Tryptophan moiety ligand based tri/tetranuclear Ni(ii) complexes: syntheses, structure and magnetic properties

Abstract

Tetra/trinuclear Ni(II) complexes, namely [Ni₄(L)₄(H₂O)₄]·5(dmf)·7(H₂O) (1) and [Ni₃(L)₂(bz)₂(dmf)₂(H₂O)₂] (2) [H₂L = N-(2-(hydroxy)-3-methoxybenzylidene)tryptophan); dmf = dimethyl formamide, bz = benzoate anion], have been synthesized and characterized by X-ray single crystal structure determination. The structural characterization discloses a tetranuclear Ni(II) complex for 1, whereas in complex 2 the competition between the coordination ability of the benzoate anion and the bridging mode of the Schiff base leads to a trinuclear species. Two of the chiral ligands in 1, acting as pentadentate, connect all metal centers, while the other two act as tri-chelating towards the side located nickel centers. On the other hand, in complex 2 the two Schiff bases act as tetradentate connecting the nickel centers in pairs in addition to the benzoate anions. Variable-temperature magnetic susceptibility data, collected in the temperature range of 2–300 K under an applied field of 0.1 Tesla, indicate weak antiferromagnetic interactions in both the complexes in agreement with Ni–O–Ni bridging angles larger than 100° measured within the molecular structures.