Tetranuclear copper(II) complex of 2-hydroxy-N,N′-bis[1-(2-hydroxyphenyl)ethylidene]propane-1,3-diamine

In the title Schiff base tetranuclear copper(II) complex, two discrete environments are present in the structure: CuNO4 and CuNO3. Two copper(II) cations are situated in distorted square-pyramidal environment, while two copper(II) cations are located in a slightly square-planar geometry. One bridging acetate group acting in an η1:η1-μ2-mode connects two copper(II) ions, while another bridging acetate group connects three copper(II) ions in an η1:-η2–μ3-mode.


Chemical context
The controlled design of new coordination complexes of transition metals from polydentate ligands is of great interest for research, because of the potential applications that these functional materials can have and for their interesting structural diversity (Popov et al., 2012;Mitra et al., 2014). In this context, important research is being devoted to the chemistry of transition-metal complexes with different oxidation states incorporating polydentate ligands with N and O donor sites (Xie et al., 2012;Banerjee & Chattopadhyay, 2019;Ferguson et al., 2006). These ligands can act in a versatile manner and generate compounds with very different structures, depending on the metal-ligand ratio and the nature of the metal cation (Fernandes et al., 2000). In this context, pentadentate Schiff bases have made it possible to synthesize several complexes with various transition-metal cations, resulting in an unusual coordination environment with interesting stereochemistry (Banerjee et al., 2011). Depending on the size of the cation and its external electronic configuration and the flexibility of the ligand, novel structures with high nuclearity have been obtained (Aly, 1999). These compounds are very attractive for the above reasons, and they have been widely used in several studies. Many multinuclear transition-metal complexes with various structures have been generated, depending on the disposition of the metal ions and donor sites (N or O). Tetranuclear (Asadi et al., 2018;Manna et al., 2019), pentanuclear (Hari et al., 2019;Ghosh, Clé rac et al., 2013) hexanuclear (Shit et al., 2013;Ké bé et al., 2021) and heptanuclear (Gheorghe et al., 2019;Ghosh, Bauzá et al., 2013) forms have reported with potential applications in the fields of magnetism (Gheorghe et al., 2019), catalysis (Nesterova et al., 2020;Das et al., 2018) or biomimetic synthesis (Nesterova et al., 2020;Sanyal et al., 2017). Our research group has already enabled us to prepare several multidentate Schiff base complexes (Mamour et al., 2018;Sarr et al., 2018a,b;Sall et al., 2019). We then explored the possibility of preparing complexes with several metal cations from a pentadentate Schiff base obtained by condensation of 1,3-diaminopropan-2-ol and 1-(2hydroxyphenyl)ethanone, which is rich in hydroxyl groups. From this Schiff base we prepared a hexanuclear complex with an open-cube structure (Ké bé et al., 2021). In a continuation of our work with this Schiff base, we obtained the title tetranuclear copper complex ( Fig. 1) whose structure is presented herein.

Structural commentary
N,N 0 -Bis{[1-(2-hydroxyphenyl)ethylidene)]}-2-hydroxypropane-1, 3-diamine (H 3 L was synthesized via a condensation reaction between 1,3-diaminopropan-2-ol and 1-(2-hydroxyphenyl)ethanone in a 1:2 ratio in ethanol. Mixing H 3 L and hydrated copper acetate yielded a tetranuclear complex formulated as [Cu 4 L 2 (CH 3 CO 2 ) 2 ]ÁH 2 O in which the ligand acts in its tri-deprotonated L À3 form. In the tetranuclear complex, one of the L À3 anions acts in 2 -mode, connecting the two pentacoordinated Cu II cations. The second L À3 anion acts in 3 mode, connecting the two tetracoordinated Cu II cations and one of the pentacoordinated Cu II cations. The second pentacoordinated Cu II cation is connected to the two tetracoordinated Cu II cations via an acetate group acting in 1 : 2 -3 mode. Additionally, the two pentacoordinated Cu II cations are connected by an acetate group acting in 1 : 1 -2 mode. For each ligand, the azomethine nitrogen atom and the phenolate oxygen atom of one arm are both linked to one Cu II cation while the corresponding atoms of the other arm are bonded to another Cu II cation. No phenolate oxygen atom acts in bridging mode. In one ligand the ethanolate oxygen atom bridges the two pentacoordinated Cu II cations, and in the second ligand the ethanolate oxygen atom bridges the two tetracoordinated Cu II cations and one pentacoordinated Cu II cation. The two L À3 ligands are coordinated differently in hexadentate (-1 -O phenolate , -1 -N imino , -2 -O enolato , -1 -N imino , -1 -O phenolato ) and heptadentate (-1 -O phenolate , -1 -N imino , -3 -O enolato , -1 -N imino , -1 -O phenolato ) fashions. Four fivemembered CuOCCN rings and four six-membered CuOCCCN rings are formed upon the coordination of the ligand molecules. In the tetranuclear complex, two discrete CuO 4 N and CuO 3 N units are observed.
Atoms Cu1 and Cu2 are pentacoordinated and their environments can be best described as slightly distorted A view of the title compound, showing the atom-numbering scheme. Table 1 Selected geometric parameters (Å , ).  (14) , respectively. The atoms forming the basal plane for Cu2 (N2, O2, O11, O3) are less coplanar than those around Cu1 (r.m.s. deviation = 0.2086 Å ) and the Cu2 atom is displaced toward the O8 atom, which occupies the apical position, by 0.0808 (1) Å . The from Cu2-O8 distance of 2.703 (4) Å is longer than those to atoms in the equatorial plane

Supramolecular features
Detail of the structure of the complex showing the O-HÁ Á ÁO and C-HÁ Á ÁO hydrogen bonds. Table 2 Hydrogen-bond geometry (Å , ).

Figure 3
Sheets parallel to the ac plane.
an oxygen atom of acetate group and C-HÁ Á ÁO phenoxo are observed (Fig. 2, Table 2). The uncoordinated water molecule is situated into the void of the tetranuclear complex and has OÁ Á ÁO contacts of 2.894 (5) and 3.158 (5) Å suggesting medium-strength hydrogen bonds. In the crystal, the complex molecules are arranged in sheets parallel to the ac plane (Fig. 3). The sheets are connected by C-HÁ Á ÁO bonds (C-HÁ Á ÁO phenoxo , C-HÁ Á ÁO water , C-HÁ Á ÁO acetate ; Table 2). The series of intermolecular and intramolecular hydrogen bonds stabilize and link the components into two-dimensional sheets parallel to the ac plane (Fig. 4).

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 3. H atoms attached to the hydroxyl group and water molecules were located in a difference-Fourier map and freely refined. Other H atoms (CH, CH 2 , CH 3 groups and hydroxyl of ethanol molecules) were geometrically optimized ( View of the two-dimensional sheets parallel to the ac plane.

(µ 3 -Acetato)(µ 2 -acetato)bis(µ 3 -1,3-bis{[1-(2-oxidophenyl)ethylidene]amino}propan-2-olato)tetracopper(II) monohydrate
Crystal data 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. Refinement. Refined as a 2-component twin.