Structural and magnetic studies of Schiff base complexes of nickel (II) nitrite: change in crystalline state, ligand rearrangement and a very rare μ-nitrito-1κO:2κN:3κO′ bridging mode

Abstract

Four new nickel (II) complexes, [Ni₂L₂ (NO₂)₂]•CH₂Cl₂•C₂H₅OH, 2H₂O (1), [Ni₂L₂(DMF)₂(μ-NO₂)]ClO₄•DMF (2a), [Ni₂L₂ (DMF)₂ (μ-NO₂)]ClO₄ (2b) and [Ni₃L′₂ (μ-₃-NO₂)₂(CH₂Cl₂)]_n•1.5H₂O (3) where HL = 2-[(3-amino-propylimino)-methyl]-phenol, H₂L′= 2-({3-[(2-hydroxy-benzylidene)-amino]-propylimino}-methyl)-phenol and DMF = N,N-dimethylformamide, have been synthesized starting with the precursor complex [NiL₂]•2H₂O, nickel (II) perchlorate and sodium nitrite and characterized structurally and magnetically. The structural analyses reveal that in all the complexes, Ni^II ions possess a distorted octahedral geometry. Complex 1 is a dinuclear di-μ ₂-phenoxo bridged species in which nitrite ion acts as chelating co-ligand. Complexes 2a and 2b also consist of dinuclear entities, but in these two compounds a cis-(μ-nitrito-1κO:2κN) bridge is present in addition to the di-μ ₂-phenoxo bridge. The molecular structures of 2a and 2b are equivalent; they differ only in that 2a contains an additional solvated DMF molecule. Complex 3 is formed by ligand rearrangement and is a one-dimensional polymer in which double phenoxo as well as μ-nitrito-1κO:2κN bridged trinuclear units are linked through a very rare μ ₃-nitrito-1κO:2κN:3κO′ bridge. Analysis of variable-temperature magnetic susceptibility data indicates that there is a global weak antiferromagnetic interaction between the nickel (II) ions in four complexes, with exchange parameters J of −5.26, −11.45, −10.66 and −5.99 cm⁻¹ for 1, 2a, 2b and 3, respectively.