ISSN:
1573-9171
Keywords:
ferromagnetic and antiferromagnetic exchange interactions
;
free-radical o-semiquinone ligands
;
square-planar coordination
;
d 8- andd 9-transition-metal complexes
;
x-ray structural and EPR studies
;
vacant and occupied atomic and molecular orbitals
Source:
Springer Online Journal Archives 1860-2000
Topics:
Chemistry and Pharmacology
Notes:
Abstract The title complexes of Ni and Cu with symmetrical 3,6-di-tert-butyl-o-benzosemiquinone are synthesized. Their EPR spectra and magnetic properties are investigated. The x-ray structure studies [Siemens R3/PC diffractometer, λ MoKα, ϑ/20-scanning in the rang 2 ≤ 2ϑ ≤ 54°, 2084 reflections withF 〉 4σ(F),R = 0.034,R w = 0.039, monoclinic crystals,a = 9.982(2),b = 11.548(2),c = 12.145(2) Å, β = 95.05(3)°,Z = 2,d calc = 1.19 g/cm−3, space groupP2 l/c) demonstrated that the complex is monomeric with square-planar coordination for the Ni with theo-semiquinone ligands. The Cu complex is isostructural with the Ni (a = 9.88,b = 11.60,c = 12.15 Å, β = 95°]. The dependence of the magnetic moment of the Cu complex on temperature is consistent with the presence in it of two pathways for exchange interaction. These are antiferromagnetic ligand-ligandJ 12 = −179 cm−1 and ferromagnetic metal-ligandJ 13 = 100 cm−1 (mean-square deviation 2%). The Ni complex is diamagnetic over the whole studied temperature range despite the fact that it contains free-radicalo-semiquinone ligands. Such an effect involving electrons belonging to the free-radical ligands is observed for the first time in the magnetochemistry ofd 8- andd 9-transition-metal complexes. It is explained by incorporation of vacantp z- and/or occupiedd xz- andd yz-orbitals of Ni in molecular orbitals containing the π-MO of the semiquinone ligands.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00863815
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