Crystal structure and Hirshfeld surface analysis of 2,2′-{(1E,1′E)-[ethane-1,2-diylbis(azanylylidene)]bis(methanylylidene)}bis[4-(trifluoromethoxy)phenol]copper(II) hydroquinone hemisolvate

The title structure has a square-planar coordination sphere around the copper(II) ion. In the crystal, molecules are linked by weak C—H⋯O and C—H⋯π hydrogen bonds and very weak π-stacking interactions, forming a three-dimensional supramolecular architecture.


Chemical context
Metal complexes of Schiff bases have different applications because of their different heteroatoms (N, S, Cl etc.), functional groups, -electron density, isomer structures and easy synthesis (El-Samanody et al., 2017). Metal complexes with less oxophilic character exhibit attractive properties, such as targeting catalysts in many polymerization reactions (Ng et al., 2016). On the other hand, in nature, metal complexes are encountered in many reactions, such as binding to DNA or enzymes (Li et al., 2010). For this reason, metal complexes are of increasing interest in the fields of medicine and chemical synthesis with attractive functional properties and stable structures. Salen-type Schiff bases [salen is N,N 0 -bis(salicylidene)ethylenediamine] have been synthesized by many research groups from different diamines and derivatives of benzaldehyde (Prushan et al., 2007). In addition, salen-type Schiff bases derived from 2-hydroxy-3-methoxybenzaldehyde (also called o-vanillin) are very effective ligands for many metal ions due to the two different binding sites, because of the presence of the methoxy group near the -OH group (Andruh, 2015). Each transition metal has different biological properties depending on the geometry of the complex and the structure of the ligand, so the biological activity of a drug may be controlled by changing the metal ion or the chemical structure of the ligand. Recently, it was reported that synthesized Schiff bases indicate antibacterial properties, more pronounced in the case of metal complexes compared to the free Schiff bases (Wu et al., 2011).
In this study, a salen-type Schiff base has been synthesized from 2-hydroxy-5-(trifluoromethoxy)benzaldehyde with ethylenediamine by a condensation reaction. The synthesized Schiff base was used as an O,N,N 0 ,O 0 -type tetradentate ligand, and a copper(II) complex was obtained and the structure confirmed by single-crystal X-ray diffraction analysis. In this study, we describe the crystal structure and Hirshfeld surface analysis of the title compound, as determined by X-ray crystallographic analysis.  Hydrogen-bond geometry (Å , ).

Figure 1
The molecular structure of the title compound, with the atom labelling. Displacement ellipsoids are drawn at the 30% probability level. The dashed line indicates a hydrogen bond. [Symmetry code: (i) Àx, Ày, Àz + 1.]

Hirshfeld surface analysis
The Hirshfeld surface analysis (Spackman & Jayatilaka, 2009) and the associated two-dimensional fingerprint plots were performed and created with CrystalExplorer17 (Turner et al., 2017). The Hirshfeld surface was mapped with d norm (Fig. 4). The view of surface were obtained in the range À0.4385 to 1.6105 a.u. (d norm ). The blue, white and red colour conventions used for the d norm -mapped Hirshfeld surfaces recognize the interatomic contacts as longer, at van der Waals separations and short interatomic contacts, respectively.
A fingerprint plot delineated into specific interatomic contacts contains information related to specific intermolecular interactions. The blue colour refers to the frequency The d norm -mapped Hirshfeld surface for visualizing the intermolecular contacts of the title compound.

Figure 5
Two-dimensional fingerprint plots of the title compound. of occurrence of the (d i , d e ) pair with the full fingerprint plot outlined in gray. Fig. 5(a) shows the two-dimensional fingerprint plot of the sum of the contacts contributing to the Hirshfeld surface represented in normal mode. The most significant contribution to the Hirshfeld surface is from FÁ Á ÁH/ HÁ Á ÁF contacts (25.7%) (Fig. 5b). Here, HÁ Á ÁH interactions are only the second most significant contribution to the total Hirshfeld surface (23.5%). In addition, CÁ Á ÁH/HÁ Á ÁC and OÁ Á ÁH/HÁ Á ÁO contacts contribute 12.6 and 11.2% to the Hirshfeld surface, respectively.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 3. All H atoms were fixed geometrically and treated as riding, with C-H = 0.97 Å and U iso (H) = 1.2U eq (C) for methylene, C-H = 0.93 Å and U iso (H) = 1.2U eq (C) for aromatic, C-H = 0.93 Å and U iso (H) =

Figure 6
The synthesis of the title compound.   where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max < 0.001 Δρ max = 0.88 e Å −3 Δρ min = −0.43 e Å −3 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.