Synthesis and crystal structure of trans-diaqua(1,4,8,11-tetraazaundecane)copper(II) isophthalate monohydrate

The complex cation of the title compound contains a tetragonally distorted trans-CuN4O2 octahedron. In the crystal, the components are linked by numerous N—H⋯O and O—H⋯O hydrogen bonds, forming electroneutral sheets oriented parallel to the ac plane, which are further consolidated into bilayers due to hydrogen-bonding with the participation of the water molecule of crystallization.

In the title hydrated molecular salt, [Cu(C 7 H 20 N 4 )(H 2 O) 2 ](C 8 H 4 O 4 )ÁH 2 O, the metal ion is coordinated by the two primary and two secondary N atoms of the amine ligand and the mutually trans O atoms of the water molecules in a tetragonally distorted octahedral geometry. The average equatorial Cu-N bond lengths (2.013 and 2.026 Å for Cu-N prim and Cu-N sec , respectively) are substantially shorter than the average axial Cu-O bond length (2.518 Å ). The tetraamine ligand adopts its energetically favored conformation with its fiveand six-membered chelate rings in gauche and chair conformations, respectively. In the crystal, the N-H donor groups of the tetraamine, the acceptor carboxylate groups of the isophthalate dianion and both the coordinated water molecules and the water molecule of crystallization are involved in numerous N-HÁ Á ÁO and O-HÁ Á ÁO hydrogen bonds, resulting in the formation of electroneutral layers oriented parallel to the ac plane.

Structural commentary
The asymmetric unit of the title hydrated molecular salt I consists of a complex di-cation [Cu(L)(H 2 O) 2 ] 2+ , a noncoordinated isophthalate di-anion ip 2and one water molecule of crystallization (Fig. 1). The Cu II ion is coordinated in the equatorial plane by the two primary and two secondary N atoms of the amine ligand in a nearly square-planar fashion (the deviations of the N atoms from the mean N 4 plane are AE0.006 Å ), and by the two O atoms from the water molecules in the axial positions.
The average equatorial Cu-N prim bond length for N1 and N4 (2.013 Å ) is slightly shorter than Cu-N sec one for N2 and N3 (2.025 Å ), probably reflecting the stronger donating ability of the N atoms of primary versus secondary amine groups ( Table 1). The average axial Cu-O bond length (2.518 Å ) is substantially longer than the equatorial Cu-N bonds, which is likely due to a large Jahn-Teller distortion inherent in metal ions with a d 9 electronic configuration. It is noteworthy that the Cu-O distances in I differ considerably (Table 1) and the Cu II ion is displaced from the mean N 4 plane of the ligand by 0.082 Å towards the O1W water molecule.
The ligand L in I adopts its energetically favored conformation with the five-membered chelate rings in gauche [average bite angle 85.74 ] and six-membered chelate ring in chair conformations, which resemble the trans-III conformation usually observed in cyclam complexes (Barefield et al., 1986;Bosnich et al., 1965). The pseudo 'bite' angle formed by the primary amine donors N1-Cu1-N4 is slightly larger than that for N2-Cu1-N3 (Table 1).
The isophthalate di-anion in the title compound counterbalances the charge of the complex cation. The mean planes of the pendant carboxylate groups are slightly tilted relative to the mean plane of the aromatic ring [average angle = 9.8 ]. The C-O bond lengths in the carboxylate groups are nearly equal (Table 1), thus indicating essentially complete electron delocalization.

Supramolecular features
In the crystal of I, the complex cation [Cu(L)(H 2 O) 2 ] 2+ , isophthalate anion ip 2and both coordinated water molecules and water molecule of crystallization are linked by numerous hydrogen bonds (Table 2), resulting in its distinct lamellar structure. In particular, hydrogen-bonding interactions between the N1, N2 and N3 amine groups and O1W and O2W water molecules as the donors and carboxylate atoms O1, O3 and O4 as the acceptors result in the formation of electroneutral sheets (Fig. 2). Additionally, due to hydrogen bonds N4-H4BÁ Á ÁO3 (Àx + 1, Ày + 1, Àz + 1) and N1-H1AÁ Á ÁO2W (Àx, Ày + 1, Àz + 1) and four bonds formed by the water molecule O3W these sheets double into bilayers oriented parallel to the ac plane ( Fig. 3). It is noteworthy that all the polar groups in I are saturated from the point of view of the number of possible hydrogen bonds, which equal to 2, 1, 2, 4 and 2 for the primary, secondary amine groups, coordinated water molecule, water molecule of crystallization and carboxylate O atoms, respectively.
View of the asymmetric unit of I, showing the atom-labelling scheme, with displacement ellipsoids drawn at the 40% probability level. H atoms attached to carbon atoms have been omitted for clarity.

Figure 2
The hydrogen-bonded (dashed lines) sheets in I. C-bound H atoms and water molecule of crystallization have been omitted.
There are no hydrogen-bonding contacts between the layers in I (Fig. 3). The three-dimensional coherence of the crystal is provided by van der Waals interactions between the methine and methylene fragments of the constituents.

Database survey
A search of the Cambridge Structural Database (CSD, version 5.43, last update March 2022; Groom et al., 2016) gave nine hits related to the compounds formed by the [Cu(L)] 2+ core. Among them, the trans-CuN 4 O 2 chromophores are characteristic of three complexes [CSD refcodes DAFYOA (Heeg et al., 2010), FICDEA (Lawrance et al., 1987) and TECCUA (Fawcett et al., 1980)] all of which contain coordinated perchlorate anions. Thus, the present work is the first structural characterization of a Cu II diaqua complex of this openchain tetraamine.
In general, conformations of the amine ligand and geometrical parameters of coordination polyhedra in both types of cations are similar, even though the axial Cu-O bond lengths in the perchlorate complexes are longer. This can be explained by poorer donating ability of this anion as compared to aqua ligand. As in I, the Cu-O distances in previously mentioned compounds are non-equivalent even though the differences between them are smaller than in I and do not exceed 0.14 Å .

trans-Diaqua(1,4,8,11-tetraazaundecane-κ 4 N 1 ,N 4 ,N 8 ,N 11 )copper(II) benzene-1,3-dicarboxylate 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.