The crucial role of polyatomic anions in molecular architecture: structural and magnetic versatility of five nickel (II) complexes derived from A N,N,O-donor Schiff base ligand

Five new nickel (II) complexes [Ni₂L₂ (N₃)₂(H₂O) ₂] (1), [Ni₂L₂(NO₃)₂] (2), [Ni₂L₂ (O₂CPh)(CH₃OH) ₂]ClO₄.0.5CH₃OH (3), [Ni₃L₂(O₂CPh)₄] (4) and [Ni₂L₂(NO₂)₂]_n (5) have been synthesized by using a tridentate Schiff base ligand, HL (2-[(3-Methylamino-propylimino)-methyl]-phenol) and the polyatomic monoanions N₃⁻, NO₃⁻, PhCOO⁻ or NO₂⁻. The complexes have been structurally and magnetically characterized. The structural analysis reveals that in all five complexes, the Ni (II) ions possess a distorted octahedral geometry. Complexes 1 and 2 are dinuclear with di-μ-1,1-azido and di-μ₂-phenoxo bridges, respectively. Complex 3 is also a di-μ₂-phenoxo-bridged dinuclear Ni(II) complex but has an additional syn−syn benzoate bridge. Compound 4 possesses a linear trinuclear structure with the tridentate Schiff base ligand coordinated to the terminal nickel atoms which are linked to the central Ni(II) by phenoxo and carboxylate bridges. Complex 5 consists of a dinuclear entity, bridged by di-μ ₂-phenoxo together with a cis-(μ-nitrito-1κO:2μN) nitrite ion. The dinuclear units are linked each other by another bridging trans-(μ-nitrito-1κO:2κN) nitrite to form a Ni(II) chain that shows the presence of unprecedented alternating cis- and trans-N,O bridging mode of the nitrite anion. Variable-temperature magnetic susceptibility measurements of complex 1 indicate the presence of ferromagnetic exchange interactions within the dimer (J = 23.5(3) cm⁻¹) together with antiferromagnetic interdimer interactions (J′ = −0.513(3) cm⁻¹), whereas compounds 2 and 3 show intradimer antiferromagnetic interactions (J = −24.27(6) and −16.48(4) cm⁻¹, respectively). Ferromagnetic coupling (J = 6.14(2) cm⁻¹) is observed in complex 4 for the linear centro-symmetric Ni(II) trimer, whereas complex 5 shows an alternating intra-chain antiferromagnetic coupling (J₁ = −32.1(1) cm⁻¹ and J₂ = −3.2(1) cm⁻¹)