Crystal structure of catena-poly[[diaquacadmium(II)]-μ-3,3′-(1,3-phenylene)diacrylato]

In the crystal of the title polymeric complex, [Cd(C12H8O4)(H2O)2]n, the CdII cation, located on a twofold rotation axis, is coordinated by two water molecules and chelated by two phenylenediacrylate anions (mpda) in a distorted octahedral geometry. The mpda anions bridge the CdII cations, forming helical chains propagating along the c-axis direction. The mpba anion has twofold symmetry with two benzene C atoms located on the twofold rotation axis. In the crystal, O—H⋯O hydrogen bonds link the polymeric helical chains into a three-dimensional supramolecular architecture.


S1. Introduction
In crystal engineering, a great interest is focused on the supramolecular self-assembly of helical or chiral coordination polymers from appropriately bridging ligands and metallic tectons through either coordinate bonds and hydrogen bonds.
Although much effort has been devoted to the assembly of helical or chiral coordination polymers based on chiral or achiral ligands, the design and construction of chiral coordination polymer based on helical topology is still a great challenge for chemists.

S2. Experimental
All reagents and solvents employed were commercially available and were used as received without further purification.

S2.1. Synthesis and crystallization
A mixture of Cd(NO 3 ) 2 ·4H 2 O (62 mg, 0.25 mmol), m-phenylenediacrylic acid (H 2 mpda, 44 mg, 0.2 mmol) and H 2 O (10 mL) was sealed in a 25 mL stainless steel reactor with a Teflon liner, heated to 413 K for 3 d and then cooled to room temperature. The crystals were washed with methanol to give the title complex in about 35% yield (based on the H 2 mpda ligand).

S2.2. Refinement
All non-hydrogen atoms are easily found from the different Fourier maps and refined anisotropically. All H atoms of H 2 O molecules are found in the difference Fourier map. The C-bound H atoms of aromatic rings were refined using a riding model [0.93 Å (CH) and U iso (H) = 1.2U eq (C)].

S3. Results and discussion
The m-phenylenediacrylate (mpda) has various conformations for the rotation of carbon-carbon bonds, such as the C-C single bonds between aromatic rings and C=C bonds. The V-shaped mpda coordinated with metal ions have been documented (Liu et al., 2013). But the mpda has not been well exploited in constructing metal-organic coordination polymers in comparison with the m-phenylenedicarboxylate ligand (Yang et al., 2014). Herein, we report a poly[(mphenylenediacrylate)(water)cadmium] with the formulae [Cd(mpda)(H 2 O) 2 ] n (1). The title compound crystallizes in the chiral C222 (1) space group, and contains a homochiral left-handed single-stranded helical chain.
In the structure of 1 (Fig. 1) are located at the benzene ring in a trans-position fashion. The dihedral angles of the CH=CH-COOand C 6 H 4 -CH=CH group are ca.11.4° and 7.9°, respectively, while that of C1···C7···C6···C1 i is 180°. These dihedral angle data indicate that the mpda ligand is nearly coplanar and there exist intramolecular π-π electronic conjugations.
The mpda ligands serve as V-shaped bridges to link the metal ions into infinite helical coordination chains running along the c-axis, with the Cd···Cd distance separated by mpda being 14.54 Å. The helical pitch of 19.767 (5)  Part of the crystal structure of the mpda ligand and Cd II centres in (1), showing the atom-numbering scheme.

catena-Poly[[diaquacadmium(II)]-µ-3,3′-(1,3-phenylene)diacrylato]
Crystal data Hydrogen site location: inferred from neighbouring sites H atoms treated by a mixture of independent and constrained refinement w = 1/[σ 2 (F o 2 ) + (0.1P) 2 + 7.5572P] where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max < 0.001 Δρ max = 0.93 e Å −3 Δρ min = −0.64 e Å −3 Absolute structure: Flack (1983), 1035 Friedel pairs Absolute structure parameter: 0.07 (19) Special details Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s. planes. Refinement. Refinement of F 2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F 2 , conventional R-factors R are based on F, with F set to zero for negative F 2 . The threshold expression of F 2 > σ(F 2 ) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F 2 are statistically about twice as large as those based on F, and R-factors based on ALL data will be even larger.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )
x y z U iso */U eq