Poly[[[diaqua­zinc(II)]-bis(μ₂-3-cyano-4-dicyano­methyl­ene-5-oxo-4,5-dihydro-1H-pyrrol-2-olato-κ²N³:N^3′)] dihydrate]

The coordination of the 3-cyano-4-dicyano­methyl­ene-5-oxo-4,5-dihydro-1H-pyrrol-2-olate anion to Zn^II, the apical sites of which are occupied by two water mol­ecules, results in the formation of two-dimensional layers of the title coordination polymer, {[Zn(C₈HN₄O₂)₂(H₂O)₂]·2H₂O}_n, in which the Zn^II cations lie on inversion centres in space group C2/c, with water ligands in the apical sites of octa­hedral geometry. Hydrogen bonds between coordinated and lattice water mol­ecules, and π–π stacking inter­actions between the anions link adjacent layers into a continuous framework.

S1. Comment

We have recently postulated that the new organic anion 3-cyano-4-(dicyanomethylene)-5-oxo-4,5-dihydro-1H-pyrrol-2-olate could be involved in different types of anion–cation interaction (Tafeenko, Peschar et al., 2004). Specifically, we proposed that this anion could be involved in π–π stacking interactions and that it could form coordination compounds. Subsequently, π–π stacking interactions have been detected not only between cations and this anion, but also between pairs of anions (Tafeenko et al., 2003, 2005; Tafeenko, Nikolaev et al., 2004). Here, we report the first example of a metal coordination compound, the title compound, (I), where the anion coordinates to Zn²⁺ (Fig. 1).

The geometry of the anion in (I) (Table 1) is essentially identical to that found in other salts (Tafeenko et al., 2003, 2005; Tafeenko, Peschar et al., 2004; Tafeenko, Nikolaev et al., 2004), alhough some minor differences are apparent. The C6—C7 and C6—-C8 bonds are shorter than the corresponding bonds found in salts with different cations, namely potassium (Tafeenko et al., 2003), N,N-dimethylanilinium (Tafeenko, Peschar et al., 2004), N-methylpiridinium (Tafeenko, Nikolaev et al., 2004) and ammonium (Tafeenko et al., 2005). The C9—C4—C6—C7 torsion angle found here has the largest value in this series. This may be compared with the value of 7.5 (1)° in the potassium salt, while for all other salts this value is substantially smaller.

The Zn^II cation of (I) is located on an inversion centre. The coordination sphere consists of the water O atoms [O3 and O3^v; symmetry code: (v) 1/2 − x, 3/2 − y, −z Please check added symmetry code] and the cyano N atoms [N2, N2^v, N3^vi, N3^vii; symmetry codes: (vi) x, 1 − y, −1/2 + z; (vii) 1/2 − x, 1/2 + y, 1/2 − z Please check added symmetry codes] of four anions (Fig.2). The Zn—N3 bond is shorter than Zn—O3 and Zn—N2 (Table 1). In the coordination octahedron, the basal angles O—Zn—N and N—Zn—N are in the range 87.80 (7)–92.20 (7)°, so that the octahedral geometry is nearly ideal. Each anion links two Zn^II centres by means of the dicyanomethylene units. Each Zn^II cation is connected to four others by four different anions to form two-dimensional layers of the coordination polymer [Zn(C₈H₁N₄O₂)₂(H₂O)₂]_n. Two additional solvate water molecules complete the composition.

The formation of the two-dimensional layers is shown in detail in Figs. 2 and 3, and the interactions betweeen these layers are shown in Fig. 4. The building block of the polymer consists of a Zn^II cation, two water molecules and two anions (Fig. 3). It resembles a slightly deformed letter Z. An arrangement of these building blocks in a ···ZZZ··· fashion can, most probably, occur in coordination compounds containing transition metals. The synthesis and structure investigation of such compounds would be of interest, given that coordination polymers containing cyano-based anions have exhibited long-range magnetic ordering (Kurmoo & Kepert, 1998; Batten et al., 1998).

S2. Experimental

The synthesis of the title salt was carried out by Dr O. V. Kaukova, Department of Chemistry, Chuvash State University, Russia. The title salt was obtained by mixing zinc iodide with 2,2,3,3-tetracyanocyclopropanecarboxylic acid in the molar ratio 1:2. The reaction was carried out in water–propan-2-ol (1:1, (v/v) at room temperature. A yellow powder was extracted from the reaction mixture by filtration and drying; this was then dissolved in acetonitrile. Yellow crystals of (I) were obtained after slow evaporation of this solution over 7 d.

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.

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 (I), with the atom-labelling scheme. Displacement ellipsoids are drawn at the 50% probability level and H atoms are shown as small spheres of arbitrary radii.
	Fig. 2. Part of the crystal structure of (I), showing how the cations and anions are arranged to form a layer. The Zn atom at (x, y, z) and those with symmetry codes (i)–(iv) lie in the same plane. Infinite [Zn(C8HN4O2)2(H2O)2]n chains are formed along the b axis via O3^*···(H1—N1)^** hydrogen bonds. Please define the meaning of the asterisks. Adjacent chains are connected by coordination of an N3^* atom from one chain to a Zn^** of another one. In the layer, anions of adjacent chains form dimers via π–π interaction, e.g. the anion at (x, y, z) and its coordinated Zn^II cation form a dimer with the anion at symmetry position (viii), which is related to cation Zn^ii. The Zn···Zn(i,ii,iii,iv) distances are equal, at 8.185 (1) Å. [Symmetry codes: (i) 1/2 − x, −1/2 + y, 1/2 − z; (ii) 1/2 − x, −1/2 + y, −1/2 − z; (iii) 1/2 − x, 1/2 + y, −1/2 − z; (iv) 1/2 − x, 1/2 + y, 1/2 − z; (v) 1/2 − x, 3/2 − y, −z; (vi) x, 1 − y, −1/2 + z; (vii) 1/2 − x, 1/2 + y, 1/2 − z; (viii) 1/2 − x, 1/2 − y, −z; (ix) x, 1 + y, z.]
	Fig. 3. Part of the chain, showing how the building blocks [each consisting of a Zn^II cation, two water molecules and two anions, e.g. with symmetry codes (x, y, z) and (ii)] interplay through the complementary hydrogen-bonding and π–π interactions. The hydrogen-bond parameters are listed in Table 2. The shortest distance between anions from adjacent blocks in the chain is N1···C8^i 3.265 Å. Adjacent chains are linked by a coordination bond from N3^* to Zn^**, thus forming a layer. Please define the meaning of the asterisks. [Symmetry codes: (i) 1/2 − x, 1/2 − y, −z; (ii) 1/2 − x, 3/2 − y, −z; (iii) x, 1 + y, z; (iv) 1/2 − x, −1/2 + y, 1/2 + z; (v) 1/2 − x, 1/2 + y, 1/2 + z; (vi) 1/2 − x, 1/2 + y, −1/2 + z; (vii) 1/2 − x, −1/2 + y, −1/2 − z; (viii) x, −1 + y, z.]
	Fig. 4. The anions of adjacent layers [e.g. an anion at (x, y, z) and an anion with symmetry code (iii)] are connected by π–π interactions to form stacks running normal to the bc plane. The hydrogen bonds between the apical (O3) and hydrate (O4) water molecules enhance the interaction. Some distances between atoms of adjacent layers are C9···C9^iii 3.322 (4), O1···C5^iii 3.272 (3), C2···C2^iii 3.266 (3) and C5···O1^iii 3.272 (3) Å. The hydrate molecules form hydrogen bonds with atoms O1^* and N4^* of the anions. Please define the meaning of the asterisks. The parameters of the hydrogen bonds are listed in Table 2. The distance between Zn atoms in the direction normal to the bc plane (e.g. Zn···Zn^iii) is the shortest [7.445 (1) Å]. [Symmetry codes: (i) 1 − x, y, 1/2 − z; (ii) 1/2 − x, 1/2 − y, −z; (iii) −x, y, 1/2 − z; (iv) 1/2 + x, 3/2 − y, 1/2 + z; (v) 1/2 − x, 1/2 + y, 1/2 − z.]

Poly[[diaquabis(µ₂-3-cyano-4-dicyanomethylene-5-oxo-4,5-dihydro-1H-pyrrol-2- olato-κ²N³:N^3')zinc(II)] dihydrate]

Crystal data

[Zn(C8HN4O2)2(H2O)2]·2H2O	F(000) = 1024
Mr = 507.69	Dx = 1.698 Mg m^−3
Monoclinic, C2/c	Melting point: 170 K
Hall symbol: -C 2yc	Cu Kα radiation, λ = 1.54179 Å
a = 19.0297 (17) Å	Cell parameters from 25 reflections
b = 11.0300 (19) Å	θ = 29–46°
c = 12.0952 (19) Å	µ = 2.33 mm^−1
β = 128.519 (9)°	T = 290 K
V = 1986.3 (6) Å^3	Prism, yellow
Z = 4	0.10 × 0.06 × 0.04 mm

Data collection

Enraf–Nonius CAD-4 diffractometer	1821 reflections with I > 2σ(I)
Radiation source: fine-focus sealed tube	Rint = 0.09
Graphite monochromator	θmax = 72.9°, θmin = 5.0°
non–profiled ω scans	h = −23→23
Absorption correction: ψ scan (North et al., 1968)	k = −11→13
Tmin = 0.861, Tmax = 0.920	l = −12→14
3976 measured reflections	2 standard reflections every 120 min
1985 independent reflections	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)] = 0.046	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.100	All H-atom parameters refined
S = 1.07	w = 1/[σ^2(Fo^2) + (0.06P)^2 + 1.4794P] where P = (Fo^2 + 2Fc^2)/3
1985 reflections	(Δ/σ)max < 0.001
171 parameters	Δρmax = 0.47 e Å^−3
2 restraints	Δρmin = −1.27 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
Zn	0.2500	0.7500	0.0000	0.02489 (16)
O1	0.06002 (12)	0.13963 (18)	−0.34569 (18)	0.0498 (5)
O2	0.18416 (13)	0.10405 (17)	0.11899 (19)	0.0513 (5)
O3	0.38289 (9)	0.67803 (14)	0.13883 (15)	0.0308 (3)
O4	0.49756 (13)	0.76345 (19)	0.0895 (2)	0.0433 (4)
N1	0.12302 (13)	0.08967 (18)	−0.1156 (2)	0.0373 (4)
N2	0.19902 (12)	0.58907 (18)	0.02650 (18)	0.0342 (4)
N3	0.23601 (12)	0.32331 (17)	0.32852 (18)	0.0339 (4)
N4	0.06127 (15)	0.4782 (2)	−0.3252 (2)	0.0514 (6)
C2	0.09485 (14)	0.1697 (2)	−0.2248 (2)	0.0342 (5)
C3	0.11360 (13)	0.2920 (2)	−0.1649 (2)	0.0293 (4)
C4	0.15095 (12)	0.2839 (2)	−0.0240 (2)	0.0262 (4)
C5	0.15589 (14)	0.14873 (19)	0.0073 (2)	0.0319 (4)
C6	0.18260 (13)	0.37114 (19)	0.07975 (19)	0.0268 (4)
C7	0.21234 (13)	0.34297 (19)	0.2170 (2)	0.0280 (4)
C8	0.19045 (12)	0.49326 (19)	0.05301 (19)	0.0269 (4)
C9	0.08689 (14)	0.3963 (2)	−0.2510 (2)	0.0340 (5)
H1	0.117 (2)	0.009 (4)	−0.132 (4)	0.077 (11)*
H2	0.417 (3)	0.707 (4)	0.113 (5)	0.084 (12)*
H3	0.408 (2)	0.704 (3)	0.215 (4)	0.050 (9)*
H4	0.479 (3)	0.721 (3)	0.020 (3)	0.087 (14)*
H5	0.505 (3)	0.8391 (18)	0.092 (5)	0.102 (15)*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Zn	0.0289 (2)	0.0281 (2)	0.0168 (2)	−0.00099 (13)	0.01372 (17)	−0.00052 (12)
O1	0.0630 (11)	0.0533 (11)	0.0335 (9)	−0.0071 (9)	0.0303 (8)	−0.0115 (8)
O2	0.0700 (12)	0.0380 (9)	0.0355 (9)	0.0019 (9)	0.0278 (9)	0.0113 (8)
O3	0.0287 (7)	0.0377 (8)	0.0203 (7)	−0.0004 (6)	0.0125 (6)	−0.0005 (6)
O4	0.0450 (10)	0.0536 (12)	0.0298 (9)	0.0010 (8)	0.0226 (8)	0.0038 (8)
N1	0.0430 (10)	0.0314 (10)	0.0370 (10)	0.0003 (8)	0.0247 (8)	−0.0016 (8)
N2	0.0422 (9)	0.0351 (10)	0.0253 (8)	−0.0054 (8)	0.0211 (8)	0.0004 (7)
N3	0.0441 (9)	0.0342 (9)	0.0250 (8)	0.0016 (8)	0.0222 (8)	0.0053 (8)
N4	0.0597 (13)	0.0516 (13)	0.0294 (10)	−0.0040 (11)	0.0211 (9)	0.0081 (10)
C2	0.0325 (10)	0.0397 (12)	0.0314 (10)	−0.0027 (9)	0.0204 (8)	−0.0053 (9)
C3	0.0316 (9)	0.0329 (11)	0.0241 (9)	0.0004 (8)	0.0177 (8)	0.0017 (8)
C4	0.0251 (8)	0.0288 (9)	0.0252 (9)	0.0001 (8)	0.0159 (8)	0.0028 (8)
C5	0.0335 (10)	0.0272 (10)	0.0318 (10)	0.0019 (8)	0.0189 (8)	0.0037 (9)
C6	0.0299 (9)	0.0298 (10)	0.0208 (9)	0.0001 (8)	0.0159 (8)	0.0037 (8)
C7	0.0294 (9)	0.0303 (10)	0.0252 (10)	−0.0005 (8)	0.0174 (8)	0.0017 (8)
C8	0.0295 (9)	0.0330 (11)	0.0193 (8)	−0.0008 (8)	0.0157 (7)	0.0013 (8)
C9	0.0371 (10)	0.0410 (12)	0.0208 (9)	−0.0031 (9)	0.0166 (8)	0.0010 (9)

Geometric parameters (Å, º)

Zn—N3^i	2.0830 (17)	N1—H1	0.90 (4)
Zn—O3	2.1344 (14)	N2—C8	1.145 (3)
Zn—N2	2.1406 (19)	N3—C7	1.146 (3)
O1—C2	1.216 (3)	N4—C9	1.146 (3)
O2—C5	1.205 (3)	C2—C3	1.466 (3)
O3—H2	0.92 (4)	C3—C4	1.381 (3)
O3—H3	0.78 (3)	C3—C9	1.417 (3)
O4—H4	0.822 (19)	C4—C6	1.387 (3)
O4—H5	0.844 (19)	C4—C5	1.527 (3)
N1—C5	1.367 (3)	C6—C7	1.415 (3)
N1—C2	1.389 (3)	C6—C8	1.415 (3)
N3^i—Zn—N3^ii	180.00 (9)	O1—C2—N1	124.7 (2)
N3^i—Zn—O3	89.60 (7)	O1—C2—C3	128.9 (2)
N3^ii—Zn—O3	90.40 (7)	N1—C2—C3	106.47 (18)
O3—Zn—O3^iii	180.00 (7)	C4—C3—C9	129.2 (2)
N3^i—Zn—N2	92.20 (7)	C4—C3—C2	109.3 (2)
N3^ii—Zn—N2	87.80 (7)	C9—C3—C2	121.23 (18)
O3—Zn—N2	89.95 (7)	C3—C4—C6	132.2 (2)
O3^iii—Zn—N2	90.05 (7)	C3—C4—C5	105.92 (19)
N2—Zn—N2^iii	180.0	C6—C4—C5	121.85 (17)
Zn—O3—H2	110 (3)	O2—C5—N1	127.4 (2)
Zn—O3—H3	110 (2)	O2—C5—C4	126.4 (2)
H2—O3—H3	103 (3)	N1—C5—C4	106.23 (18)
H4—O4—H5	124 (4)	C4—C6—C7	122.73 (19)
C5—N1—C2	112.08 (19)	C4—C6—C8	120.12 (17)
C5—N1—H1	128 (2)	C7—C6—C8	117.08 (18)
C2—N1—H1	120 (2)	N3—C7—C6	178.2 (2)
C8—N2—Zn	164.58 (17)	N2—C8—C6	175.1 (2)
C7—N3—Zn^iv	163.45 (18)	N4—C9—C3	176.7 (2)

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

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
N1—H1···O3^v	0.90 (4)	2.06 (4)	2.962 (3)	172 (4)
O3—H2···O4	0.92 (4)	1.84 (4)	2.762 (2)	172 (4)
O3—H3···O4^vi	0.78 (3)	1.99 (3)	2.748 (2)	163 (3)
O4—H4···O1^vii	0.82 (2)	1.97 (2)	2.782 (3)	172 (4)
O4—H5···N4^viii	0.84 (2)	2.21 (2)	3.017 (3)	161 (4)

Symmetry codes: (v) −x+1/2, −y+1/2, −z; (vi) −x+1, y, −z+1/2; (vii) −x+1/2, y+1/2, −z−1/2; (viii) x+1/2, −y+3/2, z+1/2.