Pampa Mukherjee

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

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.

Coordination-driven self-assembly of a novel carbonato-bridged heteromolecular neutral nickel(II) triangle by atmospheric CO2 fixation.

Formation of a quasi-symmetrical mu 3-carbonato-bridged self-assembled heteromolecular triangle of Ni(II), [(mu 3-CO 3){Ni 2(salmeNH) 2(NCS) 2}{Ni(salmeNH 2) 2].Et 2O.H 2O (HsalmeNH = 2-[(3-methylamino-propylimino)-methyl]-phenol) involves atmospheric CO 2 uptake in a neutral medium, by spontaneous self-reorganization of the starting mononuclear Ni(II)-Schiff-base complex, [Ni(salmeNH) 2]. The environment around Ni(II) in two of the subunits is different from the third one. The starting complex, [Ni(salmeNH) 2], and one of the possible intermediate species, [Ni(salmeNH 2) 2(NCS) 2], which has a very similar coordination environment to that in the third Ni(II) center, have been characterized structurally. A plausible mechanism for the formation of such a triangle has also been proposed. The compound shows a very strong antiferromagnetic coupling. Fit as a regular triangular arrangement gave J = -53.1, g = 2.24, and R = 1.5 x 10 (-4).