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

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posted on 2009-06-01, 00:00 authored by Pampa Mukherjee, Michael G. B. Drew, Carlos J. Gómez-García, Ashutosh Ghosh
Structural and magnetic characterization of compound {[Ni2(L)2(OAc)2][Ni3(L)2(OAc)4]}·2CH3CN (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, [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] (1) and [Ni3(L)2(OAc)4(H2O)2]·CH2Cl2·2CH3OH (2), have also been isolated and structurally and magnetically characterized. The structural analysis reveals that the dimeric complexes [Ni2(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.

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