Crystal structure of aqua(perchlorato)bis[μ-(E)-2-({[2-(pyridin-2-yl)ethyl]imino}methyl)phenolato-κ4 N,N′,O:O]dicopper(II) perchlorate

The title compound crystallizes as an unsymmetrical dinuclear cation bridged by the phenoxy O atoms with one Cu atom coordinated by a water molecule and the other by a perchlorate anion, thus making both Cu atoms five-coordinate, and with a further perchlorate anion present for charge balance.


Chemical context
Proteins containing dinuclear copper centers play important roles in biology, including dioxygen transport or activation, electron transfer, reduction of nitrogen oxides and hydrolytic chemistry (Karlin & Tyeklar, 1993;Torelli et al., 2000;Poater et al., 2008;Utz et al., 2003). The catalytic properties of some dicopper complexes have also been observed in some recent studies (Jagoda et al., 2005). The crystal engineering of selfassembled supramolecular architectures is currently of great interest, owing to their intriguing topologies and their applications in materials chemistry, in particular in optoelectronics, conductivity and superconductivity, charge-transfer and magnetism, nanoporous materials and biomimetic materials (Robson, 1996;Blake et al., 1999;Sauvage, 1999).
Compounds of transition metal complexes comprising the ({[2-(pyridin-2-yl)ethyl]imino}methyl)phenol ligand have been synthesized for various processes (Egekenze et al., 2017;Sanyal et al., 2014;Chakraborty et al., 2013;Tandon et al., 1994Tandon et al., , 2000Latour et al., 1989). Complexes of the tridentate ligand have been used as biomimics in the catalysis of hydrolysis of phosphate esters and as catalysts for catechol oxidation (Egekenze et al., 2017). Pyrazole and pyridine are nitrogen donors that are commonly used as ligands to mimic metalloenzymes. These heterocyclic groups are widely used to form inorganic complexes because they have pK a values similar to those present in the hystidyl functional group of many enzymes. As part of an ongoing effort to synthesize complexes to use as biomimetics, the title copper(II) complex has been synthesized. In view of the interest in these types of metal complexes, its structure has been determined. ISSN 2056-9890

Structural commentary
The title compound crystallizes in the monoclinic space group P2 1 /c as an unsymmetrical dinuclear cation bridged by the phenoxy O atoms with one Cu II atom coordinated by a water molecule and the other by a perchlorate anion, thus making both Cu II atoms five-coordinate, and with a further perchlorate anion present for charge balance (see Fig. 1). The CuÁ Á ÁCu distance in the dinuclear unit is 3.0225 (5) Å . There are previously reported dinuclear structures involving the ({[2-(pyridin-2-yl)ethyl]imino)}methyl)phenolato ligand as a bridging ligand with other metals (Chakraborty et al., 2013) and one instance involving copper (Yin et al., 1998) where the structure is very similar apart from the fact that the bond between the Cu atom and the ClO 4 À counter-ion is not indicated. There is very little information available for this structure apart from a line drawing in the Cambridge Structural Database (Groom et al., 2016).
The copper atoms are displaced from their basal coordination planes, O1, O2, N1, N2 (r.m.s. deviation = 0.186 Å ) for Cu1, and O1, O2, N3, N4 (r.m.s. deviation = 0.252 Å ) for Cu2, towards the apical ligands by 0.218 (1) and 0.037 (1) Å , respectively. The dihedral angle between these two planes is 39.31 (5) . Thus the whole dinuclear complex adopts a saddle shape similar to that observed in metalloporphyrin structures (Kuzuhara et al., 2016) with the two phenyl rings and two pyridine rings on opposite sides of the central Cu 2 O 2 bridging group. The magnitude of this distortion can be seen from the dihedral angles between the two phenyl [41.45 (7)

Figure 1
Diagram of the Cu-containing dinuclear cation showing the atom labeling. The non-coordinated anion is omitted for clarity. Displacement parameters are at drawn the 30% probability level.

Supramolecular features
In addition to the bonds involving the copper atom mentioned above, there is a longer interaction [2.9893 (5) Å ] between Cu2 and O24 of an adjoining unit (at x + 1, y, z), which links the cations into linear chains along the a-axis direction (see Fig. 2). In addition, the water H atoms link with the perchlorate counter-ion. These interactions, along with numerous C-HÁ Á ÁO interactions (Table 2) between the tetrahedral perchlorate anions link into a complex three-dimensional array.

Synthesis and crystallization
2-(2-Pyridyl)ethylamine (0.3918 g, 3.207 mmol) was dissolved in methanol. Salicylaldehyde (0.3916 g, 3.207 mmol) was dissolved in methanol and stirred overnight. Cu(ClO 4 ) 2 Á6H 2 O (4.811 g, 1.783 mmol) was dissolved in the methanol solution. The mixture was stirred at room temperature overnight. The methanol was removed by rotary evaporation. The product was crystallized by dissolving it in acetonitrile and layering the solution with diethyl ether. The green crystals formed were allowed to grow overnight before gravity filtering, air drying, and collection of the crystallized product.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 3. The H atoms were positioned geometrically and allowed to ride on their parent atoms, with C-H = 0.95-0.99 Å and N-H = 1.00 Å and with U iso (H) = xU eq (C), where x = 1.5 for methyl H atoms and 1.2 for all other C-bound H atoms. The hydrogen atoms attached to water were refined isotropically. One of the perchlorate anions is disordered over two conformations with occupancies of 0.586 (4) and 0.414 (4) and were constrained to have similar thermal and metrical parameters.   Data collection: APEX3 (Bruker, 2015); cell refinement: APEX3 (Bruker, 2015); data reduction: SAINT (Bruker, 2015); program(s) used to solve structure: SHELXT (Sheldrick, 2015a); program(s) used to refine structure: SHELXL2016 (Sheldrick, 2015b); molecular graphics: SHELXTL (Sheldrick, 2008); software used to prepare material for publication: SHELXTL (Sheldrick, 2008).

Aqua(perchlorato)bis[µ-(E)-2-({[2-(pyridin-2-yl)ethyl]imino}methyl)phenolato-κ 4 N,N′,O:O]dicopper(II)
perchlorate 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.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )
x y z U iso */U eq Occ. (