.0138 (8)	0.0156 (9)	0.0151 (9)	−0.0011 (7)	0.0056 (7)	0.0000 (7)
C8	0.0138 (8)	0.0119 (9)	0.0158 (9)	0.0026 (7)	0.0058 (7)	0.0009 (7)
C7	0.0160 (9)	0.0122 (9)	0.0158 (10)	−0.0003 (7)	0.0048 (7)	0.0015 (7)
C6	0.0102 (8)	0.0162 (9)	0.0180 (10)	−0.0001 (7)	0.0046 (7)	0.0021 (7)
C5	0.0160 (9)	0.0159 (9)	0.0200 (10)	0.0021 (7)	0.0057 (7)	0.0013 (8)
C4	0.0180 (9)	0.0133 (9)	0.0222 (11)	−0.0005 (7)	0.0065 (8)	−0.0035 (8)
N1	0.0126 (7)	0.0129 (8)	0.0208 (9)	−0.0006 (6)	0.0051 (6)	0.0014 (7)
C2	0.0146 (9)	0.0115 (9)	0.0223 (10)	−0.0005 (7)	0.0075 (7)	−0.0020 (8)
C1	0.0133 (9)	0.0135 (9)	0.0219 (11)	−0.0021 (7)	0.0041 (7)	−0.0023 (8)
O1W	0.0158 (7)	0.0167 (7)	0.0288 (9)	0.0015 (6)	0.0027 (6)	−0.0037 (6)

Geometric parameters (Å, º)

O1—C3	1.271 (2)	C5—H5	1.01 (2)
O2—N2	1.235 (2)	C4—H4	0.99 (2)
O3—N2	1.2330 (19)	N1—C2	1.494 (2)
O4—N3	1.246 (2)	N1—C1	1.496 (2)
O5—N3	1.230 (2)	N1—H2N	0.95 (2)
N2—C8	1.446 (2)	N1—H1N	0.99 (3)
N3—C6	1.438 (2)	C2—C1^i	1.508 (3)
C3—C4	1.444 (3)	C2—H2A	0.99 (2)
C3—C8	1.442 (2)	C2—H2B	0.99 (2)
C8—C7	1.385 (2)	C1—C2^i	1.508 (3)
C4—C5	1.365 (3)	C1—H1A	0.94 (2)
C6—C7	1.380 (2)	C1—H1B	0.98 (2)
C7—H7	0.94 (2)	O1W—H2W	0.77 (3)
C6—C5	1.400 (3)	O1W—H1W	0.88 (3)
O3—N2—O2	121.85 (15)	C5—C4—H4	119.8 (12)
O3—N2—C8	118.42 (15)	C3—C4—H4	117.2 (12)
O2—N2—C8	119.73 (15)	C2—N1—C1	110.98 (15)
O5—N3—O4	122.35 (16)	C2—N1—H2N	113.0 (13)
O5—N3—C6	119.04 (16)	C1—N1—H2N	108.8 (13)
O4—N3—C6	118.61 (16)	C2—N1—H1N	110.4 (15)
O1—C3—C8	125.17 (17)	C1—N1—H1N	110.0 (14)
O1—C3—C4	120.81 (16)	H2N—N1—H1N	104 (2)
C8—C3—C4	114.01 (16)	N1—C2—C1^i	109.64 (15)
C7—C8—C3	122.92 (16)	N1—C2—H2A	104.6 (13)
C7—C8—N2	115.44 (15)	C1^i—C2—H2A	115.4 (12)
C3—C8—N2	121.60 (15)	N1—C2—H2B	106.2 (13)
C6—C7—C8	119.23 (17)	C1^i—C2—H2B	110.1 (12)
C6—C7—H7	122.2 (13)	H2A—C2—H2B	110.4 (17)
C8—C7—H7	118.5 (13)	N1—C1—C2^i	110.21 (15)
C7—C6—C5	121.20 (16)	N1—C1—H1A	108.4 (14)
C7—C6—N3	118.77 (16)	C2^i—C1—H1A	109.3 (14)
C5—C6—N3	120.00 (16)	N1—C1—H1B	104.9 (11)
C4—C5—C6	119.46 (17)	C2^i—C1—H1B	113.7 (12)
C4—C5—H5	120.7 (13)	H1A—C1—H1B	110.0 (18)
C6—C5—H5	119.8 (13)	H2W—O1W—H1W	109 (3)
C5—C4—C3	123.07 (17)
O1—C3—C8—C7	177.66 (19)	O5—N3—C6—C7	−169.44 (18)
C4—C3—C8—C7	−3.2 (3)	O4—N3—C6—C7	10.8 (3)
O1—C3—C8—N2	−4.6 (3)	O5—N3—C6—C5	12.5 (3)
C4—C3—C8—N2	174.52 (17)	O4—N3—C6—C5	−167.27 (18)
O3—N2—C8—C7	18.9 (2)	C7—C6—C5—C4	−2.3 (3)
O2—N2—C8—C7	−161.57 (18)	N3—C6—C5—C4	175.67 (19)
O3—N2—C8—C3	−159.02 (18)	C6—C5—C4—C3	0.4 (3)
O2—N2—C8—C3	20.5 (3)	O1—C3—C4—C5	−178.60 (19)
C3—C8—C7—C6	1.5 (3)	C8—C3—C4—C5	2.2 (3)
N2—C8—C7—C6	−176.33 (16)	C1—N1—C2—C1^i	58.0 (2)
C8—C7—C6—C5	1.4 (3)	C2—N1—C1—C2^i	−58.3 (2)
C8—C7—C6—N3	−176.64 (17)

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
N1—H1N···O1	0.99 (2)	1.83 (2)	2.772 (2)	156 (2)
N1—H1N···O2	0.99 (2)	2.22 (2)	2.840 (2)	119 (2)
N1—H2N···O1W^ii	0.95 (2)	1.85 (3)	2.776 (2)	165 (2)
O1W—H1W···O1	0.89 (3)	1.84 (3)	2.721 (2)	171 (2)
O1W—H2W···O4^iii	0.78 (4)	2.14 (4)	2.890 (2)	162 (4)
C1—H1B···O5^iv	0.97 (2)	2.49 (2)	3.316 (2)	142 (1)
C1—H1B···O3^v	0.97 (2)	2.53 (2)	3.234 (2)	129 (1)
C2—H2A···O2	0.99 (2)	2.48 (2)	3.072 (2)	118 (2)
C2—H2B···O5^iv	0.99 (2)	2.58 (2)	3.380 (2)	137 (2)
C4—H4···O4^iii	0.99 (2)	2.53 (2)	3.513 (2)	173 (2)
C5—H5···O3^iii	1.02 (2)	2.59 (2)	3.604 (2)	178 (2)

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