An ortho­rhom­bic polymorph of pyrazino­[2,3-f][1,10]phenanthroline-2,3-dicarbonitrile

Wei Yang; Qi-Ming Qiu; Li-Li Zhou; Qiong-Hua Jin; Cun-Lin Zhang

doi:10.1107/S1600536811047039

. 2011 Nov 9;67(Pt 12):o3250–o3251. doi: 10.1107/S1600536811047039

An orthorhombic polymorph of pyrazino[2,3-f][1,10]phenanthroline-2,3-dicarbonitrile

Wei Yang ^a, Qi-Ming Qiu ^a, Li-Li Zhou ^b, Qiong-Hua Jin ^a,^*, Cun-Lin Zhang ^c

PMCID: PMC3238907 PMID: 22199760

Abstract

The title compound, C₁₆H₆N₆, is a polymorph of the previously reported structure [Kozlov & Goldberg (2008 ▶). Acta Cryst. C64, o498–o501]. Unlike the previously reported monoclinic polymorph (space group P2₁/c, Z = 8), the title compound reveals orthorhombic symmetry (space group Pnma, Z = 4). The molecule shows crystallographic mirror symmetry, while the previously reported structure exhibits two independent molecules per asymmetric unit. In the title compound, adjacent molecules are essentially parallel along the c axis and tend to be vertical along the b axis with dihedral angles of 72.02 (6)°. However, in the reported polymorph, the entire crystal structure shows an antiparallel arrangement of adjacent columns related by inversion centers and the two independent molecules are nearly parallel with a dihedral angle of 2.48 (6)°.

Related literature

For ligands based on 1,10-phenanthroline in coordination chemistry, see: Rabaca et al. (2008 ▶); Stephenson et al. (2008 ▶). For reports of the title compound in coordination chemistry, see: Kulkarni et al. (2004 ▶); Stephenson & Hardie (2006 ▶); Xiao et al. (2011 ▶); Xu et al. (2002 ▶). For examples of polymorphism, see: Demirtaş et al. (2011 ▶); Jiang et al. (2000 ▶); Okabe et al. (2001 ▶); Pan & Chen (2009 ▶); Ramos Silva et al. (2011 ▶); Thallapally et al. (2004 ▶). For the previously reported polymorph, see: Kozlov & Goldberg (2008 ▶). For related structures, see: Kozlov et al. (2008 ▶).

Experimental

Crystal data

C₁₆H₆N₆
M _r = 282.27
Orthorhombic,
a = 14.1055 (13) Å
b = 16.3331 (14) Å
c = 5.2694 (4) Å
V = 1214.00 (18) Å³
Z = 4
Mo Kα radiation
μ = 0.10 mm⁻¹
T = 293 K
0.45 × 0.30 × 0.26 mm

Data collection

Bruker SMART CCD area-detector diffractometer
Absorption correction: multi-scan (SADABS; Bruker, 2007 ▶) T _min = 0.956, T _max = 0.974
4543 measured reflections
1113 independent reflections
759 reflections with I > 2σ(I)
R _int = 0.046

Refinement

R[F ² > 2σ(F ²)] = 0.041
wR(F ²) = 0.119
S = 1.06
1113 reflections
100 parameters
H-atom parameters constrained
Δρ_max = 0.20 e Å⁻³
Δρ_min = −0.24 e Å⁻³

Data collection: SMART (Bruker, 2007 ▶); cell refinement: SAINT-Plus (Bruker, 2007 ▶); data reduction: SAINT-Plus; program(s) used to solve structure: SHELXS97 (Sheldrick, 2008 ▶); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008 ▶); molecular graphics: SHELXTL (Sheldrick, 2008 ▶) and ORTEPIII (Burnett & Johnson, 1996 ▶); software used to prepare material for publication: SHELXTL.

Supplementary Material

Crystal structure: contains datablock(s) global, I. DOI: 10.1107/S1600536811047039/zq2127sup1.cif

e-67-o3250-sup1.cif^{(13.9KB, cif)}

Structure factors: contains datablock(s) I. DOI: 10.1107/S1600536811047039/zq2127Isup2.hkl

e-67-o3250-Isup2.hkl^{(55.2KB, hkl)}

Supplementary material file. DOI: 10.1107/S1600536811047039/zq2127Isup3.cml

Additional supplementary materials: crystallographic information; 3D view; checkCIF report

Acknowledgments

This work was supported by the National Natural Science Foundation of China (No. 21171119). It was granted by the research project of recycling PET of food contact materials (No. 2010 J K022) from the Chinese Academy of Inspection and Quarantine, National Keystone Basic Research Program (973 Program) under grant Nos. 2007CB310408 and 2006CB302901, and the Funding Project for Academic Human Resources Development in Institutions of Higher Learning Under the Jurisdiction of Beijing Municipality.

supplementary crystallographic information

Comment

Ligands based on 1,10-phenanthroline are attractive building blocks for the formation of metal-organic complexes bearing diverse dimensionalities (Rabaca et al., 2008; Stephenson et al., 2008). Among 1,10-phenanthroline derivatives, the DICNQ (DICNQ = pyrazino[2,3-f][1,10]phenanthroline-2,3-dicarbonitrile) (Xu et al., 2002; Kulkarni et al., 2004) has a big conjugated system and multiple coordination including strong chelating phenanthroline ring, bridging pyrazine ring and cyanite groups, so it is good in synthesizing luminescent complexes containing multifunctional ligands. Up to date only a few complexes of DICNQ are reported, such as [Co(dicnq)₂Br₂] and [Cu(dicnq)₂Br₂][Cu(dicnq)₂Br]Br.(CH₃CN).2(H₂O) (Stephenson & Hardie, 2006). Very recently, we synthesized five Cu(I) complexes [Cu(PPh₃)(C₁₆H₆N₆)X] (C₁₆H₆N₆= pyrazino[2,3-f][1,10]phenanthroline-2,3-dicarbonitrile; X = Cl, Br, I, CN, SCN) (Xiao et al., 2011). During our attempts to synthesize Cu(II) complexes of DICNQ and 4,4'-bipyridine, we obtained crystals of a new orthorhombic polymorph of the solvent-free DICNQ.

Polymorphism can potentially be found in any crystalline material including polymers, minerals, and metals, and is related to allotropy, which refers to elemental solids. When polymorphism exists as a result of difference in crystal packing, it is called packing polymorphism. The different crystal types probably are the result of hydration, solvation or the effect of synthesis methods. There are recently reported examples of organic polymorphs: 2-(pyrimidin-2-ylsulfanyl) acetic acid, which is able to form monoclinic and orthorhombic crystals (Ramos Silva et al., 2011; Pan & Chen, 2009). 3,4,5-Trihydroxybenzoic acid monohydrate is found to form three polymorphs (Demirtaş et al., 2011; Jiang et al., 2000; Okabe et al., 2001). We herein report a new orthorhombic polymorph of DICNQ (1).

ORTEPIII (Burnett & Johnson, 1996) representation of the title compound (1) is shown in Fig. 1. The title compound belongs to orthorhombic system, space group Pnma, consisting of one symmetric unit of single molecule, unlike the reported monoclinic polymorph (space group P2₁/c), (2), (Kozlov & Goldberg, 2008), which consists of two crystallographically independent molecules.

The phenanthroline fragment of both polymorphs is nearly planar, and a similar bending of the cyano groups from the plane of the phenanthroline residues can be observed. The deviating distance of the cyano groups from the plane in (1) (0.182 (7) Å) is obviously bigger than the corresponding deviating distances in (2) (0.0345 Å and 0.0374 Å).

The packing pattern differs from the reported polymorph. In the title compound, there are two packing arrangements (Fig. 2), adjacent molecules are essentially parallel along the c axis and tend to be vertical along the b axis with dihedral angles of 72.02 (6)°. Howerver, in the reported polymorph the entire crystal structure shows an antiparallel arrangement of the adjacent columns related by inversion centers, and the two independent molecules are nearly parallel with a dihedral angle of 2.48 (6)°.

In addition, the intermolecular assembly of (1) is dominated by π-π stacking of overlaps among phenanthroline fragments and π-π stacking between phenanthroline fragment and cyano group of adjacent molecules (Fig. 2), with an interplanar distance between the parallel phenanthroline rings in the two adjacent molecules of 3.030 (1) Å. In contrast, in (2) and the ethanol solvate of DICNQ (C₁₆H₆N₆).(C₂H₆O) (3) (Kozlov et al., 2008), adjacent molecules overlap only through their phenanthroline fragments with the shortest interplanar distance of 3.380 (3) Å for (2), 3.27 Å and 3.40 Å for (3).

Various methods and conditions of the crystallization process are the main reason responsible for the formation of different polymorphic forms (Thallapally et al., 2004). The two polymorphs (1) and (2) are prepared under different catalysts. (1) was prepared under the catalysis of CuCl₂.2H₂O and 4,4'-bipy, while (2) was prepared under the catalysis of [Pd(PPh₃)Cl₂].

Experimental

A mixture of CuCl₂.2H₂O (0.0178 g, 0.1 mmol) in 5 ml CH₂Cl₂ and DICNQ (0.0290 g, 0.1 mmol) in 3 ml CH₃CN was stirred for 30 min, then a solution of 4,4'-bipyridine (0.0202 g, 0.1 mmol) in 2 ml CH₃CN was added under continuous stirring. The resulting solution was refluxed for 5 h and filtered. The filtrate was allowed to evaporate slowly at room temperature to yield yellow block crystals of the title complex. Crystals suitable for single-crystal X-ray diffraction were selected directly from the sample as prepared.

IR (KBr, disc: v/cm^-1): 3466.82 s, 1587.57m, 1571.17m, 1505.59m, 1459.84m, 1444.23m, 1384.77m, 1372.26m, 1331.97w, 1264.07w, 1219.29m, 1141.93m, 1123.84w, 1073.56w, 1028.64w, 975.09w, 817.56m, 743.23m, 688.54w, 618.37w, 527.98w, 441.00w, 420.02w, 409.42w.