Structure and Magnetic Properties of Mixed-Ligand Complexes of 3d Metal Hexafluoroacetylacetonates with 3,5- and 3,6-Di-Tert-Butyl-O-Benzoquinones

Abstract

The reaction of metal hexafluoroacetylacetonates M(hfac)2, where M = Fe, Mn, and Co, with 3,6-di-tert-butyl-o-benzoquinone (3,6-Q) in the inert atmosphere of a dry box is found to yield mixed-ligand complexes [M(hfac)2(3,6-Q)]. When the synthesis is performed under ambient conditions or the [M(hfac)2(3,6-Q)] mother liquor is kept in air in the case of Mn(II) and Co(II), crystals of [M(hfac)2(H2O)2](3,6-Q) aqua complexes precipitate into the solid phase, in which cis-coordinated H2O molecules are hydrogen bonded to o-quinone O atoms. Single crystal X-ray diffraction data for compounds, which correlate with the results of quantum chemical calculations, show that solid [M(hfac)2(3,6-Q)] and [M(hfac)2(H2O)2](3,6-Q), where M = Co(II) and Mn(II), contain initial o-quinone molecules. In the interaction of Fe(hfac)2 with 3,6-Q, there is an intramolecular redox process during which Fe(II) is oxidized to Fe(III) and o-quinone is reduced to the respective semiquinonate radical anion, which leads to the formation of [FeIII(hfac)2(3,6-SQ)]. According to the data of magnetic measurements, a strong antiferromagnetic exchange between high-spin Fe(III) unpaired electrons and SQ provide an almost complete compensation of spin of one of the unpaired electrons of the metal ion by SQ spin. For Co a complex with 3,5-di-tert-butyl-o-benzoquinone [Co(hfac)2(3,5-Q)] is also synthesized and its structure and magnetic properties are studied. The latter prove to be similar to those of [Co(hfac)2(3,6-Q)].