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)] (LnIII = Gd 1, Tb 2, and Dy 3; hfac = hexafluoroacetylacetonate) have been achieved. In these complexes, the CuII ions are linked by N atoms of pyrimidine rings of bisNITPhPyrim radicals to form a one-dimensional chain structure, whereas each LnIII 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 GdIII 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 GdIII-ON and CuII-CuII, respectively). Interestingly, ac magnetic measurements show that complex 3 exhibits slow relaxation of the magnetization.