Crystal structure, Hirshfeld surface analysis and DFT study of (5E,5′E,6Z,6′Z)-6,6′-[ethane-1,2-diylbis(azanylylidene)]bis{5-[2-(4-fluorophenyl)hydrazono]-3,3-dimethylcyclohexanone} 2.5-hydrate

The title compound was obtained by the condensation of ethylenediamine and (5E,5E,6Z,6Z)-6,6-[ethane-1,2-diylbis(azanylylidene)]bis{5-[2-(4-fluorophenyl)hydrazono)-3,3-dimethylcyclohexanone} in ethanol and crystallized as a 1:2.5 hydrate containing two different conformers stabilized by intramolecular N—H⋯N and linked by O—H⋯O (involving the water molecules) hydrogen bonds.

The title compound, C 30 H 34 F 2 N 6 O 2 Á2.5H 2 O, was obtained by condensation of 2-[2-(4-fluorophenyl)hydrazono]-5,5-dimethylcyclohexan-1,3-dione with ethylenediamine in ethanol and crystallized as a 1:2.5 hydrate in space group C2/c. The two independent molecules, with approximate crystallographic C 2 symmetries, have different conformations and packing environments, are stabilized by intramolecular N-HÁ Á ÁN hydrogen bonds and linked by O-HÁ Á ÁO hydrogen bonds involving the water molecules. A Hirshfeld surface analysis showed that HÁ Á ÁH contacts make by far the largest (48-50%) contribution to the crystal packing. From DFT calculations, the LUMO-HOMO energy gap of the molecule is 0.827 eV.

Structural commentary
The asymmetric unit contains one full molecule (A) of (II) in a general position and one-half of another molecule (B), which lies on a crystallographic twofold axis, as well as three ordered water molecules (O1W, O2W, O3W) and one that is disordered over three positions (O4W, O5W and O6W) with occupancies of 0.5, 0.125 and 0.125, respectively. Thus the crystal composition is (II)Á2.5H 2 O.
Molecule A has an approximate non-crystallographic C 2 symmetry. Each molecule comprises two approximately planar halves, whose planarity is stabilized by intramolecular N-HÁ Á ÁN hydrogen bonds, arranged in an 'open-book' mode. The connecting bridges, N3-C25-C24-N2 in molecule A and N9-C13-C13 i -N9 i in B, have gauche conformations, with torsion angles of À59.1 (3) and 63.7 (3) , respectively. However, in other respects the conformations of molecules A and B are drastically different (Fig. 1). It is noteworthy that although crystal structures with Z 0 > 1 are common, two substantially different conformers rarely co-exist in the same structure (Sona & Gautham, 1992). The bond lengths in molecules A and B are similar, and close to those reported earlier (Turkoglu et al., 2015;Shikhaliyev et al., 2019) for analogous compounds (see also Section 6).

Supramolecular features
In the crystal, molecules of (II) are linked directly through weak C-HÁ Á ÁO and C-HÁ Á ÁF hydrogen bonds and indirectly through water molecules of crystallization and strong O-HÁ Á ÁO hydrogen bonds formed by the latter (Fig. 2

Hirshfeld surface analysis
In order to visualize the intermolecular interactions, a Hirshfeld surface (HS) analysis (Hirshfeld, 1977)  The structures of molecules A and B. Displacement ellipsoids are drawn at the 40% probability level.
Two-dimensional fingerprint plots (Fig. 4) show the contributions of various contacts to the Hirshfeld surface. Thus, for both molecules A and B, by far the largest contributions are by HÁ Á ÁH contacts, 49.9% (A) and 47.9% (B). Given that H atoms comprise ca 70% of the molecular surface, a similar share would be expected if the contact distribution were entirely random. The OÁ Á ÁH/HÁ Á ÁO contacts, i.e. strong and weak hydrogen bonds, contribute 14.9% (A) and 13.8% (B), and HÁ Á ÁC/CÁ Á ÁH contacts, i.e.interactions, 14.1% (A) and 11.8% (B). Most remarkable is the different role of the fluorine atoms. In molecule B, FÁ Á ÁH/HÁ Á ÁF contacts contribute 16.8%, much more than the 6.4% in A or the 6% expected for a random distribution. In contrast, FÁ Á ÁC/CÁ Á ÁF contacts are more common in A (5.1%) than in B (1.2%). The contributions of all other contacts are negligible, except HÁ Á ÁN/NÁ Á ÁH (4.0% for A, 3.8% for B). Thus, the fingerprint plots reveal that molecules A and B have substantially different packing environments.

Frontier molecular orbital analysis
The frontier molecular orbitals (FMOs), i.e. the highest occupied MO (HOMO) and the lowest unoccupied MO (LUMO) play the most significant role in defining the molecular properties (Hoffmann et al., 1965;Fukui, 1982). The HOMO is associated with electron-donating and LUMO with the electron-accepting capability, their energies approximating the negative of the (first) ionization energy and the electron affinity of the molecule, respectively, from where useful information regarding donor-acceptor interactions can be obtained (Demir et al., 2016), and the degree of the electrophilicity or nucleophilicity of the molecule estimated (Parr et al., 1999;Chattaraj et al., 2006).
The frontier orbitals of molecule (II) (Fig. 5) were calculated at the DFT-B3LYP/6-311G(d,p) level of theory as implemented in Gaussian09 (Frisch et al., 2009). The X-raydetermined structure of molecule A was taken as the starting molecular geometry. This gave the energies of HOMO as À4.8164 eV and LUMO as À3.9894 eV, with a LUMO-HOMO gap of 0.827 eV, from which the chemical potential ( = À4.40 eV), global hardness (= 0.41 eV), softness (S = 1.21) and the global electrophilicity index (! = 23.4 eV) can be derived. Thus molecule (II) can be regarded as a good electrophile (Domingo et al., 2002) and rather soft.     The frontier molecular orbitals of (II).

Synthesis and crystallization
2 mmol of (I) were dissolved in 15-20 ml of ethanol in a threenecked flask, 1 drop of HCl was added and the solution was heated to 323 K. Then 1 mmol of ethylenediamine was added and the mixture stirred for 1 h at the same temperature. The product (II) was filtered off and purified by recrystallization from ethanol (yield 59%). The reaction and the purity of the substances were monitored by TLC (Sorbil, RF:0.72, 2-propanol).

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 2    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.