3,3′-Bis(quinolin-8-yl)-1,1′-[4,4′-methylenebis(4,1-phenylene)]diurea

The title compound, C33H26N6O2, contains two 3-(quinolin-8-yl)urea groups linked to a diphenylmethane. The asymmetric unit contains two molecules, A and B. Each quinoline plane is essentially parallel to the attached urea unit [dihedral angles = 8.97 (18) and 8.81 (19) in molecule A and 18.47 (18) and 4.09 (19)° in molecule B]. The two benzene rings are twisted, making dihedral angles of 81.36 (8)° in A and 87.20 (9)° in B. The molecular structures are stabilized by intramolecular N—H⋯N hydrogen bonds. In the crystal, each urea O atom is involved in two N—H⋯O hydrogen bonds, generating two interpenetrating three-dimensional sets of molecules.

The National Science Foundation is acknowledged for a CAREER award (CHE-1056927) to MAH. The work was supported by the National Institute of Health (G12RR013459). The NMR instrument used for this work was funded by the National Science Foundation (CHE-0821357).  (Smith et al., 1992) or acetate and glutarate in DMSO (Fan et al., 1993).

3,3'-Bis
Tren-based urea receptors with three urea units were recently reported showing high affinity and selectivity for various inorganic anions (Custelcean et al., 2005;Wu et al., 2008;Caltagirone et al., 2008). In an earlier paper, we reported a seven-coordinated hydrogen sulfate formed with three tren-based ureas via six NH···O bonds (d N···O = 2.85-3.09Å) and one OH···O bond (d O···O = 2.57Å) (Pramanik et al., 2011). In an effort to design selective receptors with a rigid framework, we synthesized a dipodal receptor consisting of a diphenylmethane linked with two quinoline groups. The title bis-urea compound contains two urea binding sites that could be an effective receptor for binding of variety of anions.
The bis-urea receptor crystallized in the tetragonal space group P4 3 with two molecules (Fig. 1) in the asymmetric unit.
The asymmetric unit contains two molecules -A and B. As shown in Fig. 1, the two carbonyls of the two urea fragments of each molecule are oriented in the same direction. Two phenyl rings are twisted giving dihedral angles of 81.36 (8)° for A and 87.20 (9)° for B. Each pyridine nitrogen of the quinoline groups is involved in strong intramolecular hydrogen bonding with one NH group with N···N distances ranging from 2.625 (4)Å to 2.647 (4)Å. Each quinoline plane is nearly parallel with the attached urea group. There was no intermolecular hydrogen bonding between the two molecules. Each oxygen atom is bonded with two intermolecular NH···O hydrogen bonds with N···O distances ranging from 2.772 (4)Å to 3.293 (4)Å.
Similar H-bonding interactions were observed in a related bis urea receptor (Saeed et al., 2010). In the extended structure viewed along the c axis, quinoline planes are found to be antiparallel (Fig. 2). No π···π stacking was observed between the aromatic groups.