Benzoate as terminal ligand in the defective double-cubane, tetranuclear cobalt(II) complex [Co4(N3)2(O2CPh)2{(py)2C(OH)O}4]•2DMF with simultaneous μ1,1-azido and μ-O bridges [(py)2C(OH)O = the monoanion of the hydrated, gem-diol form of di-2-pyridyl ketone]

The reaction of Co(O2CPh)(2) with di-2-pyridyl ketone, (py)(2)CO, and NaN3 in DMF allows isolation of the tetranuclear compound [Co-4(N-3)(2)(O2CPh)(2){(py)(2)C(OH)O}(4)].2DMF (2) instead of the expected nonanuclear cage [Co-9(N-3)(2)(O2CPh)(8){(py)(2)CO2}(4)]. The X-ray diffraction analysis reveals a defective double-cubane, tetrameric entity in which the Co-II atoms are linked by eta(1),mu(2)-N-3 azide ligand and two kinds of O-bridges. The molar magnetic susceptibility measurements of 2 in the 2-300 K range indicate bulk ferromagnetic coupling. Some synthetic aspects of the Co-II/(py)(2)CO/N-3(-) reaction system are also discussed. (C) 2002 Elsevier Science Ltd. All rights reserved.