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Structural and magnetic transformations of a tetranuclear cubane-like Ni4O4 complexes

The metal complexes possesing physical properties that can be modulated on the molecular level are very important from a fundamental or an applied point of view. Magnetism is property which depends on both the organic linkers and metallic centres but also on sorption/desorption processes and moreover on the exchange of solvent. Our investigation on synthesis of the nickel(II) complexes with Schiff base derived from salicylaldehyde and p-aminocresole [(2-hydroxy-5- methylphenyl)amine] accomplished different products depending on reaction conditions (e.g. temperature and pressure). One cubane like tetranuclear nickel(II) complex, [Ni4L4(CH3OH)4] · xCH3OH · (x-y)H2O (1) has been obtained at room temperature, while complexes [Ni4L4(CH3OH)4] · uCH3OH· (u-v)H2O (2) and dinuclear [Ni2L2(H2O)]2 (3) have been prepared by solvothermal method. Complexes 1 and 2 have been converted to [Ni4L4] (4) by heating at 180 °C. Methanol molecules in 1 and 2 exist as solvent of crystallization and coordinated ligands and can be reversibly released and reabsorbed. These processes are accompanied by a change of magnetic properties. To our best knowledge this is the first report on cubane like Ni4O4 complexes coordinated by N-(p-cresole)-2- hydroxy-1-benzaldimine and also the first report on reversibility of magnetic properties modulated by solvatation/desolvatation in this type of compounds. Investigated systems are also rare and nice example how small variation of reaction conditions can lead to variety of products with different properties as a consequence of negligible structural changes. All products were characterized by elemental analysis, IR, TG and DSC data, single-crystal and powder X-ray diffraction methods. Magnetic properties of all complexes were determined by measurements on a SQUID magnetometer.

tetranuclear cubane-like Ni4O4 complexes ; synthesis ; X-ray structural analysis

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