catena-Poly[[diaquacadmium(II)]bis(μ-2,2-dimethylbutanedioato-κ4 O,O′:O′′,O′′′)[diaquacadmium(II)]-μ-1,4-bis(3-pyridylmethyl)piperazine-κ2 N 3:N 3′]

In the title compound, [Cd2(C6H8O4)2(C16H20N4)(H2O)4]n, pentagonal-bipyramidally coordinated CdII ions are connected into {Cd2(2,2-dimethylsuccinate)2(H2O)4} centrosymmetric dimeric clusters. In turn, these clusters are linked by tethering 1,4-bis(3-pyridylmethyl)piperazine (3-bpmp) ligands into [Cd2(2,2-dimethylsuccinate)2(3-bpmp)(H2O)4]n coordination polymer chains. The chain motifs are oriented parallel to [10]. Individual chains are connected into supramolecular layers via O—H⋯N and O—H⋯O hydrogen-bonding mechanisms.

construction of divalent metal coordination polymers in tandem with aromatic dicarboxylate ligands (Johnston et al., 2008). This chemistry has been extended into an aliphatic dicarboxylate system with the synthesis of the title compound.
The asymmetric unit of the title compound contains a Cd II ion, one 2,2-dimethylsuccinate ligand, two aqua ligands, and one-half of a 3-bpmp ligand whose central piperazinyl ring is situated over a crystallographic inversion centre. The Cd II ion is pentagonal bipyramidally coordinated in a {CdO 6 N} environment, with its apical positions occupied by aqua ligands. Its basal plane consists of two chelating carboxylate groups from two 2,2-dimethylsuccinate ligands and one pyridyl N donor atom from a 3-bpmp ligand. A pair of Cd II ions is aggregated into a centrosymmetric {Cd 2 (H 2 O) 4 (2,2-dimethylsuccinate) 2 } dinuclear cluster (Fig. 1) by two bis(chelating) 2,2-dimethylsuccinate ligands, which adopt a gauche conformation.

Experimental
All starting materials were obtained commercially, except for 3-bpmp, which was prepared by a published procedure (Niu et al., 2001). A mixture of cadmium nitrate tetrahydrate (114 mg, 0.37 mmol), 2,2-dimethylsuccinic acid (54 mg, 0.37 mmol), 3-bpmp (199 mg, 0.742 mmol) and 10.0 g water (550 mmol) was placed into a 23 ml Teflon-lined Parr acid digestion bomb, which was then heated under autogenous pressure at 393 K for 72 h. Colourless blocks of the title compound (57 mg, 26% yield) were isolated after washing with distilled water and acetone, and drying in air.

Refinement
All H atoms bound to C atoms were placed in calculated positions, with C-H = 0.95 Å, and refined in riding mode with U iso = 1.2U eq (C). The H atoms bound to the aqua ligand O atom were found in a difference Fourier map, restrained with with O-H = 0.85 Å and refined with U iso = 1.2U eq (O).

Special details
Experimental. The largest peak of 0.645 e -Å 3 was located 0.90 Å from Cd1. The largest hole of -1.065 e -Å 3 was located 0.94 Å from Cd1.
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.
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 Rfactors(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.