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) center dot 4H(2)O (1) and [Mn(hfac)(2)(4-NITPhPyrim)](2) center dot 4H(2)O (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 (J(1) = 24.20 cm(-1)) and the weak FM exchange of Cu-NIT through the pyrimidine and phenyl rings (J(2) = 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 (theta = 0.39 K) in 2. (c) 2007 Elsevier B.V. All rights reserved.