Alkali metal ion mediated self-assembly of vanadium(V) ions and pyrazole based polydentate ligands leading to the formation of helix, double helix and supramolecular cage-like structures

Abstract: The anionic cis-dioxovanadium(V) complex species LVO2 − and L1VO2 − of two tridentate ONO ligands (H2L and H2L1) can bind alkali metal ions in a bis-monodentate fashion like a bridging carboxylate group. Here H2L (N′-[(E)-(2-hydroxyphenyl)methylidene]-3-methyl-1H-pyrazole-5-carbohydrazide) and H2L1 (N′-[(1E)-1-(2-hydroxyphenyl) ethylidene]-3-methyl-1H-pyrazole-5-carbohydrazide) are Schiff base ligands generated by the condensation of 5-methyl 3-pyrazole carbohydrazide with salicylaldehyde and o-hydroxy acetophenone. The six products thus obtained are water soluble polymeric compounds in which the complementary units are held together by the simultaneous use of hydrogen bonding and coulombic interactions. [L1VO2Li(H2O)2]∞ (2), [LVO2Na(H2O)2]∞ (3) and [LVO2K(H2O)2]∞ (5) have been crystallographically characterized. Crystallographic characterization reveals that 2 and 3 are polymeric helicates and 5 is a polymeric cluster with L1VO2 − or LVO2 − units bridging the labile alkali metal ions which occupy positions on the axis of the polymeric chain. [ABSTRACT FROM AUTHOR]