2,2′-[Imidazolidine-1,3-diylbis(methylene)]diphenol

In the title molecule, C17H20N2O2, the imidazolidine ring adopts a twist conformation. The mean plane through the five atoms of the imidazolidine ring makes dihedral angles of 70.18 (4) and 74.14 (4)° with the planes of the two aromatic rings. The dihedral angle between the benzene rings is 53.11 (5)°. Both phenol –OH groups form intramolecular hydrogen bonds to the N atoms, with graph-set motif S(6). In the crystal, pairs of O—H⋯O hydrogen bonds link the molecules into dimers with R 4 4(18) ring motifs. The crystal packing is further stabilized by C—H⋯O and weak C—H⋯π interactions.

In the title molecule, C 17 H 20 N 2 O 2 , the imidazolidine ring adopts a twist conformation. The mean plane through the five atoms of the imidazolidine ring makes dihedral angles of 70.18 (4) and 74.14 (4) with the planes of the two aromatic rings. The dihedral angle between the benzene rings is 53.11 (5) . Both phenol -OH groups form intramolecular hydrogen bonds to the N atoms, with graph-set motif S(6). In the crystal, pairs of O-HÁ Á ÁO hydrogen bonds link the molecules into dimers with R 4 4 (18) ring motifs. The crystal packing is further stabilized by C-HÁ Á ÁO and weak C-HÁ Á Á interactions.

Comment
The study of intramolecular hydrogen bonds is interesting because of the high thermodynamic and structural stability of these systems. Intramolecularly hydrogen-bonded systems with direct coupling between acid and base centers reveal properties which make them valuable materials for practical use (Koll et al., 2006). Of the various different bifunctional intramolecularly hydrogen bonded compounds, ortho-Mannich bases are of special interest due to the presence of an electronic coupling between the proton donating and proton accepting groups through the aromatic ring which potentially affords structural consequences (Filarowski et al., 1997). We report here the crystal structure analysis of the title compound, (I).

Refinement
All H atoms bonded to carbon atoms were positioned geometrically and treated as riding on their parent atoms. The hydroxyl H atoms were found in difference Fourier maps ant their coordinates were refined with a distance restraint of 0.87 Å with σ of 0.01. All H atoms were refined with displacement coefficients U iso (H) set to 1.5U eq (O) for hydroxyl groups and to 1.2Ueq(C) for the -CH-and CH 2 -groups.
Refinement. The refinement was carried out against all reflections. The conventional R-factor is always based on F. The goodness of fit as well as the weighted R-factor are based on F and F 2 for refinement carried out on F and F 2 , respectively. The threshold expression is used only for calculating R-factors etc. and it is not relevant to the choice of reflections for refinement.
The program used for refinement, Jana2006, uses the weighting scheme based on the experimental expectations, see _refine_ls_weighting_details, that does not force S to be one. Therefore the values of S are usually larger than the ones from the SHELX program.