Synthesis, structure and magnetic properties of Ni(II)-Co(II) heterodinuclear complexes with ONNO type Schiff bases as ligands

Four new heterodinuclear Ni(II)-Co(II) complexes, NiL center dot CoCl2.(DMF)(2) (I), NiL center dot CoBr2 center dot DMF)(2) (II), NiL'center dot CoCl2 center dot(DMF)(2) (III) and NiLDM center dot CoCl2(DMF)(2) (IV), have been prepared in non-aqueous DMF using the ONNO type Schiff bases N,N'-bis(2-hydroxyphenylidene)-1,3-propanediamine (LH2), N,N'-bis(2-hydroxyphenylidene)-1,4-butanediamine (L'H-2) and N,N'-bis(2-hydroxyphenylidene)-2,2'-dimethy1-1,3-propanediamine (LDMH2), and the inorganic salts NiCl2 and CoCl2. The complexes were characterized by elemental analysis, IR spectroscopy, thermogravimetry and X-ray diffraction. An XRD study revealed that the Ni(II) ion is situated at the center of a distorted octahedral coordination sphere formed by two iminic nitrogen and two phenolic oxygen atoms of the ONNO type Schiff base and two other oxygen atoms belonging to coordinated DMF molecules. On the other hand, the Co(II) ion is situated inside a distorted tetrahedral coordination sphere, members of which being the two halogen atoms and two oxygen atoms, bonded to form a mu-bridge. The magnetic susceptibility of the complexes was studied using a SQUID magnetometer between 2.0 and 300 K at B = 0.1 T, and the magnetization data were taken up to B = 7 T at T = 2.0 and 4.6 K. The exchange interaction between the metal centers is of a ferromagnetic nature (typically J(Co-Ni)/hc = +2 cm(-1)) and at low temperature single-ion zero-field splitting applies (D-Ni/hc = +8 cm(-1), D-Co/hc = +14 cm(-1)). (C) 2013 Elsevier Ltd. All rights reserved.