ic801555e_si_001.pdf (175.42 kB)

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

Download (175.42 kB)
journal contribution
posted on 15.12.2008, 00:00 by Theocharis C. Stamatatos, Albert Escuer, Khalil A. Abboud, Catherine P. Raptopoulou, Spyros P. Perlepes, George Christou
Syntheses, crystal structures, and magnetochemical characterization are reported for the three new nickel(II) clusters [Ni14(OH)4(N3)8(pao)14(paoH)2(H2O)2](ClO4)2 (1), [Ni12Na2(OH)4(N3)8(pao)12(H2O)10](OH)2 (2), and [Ni5(ppko)5(H2O)7](NO3)5 (3) (paoH = pyridine-2-carbaldehyde oxime, ppkoH = di-2-pyridyl ketone oxime). The reaction of Ni(ClO4)2·6H2O with paoH and NBun4N3 in H2O/MeCN in the presence of NEt3, gave 1 in 65% yield. Complex 2 was obtained in 60% yield from the reaction of NiCl2·6H2O with paoH and NaN3 in H2O/MeCN in the presence of NaOH. The reaction of Ni(NO3)2·6H2O 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 Ni4 rhombus between two Ni5. Complex 1 is the largest metal/oxime cluster discovered to date, as well as the first NiII14 coordination complex and the largest NiII/N3 cluster. Complex 2 has a Ni12Na2 topology that is very similar to that of 1, but with two central NiII atoms of 1 replaced with NaI atoms. The core of 3 consists of four NiII atoms forming a highly distorted tetrahedron, with the fifth NiII atom lying almost on one of the edges. Variable-temperature, solid-state dc susceptibility and magnetization studies were carried out on complexes 13, and these were complemented with ac susceptibility data for 1 and 2. Fitting of the obtained M/(NμB) 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 Ni6 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 Nix clusters with or without the presence of ancillary ligands.