Bis(pyridine-2-carboxylato-κ2 N,O)copper(II)]–benzene-1,3,5-tricarboxylic acid–water (1/2/2)

The structure of a copper(II) complex is described.

In the title complex, [Cu(C 6 H 4 O 2 N) 2 ]Á2C 9 H 6 O 6 Á2H 2 O, the Cu 2+ ion lies on a center of inversion and coordinates with symmetry related pyridine nitrogen and carboxyl oxygen atoms from two pyridine-2-carboxylic acid anions, giving rise to a square-planar coordination geometry. There are weak axial bonds between Cu and an O atom of a symmetry-related trimesic acid moieties [CuÁ Á ÁO = 2.837 (2) Å ] The CuÁ Á ÁO weak interactions and hydrogen bonds stabilize the whole structure.

Structure description
The asymmetric unit of the title compound contains half copper center, one pyridine-2carboxylic acid anion, one BTC (benzene-1,3,5-tricarboxylic acid) ligand and one crystal water molecule (Fig. 1). The Cu 2+ ion lies on the symmetry center and is coordinated by two symmetry-related pyridine nitrogen atoms and two symmetry-related carboxyl oxygen atoms, giving rise to a square-planar coordination geometry. In the axial position, a very weak interaction Cu1Á Á ÁO3 [2.837 (2) Å ] is observed. Interestingly, the 1,4-bis(3pyridyl)-2,3-diaza-1,3-butadiene ligand decomposed during the hydrothermal process and is oxidized into pyridine-2-carboxylic acid. According to our earlier research, the occurrence of oxidation may be caused by excess of Cu II salt, which may act as an oxidative agent to promote the formation of the carboxyl group (Sun et al., 2016). Each pyridine-2-carboxylic acid anion coordinates with one Cu 2+ ion in a bidentate N,Ochelated mode, forming a five-membered ring.
In the crystal, C-HÁ Á ÁO and O-HÁ Á ÁO hydrogen bonds (Table 1) and together with weak CuÁ Á ÁO interactions link the complex molecules into a three-dimensional frame-data reports work (Fig. 2). Although the O1Á Á ÁC9 and O6Á Á ÁC7 distances [3.002 (3)and 3.014 (3) Å , respectively] between the two symmetry-related BTC 3À ligands (symmetry code: Àx, Ày, À1 À z) are short, there are nointeractions because the inter-centroid distance between the two benzene rings is 5.4029 (15) Å , which is much larger than the normalstacking distance of 3.3-3.8 Å . The shortest distance between the two carbon atoms (C1 and C1 0 ) is 3.379 (4) Å . The other CÁ Á ÁC distances of the two rings are longer than 3.94 Å . In addition, the distance between the centroid of one benzene ring and the C atoms of another is longer than 4.28 Å .

Figure 1
The title compound showing the atom-labelling scheme with displacement ellipsoids drawn at the 30% probability level. Unlabelled atoms are generated by the symmetry operation Àx, Ày, Àz. Hydrogen bonds are shown by dashed lines Figure 2 The packing of the title compound. Hydrogen bonds and CuÁ Á ÁO interactions are shown as dashed lines.

data-1
IUCrData (  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.

data-2
IUCrData (2021). 6, x210672 Refinement. All of the non-hydrogen atoms were refined with anisotropic thermal displacement coefficients. Hydrogen atoms attached to the carbons were placed in their calculated position and refined with a idealized riding model. Those attached to oxygen were first located in a difference Fourier and then refined with a idealized riding model [U iso (H) = 1.2U eq (C) or 1.5 U eq (O)].