N,N′-[1,4-Phenylenebis(iminocarbonyl)]bis(l-phenylalanine) tetrahydrofuran disolvate

In the crystal structure of the title bis-urea derivative, the host molecules are linked by N—H⋯O=C hydrogen bonds and C—H⋯O contacts with (6) and (7) ring motifs.

The title compound, C 26 H 26 N 4 O 6 •2C 4 H 8 O, representing a bis-urea with terminal phenylalanine units, crystallized with two tetrahydrofuran (THF) molecules.The main molecule is located on a crystallographic twofold axis, while the solvent molecule is disordered over two positions, with occupancies of 0.571 (15) and 0.429 (15).The host molecules are linked by N-H� � �O C hydrogen bonds and C-H� � �O contacts with R 2 1 (6) and R 2 1 (7) ring motifs.The THF molecules enclosed in the crystal are connected to the bis-urea compound via O-H� � �O and C-H� � �O interactions.

Structure description
Bis-urea compounds containing a central 1,4-phenylene unit have been shown to be suitable molecules for anion recognition (Stapf et al., 2015;Casula et al., 2016;Manna et al., 2018;Manna & Das, 2019, 2020;Das et al., 2020).In this context, we introduced compounds combining this scaffold and various amino acids [such as l-valine, l-leucine, l-proline, (R)-3-piperidinecarboxylic acid, l-threonine or even l-phenylalanine], whose amino group is part of the urea moiety, among them the title compound, possessing l-phenylalanine units (Stapf et al., 2015).Furthermore, we have already reported the crystal structure of a supramolecular coordination polymer of the title compound with lead(II) (Stapf et al., 2012).In the present article, we describe the crystal structure of the tetrahydrofuran (THF) disolvate.
The title compound was found to crystallize in the tetragonal space group I4 1 with half a molecule of the bis-urea compound and one THF molecule (Fig. 1), which is disordered over two positions (57:43).Within a single molecule possessing a twofold rotation axis, the plane of the phenylene unit includes a dihedral angle with the peripheral arene rings of 88.4 (1) � and with the planes of the urea moieties of 19.4 (2) � .This small angle may be associated with an intramolecular C-H� � �O interaction (H� � �O = 2.35 A ˚) between the phenylene core and the urea moiety.Furthermore, the carboxy group is almost perpendicular to the central aromatic ring, showing a dihedral angle of 82.9 (1) � , and the phenylene units of adjacent molecules are oriented orthogonal with respect to each other.
The dominant intermolecular interactions between urea moieties of neighbouring molecules are inverse bifurcated hydrogen bonds of the N-H� � �O C type [H� � �O = 2.08 (4) and 2.32 (3) A ˚; Table 1], which can be described by the graph set R 1 2 (6) (Etter, 1990;Fig. 2).Unlike in the previously published coordination polymer (Stapf et al., 2012), in which the urea groups form two-dimensional hydrogen-bridged ribbons (H� � �O = 2.06-2.26A ˚), the structure presented here is characterized by supramolecular chains [graph set C( 4)].The angle between the planes of adjacent urea moieties is 83.7 (1) � , thus they are nearly perpendicular to one other.Such a motif is also well known in the literature (for examples, see: Albrecht et al., 2002;Berkessel et al., 2006;Saxena et al., 2014;Shugrue et al., 2019).The N atoms do not act as acceptors for hydrogen bonds.Instead, the linkage of two adjacent molecules is supported by the formation of C-H� � �O C contacts (H� � �O = 2.55 and 2.70 A ˚) between the C-H groups of phenylalanine and an O atom of a carboxy group which acts as a bifurcated acceptor [graph set R 1 2 (7); Fig. 2].
The crystal structure exhibits cavities which are occupied by THF molecules requiring about 961 A ˚3 (corresponding to about 29% of the unit-cell volume).The cavities are bounded by the nonpolar phenylene and arene units of the title compound.In addition, the carboxy groups point into the interior of these cavities and form O-H� � �O hydrogen bonds with the THF O atom [H� � �O = 1.73 (3) A ˚].Further stabilization of the molecular network, each involving the THF molecules, is realized by C-H� � �O contacts with the carboxy group of an adjacent molecule (H� � �O = 2.78 A ˚) and weak C-H� � �� contacts (H� � �Cg = 2.61-3.00A ˚) with the central benzene core or peripheral arene substituents.

Synthesis and crystallization
The synthetic and spectroscopic details for the title compound have been reported previously (Stapf et al., 2012(Stapf et al., , 2015)).Single crystals suitable for X-ray analysis were obtained as colourless prisms by slow evaporation of a saturated solution of the bisurea compound in tetrahydrofuran.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 2.The H atoms at N1 and N2 were located in a difference Fourier map and refined freely.The H atom at O3 was also located in the difference Fourier map but refined using a DFIX restraint at 0.84 (2) A ˚. Other H atoms were included using a riding model starting from calculated data reports 2 of 3 Stapf and Schwarzer � C 26 H 26 N 4 O 6 •2C 4 H 8 O   IUCrData (2023). 8, x230743   Table 1 Hydrogen-bond geometry (A ˚, � ).

Figure 2
Excerpt of the crystal packing showing the R 1 2 (6) and R 1 2 (7) ring motifs of the N-H� � �O C and C-H� � �O C(OH) interactions drawn as dashed lines.The THF molecules and the H atoms not involved in the interactions have been omitted for clarity.

Figure 1
The molecular structure of the title compound, including the atomnumbering scheme.Atoms are drawn with displacement ellipsoids at the 50% probability level.The intramolecular C-H� � �O interaction, as well as the intermolecular hydrogen bonding between the carboxy group and the THF molecule, are shown as dashed lines.Both disordered parts (57:43) of the THF molecule are displayed.Unlabelled atoms are generated by the symmetry operation À x + 1, À y, z.
positions (aromatic C-H = 0.95 A ˚, methylene C-H = 0.99 A ˚, and alkyl C-H = 1.00A ˚).The U iso (H) values were fixed at 1.2 times the equivalent U eq value of the parent C atoms.The THF solvent molecule is disordered over at least two positions [refined occupancies 0.571 (15) and 0.429 (15)].Therefore, the solvent molecule was refined using ISOR for C16A, C16B, C17A and C17B (approximate isotropic behaviour) and SADI (same distances over pairs of bonded atoms) restraints (Sheldrick, 2015b).The absolute structure of the title compound has been assigned by reference to an unchanging chiral centre in the synthetic procedure, not by anomalous dispersion effects in the diffraction experiment.

Table 2
Experimental details.