Ammonium 3-cyano-4-(dicyano­methyl­ene)-5-oxo-4,5-dihydro-1H-pyrrol-2-olate monohydrate

Each anion of the title salt, NH₄⁺·C₈HN₄O₂⁻·H₂O, is linked by two N—H...O hydrogen bonds to another anion, thus forming an essentially planar centrosymmetric dimer. The dimers are considered to be mol­ecular building blocks of an anionic wall. The building blocks form infinite ribbons via –C—N...N—C– dipole–dipole and π–π inter­actions. Adjacent ribbons are stacked by means of π–π inter­actions, thus forming an anionic wall. Neighbouring walls are connected by (NH₄⁺…H₂O)_n chains running along the b axis.

S1. Comment

Recently, in the exploration and crystal engineering of novel π–π-stacking organic anions, we have determined and reported structures of three organic salts. All three salts have the same anion, C₈H₁N₄O₂⁻ [hereinafter anion (I)], namely, 3-cyano-4-(dicyanomethylene)-5-oxo-4,5-dihydro-1H-pyrrol-2-olate (Fig. 1), but different cations, e.g. potassium, (II) (Tafeenko et al., 2003), N,N-dimethylanilinium, (III) (Tafeenko, Peschar et al., 2004), and N-methylpyridinium, (IV) (Tafeenko, Nikolaev et al., 2004), and show different types of molecular packing and aggregation.

In the potassium salt (II), the anions are connected via the cyano groups (π–π and dipole–dipole interactions) of the dicyanomethylene moieties. A novel type of aggregation of anion (I) was found in salt (IV). All anions of (IV) are arranged as dimers via two N—H···O hydrogen bonds and form one-dimensional columns parallel to the b axis, as a result of π–π interactions. Each dianionic stack has eight neighbouring stacks of cations and is not connected directly to other dianionic stacks. But, as the dimers have a cyanomethylene moiety on both sides, cyano–cyano type interactions may lead to the formation of ribbons and, assuming π–π interactions between adjacent ribbons, to larger assemblies. In this paper, we report the structure of the ammonium hydrate salt, (V), of anion (I), which exhibits the intermolecular forces between anions that were found in both structures (II) and (IV).

The geometry of anion (I) in the title salt, (V) (Fig. 1), is essentially the same as in the structures of (II)–(IV). Each anion is linked by two N—H···O hydrogen bonds to another anion, thus forming a centrosymmetric dimer. Adjacent dimers are connected by (–C—N)···(N—C–)* dipole–dipole and π–π interactions, thus forming infinite essentially planar ribbons Fig. 2; the angle between two adjacent molecules in the ribbon is 0.00 (3)°, and the deviations of the atoms from the plane running through three adjacent [e.g. (x,y,z), (−x, 2 − y, 1 − z) and (2 − x, 1 − y, 1 − z] five-membered rings are within 0.033 (1) and −0.022 (1) Å. The angle which the –C(CN)₂ group makes with the five-membered ring is 3.03 (8)°, demonstrating a small twist from planarity about the C4—C6 bond.

The cyano–cyano ineraction can be found in many crystals of molecules containing a cyano group, but in only a few of them does this interaction result in a planar configuration (Allen, 2002). Since each ribbon interacts with two adjacent ones by means of π–π interactions, we can consider the dimers to be molecular building blocks of anionic walls (Fig. 2). Ribbons of adjacent walls are not parallel (Fig. 3) but form a dihedral angle of 53.70 (4)°.

Besides the structural evidence of π–π interactions, a difference in colour can also be observed between the salt in solution and in the solid. In water or any organic solution (e.g. acetonitrile), all known salts with the anion in question have a vivid yellow colour, while in the solid state, the ammonium salt is dark red.

Two H atoms of the ammonium cation and the lone pair of the O atom of the water molecule form (NH₄⁺···H₂O)_n chains (Fig. 3) which run strictly along the b axis. The other two H atoms of the ammonium cation and the two H atoms of the water molecule join adjacent anionic walls together via hydrogen bonds (Table 1 and Fig.3). In our opinion, the water molecules play an important role in this type of aggregation of anion (I) in the solid state. Although the stability of the anionic wall is mainly provided by the mutual attraction of cations and anions, the integration of the water molecules in the cationic chain, owing to the hydrogen bonds, makes this attraction more evenly distributed. From this point of view, a wall-type aggregation of anion (I) may also be expected in other salts containing hydrophilic cations, for instance alkaline earth ones.

S2. Experimental

The synthesis of the title salt was carried out in the same way as for the above-mentioned salts, (II)–(IV). The starting compound, (2,2,3,3-tetracyanocyclopropanecarboxylic acid, was synthesized from α-chloroketone and TCNE (ethylene-1,1,2,2-tetracarbonitrile). Ammonium 3-cyano-4-(dicyanomethylene)-5-oxo-4,5-dihydro-1H-pyrrol-2-olate was obtained by mixing ammonium iodide with 2,2,3,3-tetracyanocyclopropanecarboxylic acid. Please give brief details of quantities or molar ratios used. The reaction was carried out in water–propan-2-ol (1:1) solvent at room temperature. Dark-red crystals were collected from the reaction mixture by filtration and drying.

S3. Refinement

The positions of the H atoms were determined from a Fourier difference map and their coordinates were refined freely with isotropic displacement parameters. The U_iso value for H1, which is involved in strong dimers to form a hydrogen bond, is 0.055 (5) Ų, and the U_iso value for H61 is 0.072 (7) Ų. For all other H atoms, U_iso(H) ranges from 0.098 (9) to 0.116 (11) Ų.

Computing details

Data collection: CAD-4 Software (Enraf-Nonius, 1989); cell refinement: CAD-4 Software; data reduction: XCAD4 (Harms & Wocadlo, 1995); program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: DIAMOND (Brandenburg, 2000) and ORTEP-3 (Farrugia, 1997); software used to prepare material for publication: SHELXL97.

Figures

	Fig. 1. A view of the title salt, (V), showing the atom-labelling scheme. Displacement ellipsoids are drawn at the 50% probability level.
	Fig. 2. The arrangement of the centrosymmetric anionic dimers (blocks) in ribbons. Adjacent blocks in each ribbon are connected by –CN···NC*– dipole–dipole and π–π interactions. The N2···C8^ii distance is 3.370 (3) Å. Adjacent ribbons interplay via π–π interactions, forming an anionic wall. The interplanar distance is 3.34 Å. The shortest distances between atoms in adjacent layers are C5···N2^iii 3.246 (3) Å and C7···O1^iv 3.314 (3) Å. [Symmetry codes: (i) −x, 2 − y, 1 − z; (ii) 2 − x, 1 − y, 1 − z; (iii) 1 − x, 1 − y, 1 − z; (iv) 1 − x, 2 − y, 1 − z.]
	Fig. 3. Part of the crystal structure of (V), showing the key hydrogen bonds for the molecular arrangement in the crystal. Symmetry codes are listed in Table 1.

Ammonium 3-cyano-4-(dicyanomethylene)-5-oxo-4,5-dihydro-1H-pyrrol-2-olate monohydrate

Crystal data

NH4^+·C8HN4O2^−·H2O	F(000) = 456
Mr = 221.19	Dx = 1.415 Mg m^−3
Monoclinic, P21/n	Melting point: 205 K
Hall symbol: -P 2yn	Cu Kα radiation, λ = 1.54179 Å
a = 7.2618 (11) Å	Cell parameters from 25 reflections
b = 7.5232 (12) Å	θ = 35–45°
c = 19.033 (5) Å	µ = 0.96 mm^−1
β = 92.745 (10)°	T = 291 K
V = 1038.6 (4) Å^3	Prism, dark red
Z = 4	0.15 × 0.13 × 0.10 mm

Data collection

Enraf-Nonius CAD-4 diffractometer	Rint = 0.040
Radiation source: fine-focus sealed tube	θmax = 72.9°, θmin = 4.7°
Graphite monochromator	h = −9→8
non–profiled ω scans	k = 0→9
2129 measured reflections	l = 0→23
2069 independent reflections	2 standard reflections every 120 min
1787 reflections with I > 2σ(I)	intensity decay: none

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)] = 0.039	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.104	All H-atom parameters refined
S = 1.08	w = 1/[σ^2(Fo^2) + (0.0538P)^2 + 0.228P] where P = (Fo^2 + 2Fc^2)/3
2069 reflections	(Δ/σ)max = 0.003
173 parameters	Δρmax = 0.18 e Å^−3
0 restraints	Δρmin = −0.20 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
O1	0.11398 (14)	0.94382 (16)	0.41899 (5)	0.0413 (3)
O2	0.37104 (16)	0.79857 (18)	0.63479 (5)	0.0482 (3)
N1	0.20714 (17)	0.89231 (19)	0.53509 (6)	0.0377 (3)
N2	0.8546 (2)	0.5659 (2)	0.43749 (8)	0.0573 (4)
N3	0.7809 (2)	0.6278 (3)	0.66182 (8)	0.0626 (5)
N4	0.5184 (2)	0.7601 (2)	0.32821 (7)	0.0532 (4)
C2	0.22753 (19)	0.8841 (2)	0.46288 (7)	0.0326 (3)
C3	0.40160 (19)	0.79942 (19)	0.45181 (7)	0.0318 (3)
C4	0.48635 (19)	0.75692 (18)	0.51703 (7)	0.0307 (3)
C5	0.3529 (2)	0.8162 (2)	0.57181 (7)	0.0349 (3)
C6	0.65296 (19)	0.6779 (2)	0.53540 (7)	0.0337 (3)
C7	0.7198 (2)	0.6522 (2)	0.60623 (8)	0.0405 (4)
C8	0.7678 (2)	0.6166 (2)	0.48185 (8)	0.0381 (3)
C9	0.4675 (2)	0.7754 (2)	0.38358 (7)	0.0354 (3)
O3	0.4991 (2)	0.3768 (2)	0.22309 (7)	0.0603 (4)
N6	0.6497 (2)	0.0191 (3)	0.22090 (8)	0.0469 (4)
H1	0.107 (3)	0.940 (3)	0.5545 (10)	0.055 (5)*
H6	0.576 (4)	−0.059 (4)	0.2406 (15)	0.105 (10)*
H61	0.599 (3)	0.123 (4)	0.2273 (12)	0.072 (7)*
H3	0.418 (4)	0.387 (5)	0.2521 (17)	0.116 (11)*
H62	0.773 (4)	0.007 (4)	0.2376 (16)	0.112 (10)*
H63	0.647 (4)	−0.001 (4)	0.1772 (18)	0.114 (11)*
H31	0.446 (4)	0.406 (4)	0.1796 (16)	0.098 (9)*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
O1	0.0375 (5)	0.0555 (7)	0.0305 (5)	0.0105 (5)	−0.0018 (4)	0.0005 (5)
O2	0.0524 (7)	0.0667 (8)	0.0256 (5)	0.0140 (6)	0.0023 (4)	0.0005 (5)
N1	0.0347 (6)	0.0520 (8)	0.0265 (6)	0.0116 (6)	0.0038 (5)	−0.0015 (5)
N2	0.0512 (8)	0.0810 (12)	0.0401 (8)	0.0207 (8)	0.0067 (6)	−0.0027 (7)
N3	0.0547 (9)	0.0950 (13)	0.0374 (8)	0.0198 (9)	−0.0044 (6)	0.0064 (8)
N4	0.0603 (9)	0.0675 (10)	0.0327 (7)	0.0084 (8)	0.0114 (6)	0.0032 (6)
C2	0.0327 (7)	0.0372 (7)	0.0279 (7)	0.0003 (6)	0.0017 (5)	−0.0017 (5)
C3	0.0331 (7)	0.0372 (7)	0.0251 (6)	0.0023 (6)	0.0019 (5)	−0.0004 (5)
C4	0.0331 (7)	0.0316 (7)	0.0274 (7)	−0.0002 (5)	0.0027 (5)	−0.0018 (5)
C5	0.0374 (7)	0.0394 (8)	0.0277 (7)	0.0042 (6)	0.0012 (5)	−0.0017 (6)
C6	0.0342 (7)	0.0393 (8)	0.0277 (7)	0.0037 (6)	0.0014 (5)	0.0001 (5)
C7	0.0370 (8)	0.0511 (9)	0.0335 (8)	0.0084 (7)	0.0009 (6)	0.0011 (6)
C8	0.0338 (7)	0.0466 (9)	0.0337 (7)	0.0075 (6)	−0.0010 (6)	0.0020 (6)
C9	0.0372 (7)	0.0397 (8)	0.0292 (7)	0.0043 (6)	0.0018 (5)	0.0025 (6)
O3	0.0549 (8)	0.0913 (11)	0.0346 (6)	0.0096 (7)	0.0001 (6)	0.0046 (7)
N6	0.0508 (9)	0.0579 (10)	0.0321 (7)	−0.0102 (8)	0.0027 (6)	0.0029 (7)

Geometric parameters (Å, º)

O1—C2	1.2303 (17)	C4—C6	1.378 (2)
O2—C5	1.2070 (17)	C4—C5	1.5240 (19)
N1—C5	1.3657 (18)	C6—C7	1.424 (2)
N1—C2	1.3908 (18)	C6—C8	1.424 (2)
N1—H1	0.91 (2)	O3—H3	0.83 (3)
N2—C8	1.143 (2)	O3—H31	0.92 (3)
N3—C7	1.143 (2)	N6—H6	0.89 (3)
N4—C9	1.139 (2)	N6—H61	0.87 (3)
C2—C3	1.4399 (19)	N6—H62	0.94 (3)
C3—C4	1.3960 (18)	N6—H63	0.85 (3)
C3—C9	1.4171 (19)
C5—N1—C2	111.74 (12)	N1—C5—C4	105.98 (11)
C5—N1—H1	125.1 (12)	C4—C6—C7	123.64 (13)
C2—N1—H1	123.1 (12)	C4—C6—C8	119.69 (13)
O1—C2—N1	123.71 (13)	C7—C6—C8	116.67 (13)
O1—C2—C3	128.81 (13)	N3—C7—C6	176.65 (17)
N1—C2—C3	107.46 (12)	N2—C8—C6	177.62 (17)
C4—C3—C9	129.18 (13)	N4—C9—C3	178.21 (17)
C4—C3—C2	108.90 (12)	H3—O3—H31	107 (3)
C9—C3—C2	121.88 (12)	H6—N6—H61	105 (2)
C6—C4—C3	131.97 (13)	H6—N6—H62	112 (3)
C6—C4—C5	122.15 (12)	H61—N6—H62	116 (2)
C3—C4—C5	105.88 (12)	H6—N6—H63	108 (3)
O2—C5—N1	126.84 (14)	H61—N6—H63	108 (2)
O2—C5—C4	127.18 (13)	H62—N6—H63	107 (3)
C5—N1—C2—O1	179.99 (15)	C2—N1—C5—O2	−177.52 (16)
C5—N1—C2—C3	−1.27 (18)	C2—N1—C5—C4	2.00 (17)
O1—C2—C3—C4	178.55 (15)	C6—C4—C5—O2	−2.2 (3)
N1—C2—C3—C4	−0.11 (17)	C3—C4—C5—O2	177.53 (16)
O1—C2—C3—C9	0.7 (3)	C6—C4—C5—N1	178.28 (14)
N1—C2—C3—C9	−177.92 (14)	C3—C4—C5—N1	−1.99 (16)
C9—C3—C4—C6	−1.4 (3)	C3—C4—C6—C7	177.19 (16)
C2—C3—C4—C6	−179.04 (16)	C5—C4—C6—C7	−3.2 (2)
C9—C3—C4—C5	178.86 (15)	C3—C4—C6—C8	−3.0 (3)
C2—C3—C4—C5	1.26 (16)	C5—C4—C6—C8	176.63 (14)

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
N6—H61···O3	0.87 (3)	2.05 (3)	2.905 (3)	169 (2)
O3—H3···N3^i	0.83 (3)	2.24 (3)	3.059 (2)	170 (3)
O3—H31···O1^ii	0.92 (3)	1.93 (3)	2.8338 (18)	167 (2)
N1—H1···O1^iii	0.91 (2)	1.92 (2)	2.8136 (16)	170.8 (18)
N6—H62···O3^iv	0.94 (3)	2.04 (3)	2.920 (2)	156 (3)
N6—H63···N2^iv	0.85 (3)	2.24 (3)	3.034 (2)	156 (3)
N6—H6···N4^v	0.89 (3)	2.21 (3)	3.011 (2)	150 (2)

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