Heteronuclear Ni()-Ln() (Ln = La, Pr, Tb, Dy) complexes: synthesis and single-molecule magnet behaviour

The reaction of hydrated nickel( ii ) salts (chloride or nitrate) and hydrated lanthanide nitrate salts with the Schiff base ligand 2-methoxy-6-[( E )-phenyliminomethyl] phenol (HL) in methanol resulted in the isolation of three isostructural linear heterometallic trinuclear complexes and a heterometallic tetranuclear complex. The molecular structures of these complexes were determined via single crystal X-ray diffraction revealing molecular structures of formulae [Ni 2 La(L − ) 6 ](NO 3 ) 0.55 (OH) 0.45 ( 1 ), [Ni 2 Pr(L − ) 6 ](NO 3 ) 0.48 (OH) 0.52 ( 2 ), [Ni 2 Tb(L − ) 6 ](NO 3 ) 0.5 (Cl) 0.5 ( 3 ) and [Ni 2 Dy 2 (L − ) 2 ( o -vanillin) 2 (CO 3 ) 2 (NO 3 ) 2 (MeOH) 2 ] ( 4 ). Structural analysis for 1-3 reveals that the lanthanide ion is sandwiched between two Ni( ii ) ions and the Ni Ln Ni metallic core displays a linear arrangement, with an average ∠Ni Ln Ni bond angle of 179.7°. Analysis of 4 reveals the metal ions are arranged such that two Ni-Dy subunits are bridged by two carbonate ligands via the Dy sites. Direct current magnetic susceptibility measurements for complexes 1-4 reveal that the Ni( ii ) ions are coupled ferromagnetically with the Tb( iii ) ( 3 ) and Dy( iii ) ( 4 ) ions, and antiferromagnetically with the Pr( iii ) ion ( 2 ). For complex 1 a long range intramolecular ferromagnetic interaction is witnessed between the Ni( ii ) ions (Ni Ni = 6.873(9) Å) via a closed shell La( iii ) ion. The magnetic data of 1 were fitted using the HDVV Hamiltonian revealing the following parameters; J = +0.46 cm −1 , g = 2.245, D = +4.91 cm −1 . Alternating current magnetic susceptibility measurements performed on complexes 2-4 revealed that 3 and 4 displayed frequency dependent χ ′′ M signals ( H ac = 3.5 Oe and H dc = 0 Oe) which is a characteristic signature of a single-molecule magnet behaviour. The crystal structures are reported for three heterometallic Ni 2 Ln and a Ni 2 Dy 2 complex, using the Schiff base ligand 2-methoxy-6-[( E )-phenyliminomethyl] phenol. Detailed dc and ac magnetic susceptibility studies were reported for all the complexes. The complexes 3 and 4 shows frequency dependent out-of-phase susceptibility signals.