Crystal structure of trans-diaqua(3,10-dimethyl-1,3,5,8,10,12-hexaazacyclotetradecane)copper(II) pamoate

The complex cation of the title compound has a six-coordinate tetragonal–bipyramidal structure with four N atoms of the azamacrocyclic ligand in the equatorial plane and two O atom of the water molecules in the axial positions. In the crystal, the carboxylic groups of the non-coordinated dianion of pamoic acid accept N—H⋯O and O—H⋯O hydrogen bonds, forming sheets of ions lying parallel to the (11) plane.

Pamoic acid [4,4 0 -methylene-bis(3-hydroxynaphthalene-2carboxylic acid), H 2 pam] is widely used as a counter-ion in ISSN 2056-9890 pharmaceutical formulations (Du et al., 2007 and references cited therein). This dicarboxylic acid is built from two naphthalene fragments, each bearing carboxylic and hydroxyl substituents and linked by a methylene bridge. The combination of this potentially bridging ligand with a biometal complex (e.g. Cu II ) could be a promising candidate for the construction of the Bio-MOFs attracting currently considerable attention (Cai et al., 2019).

Structural commentary
The title compound (I) contains two crystallographically independent centrosymmetric complex cations. Each Cu II ion lies on an inversion centre and is coordinated in the equatorial plane by four secondary amine N atoms of the azamacrocyclic ligand in a square-planar fashion, and by two O atoms from the water molecules in the axial positions, resulting in a tetragonally distorted octahedral geometry (  (17) Å ] are longer than the equatorial bonds, which can be attributed to a large Jahn-Teller distortion. The coordinated macrocyclic ligand in both cations adopts the most energetically favourable trans-III (R,R,S,S) conformation (Bosnich et al., 1965) with the fiveand six-membered chelate rings in gauche and chair conformations, respectively. The bite angles in the five-and sixmembered chelate rings equal 86.53 (8) and 93.47 (8) , respectively. The methyl substituents at the distal nitrogen atoms in the six-membered chelate rings are axially oriented. Therewith, the C-N-C angles at non-coordinated nitrogen atoms (ca 115 ) are larger than the canonical value for an sp 3hybridized nitrogen atom (109 ), thus indicating their partial sp 2 character.
The V-shaped pamoate dianion is fully deprotonated to counterbalance the charge of the complex unit and possesses a twisted conformation with the joint angle between the naphthalene rings being 115.6 (2) and the angle between the mean planes of naphthalene fragments being 88.6 (2) . The carboxylic groups adopt a transoid configuration to minimize unfavorable steric hindrance (Du et al., 2007). The C-O bond lengths in each carboxylic group are somewhat different [1.248 (3) versus 1.271 (3) and 1.245 (3) versus 1.279 (4) Å for the O1-C11-O2 and O4-C22-O5 fragments, respectively], thus indicating their incomplete delocalization. As expected, each hydroxylic group exhibits a strong intra-anion O-HÁ Á ÁO bond with the adjacent carboxyl oxygen (DÁ Á ÁA distances ca 2.5 Å ; Table 2).

Supramolecular features
Each carboxylate group of the pamoate anion acts as a proton acceptor by the formation of N-HÁ Á ÁO hydrogen bonds with adjacent secondary amine groups of the azamacrocyclic ligand and bifurcated OW-HÁ Á Á(O,O) hydrogen bonds with a coordinated water molecule of the same cation ( Fig. 2 and Table 2). Additionally, the benzene fragments of the naphthalene rings are involved in two kinds of intermolecularinteractions [interplanar separation of 3.470 and 3.717 Å ; centroid-to-centroid distances of 3.8996 (15) and 4.2107 (15) Å , respectively] (Fig. 2). These supramolecular interactions (Steed & Atwood, 2009) generate sheets of interacting ions parallel to (111), and additional N1-H1Á Á ÁO3 contacts and C-HÁ Á ÁO interactions link these sheets into a three-dimensional network.

Figure 1
View of the molecular structure of (I), showing the partial atom-labelling scheme, with thermal displacement ellipsoids drawn at the 30% probability level. H atoms at carbon atoms have been omitted for clarity. Intra-anion hydrogen-bonding interactions are shown as dashed lines.  (Ma et al., 2006;Du et al., 2007;Shi et al., 2008). Except for nine hits concerning the non-deprotonated pamoic acid, all other 84 structures are coordination polymers, thus demonstrating the availability of the pamoic acid anion for the design of MOFs.

Synthesis and crystallization
All chemicals and solvents used in this work were purchased from Sigma-Aldrich and used without further purification. The starting complex, [Cu(L)](ClO 4 ) 2 , was prepared by a method reported in the literature (Suh & Kang, 1988). The title compound (I) was prepared as follows. To a water/DMF solution (1/3 by volume, 5 ml) of [Cu(L)](ClO 4 ) 2 (123 mg, 0.25 mmol) was added a DMF solution (10 ml) containing pamoic acid (97 mg, 0.25 mmol) and 0.2 ml of triethylamine. A pink precipitate was formed in three days. This was filtered off, washed with a small amount of DMF and diethyl ether, and dried in air. Yield: 82 mg (46%). Analysis calculated for C 33 H 44 N 6 CuO 8 : C 55.33, H 6.19, N 11.73%. Found: C 55.42, H 6.24, N 11.62%. Single crystals suitable for X-ray diffraction analysis were selected from the sample resulting from the synthesis.
Safety note: Perchlorate salts of metal complexes are potentially explosive and should be handled with care.  Table 2 Hydrogen-bond geometry (Å , ).

Computing details
Data collection: APEX2 (Bruker, 2007); cell refinement: SAINT (Bruker, 2007); data reduction: SAINT (Bruker, 2007); program(s) used to solve structure: SHELXS2014 (Sheldrick, 2015a); program(s) used to refine structure: SHELXL2014 (Sheldrick, 2015b); molecular graphics: Mercury (Macrae et al., 2008); 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.