(Ni₂), (Ni₃), and (Ni₂ + Ni₃): A Unique Example of Isolated and Cocrystallized Ni₂ and Ni₃ Complexes

Abstract

Structural and magnetic characterization of compound {[Ni₂(L)₂(OAc)₂][Ni₃(L)₂(OAc)₄]}·2CH₃CN (<b>3</b>) (HL = the tridentate Schiff base ligand, 2-[(3-methylamino-propylimino)-methyl]-phenol) shows that it is a rare example of a crystal incorporating a dinuclear Ni(II) compound, [Ni₂(L)₂(OAc)₂], and a trinuclear one, [Ni₃(L)₂(OAc)₄]. Even more unusual is the fact that both Ni(II) complexes, [Ni₂(L)₂(OAc)₂] (<b>1</b>) and [Ni₃(L)₂(OAc)₄(H₂O)₂]·CH₂Cl₂·2CH₃OH (<b>2</b>), have also been isolated and structurally and magnetically characterized. The structural analysis reveals that the dimeric complexes [Ni₂(L)₂(OAc)₂] in cocrystal <b>3</b> and in compound <b>1</b> are almost identical-in both complexes, the Ni(II) ions possess a distorted octahedral geometry formed by the chelating tridentate ligand (L), a chelating acetate ion, and a bridging phenoxo group with very similar bond angles and distances. On the other hand, compound <b>2</b> and the trinuclear complex in the cocrystal <b>3</b> show a similar linear centrosymmetric structure with the tridentate ligand coordinated to the terminal Ni(II) and linked to the central Ni(II) by phenoxo and carboxylate bridges. The only difference is that a water molecule found in <b>2</b> is not present in the trinuclear unit of complex <b>3</b>; instead, the coordination sphere is completed by an additional bridging oxygen atom from an acetate ligand. Variable-temperature (2−300 K) magnetic susceptibility measurements show that the dinuclear unit is antiferromagnetically coupled in both compounds (2<i>J</i> = −36.18 and −29.5 cm⁻¹ in <b>1</b> and <b>3</b>, respectively), whereas the trinuclear unit shows a very weak ferromagnetic coupling in compound <b>3</b> (2<i>J</i> = 0.23 cm⁻¹) and a weak antiferromagnetic coupling in <b>2</b> (2<i>J</i> = −8.7(2) cm⁻¹) due to the minor changes in the coordination sphere.