A strongly fluorescent NiII complex with 2-(2-hydroxyethyl)pyridine ligands: synthesis, characterization and theoretical analysis and comparison with a related polymeric CuII complex

Abstract

The synthesis and characterization of diaquabis[2-(2-hydroxyethyl)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-hydroxyethyl)pyridine-κ2N,O]copper(II)]-μ-sulfato-κ2O:O′], [Cu(C7H9NO)2(SO4)]n [Zeghouan et al. (2016). Private communication (refcode 1481676). CCDC, Cambridge, England]. In the two complexes, the 2-(2-hydroxyethyl)pyridine ligands coordinate the metal ions through the N atom of the pyridine ring and the O atom of the hydroxy group, creating a chelate ring. The NiII or CuII ion lies on an inversion centre and exhibits a slightly distorted MO4N2 octahedral coordination geometry, build up by O and N atoms from two 2-(2-hydroxyethyl)pyridine ligands and two water molecules or two O atoms belonging to sulfate anions. The sulfate anion bridges the CuII 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.

Keywords

• transition metal
• fluorescence
• blue-light emission
• TDDFT
• crystal structure