Solvent-Mediated Synthesis of M ( II )-Coordination Polymer Part 1 : Crystal Structure of Poly ( 1 , 2-di ( 4-pyridyl ) ethylene-k 2 N , N ' )-bis ( 1 , 4-benzenediacetato-k 4 O , O ′ , O ′ ′ , O ′ ′ ' ) zinc ( II ) ] , C 22 H 18 ZnN 2 O 4

An interaction of water-methanol solution of sodium1,4-benzenediacetate (bda) and 4,4′-bipyridylethelene (bpee) with aqueous solution of Zn(NO3)2·6H2O at room temperature yielded colourless crystals of 1 after three weeks in a sealed glass tube. The compound with composition C22H18ZnN2O4 crystallizes in monoclinic space group P21/c, with the following cell dimensions: a = 10.4566(2), b = 13.3085(2), c = 13.7189(2) Å, β = 101.491(1)◦. In the structure of 1, two Zn(II) neighbours are connected by two bda ligands adopting chelating and bidentate-bridging coordination modes to form a dimeric unit (Zn2O8N4) with the Zn–Zn distance of 4.0432(6) Å. The carboxyl-bridged dimeric units are extended along the [001] direction by bpee co-ligands and further linked by bda ligand to form a three-dimensional network structure. The IR shows the characteristic bands of the carboxylates at 1611/1507 cm−1 and 1424/1373 cm−1, respectively, for asymmetric and symmetric stretching −CO2 vibrations. The separation ∆[νasym(CO2) − νsym(CO2)] values of 187 and 134 cm−1 are indicative of chelating and bidentate bridging coordination modes of the carboxylate to the metal centre.


Results and Discussion
The zinc(II)-coordination polymer was prepared by layering an aquo-methanol solution of the ligand on top of aqueous solution of the metal ion in a glass tube and allowing to stand at room temperature for three weeks.Compound 1 crystallizes in monoclinic space group P2 1 /c (Table S1).The zinc atom is six-coordinated in a distorted octahedral manner (Figure 1a).The bda ligand is tetradentate, with one carboxylate group coordinating to the zinc centre in a bidentate-bridging fashion via O1 and O2, while the other is bidentately chelating via O3 and O4.Two symmetry-related bpee ligands coordinating via N1 and N2 at the apical positions complete the sixth coordination.What is especially noteworthy about this compound is that the two Zn(II) neighbours are connected by two bda ligands through µ 2 -oxo bridge carboxylic oxygen atoms to form an eight-membered cyclic dimer (Zn 2 bda 2 ) with the Zn-Zn distance of 4.0432(6) Å.The carboxyl-bridged dimeric units are extended along the [010] direction by bpee co-ligands to produce 1D coordination polymer with Zn-bpee-Zn separation of 13.7189(6) Å.All the Zn-O bond lengths are between 2.020(4) and 2.384(5) Å (Zn-O av = 2.140(3)) and the Zn-N bond lengths are in the range of 2.172 (3)-2.185(3)Å (Table S2) and are in agreement with similar compounds in the literature [14][15][16][17][21][22][23][24][25][26][27][28].The polymeric corrugated chains are connected by chelating bda into 2D layered structure as shown in Figure 1b.The second bda ligand connects the layer into a 3D network (Figure 1c).In the isomeric structure reported by Zhang et al. [23], the zinc centre is in four coordination and the 1,3-phenylenediacetate ligand shows transtrans-configuration and adopts bis(monodentate) coordination.Furthermore, in the structural diversity for a series of metal(II) complexes based on flexible 1,2-phenylenediacetate and dipyridyl-type co-ligand reported by Xin et al. [25], the phenylenediacetate anions also adopt a bis(monodentate) coordinated mode that bridges the adjacent Zn(II) atoms to yield an undulating [Zn(phda)]n chain.In the present compound, the metal centre is in six coordination and the 1,4-phenylenediacetate ligand bidentately bridges two Zn atoms and the other bidentately chelates one Zn atom.The difference between these compounds is due to the effect of ligand isomerism.The topology of the present compound is similar to [Co(phda)(dpe)] n characterized as a six-connected self-penetrated network with (4 8 6 6 8) rob topology.It is interesting to note that although the synthesis was solvent-mediated, the solvent molecules could not be located in the lattice.
The infrared spectrum of the as-synthesized compound (Figure S2) shows the characteristic bands of the carboxylates at 1611/1507 cm −1 and 1424/1373 cm −1 , respectively, for asymmetric and symmetric stretching −CO

Synthesis of C22H18ZnN2O4, 1
Zn(NO3)2•6H2O (0.50 mmol, 0.149 g) was dissolved in 50 mL of water with constant stirring.Sodium1,4-benzenediacetate (Na-bda) (0.25 mmol, 0.060 g) and 4,4′-bipyridylethelene (bpee) (0.25 mmol, 0.045 g) were dispersed in 25 mL mixture of water (H2O) and methanol (CH3OH) (7:3), respectively, and sonicated for 15 min to make a homogeneous solution.Water/methanol mixture of the ligands (Na-bda and bpee) (2 mL) was slowly and carefully layered on top of the aqueous metal ion [Zn(NO3)2•6H2O] solution (2 mL) using the 2 mL buffer solution of water and methanol (7:3) in a crystal tube, which was sealed and left uninterrupted at room temperature.Colourless block type single crystals were grown at the junction of the two different solvents after three weeks.The crystals, which were separated and washed with water and methanol, were found to be air-stable and insoluble in a wide spectrum of solvent.A bulk amount of the compound was synthesized by direct mixing of the corresponding ligands (sodium 1,4-benzenediacetate and 4,4′-bipyridylethelene) solution with a water-methanol solution of Zn(NO3)2•6H2O under stirring for 24 h.Yield: 82%.The PXRD pattern of 1 compared with the simulated pattern from single crystal analyses is presented in Figure S3.Anal.Calcd.For C22H18N2O4Zn: C, 60.08; H, 4.13; N, 6.37.Found: C, 60.21; H, 4.08; N, 6.41%.

Physical Measurements
The elemental analysis of the compound was carried out on a Thermo Fisher Flash 2000 Elemental Analyzer (ThermoFisher Scientific Warrington, UK).Fourier transformed IR spectroscopic investigation was carried out using a KBr pellet on Bruker IFS-66v (Bruker, Ettlingen, Germany).

Synthesis of C 22 H 18 ZnN 2 O 4 , 1
Zn(NO 3 ) 2 •6H 2 O (0.50 mmol, 0.149 g) was dissolved in 50 mL of water with constant stirring.Sodium1,4-benzenediacetate (Na-bda) (0.25 mmol, 0.060 g) and 4,4 -bipyridylethelene (bpee) (0.25 mmol, 0.045 g) were dispersed in 25 mL mixture of water (H 2 O) and methanol (CH 3 OH) (7:3), respectively, and sonicated for 15 min to make a homogeneous solution.Water/methanol mixture of the ligands (Na-bda and bpee) (2 mL) was slowly and carefully layered on top of the aqueous metal ion [Zn(NO 3 ) 2 •6H 2 O] solution (2 mL) using the 2 mL buffer solution of water and methanol (7:3) in a crystal tube, which was sealed and left uninterrupted at room temperature.Colourless block type single crystals were grown at the junction of the two different solvents after three weeks.The crystals, which were separated and washed with water and methanol, were found to be air-stable and insoluble in a wide spectrum of solvent.A bulk amount of the compound was synthesized by direct mixing of the corresponding ligands (sodium 1,4-benzenediacetate and 4,4 -bipyridylethelene) solution with a water-methanol solution of Zn(NO 3 ) 2 •6H 2 O under stirring for 24 h.Yield: 82%.The PXRD pattern of 1 compared with the simulated pattern from single crystal analyses is presented in Figure S3.Anal.Calcd.For C 22 H 18 N 2 O 4 Zn: C, 60.08; H, 4.13; N, 6.37.Found: C, 60.21; H, 4.08; N, 6.41%.

Physical Measurements
The elemental analysis of the compound was carried out on a Thermo Fisher Flash 2000 Elemental Analyzer (ThermoFisher Scientific Warrington, UK).Fourier transformed IR spectroscopic investigation was carried out using a KBr pellet on Bruker IFS-66v (Bruker, Ettlingen, Germany).

Single-Crystal X-ray Diffraction.
A good single crystal of compound 1 was mounted on a thin glass fibber with commercially available super glue.X-ray single-crystal structural data were collected on a Bruker Smart-CCD diffractometer (Bruker AXS, Gmbh, Germany) equipped with a normal focus and a 2.4 kW sealed tube X-ray source with graphite monochromated Mo-Kα radiation (λ = 0.71073 Å) operating at 50 kV and 30 mA.The program SAINT [30] was used for the integration of diffraction profiles, and absorption correction was made with the SADABS [31] program.The structure was solved by SIR 92 [32] and refined by the full-matrix least-squares method using SHELXL [33].All the hydrogen atoms were fixed by HFIX and placed in ideal positions.The stilbene-type C=C atoms were positionally disordered.The potential solvent accessible area or void space was calculated using the PLATON [34] multipurpose crystallographic software.All crystallographic and structure refinement data of compound 1 is summarized in Table S1.Selected bond lengths and angles for compounds 1 are given in Tables S2

Conclusions
We have successfully constructed a Zn(II) coordination polymer under solvent diffusion condition by employing mixed linkers system of 4,4 -bipyridylethene and 1,4-benzenediacetic acid.The compound [Zn(bpee)(bda))]n, 1, has a 3D network.We are currently investigating these mixed linkers system with first row transition elements with a view to unravel their magnetic properties; the results will be published elsewhere.

2 −
vibrations.The separation ∆[ν asym (CO 2 − ) − ν sym (CO 2− )] values of 187 and 134 cm −1 are indicative of chelating and bidentate bridging coordination modes of the carboxylate to the metal centre[29].The in-plane C-H bending vibrations of the aromatic ring are observed at 1197 -1062 cm −1 , while the out-of-plane C-H bending vibrations appeared in the region 959-721 cm −1 .Bands in the region 637-451 cm −1 are due to Zn-O vibrations.