A diacylhydrazoe directed heterometallic Co(II)-K(I) coordination polymer: crystal structure, fluorescence sensing and integrated computational studies

In this work, a flexible diacylhydrazone Schiff base ligand (HL) obtained from 2-hydroxy-3-methoxybenzaldehyde and succinic dihydrazide was designed with multiple coordination donor sites. The free ligand HL also showed selective fluorescence turn-off detection of Co(II) ions, giving a Stern-Volmer quenching constant (K_SV) of 6.27 × 10⁴ M⁻¹ and a detection limit of 0.44 μM. A one-dimensional (1D) heterometallic cobalt-potassium coordination polymer, [[Co₂K₁L₂].OH]_∞, was obtained. The Co(II) centre adopts a distorted octahedral geometry while the potassium ion is eight-coordinated. Its electronic properties, such as frontier molecular orbitals, molecular electrostatic potential, and density of states analyses, have been investigated by DFT calculations. At the same time, noncovalent interaction via reduced density gradient analyses provides direct insight into the weak supramolecular interactions governing the association between the metal ions and ligand. Hirshfeld surface analysis further emphasizes the intermolecular interactions that stabilize the polymeric framework. These results provide useful guidance for the rational design and construction of structurally complex coordination polymers with flexible ligands and heterometallic functional coordination polymers.