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Synthesis, Structure, and Magnetic Properties of (6−9)-Nuclear Ni(II) Trimethylacetates and Their Heterospin Complexes with Nitroxides

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posted on 10.07.2006, 00:00 by Victor Ovcharenko, Elena Fursova, Galina Romanenko, Igor Eremenko, Evgeny Tretyakov, Vladimir Ikorskii
New polynuclear nickel trimethylacetates [Ni6(OH)4(C5H9O2)8(C5H10O2)4] (6), [Ni7(OH)7(C5H9O2)7(C5H10O2)6(H2O)]·0.5C6H14·0.5H2O (7), [Ni8(OH)4(H2O)2(C5H9O2)12] (8), and [Ni9(OH)6(C5H9O2)12(C5H10O2)4]·C5H10O2·3H2O (9), where C5H9O2 is trimethylacetate and C5H10O2 is trimethylacetic acid, have been found. Their structures were determined by X-ray crystallography. Because of their high solubility in low-polarity organic solvents, compounds 69 reacted with stable organic radicals to form the first heterospin compounds based on polynuclear Ni(II) trimethylacetate and nitronyl nitroxides containing pyrazole (L1−L3), methyl (L4), or imidazole (L5) substituent groups, respectively, in side chain [Ni7(OH)5(C5H9O2)9(C5H10O2)2(L1)2(H2O)]·0.5C6H14·H2O (6+1a), [Ni7(OH)5(C5H9O2)9(C5H10O2)2(L2)2(H2O)]·H2O (6+1b), [Ni7(OH)5(C5H9O2)9(C5H10O2)2(L3)2(H2O)]·H2O (6+1c), [Ni6(OH)3(C5H9O2)9(C5H10O2)4(L4)]·1.5C6H14 (6‘ ‘), and [Ni4(OH)3(C5H9O2)5(C5H10O2)4(L5)]·1.5C7H8 (4). Their structures were also determined by X-ray crystallography. Although Ni(II) trimethylacetates may have varying nuclearity and can change their nuclearity during recrystallization or interactions with nitroxides, this family of compounds is easy to study because of its topological relationship. For any of these complexes, the polynuclear framework may be derived from the [Ni6] polynuclear fragment {Ni64-OH)23-OH)22-C5H9O2−O,O‘)62-C5H9O2−O,O)(μ4-C5H9O2−O,O,O‘,O‘)(C5H10O2)4}, which is shaped like an open book. On the basis of this fragment, the structure of 7-nuclear compounds (7 and 6+1ac) is conveniently represented as the result of symmetric addition of other mononuclear fragments to the four Ni(II) ions lying at the vertexes of the [Ni6] open book. The 9-nuclear complex is formed by the addition of trinuclear fragments to two Ni(II) ions lying on one of the lateral edges of the [Ni6] open book. This wing of the 9-nuclear complex preserves its structure in another type of 6-nuclear complex (6‘ ‘) with the boat configuration. If, however, two edge-sharing Ni(II) ions are removed from [Ni6] (one of these lies at a vertex of the open book and the other, on the book-cover line), we obtain a 4-nuclear fragment recorded in the molecular structure of 4. Twinning of this 4-nuclear fragment forms highly symmetric molecule 8, which is a new chemical version of cubane.

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