In search of molecules displaying ferromagnetic exchange: multiple-decker ni12and ni16complexes from the use of pyridine-2-amidoxime

The use of pyridine-2-amidoxime (pyaoxH(2)) in Ni chemistry has provided access to a dodecanuclear complex and a hexadecanuclear Ni cluster, namely [Ni-12(pyaox)(6)(pyaoxH)(6)(MeOH)(2)Cl-2] Cl-4 center dot 5MeOH (1.5MeOH) and [Ni-16(pyaox)(8)(pyaoxH)(8)(MeOH)(4)](SO4)(4)center dot 10H(2)O center dot 26MeOH (2.10H(2)O center dot 26MeOH). Complex 1.5MeOH was isolated by the reaction of NiCl2 center dot 6H(2)O, pyaoxH(2) and NaOMe in a 1:1:2 molar ratio in MeOH in 60% yield. Treatment of NiSO4 center dot 6H(2)O with pyaoxH(2) and NEt3 in a 1:1:2 molar ratio in MeOH afforded 2.10H(2)O center dot 26MeOH in good yield (65%). The two compounds display a multi-decker configuration based on stacked Ni-4 layers, {Ni-4(pyaox)(2)(pyaoxH)(2)}(x)(2+) (x = 3, 1.5MeOH; x = 4, 2.10H(2)O center dot 26MeOH); each deck consists of two square planar and two octahedral Ni-II centres. The number of decks observed in 1.5MeOH and 2.10H(2)O center dot 26MeOH depends on the nature of the inorganic anion that is present in the reaction system, which provides elements of synthetic control towards new high nuclearity Ni-II species. 2.10H(2)O center dot 26MeOH is the first structurally characterized complex of any metal displaying a quadruple-decker configuration, being also the highest nuclearity metal cluster bearing pyaoxH(2) and the highest nuclearity Ni-II cluster with any type of 2-pyridyl oxime. Each cluster cation displays ferromagnetic exchange between the octahedral Ni-II ions resulting in a spin ground state of S = 6 for 1 and S = 8 for 2. Magnetothermal studies have been performed and discussed for both clusters