Complexes of 1,10-phenanthroline-mono-N-oxides with copper(II) and nickel(II) in aqueous solution and solid phase

Lihi, Norbert and May, Nóra Veronika and Udvardy, Antal and Najóczki, Ferenc and Bonczidai-Kelemen, Dóra and Diószegi, Róbert and Vargáné Szalóki, Dóra and Sánta, Szófia O. and Fábián, István (2023) Complexes of 1,10-phenanthroline-mono-N-oxides with copper(II) and nickel(II) in aqueous solution and solid phase. INORGANICA CHIMICA ACTA, 557. No-121715. ISSN 0020-1693

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Abstract

Thorough equilibrium and spectroscopic studies are reported on the complexes formed between copper(II) or nickel(II) and derivatives of phenanthroline-mono-N-oxides (1,10-phenanthroline-1-N-oxide (phenO), 2,9- dimethyl-1,10-phenanthroline-1-N-oxide (DMPO) and 3,4,7,8-tetramethyl-1,10-phenanthroline-1-N-oxide (TMPO)). PhenO exhibits excellent metal binding ability, both copper(II) and nickel(II) form bis complexes in which the ligands coordinate to the metal ions via the (N,O) donor set. In the case of copper(II), a square- pyramidal complex forms, where the phenO-s coordinate at the corners of the square and the remaining site is occupied by the water molecule. The bis complex formed between nickel(II) and phenO possesses square- planar geometry in solution, however, the Ni(II) ion exhibits a distorted octahedral geometry in solid phase. DMPO forms relatively stable complexes with copper(II), but the coordination of this ligand to nickel(II) could not be confirmed. Because of precipitate formation in the entire studied pH range (pH = 2.0 – 11.0), well defined complexes could not be identified in the copper(II) – TMPO system. In contrast, this ligand forms stable water soluble nickel(II) complexes. The noted selectivity of these ligands in complex formation reactions is explained by considering the plasticity of copper(II), the rigid, square-planar geometry of nickel(II) and the enhanced steric repulsion of the methyl substituents of DMPO.

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