Heterometallic Ln-Cu complexes derived from a phenyl pyrimidyl substituted nitronyl nitroxide biradical

Utilizing a novel nitronyl nitroxide biradical bisNITPhPyrim involving a pyrimidine group ([5-(5-pyrimidyl)-1,3-bis(1'-oxyl-3'-oxido-4',4',5',5'-tetramethyl-4,5-hydro-1H-imidazol-2-yl)]benzene), three heterometallic Ln-Cu complexes with formulas [Ln(hfac)₃Cu(hfac)₂(bisNITPhPyrim)] (Ln^III = Gd 1, Tb 2, and Dy 3; hfac = hexafluoroacetylacetonate) have been achieved. In these complexes, the Cu^II ions are linked by N atoms of pyrimidine rings of bisNITPhPyrim radicals to form a one-dimensional chain structure, whereas each Ln^III ion is chelated with two neighboring NO groups of two NIT moieties of the radical. Magnetic studies reveal the presence of ferromagnetic interactions between the Gd^III ion and coordinated NO groups, and between the pyrimidine-bridged copper(ii) spins, which are quantified by a magnetic model, giving J₁ = 4.20 cm^-1 and J₃ = 0.50 cm^-1 (J₁ and J₃ are magnetic exchanges for Gd^III-ON and Cu^II-Cu^II, respectively). Interestingly, ac magnetic measurements show that complex 3 exhibits slow relaxation of the magnetization.