Unusual Structural Types in Nickel Cluster Chemistry from the Use of Pyridyl Oximes: Ni5, Ni12Na2, and Ni14 Clusters
journal contributionposted 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 1−3, 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.