Poly[[piperazine-1,4-dium [diaquatetrakis(μ-sulfanediyldiacetato)dicerate(III)]] trihydrate]

The title compound, (C4H12N2)[Ce2(C4H4O4S)4(H2O)2]·3H2O, features a polymeric anion with a centrosymmetric Ce2O2 core and a Ce⋯Ce distance of 4.3625 (4) Å. The anions form ribbons {[Ce2(C4H4O4S)4(H2O)2]2−}n extending along [100]. The doubly protonated piperazinium cations reside on centers of inversion and link the polymeric ribbons via N—H⋯O hydrogen bonding. Each CeIII cation is ten-coordinated by an O2S donor set from two tridentate sulfanediyldiacetate (tda) ligands, one water molecule and three other tda O donors from adjacent {Ce(tda)2(H2O)} units in a distorted bicapped cubic environment. Additional O—H⋯O hydrogen bonding involving the coordinated and solvent water molecules is also present. H atoms of the crystal water molecules could not be located and were not included in the refinement.

The title compound, (C 4 H 12 N 2 )[Ce 2 (C 4 H 4 O 4 S) 4 (H 2 O) 2 ]Á-3H 2 O, features a polymeric anion with a centrosymmetric Ce 2 O 2 core and a CeÁ Á ÁCe distance of 4.3625 (4) Å . The anions form ribbons {[Ce 2 (C 4 H 4 O 4 S) 4 (H 2 O) 2 ] 2À } n extending along [100]. The doubly protonated piperazinium cations reside on centers of inversion and link the polymeric ribbons via N-HÁ Á ÁO hydrogen bonding. Each Ce III cation is tencoordinated by an O 2 S donor set from two tridentate sulfanediyldiacetate (tda) ligands, one water molecule and three other tda O donors from adjacent {Ce(tda) 2 (H 2 O)} units in a distorted bicapped cubic environment. Additional O-HÁ Á ÁO hydrogen bonding involving the coordinated and solvent water molecules is also present. H atoms of the crystal water molecules could not be located and were not included in the refinement.

Experimental
Crystal data (C 4

S1. Comment
Thiodiacetic acid is one class of dicarboxylic acid ligands that has been used for construction of coordination polymers. It is a versatile complexing agent with one sulfur and two oxygen donor atoms and can strongly complex metal ions.
Although the structural study of sulfanediyldiacetate-transition metal compounds was initiated several decades ago (Delaunay, et al., 1976), interest in the structural aspects of sulfanediyldiacetate compounds has remarkably increased in recent years, and many structures with d-and f-block metals are known to date. The ligand is usually tridentate, but at least one Mn(II) complex has been reported in which it is solely bidentate where the thioether S atom is not involved in bonding to the metal (Marek et al., 2003). The ligand can be simply chelating or is involved in both bridging and chelating modes to give rise to dinuclear complexes (Baggio et al., 1999).  Fig. 1. The sulfanediyldiacetate group involving S1 behaves as both a tridentate chelating ligand and a bridging ligand to form a centrosymmetric dimer. The Ce1···Ce1 i (i = 1 -x, 1 -y, -z) distance is 4.3625 (4) Å. The sulfanediyldiacetate ligand involving S2 is also a tridentate chelating ligand while its oxygen, O8, coordinates to the Ce of an adjoining dimer and propagates the structure as a coordination polymer parallel to [100] (Fig. 2). The more distant Ce1 iii (iii = 1 + x, y, z) is 6.4361 (7) Å away from Ce1. The local coordination of the Ce III cations consists of two thioethers (S1

S2. Experimental
The title compound was prepared by mixing two solutions containing 1.5 g (10 mmol) of 2,2′-thiodiacetic acid in 10 ml THF and 0.86 g (10 mmol) piperazine in 10 ml THF. A white precipitate was obtained after evaporating the solvent. An aqueous solution containing 0.34 g (1.5 mmol) of the obtained ion pair in 20 ml water was added dropwise to 0.21 g (0.5 mmol) Ce(NO 3 ) 3 . 6H 2 O in 15 ml water. After 60 min stirring and heating to 303 K, the solution became clear. Yellow crystals of the title compound were obtained after allowing the mixture to stand for 3 weeks at room temperature to supporting information evaporate the solvent.

S3. Refinement
The C-bound and N-bound hydrogen atoms were placed at calculated positions (C-H 0.99 Å, N-H 0.92 Å) and were treated as riding on their parent atoms with U(H) set to 1.2 U eq (C). The hydrogen atoms bonded to the coordinated water were located in a difference Fourier map and were refined with distance restraints of O-H 0.83 (2) Å and H···H 1.34 (4) Å and their isotropic displacement parameters allowed to refine. There are two sites for water moleculess of hydration.
One of the hydrate molecules is disordered with respect to a center of symmetry and was kept at 0.5 occupancy and refined with an isotropic displacement parameter. Hydrogen atoms bonded to the water molecules of crystallisation could not be reliably located and were eventually omitted from the refinement. The highest peak in the final difference map is 0.83 Å from Ce1 and the largest hole is 0.87 Å from the same atom.

Figure 1
Thermal ellipsoid plot of the title compound at the 50% probability level. Hydrogen atoms are removed for clarity except those bonded to the piperazine N atoms and the coordinated water molecule. Hydrogen atoms are drawn as spheres of arbitrary radius. Atoms that indicate the propagation of the coordination polymer are shown. Symmetry codes: i = 1 -x, 1 -y, -z; ii = x -1, y z; iii = 1 + x, y, z; iv = -x, 1 -y, -z; v = -x, 2 -y, -z.

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.