(Ni₂), (Ni₃), and (Ni₂+ Ni₃): A Unique Example of Isolated and Cocrystallized Ni₂and Ni₃Complexes

Abstract

Structural and magnetic characterization of compound {[Ni(2)(L)(2)(OAc)(2)][Ni(3)(L)(2)(OAc)(4)]}.2CH(3)CN (3) (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, [Ni(2)(L)(2)(OAc)(2)], and a trinuclear one, [Ni(3)(L)(2)(OAc)(4)]. Even more unusual is the fact that both Ni(II) complexes, [Ni(2)(L)(2)(OAc)(2)] (1) and [Ni(3)(L)(2)(OAc)(4)(H(2)O)(2)].CH(2)Cl(2).2CH(3)OH (2), have also been isolated and structurally and magnetically characterized. The structural analysis reveals that the dimeric complexes [Ni(2)(L)(2)(OAc)(2)] in cocrystal 3 and in compound 1 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 2 and the trinuclear complex in the cocrystal 3 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 2 is not present in the trinuclear unit of complex 3; 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 (2J = -36.18 and -29.5 cm(-1) in 1 and 3, respectively), whereas the trinuclear unit shows a very weak ferromagnetic coupling in compound 3 (2J = 0.23 cm(-1)) and a weak antiferromagnetic coupling in 2 (2J = -8.7(2) cm(-1)) due to the minor changes in the coordination sphere.

A ferromagnetic linear trinuclear Ni(II)-Schiff base complex supported by phenoxo and cinnamato bridges

“…To our knowledge, formation of trinuclear Ni(II) complex using tridentate Schiff base ligand was unprecedented until recently when we reported the first one with the acetate bridges [14] although similar complexes with reduced Schiff base ligands were known [13]. That complex was ferromagnetic in cocrystalline state but antiferromagnetic in the discrete state.…”

“…From this perspective we have synthesized a new Ni 3 complex using a phenol-based tridentate Schiff base ligand, 2-[(3-methylamino-propylimino)-methyl]-phenol (Hsalme) in its deprotonated form, and the cinnamate ion which acts as a bridging ligand. Here, we present the crystal structure and magnetic behaviour of this complex (see Scheme 1).To our knowledge, formation of trinuclear Ni(II) complex using tridentate Schiff base ligand was unprecedented until recently when we reported the first one with the acetate bridges [14] although similar complexes with reduced Schiff base ligands were known [13]. That complex was ferromagnetic in cocrystalline state but antiferromagnetic in the discrete state.…”

“…That complex was ferromagnetic in cocrystalline state but antiferromagnetic in the discrete state. Here, we utilized the bridging properties of the cinnamate ion for the first time to produce this type of complex which is found to be ferromagnetic in the discrete state unlike its acetate analogue [14].…”

“…That complex was ferromagnetic in cocrystalline state but antiferromagnetic in the discrete state. Here, we utilized the bridging properties of the cinnamate ion for the first time to produce this type of complex which is found to be ferromagnetic in the discrete state unlike its acetate analogue [14].The ligand Hsalme was synthesized by condensation of Nmethyl-1,3-propanediamine with salicylaldehyde in methanol following the literature method [15]. All other chemicals were of reagent grade and used without further purification.…”

“…Only two such compounds are reported with the reduced Schiff base ligands, 2-methyl-2-(2-methyl-benzylamino)-propan-1-ol [13] and N-(2-hydroxybenzyl)propanolamine [20] with acetate as carboxylate bridge and it was proposed that the higher flexibility of the reduced Schiff base is responsible for the formation of the trinuclear complexes. However, only very recently we succeeded to synthesize a linear trinuclear complex with the Schiff base ligand, salme and acetate bridges [14]. For the synthesis of complex 1, we use the cinnamate ion instead of acetate.…”