Crystal structure of diaqua(3,14-diethyl-2,6,13,17-tetraazatricyclo[16.4.0.07,12]docosane)copper(II) dichloride tetrahydrate

In the title complex, [Cu(C22H44N4)(H2O)2]Cl2·4H2O, the complex cation lies about an inversion center. The macrocyclic ring adopts a stable trans-III conformation. In the crystal, O—H⋯Cl, N—H⋯Cl and O—H⋯O hydrogen bonds connect the chloride anions, complex cation and water molecules, forming a three-dimensional network.

The crystal structure of the novel hydrated Cu II salt, [Cu(L)(H 2 O) 2 ]Cl 2 Á4H 2 O (L = 3, 14-diethyl-2,6,13,17-tetraazatricyclo[16.4.0.0 7,12 ]docosane, C 22 H 44 N 4 ) has been determined using synchrotron radiation. The asymmetric unit contains one half of the [Cu(L)(H 2 O) 2 ] 2+ cation (completed by crystallographic inversion symmetry), one chloride anion and two lattice water molecules. The copper(II) atom exists in a tetragonally distorted octahedral environment with the four N atoms of the macrocyclic ligand in equatorial and two O atoms from water molecules in axial positions. The latter exhibit a long axial Cu-O bond length of 2.7866 (16) Å due to the Jahn-Teller distortion. The macrocyclic ring adopts a stable trans-III conformation with typical Cu-N bond lengths of 2.0240 (11) and 2.0441 (3) Å . The complex is stabilized by hydrogen bonds formed between the O atoms of coordinated water molecules and the NH groups as donors, and chloride anions as acceptors. The chloride anions are further connected to the lattice water solvent molecules through O-HÁ Á ÁCl hydrogen bonds, giving rise to a three-dimensional network structure.

Chemical context
The macrocycle 3, 14-diethyl-2,6,13,17-tetraazatricyclo-(16.4.0.07,12)docosane (C 22 H 44 N 4 , L) contains a cyclam backbone with two cyclohexane subunits and two ethyl groups attached to carbon atoms of the propyl chains that bridge opposite pairs of N atoms. The syntheses, crystal structures and spectroscopic properties of numerous metal complexes with this ligand have previously been reported, viz.

Structural commentary
The molecular structure of (I) is shown in Fig. 1 (Choi et al., 2012). The coordination environment of the copper(II) atom may be considered as square-planar or octahedral with a tetragonal distortion, depending upon whether or not the remote oxygen atoms of the water molecules are considered to be bonded to the copper(II) atom. The concept of a semicoordinating atom was introduced to describe a situation where a polyatomic anion or ligand occupies the long axial position in an otherwise square-planar copper(II) complex with an atom in the distance range of 2.5-3.0 Å (Murphy & Hathaway, 2003 (Choi et al., 2012). The tetragonally elongated octahedron is a common polyhedron around six-coordinate Cu II atoms in complexes (involving also non-equivalent ligands), and the distortion arises from the Jahn-Teller effect operative on the metal cation with its d 9 electronic configuration (Murphy & Hathaway, 2003).
The two ethyl groups on the six-membered chelate rings and the two -(CH 2 ) 4 -parts of the cyclohexane backbones are anti with respect to the macrocyclic plane. As usually observed, the five-membered chelate rings adopt a gauche conformation whereas the six-membered rings are in chair conformations. The ethyl groups are attached axially as substituents to the six-membered rings, while the methylene C substituents at the five-membered rings are equatorial. The cyclohexane rings are also in a chair conformation, with the N substituents in equatorial positions.
as acceptors, resulting in a three-dimensional network structure. The chloride anions remain outside the coordination sphere [CuÁ Á ÁCl (4.523 Å )] and are connected both to the semi-coordinated and to the lattice water solvents through O-HÁ Á ÁCl hydrogen bonds. The lattice water solvents are additionally linked to the semi-coordinated water molecules and other lattice water solvents via O-HÁ Á ÁO hydrogen bonds. The crystal packing of (I) in a view perpendicular to the bc plane is shown in Fig. 2.

Synthesis and crystallization
Ethyl vinyl ketone (97%), trans-1,2-cyclohexanediamine (99%) and copper(II) chloride dihydrate (99%) were purchased from Sigma-Aldrich and were used as received. All other chemicals were analytical reagent grade. 3,14-Diethyl-2,6,13,17-tetraazatricyclo(16.4.0.0 7,12 )docosane (L) was prepared according to a published procedure (Lim et al., 2006). A solution of the macrocycle L (0.091 g, 0.25 mmol) in water (10 mL) was added dropwise to a stirred solution of CuCl 2 Á2H 2 O (0.085 g, 0.5 mmol) in water (20 mL). After cooling to 298 K, the pH was adjusted to 3.0 by the addition of 1.0 M HCl. A mixture of colorless and violet crystals had formed from the solution over the next few days. To the mixture were added 30 mL of MeOH under stirring, and the stirring was continued for 30 min. The colourless crystals of [H 4 L]Cl 4 Á4H 2 O (Moon & Choi, 2021) were removed by filtration. The filtrate was left at 298 K. After few days, platelike violet single crystals of (I) suitable for X-ray analysis were obtained.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 2. All C-and N-bound H atoms in the complex were placed in geometrically idealized positions and constrained to ride on their parent atoms, with C-H distances of 0.97-0.99 Å , and with an N-H distance of 0.99 Å with U iso (H) values of 1.2 and 1.5 U eq of the parent atoms, respectively. The hydrogen atoms of the water molecules were found in difference-Fourier maps, and were restrained using DFIX and DANG commands during the least-squares refinement with U iso (H) values of 1.2U eq of the oxygen atom.    Data collection: PAL BL2D-SMDC (Shin et al., 2016); cell refinement: HKL3000sm (Otwinowski et al., 2003); data reduction: HKL3000sm (Otwinowski et al., 2003); program(s) used to solve structure: SHELXT2018 (Sheldrick, 2015a); program(s) used to refine structure: SHELXL2018 (Sheldrick, 2015b); molecular graphics: DIAMOND (Putz & Brandenburg, 2014); software used to prepare material for publication: publCIF (Westrip, 2010). 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.