By simple reactions involving various cobalt(II) carboxylates (acetate and in situ prepared pivalate and 4-hydroxybenzoate salts) and neocuproine (neo), we were able to prepare three different carboxylate complexes with the general formula [Co(neo)(RCOO)2] (R = -CH3 for 1, (CH3)3C- for 2, and 4OH-C4H6- for 3). The [Co(neo)(RCOO)2] molecules in the crystal structures of 1-3 adopt a rather distorted coordination environment, with the largest trigonal distortion observed for 1, whereas 2 and 3 are similarly distorted from ideal octahedral geometry. The combined theoretical and experimental investigations of magnetic properties revealed that the spin Hamiltonian formalism was not a valid approach and the L-S Hamiltonian had to be used to reveal very large magnetic anisotropies for 1-3. The measurements of AC susceptibility showed that all three compounds exhibited slow-relaxation of magnetization in a weak external static magnetic field, and thus can be classified as field-induced single-ion magnets. It is noteworthy that 1 also exhibits a weak AC signal in a zero-external magnetic field.

Central European Institute of Technology Brno University of Technology Purkynova 123 61200 Brno Czech Republic

Department of Inorganic Chemistry Faculty of Science Palacký University 17 Listopadu 12 77146 Olomouc Czech Republic

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