Poly[[μ7-l-cysteato(2−)]disodium]

The title compound {systematic name: poly[[μ(7)-(2R)-2-amino-3-sulfonato-propano-ato]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 carboxyl-ate 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, inter-mediate 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 carb-oxy-lic residue and to two O atoms of the sulfonate group in a distorted tetra-hedral arrangement. As the sulfonate O atoms bind to both Na(+) ions, a three-dimensional polymeric framework is obtained.