New types of heterospin complexes from trans-oxamido-bridged copper(II) binuclear units and nitronyl nitroxide radicals: crystal structure and magnetic characterization.
Three new heterospin complexes derived from trans-oxamido-bridged copper(II) binuclear units [Cu(2)(oxen), oxen = N,N-bis(2-aminoethyl)oxamide] and pyridine-substituted nitronyl nitroxides (o-, m-, and p-PYNN) were synthesized and characterized structurally and magnetically. Complexes 1 and 2 are four-spin complexes. Interestingly, it is found that in complex 3, the Cu(II) ions and m-PYNN units are arranged to form 1D double-stranded helical chains, which to the best of our knowledge is the first example of a metal nitronyl nitroxide complex with such a 1D helical structure. The temperature dependencies of the magnetic susceptibilities of 1 and 2 were fitted to the four-spin model with the Hamiltonian H = -2Js(Cu1)s(Cu2) - 2j(s(Cu1)s(rad1) - s(Cu2)s(rad2)), leading to J = -150.5 cm(-)(1) and j = 47.2 cm(-)(1) for complex 1 and J = -191.7 cm(-)(1) and j = -18.9 cm(-)(1) for complex 2. The temperature dependence of the magnetic susceptibility of complex 3 was approximately simulated with a simple model composed of a dimer of Cu(II) ions and two m-PYNN molecules. The best fitting leads to the values of J = -183.0 cm(-)(1) and zJ' = -0.55 cm(-)(1) for the magnetic exchange of two Cu(II) ions through the oxamide bridge and that between the dimer of Cu(II) ions and two m-PYNN molecules, respectively. The antiferromagnetic exchange of oxamido-bridged Cu(II) ions in complexes 1-3 is strong. The strength of such antiferromagnetic interactions is also similar for the three complexes.
Organic Solids Laboratory, Center for Molecular Sciences, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100080, PRC.
Zhiliang
Z
Liu
Zhengliang
Z
Lü
Deqing
D
Zhang
Zonghui
Z
Jiang
Licun
L
Li
Caiming
C
Liu
Daoben
D
Zhu