Pyridine-4-carboxamidoxime N-oxide

The molecular structure of pyridine-4-carboxamidoxime N-oxide is presented, which gives a two-dimensional supramolecular crystal structure.


Structure description
Since their first reported syntheses (Meisenheimer et al., 1926), pyridine N-oxide and related compounds have garnered much interest in chemistry. We are particularly interested in their uses in coordination polymers and as potential catalysts. The utility of these aromatic N-oxides to facilitate organic oxotransfer reactions has been well documented over the years (see, for example: Espenson, 2003). Many of these reactions are actually catalyzed by transition-metal interactions with the N-oxide ligands (see, for example: Moustafa et al., 2014). Others have reported their use as coordination polymers (Ren et al., 2018). We have also previously reported N-oxides used in coordination polymers of Mn (Kang et al., 2017 andLynch et al., 2018). In this work, the syntheses of metal complexes of the title compound were attempted (Mn, Cu, Ce, Nd, Er, and Pr) by mixing the halide or nitrate salts of the metals with the title compound in methanol; unfortunately, all resulting crystals were of the uncomplexed ligand.
Herein we report the first crystal structure of pyridine-4-carboxamidoxime N-oxide ( Fig. 1), which crystallizes in the monoclinic space group P2 1 /c. The molecule is nearly data reports planar with a r.m.s.d. of 0.112 Å for all non-hydrogen atoms, with the carbamimidoyl group slightly rotated by 15.09 (8) with respect to the pyridine ring plane. N1-O1 has a distance of 1.3226 (18) Å and is consistent with normal N-oxide distances. The crystal structure contains a strong intermolecular hydrogen bond between O2Á Á ÁO1 i which forms a chain running parallel to the b axis; the O2Á Á ÁO1 i separation is 2.6747 (19) Å . Another hydrogen bond is formed between N3Á Á ÁO1 ii which links neighboring chains together; the N3Á Á ÁO1 ii separation is 2.899 (2) Å [symmetry codes: (i) x, y + 1, z; (ii) x, Ày + 1 2 , z + 1 2 , see Table 1]. These hydrogen bonds link four molecules together and form an R 3 4 (24) ring motif in the crystal. Each molecule is also part of four different R(24) synthons, generating sheets of hydrogen-bonding molecules parallel to the (100) face of the unit cell (Fig. 2). There are no other short contacts orinteractions observed in the crystal.

Synthesis and crystallization
An amount of 0.025 g of pyridine-4-carboxamidoxime N-oxide (Alfa Aesar) was weighed and dissolved in a 25 ml beaker in enough methanol to form a solution that allowed to slowly evaporate at room temperature. The clear crystals were analyzed on a Rigaku Xtal Miniflex.

Figure 2
Crystal packing diagram of title compound viewed along [100]. Hydrogen bonds are colored red.

Figure 1
A view of the molecular structure of the title compound, with the atomlabeling scheme. Displacement ellipsoids are drawn at the 50% probability level.

Special details
Refinement. All carbon-bound H atoms were positioned geometrically and refined as riding, with C-H = 0.95 Å and U iso (H) = 1.2U eq (C). N-H and O-H hydrogen atoms were refined with free coordinates and isotropic displacement parameters.