A strongly fluorescent Ni^II complex with 2-(2-hy-droxy-eth-yl)pyridine ligands: synthesis, characterization and theoretical analysis and comparison with a related polymeric Cu^II complex

The synthesis and characterization of di-aqua-bis-[2-(2-hy-droxy-eth-yl)pyridine-κ²N,O)nickel(II) dinitrate, [Ni(C₇H₉NO)₂(H₂O)₂](NO₃)₂, under ambient conditions is reported and compared with catena-poly[[bis-[2-(2-hy-droxy-eth-yl)pyridine-κ²N,O]copper(II)]-μ-sulfato-κ²O:O'], [Cu(C₇H₉NO)₂(SO₄)] _n [Zegh-ouan et al. (2016 ▸). Private communication (refcode 1481676). CCDC, Cambridge, England]. In the two complexes, the 2-(2-hy-droxy-eth-yl)pyridine ligands coordinate the metal ions through the N atom of the pyridine ring and the O atom of the hy-droxy group, creating a chelate ring. The Ni^II or Cu^II ion lies on an inversion centre and exhibits a slightly distorted MO₄N₂ octa-hedral coordination geometry, build up by O and N atoms from two 2-(2-hy-droxy-eth-yl)pyridine ligands and two water mol-ecules or two O atoms belonging to sulfate anions. The sulfate anion bridges the Cu^II ions, forming a polymeric chain. The photoluminescence properties of these complexes have been studied on as-synthesized samples and reveal that both compounds display a strong blue-light emission with maxima around 497 nm. From DFT/TDDFT studies, the blue emission appears to be derived from the ligand-to-metal charge-transfer (LMCT) excited state. In addition, the IR spectroscopic properties and thermogravimetric behaviours of both complexes have been investigated.