Crystal structure of 1,1′-[imidazolidine-1,3-diylbis(methylene)]bis(naphthalen-2-ol)

The crystal structure of the title compound displays a twist conformation of the imidazolidine ring with two (2-hydroxynaphthalen-1-yl)methyl substituents stabilized by two intramolecular O—H⋯N hydrogen bonds.

The crystal structure of the title compound, C 25 H 24 N 2 O 2 , at 173 K has monoclinic (C2/c) symmetry. The molecule is located on a crystallographic twofold rotation axis with only half a molecule in the asymmetric unit. The imidazolidine ring adopts a twist conformation, with a twist about the ring C-C bond. The crystal structure shows the anticlinal disposition of the two (2hydroxynaphthalen-1-yl)methyl substituents of the imidazolidine ring. The structure displays two intramolecular O-HÁ Á ÁN hydrogen bonds, each forming an S(6) ring motif.

Chemical context
We have been interested in the synthesis and characterization of a family of symmetrical N,N 0 -disubstituted imidazolidines by the use of a Mannich-type condensation of cyclic cage aminals with phenols in a one-pot reaction. The main structural feature of the symmetrical N,N 0 -disubstituted imidazolidines, the so-called aromatic di-Mannich bases, is to form intramolecular hydrogen bonds that reveal great structural and thermodynamic stability. These di-Mannich bases which contain a phenolic or naphtholic hydroxyl group as a proton donor, as well as an ortho-aminomethyl group as a proton acceptor in the same molecule are convenient models for studying the nature of hydrogen bonding and other weak noncovalent interactions (Koll et al., 2006).
As with related structures in this series, the molecular conformation is stabilized by two intramolecular O-HÁ Á ÁN hydrogen-bond interactions with S(6) graph-set motifs (Bernstein et al., 1995). Due to symmetry and contrary to other structures, where hydrogen-bond distances were different, the two observed intramolecular hydrogen-bond distances were identical (Table 1).

Supramolecular features
Unlike the situation found in related structures, there is only one significant intermolecular interaction involving the O-H group (as acceptor) and a methylene-H atom (as donor) to consolidate the crystal packing. These weak interactions led to the formation of parallel sets of zigzag chains extending along the c axis of the crystal (Fig. 2).

Synthesis and crystallization
The title compound has been synthesized in solution according to a literature procedure (Rivera et al., 2006); however, in this instance, the synthesis was carried out under microwaveassisted solvent free conditions. Symmetry code: (i) x; Ày þ 2; z À 1 2 .

Figure 1
The molecular structure of the title compound, with displacement ellipsoids drawn at the 50% probability level. Hydrogen bonds are drawn as dashed lines. Atoms labelled with the suffix 'A' are generated using the symmetry operator (Àx + 1, y, Àz + 1 2 ).

Figure 2
The crystal packing of the title compound, howing one of the zigzag chains that extend along the crystal c-axis direction. Hydrogen bonds are drawn as dashed lines.

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.
Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )