4,4,5,5-Tetramethyl-2-(4-pyridyl)imidazolidin-1-oxyl-3-oxide trichloroacetic acid solvate

In the title compound, C12H16N3O2·C2HCl3O2, the imidazolidine ring adopts a twist conformation. The crystal structure is stabilized by intermolecular O—H⋯N hydrogen bonds.


Related literature
Transition metal compounds containing nitroxide radical ligands are of great interest, as these compounds play an important role in molecule-based magnetic materials (Oshio et al., 2002;Vostrikova et al., 2000). In order to investigate the crystal structure of such ligands, the title compound has been synthesized and its crystal structure is reported here.
In the title compound ( Fig. 1), the imidazole ring adopts a twist conformation, with atoms C7 and C10 displaced by 0.218 (4) and 0.240 (4) Å respectively on opposite sides of the plane through atoms N2, N3, C6. The dihedral angle between the pyridine and the mean plane of the imidazole ring is 20.31 (27)°. This angle is smaller than that of 25.66 (15)° observed in the unsolvated compound (Zhang et al., 2006). In the crystal structure, an intermolecular hydrogen bonding interaction involving the hydroxyl group of the trichloroacetic acid and the N atom of the pyridine ring is observed (Table 1).

S3. Refinement
All H atoms were placed at calculated positions and allowed to ride on their parent atoms, with C-H = 0.93-0.96 Å, O -H = 0.82 Å, and with U iso (H) = 1.5 U eq (C, O) or 1.2 U eq (C) for aromatic H atoms.  The molecular structure of the title compound with the atom-numbering scheme. All hydrogen atoms are omitted except for H4B. Displacement ellipsoids are drawn at the 30% probability level.

Figure 2
Packing diagram of the title compound viewed along the b axis. Hydrogen bonds are shown as dashed lines. All hydrogen atoms are omitted except for H4B.

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 F 2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F 2 , conventional R-factors R are based on F, with F set to zero for negative F 2 . The threshold expression of F 2 > σ(F 2 ) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F 2 are statistically about twice as large as those based on F, and R-factors based on ALL data will be even larger.