Design Of Radical-Metal Complexes With Different Coordination Sites: Structures And Magnetic Properties

In recent years, metal-radical complexes have been attracted much moreattention due to their unusual magnetic properties. A large number of metal-radicalcomplexes had been synthesized using different methods and had been characterizedperfectly. However, up to now, the relationship between the structure of metal-radicalcomplexes and the number of coordination sites in radical ligands are not too clear.Thus, in this paper,38metal-radical complexes were synthesized with differentstructures using ten kinds of nitronyl nitroxide radicals, and characterized structurallyand magnetically. Many methods are also used to evaluate the magnetic interactionsbetween the spin carriers in these complexes.In this paper, three kinds of non-functional radicals were employed to coordinatewith metal-hfac moieties, resulting six mononuclear tri-spin complexes and three onedimensional complexes. Among them, a one dimensional ladder-like complex wasprepared based on biradical and copper-hfac moiety. When four kinds of radicals withone functional coordination site were used,23metal-radical complexes were obtainedwith mostly binuclear four-spin rectangle structure. During these complexes, a onedimensional complex was obtained with signal in χ” measurements when the hfacwas replaced with tfa, suggesting slow magnetic relaxtion in this complex; incomplex25, a small amplitude spin transition behavior (Tc=80K, ΔTc=50K, Δμeff=0.23B.M.) has been observed, only few examples have been reported. However, whenthe radicals with two functional coordination sites were employed to coordinate withmetal ion, four transitional metal-radical complexes were obtained. It is worth notingthat a trinuclear five-spin complex was synthesized using quinoxalinal substitutednitronyl nitroxide radical and copper-hfac moiety.Comparing structures of these38metal-radical complexes, we see that in general,the more functional coordination sites radical ligands has, more complicate structureits complexes has.