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, 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 mol-ecule in the asymmetric unit of a triclinic P unit cell. The whole mol-ecules 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, mol-ecules 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 supra-molecular framework. In the crystal of H(4)L1_B, mol-ecules 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-carb-oxy-eth-yl)sulfan-yl]meth-yl}pyrazin-2-yl)meth-yl]sulfan-yl}propano-ato)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 carb-oxy 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-carb-oxy-eth-yl)sulfan-yl]meth-yl}pyrazine-2,5-di-yl)bis(methyl-ene)]bis-(sulfanedi-yl)}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.