Crystal structure of the di-Mannich base 4,4'-di-chloro-3,3',5,5'-tetra-methyl-2,2'-[imidazolidine-1,3-diylbis(methyl-ene)]diphenol.

The title compound, C21H26Cl2N2O2, was prepared in a solvent-free microwave-assisted synthesis, and crystallizes in the ortho-rhom-bic space group Pna21. The imidazolidine ring adopts an envelope conformation and its mean plane is almost perpendicular to the two pendant aromatic rings [dihedral angles = 84.61 (9) and 86.54 (9)°]. The mol-ecular structure shows the presence of two intra-molecular O-H⋯N hydrogen bonds between the phenolic hy-droxy groups and imidazolidine N atoms. The two 3-chloro-6-hy-droxy-2,4-di-methyl-benzyl groups are located in a cis orientation with respect to the imidazolidine fragment. As a result, the lone pairs of electrons on the N atoms are presumed to be disposed in a syn conformation. This is therefore the first example of an exception to the 'rabbit-ears' effect in such 2,2'-[imidazolidine-1,3-diylbis(methyl-ene)]diphenol derivatives.