Configurational alterations and Cu(II)/Ni(II) coordination polymers for an asymmetrical pyrazolone/pyridone dye

Abstract In this work, an asymmetrical pyrazolone/pyridone bi-heterocyclic dye was synthesized showing good solubility in both water and organic solvents. This dye has three possible azo/hydrazone tautomers because multiple N and O heteroatoms in its molecular structure could serve as the protonated sites for two active protons. NMR techniques have been used to deduce its specific configurations in different solvents, and the results reveal that it adopts the monohydrazone form in pyridone with 5-OH-pyrazolone in MeOH and double-azo form in water. The following solvatochromic and acid-base titration experiments verify the transfer of proton sites within the multiple heteratoms for the dye and the configurational alterations in non-aqueous and aqueous solvents. Furthermore, two one-dimensional copper(II) and nickel(II) coordination polymers have been obtained and structurally characterized, in which this asymmetrical pyrazolone/pyridone dye adopts the same depronated double-azo form. However, the two dye-metal complexes show distinguishable supramolecular architectures (layer/stair) due to the different 3d9/3d8 electronic structures for Cu(II)/Ni(II) cations and hence different spacial requirements for the coordination spheres (five-coordinate pyramid/six-coordinate octahedron).