Crystal structure of the coordination polymer catena-poly[[bis[hydroxy(phenyl)acetato-κ2 O 1,O 2]zinc(II)]-μ2-1,2-bis(pyridin-4-yl)ethane-κ2 N:N′]

The synthesis and characterization of a new mandelato ZnII complex with 1,2-bi(4-pyridyl)ethane is reported. The Zn cation is coordinated by two N atoms from the 1,2-bi(4-pyridyl)ethane unit and four O atoms from two mandelate anions in a slight distorted octahedral coordination geometry.


Chemical context
-Hydroxycarboxylic acids play an important role in many biological processes and in coordination chemistry (Miyamoto et al., 1989). The deprotonated anion of one example, mandelic acid (2-hydroxy-2-phenylacetic acid), can behave as a multifunctional ligand and can act as a bridging ligand in metal complexes by involving the oxygen atoms of the carboxylate and hydroxy groups (Zechel et al., 2019;Smatanová et al., 2000;Bromant et al., 2005). We report the preparation and structural characterization of a new coordination polymer in which the Zn II cations are coordinated to two mandelate anions, behaving as bidentate ligands, and linked together via 1,2-bis(4-pyridyl)ethane molecules. 1,2-Bis(4-pyridyl)ethane is a versatile building block for the purposes of crystal engineering as the pyridyl N atoms can connect to adjacent metals to form a chain (Lee & Kim, 2015). ISSN 2056-9890

Structural commentary
The asymmetric unit of the title compound comprises one Zn II cation, one mandelate anion and one half of a 1,2-bis(4pyridin-4-yl)ethane molecule. There is an inversion centre located at the mid-point of the ethane C-C bond in the 1,2bis(4-pyridin-4-yl)ethane molecule. Each Zn II cation is coordinated by two N atoms from two 1,2-bis(4-pyridin-4yl)ethane molecules in a trans arrangement and four O atoms from two mandelate anions in a slightly distorted octahedral coordination geometry, as shown in Table 1 and Fig. 1

Figure 2
The molecular packing of the title compound. Hydrogen bonds are shown as dashed lines. The minor occupancy components of the disordered pyridine carbon atoms have been omitted for clarity.

Synthesis and crystallization
Zn(NO 3 ) 2 (91.4 mg, 0.50 mmol), 1,2-bi(4-pyridyl)ethane (92.1 mg, 0.50 mmol) and mandelic acid (76.0 mg, 0.50 mmol) were mixed in deionized water. The mixture was placed in a 25 mL Teflon linear reactor and heated at 423 K in an autoclave for 24 h. The resulting solution was slowly cooled to room temperature. Yellow transparent single crystals of the title compound were obtained in 75% yield (based on Zn).

Refinement details
Crystal data, data collection and structure refinement details are summarized in Table 3. Atoms C10, C11, C12, C14 of the pyridine ring are disordered over two sets of sites with an occupancy of 0.578 (14) for the major moiety. C-bound H atoms were included in calculated positions and treated as riding: C-H = 0.95 Å with U iso (H) = 1.5U eq (C-methyl) and 1.2U eq (C) for other H atomsÁThe hydroxy H atoms, which could not be located in a difference-Fourier map, were included in idealized calculated positions that gave the most sensible geometry.

Funding information
This work was supported financially by Yuanpei University, Taiwan.