Structural and Multi-functional properties of isoelectronic guanyl hydrazinium picolinic derivatives exhibit centric and non-centric space group

Abstract

The equimolar reaction mixture of isoelectronic picolinic acid N-oxide (PAHNO) and/or 3-hydroxy picolinic acid (3-HPAH) with guanyl hydrazine bicarbonate (AgunH.HCO3) in aqueous medium at room temperature produce 1:1 salt. Irrespective of the molar ratios (1; 1, 1:2 & 2:1) and reaction conditions maintained, invariably gives the same product in the form of polycrystalline nature except 1:1 ratio which yields a single crystal. The isoelectronic salts were characterized by spectroscopic, PXRD, thermal study and single crystal X-ray diffraction techniques. In general, most of the salts were crystallized in a centric space group rather than a non-centric, the prevailing factors are nature of the organic species and reaction conditions like pH, pKa, solvent effects, temperature and molar ratio etc,. Surprisingly, in the present case, the isoelectric salt of [AgunH]+[PANO]- crystalized in centric (P21/n), where in case of [AgunH]+[3-HPA]- crystalized in non-centric (Pca21) space group even though in the same reaction conditions. This may be due to the presence of the 3rd position of hydroxyl group and non-covalent interactions in [AgunH]+[3-HPA]- that facilitate non-centric space group. Both salts are stabilized by the variety of hydrogen bond features leading to intra- and intermolecular N-H⋯O, N-H⋯N, and C-H⋯N hydrogen bonds and π-π stacking interactions along with homo- and hetero ring motifs [two R22 (8), R11 (6), and two R22 (9)]. These interactions render them an appropriate acid-base ion pair for the formation of sturdy hydrogen-bonded supramolecular synthons. Thermal studies on these salts reveal that the thermal degradation occurs via melting followed by complete loss of organic species. The solid-state emission spectra of free acids and its salts were recorded and compared. The materials exhibit a prominent luminescent character towards red shift than the starting compounds. Further, these materials show enhanced secondary antioxidant and antimicrobial activities, this is due to the crucial role of hydrazine species in guanyl hydrazinium cation.