A new tetra-kis-substituted pyrazine carb-oxy-lic acid, 3,3',3'',3'''-{[pyrazine-2,3,5,6-tetra-yltetra-kis(methyl-ene)]tetra-kis-(sulfanedi-yl)}tetra-propionic acid: crystal structures of two triclinic polymorphs and of two potassium-organic frameworks.

Two polymorphs of the title tetra-kis-substituted pyrazine carb-oxy-lic acid, 3,3',3'',3'''-{[pyrazine-2,3,5,6-tetra-yltetra-kis-(methyl-ene))tetra-kis-(sulfanedi-yl]}tetra-propionic acid, CHNOS, (), have been obtained, and . Each structure crystallized with half a mol-ecule in the asymmetric unit of a triclinic unit cell. The whole mol-ecules are generated by inversion symmetry, with the pyrazine rings being located about inversion centers. The crystals of were of poor quality, but the X-ray diffraction analysis does show the change in conformation of the -CH-S-CH-CH- side chains compared to those in polymorph . In the crystal of , mol-ecules are linked by two pairs of O-H⋯O hydrogen bonds, enclosing (8) ring motifs forming layers parallel to plane (100), which are linked by C-H⋯O hydrogen bonds to form a supra-molecular framework. In the crystal of , mol-ecules are also linked by two pairs of O-H⋯O hydrogen bonds enclosing (8) ring motifs, however here, chains are formed propagating in the [001] direction and stacking up the -axis. Reaction of with Hg(NO) in the presence of a potassium acetate buffer did not produce the expected binuclear complex, instead crystals of a potassium-organic framework were obtained, poly[(μ-3-{[(3,5,6-tris-{[(2-carb-oxy-eth-yl)sulfan-yl]meth-yl}pyrazin-2-yl)meth-yl]sulfan-yl}propano-ato)potassium], [K(CHNOS)] (). The organic mono-anion possesses inversion symmetry with the pyrazine ring being located about an inversion center. A carb-oxy H atom is disordered by symmetry and the charge is compensated for by a potassium ion. A similar reaction with Zn(NO) resulted in the formation of crystals of a dipotassium-organic framework, poly[(μ-3,3'-{[(3,6-bis-{[(2-carb-oxy-eth-yl)sulfan-yl]meth-yl}pyrazine-2,5-di-yl)bis(methyl-ene)]bis-(sulfanedi-yl)}dipropionato)dipotassium], [K(CHNOS)] (). Here, the organic di-anion possesses inversion symmetry with the pyrazine ring being located about an inversion center. Two symmetry-related acid groups are deprotonated and the charges are compensated for by two potassium ions.