Cyclic [Cu-biRadical]₂ Secondary Building Unit in 2p-3d and 2p-3d-4f Complexes: Crystal Structure and Magnetic Properties

Employing the new nitronyl nitroxide biradical ligand biNIT-3Py-5-Ph (2-(5-phenyl-3-pyridyl)-bis(4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide)), a 16-spin Cu-radical complex, [Cu₈(biNIT-3Py-5-Ph)₄(hfac)₁₆] 1, and three 2p-3d-4f chain complexes, {[Ln(hfac)₃][Cu(hfac)₂]₂(biNIT-3Py-5-Ph)₂}_n (Ln^Ⅲ= Gd 2, Tb 3, Dy 4; hfac = hexafluoroacetylacetonate), have been prepared and characterized. X-ray crystallographic analysis revealed in all derivatives a common cyclic [Cu-biNIT]₂ secondary building unit in which two bi-NIT-3Py-5-Ph biradical ligands and two Cu^II ions are associated via the pyridine N atoms and NO units. For complex 1, two such units assemble with four additional Cu^II ions to form a discrete complex involving 16 S = 1/2 spin centers. For complexes 2-4, the [Cu-biNIT]₂ units are linked by Ln^III ions via NO groups in a 1D coordination polymer. Magnetic studies show that the coordination of the aminoxyl groups with Cu or Ln ions results in behaviors combining ferromagnetic and antiferromagnetic interactions. No slow magnetic relaxation behavior was observed for Tb and Dy derivatives.