Crystal structures of 2,6-bis[(1H-1,2,4-triazol-1-yl)methyl]pyridine and 1,1-[pyridine-2,6-diylbis(methylene)]bis(4-methyl-1H-1,2,4-triazol-4-ium) iodide triiodide

The predominant intermolecular interactions for triazole rings involve the acidic hydrogen in the third position as shown by the title compound, 2,6-bis[(1H-1,2,4-triazol-1-yl)methyl]pyridine, (I), and the salt 1,1′-[pyridine-2,6-diylbis(methylene))bis(4-methyl-1H-1,2,4-triazol-4 -ium] iodide triiodide, (II).

In the structures of the 2,6-bis(1,2,4-triazoly-3-yl)methyl-substituted pyridine compound, C 11 H 11 N 7 , (I) and the iodide triiodide salt, C 13 H 17 N 7 2+ ÁI À ÁI 3 À , (II), the dihedral angles between the two triazole rings and the pyridine ring are 66.4 (1) and 74.6 (1) in (I), and 68.4 (2) in (II), in which the dication lies across a crystallographic mirror plane. The overall packing structure for (I) is twodimensional with the layers lying parallel to the (001) plane. In (II), the triiodide anion lies within the mirror plane, occupying the space between the two triazole substituent groups and was found to have minor disorder [occupancy ratio 0.9761 (9):0.0239 (9)]. The overall packing of structure (II) can be described as two-dimensional with the layers stacking parallel to the (001) plane. In the crystal, the predominant intermolecular interactions in (I) and (II) involve the acidic hydrogen atom in the third position of the triazole ring, with either the triazole N-atom acceptor in weak C-HÁ Á ÁN hydrogen bonds in (I), or with halide counter-ions through C-HÁ Á ÁI interactions, in (II).
To better understand the suitability of the title compounds for use as ligands for the formation of lanthanide complexes, we became interested in the predominant interactions of 1,2,4triazole rings in the solid state. Herein, we report the struc- ISSN 2056-9890

Supramolecular features
In compound (I), the predominant intermolecular interactions are the C-HÁ Á ÁN hydrogen bonds between the acidic hydrogen atoms of the triazole ring and the nitrogen lone pairs of the neighboring triazole molecule (Table 1). For one asymmetric unit, there are a total of six hydrogen bonds with three neighboring molecules (Fig. 3). These hydrogen bonds can be simplified into two categories: a) the nitrogen atoms involved are in the fourth position of the triazole ring (C1-H1Á Á ÁN7 and C11-H11Á Á ÁN7), and b) the nitrogen atom is in the second position of the ring (C2-H2Á Á ÁN6). Pyridine nitrogen atoms, on the other hand, are involved as acceptors in hydrogen bonds arising from the methylene hydrogen atoms, A perspective view of compound (I), showing the atom-numbering scheme. Anisotropic displacement parameters are drawn at the 50% probability level.
forming a stack of one molecule on top of the other (Fig. 4), although noring interactions are present [minimum ring centroid separation, 4.4323 (3) Å ]. Additionally, a non-acidic C-HÁ Á ÁN interaction is observed between the triazole nitrogen atom and the meta-hydrogen atom of the pyridine ring (C5-H5Á Á ÁN2) ( Table 1). The overall packing of structure (I) can be described as layers that lie parallel to (001).
In compound (II), when viewed along the c-axis, the triiodide anion lies on the mirror plane in the middle of the dication-iodide units, filling up a pore-like groove within the structure (Fig. 5). There are no C-HÁ Á ÁN interactions in compound (II) because the triazole nitrogen atoms are bonded to the methyl groups. The acidic hydrogen atoms in the triazole ring now prefer to interact with the iodide ion.

Figure 4
Hydrogen-bond stacking of the pyridine N atoms and the methylene H atoms in compound (I for other symmetry codes, see Table 2.] dide anion is involved in two C-HÁ Á ÁI(triiodide) interactions with, a) the meta-hydrogen atoms of the pyridine ring (C6-H6Á Á ÁI1), and b) the methylene hydrogen atoms (C4-H4BÁ Á ÁI2) (Fig. 7). The minor occupancy triiodide molecule is not shown, but gives similar interactions to those described above for the major component (C6-H6Á Á ÁI1 0 and C4-H4Á Á ÁI2 0 as well as C4-H4AÁ Á ÁI1 0 ; Table 2). The overall packing of structure (II) can be described as two-dimensional with the layers stacking parallel to the (001) plane. (Meng et al., 2005) is a structure closely related to compound (I). In the solid-state structure, the imidazole nitrogen atoms prefer to form hydrogen bonds with water molecules in the asymmetric unit, not with the hydrogen atoms of the imidazole ring. In another closely related structure, 2,5-bis[(1H-1,2,4-triazol-1-yl)methyl]-1H-pyrrole (Lin et al., 2014), the acidic triazole hydrogen atom also forms C-HÁ Á ÁN hydrogen-bonding interactions similar to those in compound (I).

Database survey
3 (Nielsen et al., 2002), a structure closely related to compound (II), crystallizes as a monohydrate. An imidazole hydrogen atom also shows C-HÁ Á Áhalide(Br) interactions, and at the the same time these bromide anions also form hydrogen bonds with the water molecule in the asymmetric unit. Triazolium salt C-HÁ Á Áhalide interactions similar to those shown by compound (II) are also observed in ionic liquids utilizing triazolium cations (Porcar et al., 2013).