2,2′-[1,3-Diazinane-1,3-diylbis(methylene)]bis(4-bromophenol)

The title compound, C18H20Br2N2O2, the heterocyclic ring adopts a chair conformation. The benzene rings make dihedral angles of 86.84 (10) and 60.73 (10)° with the mean plane of the heterocyclic ring. The dihedral angle between the two benzene rings is 79.77 (10)°. The molecular structure is stabilized by two intramolecular hydrogen bonds between the phenolic hydroxy groups and N atoms with graph-set motif S(6). The crystal structure is stabilized by weak C—H⋯π interactions.

The title compound, C 18 H 20 Br 2 N 2 O 2 , the heterocyclic ring adopts a chair conformation. The benzene rings make dihedral angles of 86.84 (10) and 60.73 (10) with the mean plane of the heterocyclic ring. The dihedral angle between the two benzene rings is 79.77 (10) . The molecular structure is stabilized by two intramolecular hydrogen bonds between the phenolic hydroxy groups and N atoms with graph-set motif S(6). The crystal structure is stabilized by weak C-HÁ Á Á interactions.

Comment
In our group, research has been focused on the synthesis of ortho-Mannich bases and their structure, properties, and hydrogen-bonded properties. Very recently we reported the molecular structure of 2,2'-(dihydropyrimidine-1,3(2H, 4H)diyldimethanediyl)bis-(6-tertbutyl-4-methoxyphenol) a novel di-Mannich base (Rivera, et al. 2012). Unlike related structure, the title compound crystallizes in an orthorhombic chiral P2 1 2 1 2 1 space group. The molecular structure and atom-numbering scheme for (I) are shown in Fig. 1. In the crystal structure of the title compound (I), the hexahydropyrimidine ring adopts a chair conformation with a diequatorial substitution (Cremer & Pople, 1975) with puckering parameters Q, θ and φ  (Table 1)

Refinement
The hydroxy hydrogen atoms were found in difference Fourier maps and their coordinates were refined with a distance All other H atoms atoms were positioned geometrically and treated as riding on their parent atoms. The isotropic atomic displacement parameters of hydrogen atoms were evaluated as 1.2×U eq (C,O) of the parent atom . Figures   Fig. 1. A
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.