Syntheses, crystal structures, and magnetic properties of two cyclic dimer M2L2 complexes constructed from a new nitronyl nitroxide ligand and M(hfac)2 (M = Cu2+, Mn2+)

Two new binuclear radical complexes derived from a new long nitronyl nitroxide ligand, 2-[4-(5-pyrimidyl)phenyl]-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (4-NITPhPyrim), and M(hfac)2 (M2+ = Cu2+, Mn2+; hfac− = hexafluoroacetylacetonato), [Cu(hfac)2(4-NITPhPyrim)]2 · 4H2O (1) and [Mn(hfac)2(4-NITPhPyrim)]2 · 4H2O (2), were synthesized as well as characterized structurally and magnetically. X-ray analysis indicates that 1 and 2 are rectangle-like centrosymmetric dimer M2L2 complexes. Magnetic measurements indicate that there are two types of magnetic exchanges in 1: the ferromagnetic (FM) exchange between the Cu(II) ion and the directly bonded nitroxide unit (J1 = 24.20 cm−1) and the weak FM exchange of Cu–NIT through the pyrimidine and phenyl rings (J2 = 0.62 cm−1). Besides the strong antiferromagnetic (AFM) coupling between the Mn(II) ion and the directly bonded nitroxide unit (J = −87.61 cm−1), there is a weak FM interaction between the two Mn–NIT pairs (θ = 0.39 K) in 2.