4,4′-Difluoro-2,2′-[imidazolidine-1,3-diylbis(methylene)]diphenol

In the title compound, C17H18F2N2O2, the imidazolidine ring system exists in a twist conformation. The mean plane through this ring system forms dihedral angles of 80.8 (8)° and 66.2 (13)°, with the benzene rings. The dihedral angle between the benzene rings is 52.0 (14)°. Two intramolecular O—H⋯N hydrogen bonds each generate S(6) ring motifs. In the crystal, weak C—H⋯O hydrogen bonds form dimers, which are connected by further C—H⋯O interactions.

In the title compound, C 17 H 18 F 2 N 2 O 2 , the imidazolidine ring system exists in a twist conformation. The mean plane through this ring system forms dihedral angles of 80.8 (8) and 66.2 (13) , with the benzene rings. The dihedral angle between the benzene rings is 52.0 (14) . Two intramolecular O-HÁ Á ÁN hydrogen bonds each generate S(6) ring motifs. In the crystal, weak C-HÁ Á ÁO hydrogen bonds form dimers, which are connected by further C-HÁ Á ÁO interactions.

sup-1
Acta Cryst. Organic halide compounds have attracted much attention due to the role of weak intermolecular C-H···X interactions in supramolecular assembly (Rathore et al. 2011, Steiner 2002. In recent literature, the importance of interactions involving fluorine as possible tools in crystal engineering has been explored in greater detail (Chopra & Guru Row, 2005). With the purpose to understand its effects in Mannich bases, we turn our attention to title compound (I) because fluorine is also able to form non-classical intermolecular C-H···F hydrogen bonds. In this study, we describe the crystal structure of the The molecular structure and atom-numbering scheme for (I) are shown in Fig. 1. The bond lengths (Allen et al., 1987) and angles of (I) are within normal ranges and are comparable to those related structures (Rivera et al., 2011(Rivera et al., , 2012. As observed in related structures (Rivera et al., 2011(Rivera et al., , 2012. The imidazoline ring adopts a twist conformation, Q2 = 0.4008 (13) Å and φ2 = 51.81 (18)° (Cremer & Pople, 1975), with a twist about the N2 -C14 bond. In order to reduce steric congestion, the benzene rings have different orientations with respect to the central imidazolidine ring. Thus, one pfluoro-substituted benzene ring (C1/C2/C5/C10/C6/C17)is approximately orthogonal to the mean plane of the imidazolidine ring defined by N1, C13 and C9, making a dihedral angle of 80.82 (79)°, whereas the other ring (C3/C4/C7/C13/C16/C12) forms a dihedral angle of 66.18 (130)°. The dihedral angle between the benzene rings is 52.04 (136)°. There are two intramolecular hydrogen bonds between the phenolic hydroxyl groups and the nitrogen atoms with graph-set motif S(6) (Bernstein et al., 1995).
The results demonstrate, that not only the packing in (I) is governed by weak C-H···O hydrogen bonds (Table 1), resulting in a hydrogen bonded dimer, which is connected by further C-H···O interactions, but also that fluorine does not participate in any intermolecular interactions. Similarly, in ortho-F and ortho-Cl substituted analogs (Rivera et al., 2012(Rivera et al., , 2011, the halogen fails to participate in any non-bonded interaction.

Experimental
For the originally reported synthesis of the title compound, see: Rivera et al. (1993). Crystals suitable for X-ray diffraction were obtained from chloroform with a few drops of MeOH upon slow evaporation of the solvents over 3 days at room temperature.

Refinement
All hydrogen atoms were discernible in difference Fourier maps and could be refined to reasonable geometry. According to common practice H atoms bonded C atoms were kept in ideal positions with C-H distance 0.96 Å during the refinement. The hydroxyl H atoms were found in difference Fourier maps and their coordinates were refined freely. All H atoms were refined with displacement displacement coefficients Uiso(H) set to 1.5Ueq(C, O) for methyl and hydroxyl supplementary materials sup-2 Acta Cryst. (2012). E68, o3043-o3044 groups and to to 1.2Ueq(C) for the CH-and CH 2 -groups.

Special details
Experimental. CrysAlisPro, Agilent, 2010 Empirical absorption correction using spherical harmonics, implemented in SCALE3 ABSPACK scaling algorithm. 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.