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

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 (H 2 O) 2 ](3,6-Q) aqua complexes precipitate into the solid phase, in which cis -coordinated H 2 O 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 (H 2 O) 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 [Fe III (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)].