Unusual Structural Types in Nickel Cluster Chemistry from the Use of Pyridyl Oximes: Ni5, Ni12Na2, and Ni14 Clusters

Syntheses, crystal structures, and magnetochemical characterization are reported for the three new nickel(II) clusters [Ni-14(OH)(4)(N-3)(8)(pao)(14)(paoH)(2)(H2O)(2)](ClO4)(2) (1), [Ni12Na2(OH)(4)(N-3)(8)(pao)(12)(H2O)(10)](OH)(2) (2), and [Ni-5(ppko)(5)(H2O)(7)]-(NO3)(5) (3) (paoH = pyridine-2-carbaldehyde oxime, ppkoH = di-2-pyridyl ketone oxime). The reaction of Ni(ClO4)(2)center dot 6H(2)O with paoH and (NBu4N3)-N-n in H2O/MeCN in the presence of NEt3, gave 1 in 65% yield. Complex 2 was obtained in 60% yield from the reaction of NiCl2 center dot 6H(2)O with paoH and NaN3 in H2O/MeCN in the presence of NaOH. The reaction of Ni(NO3)(2)center dot 6H(2)O with ppkoH in EtOH in the presence of LiOH afforded complex 3 in 75% yield. The complexes all contain novel core topologies. The core of 1 comprises a central Ni-4 rhombus between two Ni-5. Complex 1 is the largest metal/oxime cluster discovered to date, as well as the first Ni-14(II) coordination complex and the largest Ni-II/N-3(-) cluster, Complex 2 has a Ni12Na2 topology that is very similar to that of 1, but with two central Ni-II atoms of 1 replaced with Na-I atoms, The core of 3 consists of four Ni-II atoms forming a highly distorted tetrahedron, with the fifth Ni-II atom lying almost on one of the edges. Variable-temperature, solid-state dc susceptibility and magnetization studies were carried out on complexes 1-3, and these were complemented with ac susceptibility data for 1 and 2. Fitting of the obtained M/(N mu(B)) vs H/T data by matrix diagonalization and including axial zero-field splitting (D) gave ground-state spin (S) and D values of S = 6, D = -0.12(3) cm(-1) for 1 and S = 3, D = -0.20(5) cm(-1) for each of the two essentially noninteracting S = 3 Ni-6 subunits of 2. The data for 3 indicate antiferromagnetic exchange interactions and an S = 1 ground state. A simple 2-J model was found to be adequate to describe the variable-temperature dc susceptibility data. The combined work demonstrates the ligating flexibility of pao(-) and ppko(-), and their usefulness in the synthesis of polynuclear Ni, clusters with or without the presence of ancillary ligands.