A new tetra­kis-substituted pyrazine carb­oxy­lic acid, 3,3′,3′′,3′′′-{[pyrazine-2,3,5,6-tetra­yltetra­kis(methyl­ene)]tetra­kis­(sulfanedi­yl)}tetra­propionic acid: crystal structures of two triclinic polymorphs and of two potassium–organic frameworks

Two polymorphs of the title tetra­kis-substituted pyrazine carb­oxy­lic acid, 3,3′,3′′,3′′′-{[pyrazine-2,3,5,6-tetra­yltetra­kis­(methyl­ene))tetra­kis­(sulfanedi­yl]}tetra­propionic acid, C(20)H(28)N(2)O(8)S(4), (H(4)L1), have been obtained, H(4)L1_A and H(4)L1_B. Each structure crystallized with half a mol­ecule in the asymmetric unit of a triclinic P [Image: see text] unit cell. The whole mol­ecules are generated by inversion symmetry, with the pyrazine rings being located about inversion centers. The crystals of H(4)L1_B were of poor quality, but the X-ray diffraction analysis does show the change in conformation of the –CH(2)—S—CH(2)—CH(2)– side chains compared to those in polymorph H(4)L1_A. In the crystal of H(4)L1_A, mol­ecules are linked by two pairs of O—H⋯O hydrogen bonds, enclosing R (2) (2)(8) ring motifs forming layers parallel to plane (100), which are linked by C—H⋯O hydrogen bonds to form a supra­molecular framework. In the crystal of H(4)L1_B, mol­ecules are also linked by two pairs of O—H⋯O hydrogen bonds enclosing R (2) (2)(8) ring motifs, however here, chains are formed propagating in the [001] direction and stacking up the a-axis. Reaction of H(4)L1 with Hg(NO(3))(2) 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-carb­oxy­eth­yl)sulfan­yl]meth­yl}pyrazin-2-yl)meth­yl]sulfan­yl}propano­ato)potassium], [K(C(20)H(27)N(2)O(8)S(4))](n) (KH(3)L1). The organic mono-anion possesses inversion symmetry with the pyrazine ring being located about an inversion center. A carb­oxy H atom is disordered by symmetry and the charge is compensated for by a potassium ion. A similar reaction with Zn(NO(3))(2) resulted in the formation of crystals of a dipotassium-organic framework, poly[(μ-3,3′-{[(3,6-bis­{[(2-carb­oxy­eth­yl)sulfan­yl]meth­yl}pyrazine-2,5-di­yl)bis(methyl­ene)]bis­(sulfanedi­yl)}dipropionato)dipotassium], [K(2)(C(20)H(26)N(2)O(8)S(4))](n) (K(2)H(2)L1). 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.