Ferro- and Ferrimagnetic Chains of hin-Bridged Copper(II) and Manganese(II) and hnn-Bridged Manganese(II) Complexes (hin = 4,4,5,5-Tetramethylimidazolin-1-oxyl; hnn = 4,4,5,5-Tetramethylimidazolin-1-oxyl 3-Oxide)

We have exploited potential utility of 4,4,5,5-tetramethylimidazolin-1-oxyl (hin) and 4,4,5,5-tetramethylimidazolin-1-oxyl 3-oxide (hnn) as μ-1,4 and μ-1,5 bridging ligands, respectively, carrying an unpaired electron in development of metal−radical hybrid magnets. X-ray diffraction measurements of [Cu(hfac)2hin] (1), [Mn(hfac)2hin] (2), and
[Mn(hfac)2hnn] (3) revealed one-dimensional metal−radical alternating chain structures, where hfac denotes 1,1,1,5,5,5-hexafluoropentane-2,4-dionate. Magnetic measurements of 1 indicate the presence of intrachain ferromagnetic
coupling between copper and radical spins. The magnetic exchange parameter was estimated as 2J/k = 56.8 K
based on an S = 1/2 equally spaced ferromagnetic chain model (H = −2J∑Si·Si+1). This ferromagnetic interaction
can be explained in terms of the axial coordination of the hin nitrogen or oxygen to CuII. The χmT value of 2 and
3 increased on cooling, and the magnetic data could be analyzed by Seiden's ferrimagnetic chain model, giving
2J/k = −325 and −740 K, respectively. The antiferromagnetic interaction of 2 and 3 can be attributed to orbital
overlap between the manganese and the oxygen or nitrogen magnetic orbitals. The exchange interactions between
Cu−hin and Mn−hnn are larger than those of typical Cu− and Mn−nitronyl nitroxide complexes, indicating that the
choice of small ligands is a promising strategy to bestow strong exchange interaction. Compound 3 became a
ferrimagnet below 4.4 K, owing to ferromagnetic coupling among the ferrimagnetic chains.