A FLATTENED OCTAHEDRON – THE METAL ENVIRONMENT IN COMPLEXES WITH PYRROLYL-SUBSTITUTED NITROXIDE DIRADICALS

• Published in: Journal of structural chemistry 2022-03, Vol.63 (3), p.441-450
• Main Authors: Romanenko, G. V., Fokin, S. V., Bogomyakov, A. S., Zueva, E. M., Ovcharenko, V. I.
• Format: Article
• Language: English
• Subjects: Antiferromagnetism; Atomic; Atomic/Molecular Structure and Spectra; Chemistry; Chemistry and Materials Science; Coordination compounds; Copper; Ferromagnetism; Imidazole; Inorganic Chemistry; Ligands; Magnetic moments; Metal ions; Molecular; Nickel; Optical and Plasma Physics; Physical Chemistry; Solid State Physics; Temperature dependence
• ISSN: 0022-4766; 1573-8779
• DOI: 10.1134/S0022476622030106

The structures of Ni(II), Cu(II), and Zn(II) complexes with anions of 2,5-pyrrolyl-disubstituted nitronyl nitroxide (L 1 ) and iminonitroxide (L 2 ) diradicals (HL 1 is 2,2′-(1 H -pyrrole-2,5diyl)-bis(4,4,5,5-tetramethyl-4,5-dihydro-1 H -imidazole-3-oxide-1-oxyl; HL 2 is 2,2′-(1 H -pyrrole-2,5-diyl)-bis(4,4,5,5-tetramethyl-4,5-dihydro-1 H -imidazole-1-oxyl) are studied. It is established that in all synthesized compounds, a tridentate meridional coordination of paramagnetic ligands is responsible for a distorted octahedral environment of the metal ion. In bis-chelates, the metal ion environment is an octahedron compressed along the N Pyr – M – M Pyr axis. When one of the ligands in the molecule is replaced by a reduced L 2H monoradical, a typical Cu(II) environment in the form of elongated octahedron arises in [CuL 2 L 2H ]. It is found that in complexes with bis-nitronyl nitroxide, the character of the temperature dependence of the effective magnetic moment μ eff ( T ) is determined by antiferromagnetic exchange in coordinated diradicals. In complexes with iminonitroxides, ferromagnetic exchange interactions between unpaired electrons of the metal ion and diradicals dominate.