Crystal structure, Hirshfeld surface analysis and interaction energy and DFT studies of 5,5-diphenyl-1,3-bis(prop-2-yn-1-yl)imidazolidine-2,4-dione

The title molecule consists of an imidazolidine unit linked to two phenyl rings and two prop-2-yn-1-yl moieties. The imidazolidine ring is oriented at dihedral angles of 79.10 (5) and 82.61 (5)° with respect to the phenyl rings, while the dihedral angle between the two phenyl rings is 62.06 (5)°. In the crystal, C—HProp⋯OImdzln (Prop = prop-2-yn-1-yl and Imdzln = imidazolidine) hydrogen bonds link the molecules into infinite chains along the b-axis direction. Two weak C—HPhen⋯π interactions are also observed.


Chemical context
Pyrazolones are an important class of heterocyclic compounds that occur in many drugs and their derivatives have long been of interest to medicinal chemists for their wide range of biological activities (Pawar & Patil, 1994), including antibacterial, antidiabetic, immunosuppressive agents, and substances displaying hypoglycemic, antiviral and antineoplastic actions (Pathak & Bahel, 1980;Naik & Malik, 2010;Srivalli et al., 2011). Their pharmaceutical applications include use as a non-steroidal anti-inflammatory agent in the treatment of arthritis and other musculoskeletal and joint disorders (Amir & Kumar, 2005), and as analgesic, antipyretic (Badawey & El-Ashmawey, 1998) and hypoglycemic agents (Das et al., 2008). They also have fungicidal (Singh & Singh, 1991) and antimicrobial properties (Sahu et al., 2007), and some have been tested as potential cardiovascular drugs (Higashi et al., 2006). In the past few years, research has been focused on existing molecules and their modifications in order to reduce side effects and to explore other pharmacological and biological activity (Sahu et al., 2007;Naik & Malik, 2010;Srivalli et al., 2011). As a continuation of our research on the development of new N-substituted pyrazolone derivatives and the evaluation of their potential pharmacological activities, we report herein the synthesis, the molecular and crystal structures, the Hirshfeld surface analysis and intermolecular interaction energies and density functional theory (DFT) computational calculation of the title compound, (I).

Supramolecular features
In the crystal, C-H Prop Á Á ÁO Imdzln (Prop = prop-2-yn-1-yl and Imdzln = imidazolidine) hydrogen bonds (Table 1 and Fig. 2) link the molecules into infinite chains along the b-axis direction. Two weak C-H Phen Á Á Á interactions (Table 1) may also contribute to the stabilization of the crystal structure.

Hirshfeld surface analysis
In order to visualize the intermolecular interactions in the crystal of the title compound, a Hirshfeld surface (HS) analysis (Hirshfeld, 1977;Spackman & Jayatilaka, 2009) was carried out by using CrystalExplorer17.5 (Turner et al., 2017). In the HS plotted over d norm (Fig. 3), the white surface indicates contacts with distances equal to the sum of van der Waals radii, and the red and blue colours indicate distances shorter (in close contact) or longer (distinct contact) than the van der Waals radii, respectively (Venkatesan et al., 2016). The brightred spots appearing near O2 and hydrogen atom H16B indicate their roles as the respective donors and/or acceptors; they also appear as blue and red regions corresponding to positive and negative potentials on the HS mapped over electrostatic potential (Spackman et al., 2008;Jayatilaka et al., 2005) as shown in Fig. 4 Table 1 Hydrogen-bond geometry (Å , ).

Figure 1
The molecular structure of the title compound with the atom-numbering scheme. Displacement ellipsoids are drawn at the 50% probability level.
(hydrogen-bond acceptors). The shape-index of the HS is a tool to visualize thestacking by the presence of adjacent red and blue triangles; if there are no adjacent red and/or blue triangles, then there are no -Á interactions.  Table 2. The most important interaction is HÁ Á ÁH contributing 43.3% to the overall crystal packing, which is reflected in Fig. 6b as widely scattered points of high density due to the large hydrogen content of the molecule with the tip at d e + d i $2.44 Å . In the presence of two weak C-HÁ Á Á interactions, the pair of the scattered points of wings resulting from HÁ Á ÁC/CÁ Á ÁH contacts, with a 37.8% contribution to the HS, have a symmetrical distribution of points, View of the three-dimensional Hirshfeld surface of the title compound plotted over electrostatic potential energy in the range À0.0500 to 0.0500 a.u. using the STO-3 G basis set at the Hartree-Fock level of theory. Hydrogen-bond donors and acceptors are shown as blue and red regions around the atoms corresponding to positive and negative potentials, respectively. Table 2 Selected interatomic distances (Å ).

Figure 3
View of the three-dimensional Hirshfeld surface of the title compound plotted over d norm in the range À0.2703 to 1.2169 a.u.

Figure 5
Hirshfeld surface of the title compound plotted over shape-index.
The Hirshfeld surface analysis confirms the importance of H-atom contacts in establishing the packing. The large number of HÁ Á ÁH, HÁ Á ÁC/CÁ Á ÁH and H Á Á Á O/OÁ Á ÁH interactions suggest that van der Waals interactions and hydrogen bonding play the major roles in the crystal packing (Hathwar et al., 2015).

DFT calculations
The optimized structure of the title compound in the gas phase was generated theoretically via density functional theory (DFT) calculations using the standard B3LYP functional and     (Becke, 1993) as implemented in GAUSSIAN 09 (Frisch et al., 2009). The theoretical and experimental results are in good agreement (Table 4). The highest occupied molecular orbital (HOMO), acting as an electron donor, and the lowest unoccupied molecular orbital (LUMO), acting as an electron acceptor, are very important parameters for quantum chemistry. When the energy gap is small, the molecule is highly polarizable and has high chemical reactivity. The DFT calculations provide some important information on the reactivity and site selectivity of the molecular framework. E HOMO and E LUMO clarify the inevitable charge-exchange collaboration inside the studied material; the electronegativity (), hardness (), potential (), electrophilicity (!) and softness () are recorded in Table 3. The significance of and is to evaluate both the reactivity and stability of a compound. The electron transition from the HOMO to the LUMO energy level is shown in Fig. 8. The HOMO and LUMO are localized in the plane extending from the whole 5,5-diphenyl-1,3-di(prop-2-yn-1-yl)imidazolidine-2,4-dione ring. The energy band gap [ÁE = E LUMO -E HOMO ] of the molecule is about 5.8874 eV, and the frontier molecular orbital energies, E HOMO and E LUMO are À6.6964 and À0.8090 eV, respectively.

Figure 8
The energy band gap of the title compound. 1.0 mmol) at room temperature. The reaction was monitored using TLC. After removal of the inorganic salt by filtration, the solution was evaporated under reduced pressure. The residue was separated by chromatography on a column of silica gel with ethyl acetate-hexane (v:v 3:7) as eluent. The isolated solid was crystallized from ethanol solution to afford colourless crystals (yield: 82%).

Special details
Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes.