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

The crystal structure of the title potassium salt, K⁺·C₈HN₄O₂^-, of the organic anion 3-cyano-4-(di­cyano­methyl­ene)-5-oxo-4,5-di­hydro-1H-pyrrol-2-olate shows that the di­cyano­methyl­ene moiety is able to accept an electron in the same way as does tetra­cyano­ethyl­ene, to yield the novel product. The organic anion is nearly planar, with deviations caused by steric crowding among the exocyclic cyano groups. The K⁺ cations lie within tricapped trigonal prisms that stack to form channels. The three-dimensional structure is completed by the formation of hydrogen-bonded chains by the anions.

S1. Comment

Tetracyanoethylene (TCNE) is widely used for preparing photochromic materials (Huffman et al., 1967), anticancerous (Nasakin et al., 2000) and biologically active compounds (Abdel-Rahman, 1989; Tacconi et al., 1976) and is the basic reagent for the synthesis of new hetero- and carbocyclic compounds with specific physical and chemical properties (Nasakin et al., 1992, 1994, 1997; Sheverdov et al., 2001). One of the most remarkable features of TCNE is its ability to accept an electron easily, to be transformed into an anion or radical anion (Lemenovskiy et al., 1981; Zheludev et al., 1994). Hence, we hypothesize that the same ability could be an intrinsic property of substances or intermediates that contain a fragment of TCNE, specifically dicyanomethylene. This article reports on the positive realisation of this idea. We suppose that hetero- and carbocyclic compounds containing two, three or four cyano groups are promising starting reagents for transformations to anions or radical anions. An iodide anion was used as the reducing agent in the reaction with 4,13-dioxo-5,12-dioxadispiro[2.2.5.2]-tridecane-1,1,2,2-tetra-carbonitrile (see Scheme). \sch

The X-ray analysis of the product isolated from a water-dioxane solution showed that a salt with a new organic anion, potassium 3-cyano-4-(dicyanomethylene)-5-oxo-4,5-dihydro-1H-pyrrol-2-olate, (I), had been synthesized. Although the mechanism of this reaction needs further clarification, we can formulate two aspects of the reaction on the basis of the resulting molecular structure: a) electron transport from the iodide anion into the organic moiety and b) recyclization as a consequence of (NC)₂C—C(CN)₂ C—C bond breaking. Note that the negative charge on one C atom (see Scheme) only partly reflects the real charge distribution. The charges on the atoms of the anion and on the corresponding radical were calculated by quantum-chemical methods using the semi-empirical AM1 Hamiltonian (Dewar et al., 1985). The results of the calculation are represented in Table 2 (see also Fig. 1), which shows the charge distribution in the anion and the difference in charge distribution between anion and radical. Going from the radical to the anion noticeably increases the negative charge on the external heteroatoms and atoms C3 and C7.

All external heteroatoms of (I) are involved in the formation of a practically ideal tricapped trigonal prism that encloses a cation (Figs. 2 and 3). There is good indirect evidence that all external heteroatoms bear negative charge. The K···A distances (where A is O or N) range from 2.833 (1) for K···O1ⁱ to 3.174 (2) Å for K···N3^vi [Table 1; symmetry codes: (i) x − 1, y, z; (vi) 1 − x, 2 − y, 1 − z]. Each prism is joined to two neighbouring prisms through a common base, and in this way a channel along the a axis is formed, in which the K⁺ cations are located (Figs. 2 and 3). The shortest K···K distance is 4.161 (1) Å.

The anions in (I) are connected by an N—H···O2^vii interaction to form extended chains which run along the b axis, with N—H 0.82 (2), H···O2^vii 2.31 (2) and N···O2^vii 3.056 (2) Å, and N—H···O2^vii 151 (2)° [symmetry code: (vii) 2 − x, y − 1/2, 1/2 − z].

The five-membered ring of (I) is planar, with a maximum deviation (for N) of 0.011 (1) Å. Atoms O1 [deviation 0.025 (1) Å] and O2 [deviation 0.015 (1) Å] lie in this plane. While atom C7 [deviation 0.0095 (16) Å] also lies nearly exactly in the plane, atoms C6 [deviation −0.116 (2) Å] and N1 [deviation −0.230 (2) Å] are displaced from this plane, as a result of steric hindrance and repulsion by the neighbouring cyano groups (Fig. 1). The angle which the –C(CN)₂ group makes with the five-membered ring is 4.1 (1)°, demonstrating a small twist from planarity about the C4—C7 bond.

S2. Experimental

The starting compound was synthesized from α-chloro ketone and tetracyanoethylene. Potassium 3-cyano-4-(dicyanomethylene)-5-oxo-4,5-dihydro-1H-pyrrol-2-olate, (I), was obtained by mixing 4,13-dioxo-5,12-dioxadispiro[2.2.5.2]tridecane-1,1,2,2-tetracarbonitrile with potassium iodide in water-1,4-dioxane (Ratio?), followed by refluxing of the resulting solution for 1 h. Yellow crystals of (I) were collected from the reaction mixture by filtration and drying.

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, 1990); 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 molecular view of (I) with the atom-labelling scheme. Displacement ellipsoids are drawn at the 50% probability level and the H atom is shown as a small sphere of arbitrary radius.
	Fig. 2. Part of the crystal structure of (I), showing the hydrogen-bonded chain of anions along the b axis (dashed lines), the cation arrangement along the a axis (solid lines) and the cation-anion interaction (dotted lines) [symmetry codes: (i) x − 1, y, z; (ii) x, y − 1, z; (iii) 1 − x, y − 1/2, 1/2 − z; (iv) −x, 2 − y, 1 − z; (v) x − 1, y − 1, z; (vi) 1 − x, 2 − y, 1 − z].
	Fig. 3. The tricapped trigonal prism surrounding a cation of (I). The unlabelled vertex is N3^iv. Symmetry codes are as given for Fig. 2.

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

Crystal data

[K(C8HN4O2)]	Dx = 1.773 Mg m^−3
Mr = 224.23	Melting point: 618 K
Monoclinic, P21/c	Mo Kα radiation, λ = 0.71073 Å
a = 4.1614 (10) Å	Cell parameters from 23 reflections
b = 9.391 (2) Å	θ = 14–24°
c = 21.571 (3) Å	µ = 0.61 mm^−1
β = 95.02 (1)°	T = 293 K
V = 839.7 (3) Å^3	Prism, yellow
Z = 4	0.20 × 0.15 × 0.10 mm
F(000) = 448

Data collection

Enraf-Nonius CAD-4 diffractometer	Rint = 0.000
Radiation source: fine-focus sealed tube	θmax = 30.0°, θmin = 1.9°
Graphite monochromator	h = −5→5
non–profiled ω scan	k = 0→13
2434 measured reflections	l = 0→30
2434 independent reflections	2 standard reflections every 60 min
1935 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)] = 0.037	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.095	All H-atom parameters refined
S = 1.04	w = 1/[σ^2(Fo^2) + (0.0469P)^2 + 0.203P] where P = (Fo^2 + 2Fc^2)/3
2434 reflections	(Δ/σ)max = 0.001
141 parameters	Δρmax = 0.29 e Å^−3
0 restraints	Δρmin = −0.33 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
K	0.14533 (9)	0.88691 (4)	0.400597 (18)	0.03293 (12)
O1	0.6384 (3)	1.08161 (12)	0.36809 (6)	0.0359 (3)
O2	0.9404 (4)	1.42910 (15)	0.23638 (6)	0.0425 (3)
N	0.8321 (4)	1.22833 (16)	0.29427 (7)	0.0323 (3)
N1	0.6057 (4)	1.71163 (17)	0.33655 (8)	0.0431 (4)
N2	0.1762 (4)	1.59565 (16)	0.44838 (7)	0.0380 (4)
N3	0.2725 (4)	1.14414 (17)	0.49494 (8)	0.0432 (4)
C2	0.8220 (4)	1.37460 (18)	0.28018 (8)	0.0297 (3)
C3	0.6544 (4)	1.44146 (17)	0.32824 (7)	0.0261 (3)
C4	0.5583 (4)	1.33835 (16)	0.36916 (7)	0.0235 (3)
C5	0.6759 (4)	1.19805 (16)	0.34570 (7)	0.0257 (3)
C6	0.6248 (4)	1.59091 (17)	0.33237 (8)	0.0291 (3)
C7	0.3885 (4)	1.34901 (16)	0.42127 (7)	0.0247 (3)
C8	0.2696 (4)	1.48459 (17)	0.43802 (7)	0.0265 (3)
C9	0.3285 (4)	1.23226 (17)	0.46078 (8)	0.0288 (3)
H	0.905 (6)	1.164 (3)	0.2740 (10)	0.049 (7)*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
K	0.0342 (2)	0.02549 (18)	0.0402 (2)	0.00231 (14)	0.00941 (15)	0.00279 (14)
O1	0.0461 (8)	0.0220 (6)	0.0410 (7)	0.0046 (5)	0.0113 (6)	0.0014 (5)
O2	0.0519 (8)	0.0429 (8)	0.0354 (7)	−0.0045 (6)	0.0189 (6)	0.0029 (6)
N	0.0414 (8)	0.0278 (7)	0.0291 (7)	0.0042 (6)	0.0112 (6)	−0.0048 (6)
N1	0.0509 (10)	0.0290 (8)	0.0501 (10)	0.0024 (7)	0.0085 (8)	0.0077 (7)
N2	0.0478 (9)	0.0294 (7)	0.0376 (8)	0.0071 (7)	0.0090 (7)	−0.0012 (6)
N3	0.0557 (11)	0.0306 (8)	0.0461 (9)	0.0021 (7)	0.0208 (8)	0.0052 (7)
C2	0.0310 (8)	0.0321 (8)	0.0262 (8)	−0.0018 (7)	0.0031 (6)	0.0002 (6)
C3	0.0314 (8)	0.0230 (7)	0.0240 (7)	0.0004 (6)	0.0028 (6)	0.0017 (6)
C4	0.0248 (7)	0.0211 (7)	0.0241 (7)	0.0015 (5)	−0.0008 (6)	−0.0006 (6)
C5	0.0277 (7)	0.0238 (7)	0.0252 (7)	0.0016 (6)	0.0012 (6)	−0.0029 (6)
C6	0.0312 (8)	0.0278 (8)	0.0287 (8)	0.0002 (6)	0.0049 (6)	0.0056 (6)
C7	0.0291 (8)	0.0207 (6)	0.0244 (7)	0.0020 (6)	0.0034 (6)	0.0000 (6)
C8	0.0305 (8)	0.0258 (7)	0.0236 (7)	0.0016 (6)	0.0047 (6)	0.0008 (6)
C9	0.0331 (8)	0.0246 (7)	0.0298 (8)	0.0022 (6)	0.0085 (6)	−0.0018 (6)

Geometric parameters (Å, º)

K—O1^i	2.8329 (14)	N—C2	1.407 (2)
K—O1	2.8805 (14)	N—H	0.82 (2)
K—N2^ii	2.9218 (16)	N1—C6	1.141 (2)
K—N1^ii	2.9584 (18)	N2—C8	1.142 (2)
K—O2^iii	2.9716 (14)	N3—C9	1.145 (2)
K—N3^iv	2.9787 (17)	C4—C5	1.508 (2)
K—N1^v	3.0195 (19)	C4—C7	1.383 (2)
K—N3	3.1730 (19)	C3—C4	1.392 (2)
K—N3^vi	3.174 (2)	C3—C6	1.412 (2)
K—K^i	4.1614 (10)	C2—C3	1.443 (2)
O1—C5	1.2109 (19)	C7—C8	1.424 (2)
O2—C2	1.216 (2)	C7—C9	1.424 (2)
N—C5	1.364 (2)
O1^i—K—O1	93.49 (4)	O1—K—N3^vi	73.47 (4)
O1^i—K—N2^ii	134.45 (5)	N2^ii—K—N3^vi	69.90 (5)
O1—K—N2^ii	132.05 (5)	N1^ii—K—N3^vi	78.18 (5)
O1^i—K—N1^ii	137.91 (5)	O2^iii—K—N3^vi	137.38 (4)
O1—K—N1^ii	74.65 (4)	N3^iv—K—N3^vi	85.05 (5)
N2^ii—K—N1^ii	68.50 (4)	N1^v—K—N3^vi	139.95 (4)
O1^i—K—O2^iii	69.26 (4)	N3—K—N3^vi	62.65 (5)
O1—K—O2^iii	72.51 (4)	K^i—K—K^vii	180.0
N2^ii—K—O2^iii	118.25 (4)	C2—N—C5	111.84 (14)
N1^ii—K—O2^iii	68.66 (4)	C5—N—H	120.3 (16)
O1^i—K—N3^iv	77.24 (4)	C2—N—H	127.7 (16)
O1—K—N3^iv	136.20 (5)	O1—C5—N	126.86 (15)
N2^ii—K—N3^iv	69.64 (4)	O1—C5—C4	126.74 (14)
N1^ii—K—N3^iv	138.04 (5)	N—C5—C4	106.41 (13)
O2^iii—K—N3^iv	137.57 (5)	C7—C4—C3	131.35 (15)
O1^i—K—N1^v	74.38 (5)	C7—C4—C5	122.67 (14)
O1—K—N1^v	138.74 (4)	C3—C4—C5	105.97 (13)
N2^ii—K—N1^v	70.06 (5)	C4—C3—C6	128.29 (15)
N1^ii—K—N1^v	88.23 (5)	C4—C3—C2	109.67 (14)
O2^iii—K—N1^v	66.30 (4)	C6—C3—C2	121.87 (15)
N3^iv—K—N1^v	80.38 (5)	O2—C2—N	124.92 (16)
O1^i—K—N3	75.30 (4)	O2—C2—C3	128.99 (17)
O1—K—N3	65.82 (4)	N—C2—C3	106.07 (14)
N2^ii—K—N3	119.13 (5)	N1—C6—C3	178.7 (2)
N1^ii—K—N3	130.13 (5)	C4—C7—C8	118.99 (14)
O2^iii—K—N3	122.34 (4)	C4—C7—C9	124.03 (14)
N3^iv—K—N3	70.43 (5)	C8—C7—C9	116.97 (14)
N1^v—K—N3	141.64 (5)	N2—C8—C7	176.43 (17)
O1^i—K—N3^vi	137.77 (4)	N3—C9—C7	175.85 (18)
C2—N—C5—O1	178.22 (17)	C5—N—C2—O2	−179.29 (17)
C2—N—C5—C4	−1.70 (19)	C5—N—C2—C3	2.1 (2)
O1—C5—C4—C7	0.2 (3)	C4—C3—C2—O2	179.84 (18)
N—C5—C4—C7	−179.83 (15)	C6—C3—C2—O2	−4.5 (3)
O1—C5—C4—C3	−179.27 (17)	C4—C3—C2—N	−1.59 (19)
N—C5—C4—C3	0.65 (17)	C6—C3—C2—N	174.06 (16)
C7—C4—C3—C6	5.8 (3)	C3—C4—C7—C8	3.2 (3)
C5—C4—C3—C6	−174.70 (17)	C5—C4—C7—C8	−176.23 (14)
C7—C4—C3—C2	−178.86 (16)	C3—C4—C7—C9	−175.56 (17)
C5—C4—C3—C2	0.59 (17)	C5—C4—C7—C9	5.1 (2)

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