Crystal structure and Hirshfeld surface analysis of one-dimensional copper(II) coordination polymer incorporating succinate and tetramethylethylenediamine ligands

The title compound, {[Cu(succ)(tmeda)]·4H2O}n, consists of one-dimensional polymeric chains in which the central metal atom is coordinated in a distorted square-planar geometry by one oxygen atom each from two succ ligands and two TMEDA ligand nitrogen atoms.

The reaction of copper nitrate with succinic acid (succH) and N,N,N 0 ,N 0tetramethylethylenediamine (TMEDA) in basic solution produces the complex catena-poly [[[(N,N,N 0 ,N 0 -tetramethylethylenediamine-2 N,N 0 )copper(II)]-succinato-2 O 1 :O 4 ] tetrahydrate], {[Cu(C 4 H 4 O 4 )(C 6 H 16 N 2 )]Á4H 2 O} n or {[Cu(succ)(tmeda)]Á4H 2 O} n . Each carboxylate group of the succinate ligand coordinates to a Cu II atom in a monodentate fashion, giving rise to a distorted square-planar geometry. The succinate ligands bridge the Cu II centres, forming one-dimensional polymeric chains. Hydrogen bonds between the ligands and water molecules link these chains into sheets that lie parallel to the ac plane. Hirshfeld surface analysis, d norm and two-dimensional fingerprint plots were examined to verify the contributions of the different intermolecular contacts within the supramolecular structure.

Chemical context
Coordination polymers are a key area of development in supramolecular chemistry. Aliphatic saturated dicarboxylates are versatile linkage ligands for construction of supramolecular frameworks. These possess conformational freedom and coordinating ability owing to the single carbon chain. Aliphatic dicarboxylate anions exhibit different coordination modes such as uni-bidentate, bis-monodentate, bis-bidentate, tridentate or tetradentate, linking metal atoms into 1-D coordination polymers, 2-D layers or 3-D networks. Copper(II) carboxylate complexes are known to possess various biological activities including antifungal (Melník et al., 1982), antibacterial (Mojumdar et al., 2005), antiviral and cytotoxic activities (Ranford et al., 1993). Copper(II) is present at the active site some of proteins. The proteins containing copper(II) display biological functions such as electron transfer, dioxygen transfer, oxygenation, reduction, oxidation and disproportionation (Mukherjee, 2003). In this work, the synthesis, single crystal structure and Hirshfeld surface analysis of a copper(II) complex involving N,N,N 0 ,N 0tetramethylethylenediamine and succinate ligands are reported.

Figure 3
The two-dimensional layered structure of {[Cu(succ)(tmeda)]Á4H 2 O} n . For clarity, the TMEDA ligands are shown only by their N atoms.
Hirshfeld surface analysis enables the visualization of intermolecular interactions by different colours and colour intensity, representing short or long contacts and indicating the relative strength of the interactions. Fig. 4 shows the Hirshfeld surface mapped over d norm (-0.629 to 1.578 a.u.). The overall two-dimensional fingerprint plot for the title complex and those delineated into HÁ Á ÁH, OÁ Á ÁH/HÁ Á ÁO and CuÁ Á ÁO/ OÁ Á ÁCu contacts are illustrated in Fig. 5. The percentage contributions from the different inter-atomic contacts to the Hirshfeld surface are as follows: HÁ Á ÁH (63.2%), OÁ Á ÁH/ HÁ Á ÁO (29.5%) and CuÁ Á ÁO/OÁ Á ÁCu (3.8%). The percentage contributions for other intermolecular contacts amount to less than 3% of the Hirshfeld surface mapping.

Synthesis and crystallization
An aqueous solution of sodium succinate (10 mmol, 1.6 g) was added to an aqueous solution of Cu(NO 3 ) 2 Á3H 2 O (10 mmol, 2.4 g) under stirring. A light-blue precipitate was formed. The precipitate was filtered and washed with water. The precipitate was dispersed in water and tetramethylethylenediamine (10 mmol, 1.2 g) was added giving a dark-blue solution. The solution was filtered. Single crystals were obtained on slow evaporation of the solution after one week.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 3 Hirshfeld surface mapped over d norm for {[Cu(succ)(tmeda)]Á4H 2 O} n .

Figure 5
The two-dimensional fingerprint plots for {[Cu(succ)(tmeda)]Á4H 2 O} n showing the main interactions and their percentage contributions (d i is the closest internal distance from a given point on the Hirshfeld surface and d e is the closest external contact). positioned geometrically and refined using a riding model, with C-H = 0.93, 0.96 and 0.97 Å with U iso (H) = 1.5U eq (C) for methyl H atoms and 1.2U eq (C) otherwise. The methyl groups were modelled as disordered over two torsional orientations. Water hydrogen-atom coordinates were refined, but U iso (H) was set to 1.5U eq (water O).

catena-Poly[[[(N,N,N′,N′-tetramethylethylenediamine-κ 2 N,N′)copper(II)]-µ-succinato-κ 2 O 1 :O 4 ] tetrahydrate]
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. (