Crystal structure and Hirshfeld surface analysis of (μ-2-{4-[(carboxylatomethyl)carbamoyl]benzamido}acetato-κ2 O:O′)bis[bis(1,10-phenanthroline-κ2 N,N′)copper(II)] dinitrate N,N′-(1,4-phenylenedicarbonyl)diglycine monosolvate octahydrate

The CuII atom in the title compound has a distorted trigonal–bipyramidal coordination environment defined by four N atoms from two bidentate 1,10-phenanthroline ligands and one oxygen atom from one-half of the monodentate N,N′-(1,4-phenylenedicarbonyl)diglycinate ligand. The dinuclear complex cations and the nitrate counter-anions as well as the solvate molecules are linked by an intricate network of hydrogen bonds.


Chemical context
Over the past two decades, the syntheses and structural investigations of coordination polymers with different dimensions as well as metal-organic frameworks (MOFs) have attracted much attention because of their intriguing functional architectures and applications (Batten et al., 2013;Leong & Vittal, 2011;Yamada et al., 2013). Potential applications of these materials are in catalysis, gas storage (Kitagawa et al., 2004), luminescence (Allendorf et al., 2015) or as scintillators Doty et al., 2009;Perry et al., 2012). Their crystal structures show various non-covalent intermolecular interactions and forces, and therefore are highly connected to their supramolecular chemistry (Schneider, 2009) and self-assembly (Cook et al., 2013). Moreover, these compounds have a high relevance in biological systems interacting with macromolecules such as DNA, RNA or proteins (Salonen et al., 2011), and also in biochemical reactions as protein-ligand recognitions or in drug-delivery systems of biologically active agents (Meyer et al., 2003). In general, for all these supramolecular interactions, weaker and reversible intermolecular forces play the key role, including metal coordination, classical and non-classical hydrogen bonding of the types O-HÁ Á ÁO, N-HÁ Á ÁO and C-HÁ Á ÁO, respectively, different -interactions involving the aromatic rings such asstacking, C-HÁ Á Á, ionÁ Á Á and lone-pairÁ Á Á interactions. Metal-coordinating and nitrogencontaining heterocycles such as bipyridines and phenanthrolines are electron-deficient aromatic ring systems and thus predestined to be acceptors instacking, ionÁ Á Á or lone-pairÁ Á Á interactions (Janiak, 2000;Berryman & Johnson, 2009). In addition, -donorÁ Á Áacceptor functions in different parts of an aromatic molecule can lead to remarkable properties (Albrecht et al., 2010). Transition-metal coordination compounds with the pseudo aromatic diamino acid N,N 0 -(1,4phenylenedicarbonyl)diglycine, forming zigzag chains and constructing interpenetrating networks, have been described in the literature (see Database survey).
In our synthetic approach, we employ such systems as electron-deficient bidentate aromatic ring systems such as phenanthroline or bipyridine in order to block parts of the metal cation coordination sphere. Thus, the alternative assembly process lies in the use of the offered differentinteraction possibilities, viz.stacking, C-HÁ Á Á, ionÁ Á Á and lone-pairÁ Á Á and not in forming the aforementioned zigzag chains. We have previously reported structural studies of two cobalt complexes with bidentate bipyridine or bidentate phenanthroline ligands and a non-coordinating N,N 0 -(1,4phenylenedicarbonyl)diglycine molecule in the crystal (Pook et al., 2014(Pook et al., , 2015. In these structures, the N,N 0 -(1,4-phenylenedicarbonyl)diglycine molecule is deprotonated and thus acts as counter-anion. In the two structures, the embedded N,N 0 -(1,4-phenylenedicarbonyl)diglycate molecule links the cationic buildings blocks by numerous supramolecular interactions.
In a continuation of this work, we have now synthesized and determined the structure of a novel copper(II) coordination compound where the N,N 0 -(1,4-phenylenedicarbonyl)diglycine moiety is a bis-monodentate bridging anionic ligand in its deprotonated form, as well as a solvent molecule in its neutral form in one crystal structure. The structural investigation and description of the supramolecular network is confirmed and discussed with the aid of a Hirshfeld surface analysis (Hirshfeld, 1977;Spackman & Jayatilaka, 2009) of the cationic complex and the N,N 0 -(1,4-phenylenedicarbonyl)diglycine solvent molecule.

Supramolecular features
In the crystal structure, numerous non-covalent interactions are observed. The nitrate anions are linked via O-HÁ Á ÁO, C-HÁ Á ÁO and partly via N-HÁ Á ÁO hydrogen bonds with water solvent molecules, the phenanthroline ligands and the metal-coordinating N,N 0 -(1,4-phenylenedicarbonyl)diglycinate ligands (Figs. 1-3; Table 1).interactions between parallel-displaced phenanthroline ligands and between phenanthroline and the free N,N 0 -(1,4-phenylenedicarbonyl)diglycine solvent molecule, as well as between phenanthroline ligands and the metal-coordinating N,N 0 -(1,4phenylenedicarbonyl)diglycinate ligand stack these components along the different axes  The crystal packing of the title structure in a view along the b axis. Selectedstacking interactions between phenanthroline ligands and N,N 0 -(1,4-phenylenedicarbonyl)diglycine solvent and phenanthroline ligands are shown as orange dashed lines as well as classical hydrogen bonding indicated by black dashed lines. The hydrogen atoms of aromatic moieties and methylene groups have been omitted for clarity.

Hirshfeld surface analysis
Substantiation and visualization of the described supramolecular features in the crystal structure and their close contacts between different molecular moieties, molecules, ionic and complex subunits can be achieved by using a Hirshfeld surface (HS) analysis (Hirshfeld, 1977;Spackman & Jayatilaka, 2009). Crystal Explorer (Turner et al., 2017, Wolff et al., 2012 offers the possibility to investigate and explore the short atom-to-atom contacts to identify their potential for hydrogen-bonding and -stacking interactions by generating the Hirshfeld surfaces mapped over d norm , the electrostatic potential, the shape-index and the curvedness. The HS mapped over d norm of the cationic complex subunit in the range À0.7078 to 1.7629 a.u. and of the non-coordinating N,N 0 -(1,4-phenylenedicarbonyl)diglycine solvent molecule in the range À0.6806 to 1.9484 a.u. are shown in Fig. 5 and Fig. 8, respectively. The corresponding quantitative contribution of intermolecular interactions are displayed in the overall two-dimensional fingerprint plots (FPs) and those Graphical representation of the three-dimensional Hirshfeld surface (d norm ) for the cationic complex plotted in the range À0.7078 to 1.7629 a.u.. The surface is drawn with transparency and the surface regions with strongest intermolecular interactions are drawn in red.

Figure 4
View of the lone-pairÁ Á Á interaction andstacking between the complex cation subunits. Non-covalent interactions are indicated by darkyellow dashed lines. The hydrogen atoms not involved in interactions have been omitted for clarity. Distances are given in Å . [Symmetry codes: (xii) Àx + 1, Ày, Àz + 1; (xiii) x + 1, y, z.] split up into their descending order of crystal cohesion contributions in Fig. 7 and Fig. 11, respectively. The white areas of the HS indicate contacts with distances equal to the sum of van der Waals radii and the blue regions indicate longer distances than the van der Waals radii as depicted in Figs. 5 and 8. The bright-red spots as indicators of close contacts with shorter distances than the van der Waals radii represent the donor and acceptor functions of dominant classical and non-classical hydrogen-bonding interactions of the types O-HÁ Á ÁO, N-HÁ Á ÁO and C-HÁ Á ÁO. This is confirmed by the appearance of large sharp asymmetrical spikes in the HÁ Á ÁO/OÁ Á ÁH FPs (Figs. 7,11) in the region of d e $ 1.19 Å /d i $ 0.85 Å and d i $ 0.68 Å /d e $ 1.02 Å as well as d e $ 1.05 Å /d i $ 0.70 Å and d i $ 1.12 Å /d e $ 0.78 Å , which comprise 27.9% and 42.2% of the total amount on the HS, respectively.
In order to classify the donor and acceptor groups of the N,N 0 -(1,4-phenylenedicarbonyl)diglycine solvent molecule involved in hydrogen bonding, the HS mapped over the electrostatic potentials were calculated using TONTO (Spackman et al., 2008;Jayatilaka et al., 2005) with standard settings of the STP-3G basis set at Hartree-Fock theory. The appearance of blue and red surface regions indicates the positive and negative electrostatic potential as shown in Fig. 10, suggesting that the carbonyl oxygen atom of the amide group and the non-protonated oxygen atom of the carboxylate group act as hydrogen-bond acceptors whereas the nitrogen/ hydrogen atoms of the amide group and the protonated oxygen atom of the carboxy group as well as the carbon/ hydrogen atoms of the aromatic moiety act as hydrogen-bond donors. HÁ Á ÁH contacts compromise 36.4% to the cationic complex as the largest contribution and 29.8% to the N,N 0 -(1,4-phenylenedicarbonyl)diglycine solvent molecule as the second largest contribution within the HS. This high relevance for the HS is attributed to the high proportion of hydrogen atoms in the structure of these entities. The HÁ Á ÁN/NÁ Á ÁH contacts contribute 3.7% to the cationic complex and 3.4% to the solvent molecule to the total HS, respectively. Short     Hirshfeld surfaces drawn with transparency and mapped over the shapeindex for the N,N 0 -(1,4-phenylenedicarbonyl)diglycine solvent molecule. Red and blue triangles indicate the region involved instacking interactions.

Figure 10
View of the transparent three-dimensional Hirshfeld surface of the N,N 0 -(1,4-phenylenedicarbonyl)diglycine solvent molecule plotted over electrostatic potential energy in the range À0.0828 to 0.1815 a.u. using the STO-3G basis set at the Hartree-Fock level. The O-HÁ Á ÁO, N-HÁ Á ÁO and C-HÁ Á ÁO hydrogen-bond donor and acceptor atoms are displayed as blue and red regions around the atoms corresponding to positive and negative potentials, respectively.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 2. All C-bound H atoms were positioned with idealized geometry and refined with U iso (H) = 1.2U eq (C) and C-H(aromatic) = 0.94 Å and C-H(methylene) = 0.98 Å using a riding model. The water H atoms were located in a difference-Fourier map and were refined with O-H distances restrained to 0.82-0.87 Å and with U iso (H) = 1.5U eq (O), except O11-H11A with a fixed distance of 1.00 Å , which led to a stable and consolidated hydrogen-bonding network.