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, C20H28N2O8S4, (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 (1) over bar 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 -CH2-S-CH2-CH2- 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 center dot center dot center dot O hydrogen bonds, enclosing R-2(2)(8) ring motifs forming layers parallel to plane (100), which are linked by C-H center dot center dot center dot 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 center dot center dot center dot 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(NO3)(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[(mu-3-{[(3,5,6-tris{[(2-carboxyethyl) sulfanyl]methyl}pyrazin-2-yl)methyl]-sulfanyl}propanoato)potassium], [K(C20H27N2O8S4)](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(NO3)(2) resulted in the formation of crystals of a dipotassium-organic framework, poly[(mu-3,3'-{[(3,6-bis{[(2-carboxyethyl)sulfanyl]methyl}pyrazine-2,5-diyl) bis(methylene)]bis(sulfanediyl)}dipropionato)dipotassium], [K-2(C20H26N2O8S4)](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.

Automated summary

This study reports the synthesis and structural characterization of two polymorphs of the tetrakis-substituted pyrazine carboxylic acid, investigating the differences in crystal structures, molecular conformations, and interactions within the crystals.