Poly[[μ7-l-cysteato(2−)]disodium]

The title compound {systematic name: poly[[μ7-(2R)-2-amino-3-sulfonatopropanoato]disodium]}, [Na2(C3H5NO5S)]n, was obtained through solvent-thermal reaction of l-cysteic acid and aqueous sodium hydroxide. The monomer consists of two Na+ cations that are coordinated to the deprotonated amino acid. The latter acts as donor utilizing all available coordination sites, viz. the amino, the carboxylate and the sulfonate residues, so producing a monomeric framework in which the two coordinated Na+ ions have different coordination spheres and geometries. One of the Na+ ions has an O5 coordination sphere with a typical geometric arrangement, intermediate between trigonal–bipyramidal and square–pyramidal; all the O atoms from the amino acid (three from the sulfonate and two from the caboxylate residues) act as donors. The second Na+ ion is tetracoordinated within an NO3 coordination sphere. The Na+ ion binds to the amino N atom, to one of the O atom of the carboxylic residue and to two O atoms of the sulfonate group in a distorted tetrahedral arrangement. As the sulfonate O atoms bind to both Na+ ions, a three-dimensional polymeric framework is obtained.

The title compound {systematic name: poly[[ 7 -(2R)-2-amino-3-sulfonatopropanoato]disodium]}, [Na 2 (C 3 H 5 NO 5 S)] n , was obtained through solvent-thermal reaction of l-cysteic acid and aqueous sodium hydroxide. The monomer consists of two Na + cations that are coordinated to the deprotonated amino acid. The latter acts as donor utilizing all available coordination sites, viz. the amino, the carboxylate and the sulfonate residues, so producing a monomeric framework in which the two coordinated Na + ions have different coordination spheres and geometries. One of the Na + ions has an O 5 coordination sphere with a typical geometric arrangement, intermediate between trigonal-bipyramidal and square-pyramidal; all the O atoms from the amino acid (three from the sulfonate and two from the caboxylate residues) act as donors. The second Na + ion is tetracoordinated within an NO 3 coordination sphere. The Na + ion binds to the amino N atom, to one of the O atom of the carboxylic residue and to two O atoms of the sulfonate group in a distorted tetrahedral arrangement. As the sulfonate O atoms bind to both Na + ions, a three-dimensional polymeric framework is obtained.
The author thanks Jilin Business and Technology College for financial support.
Amino acids are of interest in coordination chemistry because they have a large number of highly flexible derivatives capable of forming a wide range of metal compexes. Recently, L-Cysteic acid, (Hendrickson et al., 1971), (Ramanadham et al. 1973) has become an important ligand in the coordination and construction of metal-organic frameworks (MOFs), as a result, some of these frameworks with unusual topologies have been reported by (Bharadwaj et al., 1985, Riley et al., 2002, and Huang et al. 2009). As a part of our work in amino acid coordination research we chose L-Cysteic acid as our ligand. The title compound has recently been prepared in our laboratory and its structure is reported here.
The molecular structure of [C 3 H 5 NNa 2 O 5 S] n is presented in Fig.1a-c. Fig.1a shows that two Na + cations are coordinated to one L-Cysteic acid while Fig.1b shows the µ7 connectivity of each L-Cysteic acid. Each L-Cysteic acid chelates one Na + cation with its O-donor of sulfonate group and of the carboxylate one, and chelates the other Na + cation with another O-donor from the same sulfonate group and the amine N-donor. Fig.1c shows the coordination environment of the two Na + cations: for Na1 it is five coordinated while for Na2 forms a 4 coordinated Na node. Moreover, Na1 and Na2 are bridged by one O atom from sulfonyl group. In conclusion, the Na cation and the L-Cysteic acid ligand construct a three-dimensional frameword with space group P21/c, Fig.2.

Experimental
The title complex was synthesized through solvent-thermal reaction by L-Cysteic acid with NaOH aqueous as following method: 84.58 mg (0.5 mmol) of L-Cysteic acid, 10 mL 0.5% NaOH aqueous, were added to a 20 ml Teflon vessel. The vessel was sealed and placed inside a stainless steel autoclave, which was kept at 140°C for 72 h. Then the crystal suiting for X-ray single-crystal analysis was obtained.

Refinement
H atoms bonded to N atom were located in a difference map and refined with distance restraints of N-H = 0.899-0.900 Å, and with U iso (H) = 1.2Ueq(N). Other H atoms were positioned geometrically and refined using a riding model, with C-H = 0.970-0.981 Å and with U iso (H) = 1.2 times U eq (C). Fig. 1. The ORTEP-3 view of the title complex with atom labels and 50% probability displacement ellipsoids for non-H atoms. a. The asymmetric unit of the title complex. b. The µ7 connectivity of each L-Cysteic acid. Other Na + cations are hidden for breifness. c. The coordination mode for Na1 and Na2. The other L-Cysteic acid is hidden for breifness. 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.