| 19552389 |
Biswas B, Pieper U, Weyhermuller T, Chaudhuri P: Polynuclear Nickel (II) Complexes: A Magnetostructural Study of Ni (II)(4), Ni (II)(6), and Ni (II)(9) Species with Oxime Ligands. Inorg Chem. 2009 Jun 24.
Syntheses, crystal structures, and magnetic properties are reported for a tetrametallic (complex 1), a nonametallic (complex 2), and two hexametallic (complexes 3 and 4) nickel (II) clusters, namely, [Ni (4)(HL (1))(2)(mu-OAc)(2)(MeOH)] (1), [Ni (9)(L (2))(10)(mu (3)-OH) (2) (mu-OH) (2) (mu-OH (2))(2)(OH (2))(6)](ClO (4)) (4) (2), [Ni (6)(L (2))(9)(L (2) H)(MeOH)(H (2) O)(2)](ClO (4))(3) (3), and [Ni (6)(L (3))(3)(mu (3)-O)(2)](ClO (4))(2) (4), where H (4) L (1) represents N,N'-dimethyl-N,N'-ethylene-bis (5-bromo-3-formyloxime-2-hydroxybenzylamine ); HL (2), 1-methylimidazole-2-aldoxime; and H (2) L (3), N,N'-bis (2,3-butanedionemonoxime-2-ene)-3 (aminomethyl) benzylamine. The structure of 1 can be considered as two face-sharing bioctahedral units of [Ni (2)(mu-O (phen))(2)(mu-OAc)] bridged by a two-atom (-N-O-) oximate linker. The Ni (II)...Ni (II) distances of av. 2.935 A preclude metal-metal bonding, although they are remarkably short. Variable-temperature magnetic susceptibility data are fitted to obtain the parameters J (1) = +8.0 cm (-1), J (2) = -16.0 cm (-1), and g = 2.19 (H= -2 JS (i).S (j)). The ferromagnetic coupling J (1) operates between the nickel (II) centers in the face-sharing bioctahedral units, whereas J (2) represents the antiferromagnetic interactions mediated by a single (-N-O-) bridge separating the two nickel centers at a distance of approximately 4.71 A. A rationale for the disparate nature of interactions based on a comparison with those reported in the literature is forwarded. The structure of 2 consists of two [Ni (4)(L (2))(5)] units linked covalently to a central nickel atom by four oximate and two hydroxy oxygen atoms, resulting in a central octahedral NiO (6) core and thus yielding the nonanuclear nickel (II) cluster. The magnetic data were analyzed by a "two-J" model, yielding pairwise antiferromagnetic exchange interactions, J (1) = -24.0 cm (-1) and J (2) = -5.8 cm (-1), between the nickel centers. The spin ground state of S (t) = 1.0 has been confirmed by magnetization measurements (variable-temperature, variable-field) at different fields. The structure of 3 contains six nickel (II) centers, each of which is six-coordinated but with different coordination environments: NiN (6), NiO (6), NiN (3) O (3)(2x), NiN (4) O (2), and NiNO (5). The ground-state spin has been observed to be S (t) = 1.0 with the axial zero-field splitting parameter D = -7.2 cm (-1). Complex 4 is a rare example of dimeric [Ni (3)(mu (3)-O)](4+) units, in which each of six nickel (II) centers is in square-planar geometry with low-spin d (8) Ni (II) centers, thus rendering diamagnetism to complex 4. |
31(0,1,1,1) |