Co(II) Complexes with CF3 Derivatives of Pyrazolyl Substituted Nitronilnitroxyls

Structures of new heterospin cobalt(II) hexafluoroacetylacetonate complexes (Co(hfac)2) with stable nitronylnitroxyl radicals containing 1-methyl-3-trifluoromethyl- (L1), 1-ethyl-3-trifluoromethyl- (L2), or 1-ethyl-5-trifluoromethylpyrazol-4-yl substituents (L3) are considered. It is shown that the interaction of Co(hfac)2 with L1 and L2 yields a new type of heterospin complexes with the [Co(hfac)2(L)2] stoichiometry, where L is coordinated by the oxygen atom of the nitronyl nitroxide fragment. The interaction with L3 yields a dimeric complex [Co(hfac)2(L3)]2 with paramagnetic ligands performing a bidentate-bridging function due to the coordination of imine N atoms of the pyrazole ring and O atoms of the paramagnetic moiety. Magnetic behavior of [Co(hfac)2(L)2] complexes indicates an antiferromagnetic interaction between the cobalt ion and coordinated nitronyl-nitroxide groups.