3-(1H-Pyrrol-2-yl)-1H-pyrazole forms an unusual hydrogen-bonded two-dimensional (3,4)-connected net

The title compound, C₇H₇N₃, is the first crystallographically characterized 1H-pyrrolyl-1H-pyrazole derivative and con­tains two unique mol­ecules in its asymmetric unit (Z′ = 2). These mol­ecules associate into centrosymmetric tetra­mers through N—H...N hydrogen bonding, including a cyclic dimerization of one of the two unique pyrazole rings. These tetra­mers are linked further by two weaker N—H...π contacts to give a novel two-dimensional (3,4)-connected net with a (3².8)₂(3.8²)₂ topology.

S1. Comment

The 1H-pyrazole ring is an attractive synthon in inorganic supramolecular chemistry, since it possesses a metal-binding Lewis basic N-donor, and a Lewis acidic pyrrolic N—H group, in adjacent sites. A pyrazole ring can therefore bind a metal cation and anion simultaneously, and several 1H-pyrazole complexes have proved to be useful hosts for inorganic anions (Pérez & Riera, 2008). As part of our own investigations of the supramolecular chemistry of N—H pyrazole derivatives (Renard et al., 2002, 2006; Liu et al., 2004; Pask et al., 2006; Jones et al., 2006), we have achieved the first synthesis of the title compound, (I). Given the well known ability of pyrrole derivatives to act as anion hosts in their own right (Sessler, Camiolo & Gale, 2003), the combination of pyrrole and pyrazole groups in (I) makes it a potentially useful reagent for supramolecular chemistry. The Cambridge Structural Database (CSD, Version?; Allen, 2002) contains no other 1H-pyrrolyl-1H-pyrazole derivatives, although protonated and N-methylated derivatives of 3,5-bis(pyrrol-2-yl)pyrazole have been crystallographically characterized (Maeda et al., 2007).

The asymmetric unit of (I) contains two unique molecules, labelled A and B (Fig. 1). The molecules adopt essentially the same conformation, with the 3-substituted tautomer at the pyrazole ring and syn-pyrrole and pyrazole groups that are almost coplanar. The dihedral angle between the least-squares planes of the two heterocyclic rings is 4.57 (11)° for molecule A and 10.15 (7)° for molecule B. Molecules A and B associate through the N6B—H6B···N2A hydrogen bond, between the pyrrole group of molecule A and the pyrazole ring of molecule B (Fig. 1). Molecule B then forms a hydrogen-bonded dimer with its symmetry equivalent related by the inversion centre at (0, 0, 1/2), their pyrazole rings forming a cyclic dimer through the N1B—H1B···N2Bⁱ interaction [symmetry code: (i) -x, -y, 1 - z] and its symmetry equivalent (Fig. 1). This cyclic dimer motif is common in crystalline pyrazoles substituted at the C3 and/or C5 positions (Claramunt et al., 2006). It is noteworthy that (I) does not adopt the alternative supramolecular dimer motif that is often exhibited by crystalline (1H-pyrrol-2-yl)aldimines (Fig. 2; see e.g. Franceschi et al., 2001; Sessler, Berthon-Gelloz et al., 2003; Matsui et al., 2004; Munro et al., 2006; Carabineiro et al., 2007; Wang et al., 2007).

The two N—H groups in molecule A form intermolecular N—H···C contacts to the π-systems of the two unique pyrrole rings. These are N1A—H1A···C10Aⁱⁱ and N6A—H6A···C9Bⁱⁱⁱ [symmetry codes: (ii) x + 1/2, -y + 1/2, z + 1/2; (iii) x - 1/2, -y + 1/2, z - 1/2] (Fig. 3), (Table 1). The H···C distances are longer than the N—H···N hydrogen bonds in the structure, but still 0.2–0.4 Å shorter than the sum of the van der Waals radii of an aromatic group and an H atom (Pauling, 1960). In total, molecule A forms N—H···N or N—H···C contacts to four other adjacent molecules, while molecule B is connected to three neighbours. These interactions combine to give a puckered two-dimensional (3,4)-connected network, running parallel to the crystallographic (101) plane. The topology of the network is (3.8²)₂(3².8²)₂ in the short Schläfli notation (Fig. 4). While several different two-dimensional (3,4)-connected nets have been reported before, this example is new to our knowledge. The most common topology of this type in molecular crystals is (4.6²)(4².6².8²), which has been observed on at least five previous occasions (Zhong et al., 2001; Zheng et al., 2004; Xu et al., 2006; Xue et al., 2008; Li et al., 2008). Other known (3,4)-connected two-dimensional networks in metal–organic stuctures include (3.8²)(4².8²) (Zhong et al., 2008), (4².6)(4².6⁴) (Qi et al., 2008) and the V₂O₅ net (4².6)(4².6³.8) (Li et al., 2009).

S2. Experimental

Compound (I) was prepared following the procedure of Lin & Lang (1977). A solution of 2-acetylpyrrole (20 g, 0.18 mol) in dimethylformamide dimethylacetal (100 g, 0.84 mol) was refluxed under N₂ for 48 h. Evaporation of the solvent gave a dark-brown solid residue that was purified by dissolution in CH₂Cl₂ and filtration through a silica plug. Pure 3-(dimethylamino)-1-(1H-pyrrol-2-yl)-2-propen-1-one was obtained from the resultant solution as a yellow solid, by addition of ethyl acetate. A solution of this intermediate (12 g, 0.073 mol) and hydrazine monohydrate (25 g, 0.50 mol) in methanol (200 ml) was refluxed for 6 h. The reaction was quenched with water, and the solution extracted with CH₂Cl₂ (3 × 100 ml). Evaporation of the extracts to dryness yielded an orange oil which slowly solidified upon storage at 253 K. Two further recrystallizations from CH₂Cl₂–hexanes [Solvent ratio?] afforded analytically pure yellow crystals of (I) (yield 5.5 g, 57%). Analysis, found: C 62.9, H 5.3, N 31.5%; calculated for C₇H₇N₃: C 63.1, H 5.3, N 31.6%. ¹H NMR [(CD₃)₂SO, 298 K, δ, p.p.m.]: 6.09 (d, J = 2.6 Hz, 1H), 6.41 (s, 1H), 6.47 (d, J = 2.0 Hz, 1H), 6.79 (d, J = 1.3 Hz, 1H), 7.62 (s, 1H), 11.14 (br s, 1H), 12.72 (br s, 1H); EI mass spectrum m/z 133.0 ([M]⁺), 104.0 ([M—N₂]⁺).

S3. Refinement

The pyrrole and pyrazole rings in molecules A and B were distinguished by the isotropic displacement parameters of their atoms N1 and C10, by the absence of an H atom on atom N2 in the Fourier map, and by the short hydrogen bonds accepted by both pyrazole N2 atoms. All H atoms were located in a difference Fourier map and allowed to refine freely. The refined C—H distances are in the range 0.952 (17)–1.001 (15) Å, and N—H distances are in the range 0.880 (16)–0.911 (16) Å.

Computing details

Data collection: APEX2 (Bruker, 2004); cell refinement: APEX2 (Bruker, 2004); data reduction: SAINT (Bruker, 2004); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: X-SEED (Barbour, 2001); software used to prepare material for publication: local program.

Figures

	Fig. 1. A view of the centrosymmetric hydrogen-bonded tetramer in the crystal structure of (I), showing the atom-numbering scheme employed. The additional intermolecular N—H···C interactions linking these tetramers into a two-dimensional network are not shown. Displacement ellipsoids are drawn at the 50% probability level and H atoms are shown as small spheres of arbitrary radii. [Symmetry code: (i) -x, -y, 1 - z.]
	Fig. 2. Alternative dimer structure which could have been adopted by (I), based on the cyclic dimer motif exhibited by (1H-pyrrol-2-yl)aldimines (Munro et al., 2006).
	Fig. 3. View of the intermolecular environment about molecule A, showing the N—H···N and N—H···C interactions. See Fig. 1 for the full atom-numbering scheme. [Symmetry codes: (ii) x + 1/2, -y + 1/2, z + 1/2; (iii) x - 1/2, -y + 1/2, z - 1/2.]
	Fig. 4. Topology of the (3.8^2)2(3^2.8^2)2 net formed by the intermolecular N—H···N and N—H···C hydrogen bonds in (I). The view is parallel to the (101) plane, with the b axis horizontal. The intermolecular links are between the centroids of each molecule.

3-(1H-Pyrrol-2-yl)-1H-pyrazole

Crystal data

C7H7N3	F(000) = 560
Mr = 133.16	Dx = 1.283 Mg m^−3
Monoclinic, P21/n	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2yn	Cell parameters from 17932 reflections
a = 10.442 (2) Å	θ = 2.3–28.9°
b = 13.004 (2) Å	µ = 0.08 mm^−1
c = 10.8849 (19) Å	T = 150 K
β = 111.119 (9)°	Fragment, pale yellow
V = 1378.7 (4) Å^3	0.18 × 0.15 × 0.09 mm
Z = 8

Data collection

Bruker X8 APEX diffractometer	3601 independent reflections
Radiation source: rotating anode	2789 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.040
Detector resolution: 120 microns pixels mm^-1	θmax = 28.9°, θmin = 2.3°
rotation images scans	h = −14→14
Absorption correction: multi-scan (SADABS; Sheldrick, 2002)	k = −17→17
Tmin = 0.795, Tmax = 0.925	l = −14→14
17932 measured reflections

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) = 0.111	All H-atom parameters refined
S = 1.02	w = 1/[σ^2(Fo^2) + (0.0551P)^2 + 0.2494P] where P = (Fo^2 + 2Fc^2)/3
3601 reflections	(Δ/σ)max = 0.001
237 parameters	Δρmax = 0.22 e Å^−3
0 restraints	Δρmin = −0.18 e Å^−3

Special details

Experimental. Rotating anode power 3 kW.

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.

There are two unique molecules in the asymmetric unit, which are labelled 'A' and 'B'. No disorder was detected during refinement, and no restraints were applied. All non-H atoms were refined anisotropically. All H atoms were located in the Fourier map, and allowed to refine freely. The refined C—H distances range from 0.952 (17)–1.001 (15) Å, and N—H distances are between 0.880 (16)–0.911 (16) Å.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Ų)

	x	y	z	Uiso*/Ueq
N1A	0.33632 (12)	0.19259 (9)	0.56261 (11)	0.0434 (3)
H1A	0.3511 (19)	0.1458 (15)	0.6271 (19)	0.069 (6)*
N2A	0.22010 (11)	0.25217 (8)	0.52432 (10)	0.0362 (2)
C3A	0.22918 (12)	0.30883 (9)	0.42394 (11)	0.0314 (2)
C4A	0.35031 (14)	0.28413 (11)	0.39908 (13)	0.0412 (3)
H4A	0.3769 (16)	0.3152 (12)	0.3328 (16)	0.052 (4)*
C5A	0.41629 (15)	0.21050 (12)	0.49051 (14)	0.0466 (3)
H5A	0.5024 (18)	0.1729 (13)	0.5072 (17)	0.059 (5)*
N6A	0.00975 (10)	0.40392 (8)	0.38763 (10)	0.0334 (2)
H6A	−0.0179 (16)	0.3669 (12)	0.4447 (15)	0.048 (4)*
C7A	0.12521 (12)	0.38570 (9)	0.35650 (11)	0.0315 (2)
C8A	0.12154 (14)	0.45528 (10)	0.25846 (13)	0.0416 (3)
H8A	0.1909 (17)	0.4605 (11)	0.2179 (15)	0.050 (4)*
C9A	0.00137 (15)	0.51698 (11)	0.23154 (14)	0.0461 (3)
H9A	−0.0288 (17)	0.5726 (13)	0.1674 (16)	0.060 (5)*
C10A	−0.06594 (14)	0.48382 (10)	0.31227 (13)	0.0393 (3)
H10A	−0.1529 (17)	0.5075 (12)	0.3198 (15)	0.053 (4)*
N1B	−0.03790 (10)	−0.04424 (7)	0.62179 (10)	0.0319 (2)
H1B	−0.0668 (16)	−0.0668 (11)	0.5389 (15)	0.044 (4)*
N2B	0.04056 (10)	0.04353 (7)	0.65025 (9)	0.0284 (2)
C3B	0.08013 (10)	0.05347 (8)	0.78201 (10)	0.0249 (2)
C4B	0.02943 (13)	−0.02912 (9)	0.83664 (12)	0.0339 (3)
H4B	0.0438 (15)	−0.0422 (11)	0.9313 (15)	0.042 (4)*
C5B	−0.04538 (13)	−0.08947 (9)	0.73075 (13)	0.0363 (3)
H5B	−0.0974 (16)	−0.1541 (12)	0.7257 (15)	0.049 (4)*
N6B	0.19094 (10)	0.22454 (7)	0.78617 (10)	0.0303 (2)
H6B	0.1651 (15)	0.2314 (11)	0.7002 (16)	0.041 (4)*
C7B	0.16455 (11)	0.14056 (8)	0.85149 (10)	0.0258 (2)
C8B	0.23231 (12)	0.15669 (10)	0.98512 (12)	0.0348 (3)
H8B	0.2346 (15)	0.1082 (11)	1.0560 (15)	0.046 (4)*
C9B	0.30167 (13)	0.25384 (10)	0.99986 (13)	0.0392 (3)
H9B	0.3597 (17)	0.2878 (12)	1.0816 (16)	0.052 (4)*
C10B	0.27445 (13)	0.29310 (9)	0.87627 (14)	0.0373 (3)
H10B	0.3049 (16)	0.3565 (12)	0.8458 (15)	0.048 (4)*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
N1A	0.0435 (6)	0.0471 (6)	0.0378 (6)	0.0061 (5)	0.0124 (5)	0.0013 (5)
N2A	0.0344 (5)	0.0428 (5)	0.0306 (5)	−0.0019 (4)	0.0109 (4)	0.0015 (4)
C3A	0.0329 (6)	0.0353 (6)	0.0267 (5)	−0.0110 (4)	0.0114 (4)	−0.0075 (4)
C4A	0.0408 (7)	0.0508 (7)	0.0374 (7)	−0.0064 (6)	0.0207 (6)	−0.0084 (6)
C5A	0.0425 (7)	0.0545 (8)	0.0443 (7)	0.0049 (6)	0.0173 (6)	−0.0106 (6)
N6A	0.0339 (5)	0.0365 (5)	0.0313 (5)	−0.0070 (4)	0.0135 (4)	0.0027 (4)
C7A	0.0319 (6)	0.0348 (5)	0.0285 (5)	−0.0120 (4)	0.0117 (4)	−0.0039 (4)
C8A	0.0406 (7)	0.0473 (7)	0.0391 (7)	−0.0138 (6)	0.0168 (6)	0.0053 (5)
C9A	0.0443 (7)	0.0451 (7)	0.0454 (7)	−0.0090 (6)	0.0120 (6)	0.0131 (6)
C10A	0.0351 (6)	0.0391 (6)	0.0409 (7)	−0.0053 (5)	0.0105 (5)	0.0037 (5)
N1B	0.0339 (5)	0.0289 (5)	0.0300 (5)	−0.0029 (4)	0.0078 (4)	−0.0065 (4)
N2B	0.0303 (5)	0.0265 (4)	0.0250 (4)	−0.0007 (3)	0.0056 (4)	−0.0012 (3)
C3B	0.0236 (5)	0.0265 (5)	0.0242 (5)	0.0034 (4)	0.0081 (4)	−0.0011 (4)
C4B	0.0438 (7)	0.0308 (5)	0.0313 (6)	−0.0028 (5)	0.0185 (5)	−0.0019 (4)
C5B	0.0422 (7)	0.0287 (5)	0.0422 (7)	−0.0060 (5)	0.0202 (5)	−0.0059 (5)
N6B	0.0304 (5)	0.0284 (5)	0.0309 (5)	−0.0011 (4)	0.0097 (4)	−0.0003 (4)
C7B	0.0244 (5)	0.0282 (5)	0.0256 (5)	0.0010 (4)	0.0102 (4)	−0.0023 (4)
C8B	0.0340 (6)	0.0437 (6)	0.0270 (6)	−0.0046 (5)	0.0114 (5)	−0.0056 (5)
C9B	0.0327 (6)	0.0464 (7)	0.0375 (7)	−0.0070 (5)	0.0113 (5)	−0.0171 (5)
C10B	0.0324 (6)	0.0310 (6)	0.0484 (7)	−0.0052 (5)	0.0146 (5)	−0.0077 (5)

Geometric parameters (Å, º)

N1A—C5A	1.3563 (19)	N1B—C5B	1.3511 (16)
N1A—N2A	1.3719 (16)	N1B—N2B	1.3736 (13)
N1A—H1A	0.90 (2)	N1B—H1B	0.892 (15)
N2A—C3A	1.3491 (15)	N2B—C3B	1.3481 (14)
C3A—C4A	1.4222 (18)	C3B—C4B	1.4193 (15)
C3A—C7A	1.4637 (17)	C3B—C7B	1.4666 (14)
C4A—C5A	1.374 (2)	C4B—C5B	1.3805 (17)
C4A—H4A	0.952 (17)	C4B—H4B	1.001 (15)
C5A—H5A	0.981 (17)	C5B—H5B	0.992 (16)
N6A—C10A	1.3820 (17)	N6B—C10B	1.3787 (15)
N6A—C7A	1.3852 (16)	N6B—C7B	1.3840 (14)
N6A—H6A	0.911 (16)	N6B—H6B	0.880 (16)
C7A—C8A	1.3890 (17)	C7B—C8B	1.3851 (16)
C8A—C9A	1.428 (2)	C8B—C9B	1.4361 (18)
C8A—H8A	0.977 (16)	C8B—H8B	0.990 (15)
C9A—C10A	1.3773 (19)	C9B—C10B	1.369 (2)
C9A—H9A	0.975 (17)	C9B—H9B	0.982 (16)
C10A—H10A	0.990 (16)	C10B—H10B	0.983 (16)
C5A—N1A—N2A	112.88 (12)	C5B—N1B—N2B	112.46 (10)
C5A—N1A—H1A	126.8 (12)	C5B—N1B—H1B	129.7 (10)
N2A—N1A—H1A	120.2 (12)	N2B—N1B—H1B	117.3 (10)
C3A—N2A—N1A	104.00 (10)	C3B—N2B—N1B	104.41 (9)
N2A—C3A—C4A	110.95 (11)	N2B—C3B—C4B	110.83 (9)
N2A—C3A—C7A	121.55 (10)	N2B—C3B—C7B	121.31 (9)
C4A—C3A—C7A	127.48 (11)	C4B—C3B—C7B	127.87 (10)
C5A—C4A—C3A	105.53 (12)	C5B—C4B—C3B	105.34 (10)
C5A—C4A—H4A	129.6 (10)	C5B—C4B—H4B	126.3 (8)
C3A—C4A—H4A	124.8 (10)	C3B—C4B—H4B	128.3 (8)
N1A—C5A—C4A	106.63 (12)	N1B—C5B—C4B	106.93 (10)
N1A—C5A—H5A	121.4 (10)	N1B—C5B—H5B	121.6 (9)
C4A—C5A—H5A	131.9 (10)	C4B—C5B—H5B	131.4 (9)
C10A—N6A—C7A	110.21 (10)	C10B—N6B—C7B	109.68 (10)
C10A—N6A—H6A	123.3 (10)	C10B—N6B—H6B	124.3 (10)
C7A—N6A—H6A	126.4 (10)	C7B—N6B—H6B	125.8 (9)
N6A—C7A—C8A	106.92 (11)	N6B—C7B—C8B	107.40 (10)
N6A—C7A—C3A	123.21 (10)	N6B—C7B—C3B	122.56 (9)
C8A—C7A—C3A	129.82 (11)	C8B—C7B—C3B	130.03 (10)
C7A—C8A—C9A	107.62 (12)	C7B—C8B—C9B	107.27 (11)
C7A—C8A—H8A	124.9 (9)	C7B—C8B—H8B	125.5 (9)
C9A—C8A—H8A	127.4 (9)	C9B—C8B—H8B	127.2 (9)
C10A—C9A—C8A	107.81 (12)	C10B—C9B—C8B	107.48 (10)
C10A—C9A—H9A	125.6 (10)	C10B—C9B—H9B	124.4 (9)
C8A—C9A—H9A	126.6 (10)	C8B—C9B—H9B	128.2 (9)
C9A—C10A—N6A	107.45 (12)	C9B—C10B—N6B	108.18 (11)
C9A—C10A—H10A	130.5 (9)	C9B—C10B—H10B	131.8 (9)
N6A—C10A—H10A	122.0 (9)	N6B—C10B—H10B	120.0 (9)

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
N1A—H1A···XA^i	0.90 (2)	2.55	3.31	143.5
N6A—H6A···XB^ii	0.911 (16)	2.68	3.32	127.4
N1B—H1B···N2B^iii	0.892 (15)	2.193 (15)	2.9512 (15)	142.5 (13)
N6B—H6B···N2A	0.880 (16)	2.204 (16)	2.9952 (16)	149.3 (13)

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