Hexanuclear copper(II) complex of 2-hydroxy-N,N′-bis[1-(2-hydroxyphenyl)ethylidene]propane-1,3-diamine incorporating an open-cubane core

In the title Schiff base hexanuclear copper(II) complex, two discrete environments are present in the structure: CuNO4 and CuNO3. Four copper(II) cations are situated in a distorted square-pyramidal environment, while two copper(II) cations are located in a slightly square-planar geometry. Three of the copper(II) cations occupy three vertices of an open cubane Cu3O4.

The title molecular structure, namely, diaquatris( 3 -1,3-bis{[1-(2-oxidophenyl)ethylidene]amino}propan-2-olato)-3 -hydroxido-dinitratohexacopper(II) ethanol trisolvate, [Cu 6 (C 19 H 19 N 2 O 3 ) 3 (NO 3 ) 2 (OH)(H 2 O) 2 ]Á3C 2 H 5 OH, corresponds to a non-symmetric hexanuclear copper complex. The complex exhibits one core in which three Cu II metal centres are mutually interconnected, two by two, via three phenolato oxygen anions acting in a 2 -mode. These three copper cations are interconnected in a 3 -mode by one hydroxyl group. An open-cube structure is generated in which each of the Cu II cations of the three CuO 4 N units is connected by two 2 -O anions from phenolate groups and one 3 -O atom from a hydroxy anion. Each of the three pentacoordinated Cu II cations situated in the open-cube unit has a distorted NO 4 square-pyramidal environment. Each of these three Cu II centres is interconnected with another Cu II cation via one enolate O atom in 2 -mode, yielding one CuNO 4 unit and two CuNO 3 units. The pentacoordinated Cu II atom has a distorted square-pyramidal environment while the two tetracoordinated copper(II) cations are situated in a squareplanar environment. A series of intramolecular O-HÁ Á ÁO hydrogen bonds are observed. In the crystal, the units are connected two by two by intermolecular C-HÁ Á ÁO and O-HÁ Á ÁO hydrogen bonds, thus forming sheets parallel to the ac plane.

Chemical context
The coordination chemistry of pentadentate ligands has been studied extensively. That their structures present symmetrical or asymmetrical pendant arms and bear donor atoms is an asset widely exploited in coordination chemistry. The presence of donor sites on aliphatic or aromatic arms has made it possible to prepare a wide variety of compounds with various structures and interesting physical and chemical properties. 1,3-Diaminopropan-2-ol, which has three donor sites, is a good precursor for the synthesis of ligands with several cavities that can act as chelating agents and/or as bridging ligands (Song et al., 2004;Shit et al., 2013). These types of ligands can generate high nuclearity complexes with original structures. Indeed, ligands rich in hydroxyl groups and containing other donor sites such as nitrogen are used to prepare complexes with very diverse structures (Gungor & Kara, 2015;Dutta et al., 2020;Shit et al., 2013;Sarı et al., 2006). Several synthetic strategies have been developed to control the nuclearity and lead to ISSN 2056-9890 specific applications in molecular magnetism (Popov et al., 2012;Mikuriya et al., 2018), molecular biology (Grundmeier & Dau, 2012), electrochemistry (Musie et al., 2003) and catalysis (Gamez et al., 2001). The self-assembly synthetic strategy involving transition-metal cations and multidentate ligands has been widely used by coordination chemists, as a result of the wide variety of fascinating structures with the presence of multiple metal centres. The high nuclearity of these complexes and the interactions that can take place between metal cations has increased their interest to chemists (Bonanno et al., 2018;Yang et al., 2014;Haldar et al., 2019).
In a continuation of our work on multidentate Schiff base complexes (Sall et al., 2019;Sarr et al., 2018a,b;Mamour et al., 2018), we have explored the possibility of preparing high nuclearity complexes using a Schiff base rich in hydroxyl groups. From 1,3-diaminopropan-2-ol and 1-(2-hydroxyphenyl)ethanone, we obtained a ligand containing three hydroxyl groups. The reaction of this ligand with copper nitrate resulted in the hexanuclear title complex, whose structure presents an open cube involving three of the six copper cations.

Supramolecular features
In the crystal, intramolecular and intermolecular O-HÁ Á ÁO hydrogen bonds involving the hydroxyl group, the coordinated water molecules and the nitrate and ethanol groups are observed. The complex molecules are interconnected by intermolecular hydrogen bonds of type O-HÁ Á ÁO (O water -HÁ Á ÁO ethanol and O water -HÁ Á ÁO nitrate ) and C-HÁ Á ÁO (C phenolate -HÁ Á ÁO nitrate ) (Fig. 2, Table 2). The complex molecules are disposed into zigzagging two-dimensional sheets Table 1 Selected geometric parameters (Å , ).
171.10 (9) Cu5-O7-Cu3 96.20 (7) parallel to the ac plane (Fig. 3). The coordinating water molecules are directed toward the interlayer region, which is also occupied by the uncoordinated ethanol molecules. Adjacent sheets are linked to one another by hydrogen bonds of type C-HÁ Á ÁO ethanol or C-HÁ Á ÁO nitrate ) (C11-H11BÁ Á ÁO4 ethanol and C18-H18Á Á ÁO13 nitrate ; Table 3). The series of intermolecular and intramolecular hydrogen bonds stabilize and link the components into a three-dimensional network.

Figure 2
Sheets parallel to the ac plane.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 3. Hydroxyl H atoms were located from difference-Fourier maps and refined. Other H atoms (CH, CH 2 , CH 3 groups, hydroxyl groups of ethanol molecules and water molecules) were geometrically optimized (C-H = 0.93-0.98 Å , O-H hydroxy = 0.82 Å and O-H water = 0.86-0.87 Å ) and refined as riding with U iso (H) = 1.2U eq (C) (1.5 for CH 3 and OH groups). Acta Cryst. (2021). E77, 708-713 research communications  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.