The use of di-2-pyridyl ketone oxime [(py)2CNOH] in reactions with Ni(O2CMe)2.4H2O, in the presence or absence of extra inorganic anions (N3- and SCN-) has led to Ni4, Ni5, and Ni7 clusters; the magnetic study of the heptanuclear nickel(II) complex reveals an S = 3 ground state.

The preparation and properties are described of two related NiII 5 clusters. The reactions of [Ni(acac)2(H2O)2] (acacH = acetylacetone) with benzotriazole (btaH) and 5,6-dimethylbenzotriazole (5,6diMebtaH) in refluxing Me2CO in the presence of H2O leads to the isolation of [Ni5(OH)(bta)5(acac)4(H2O)4] (1) and [Ni5(OH)(5,6diMebta)5(acac)4(H2O)4] (2) in 70−75 and 40−50% yields, respectively. Complex 1·4Me2CO·0.5C6H14 crystallizes in the triclinic space group P1̄ with (at 25 °C) a = 13.885(1) Å, b = 12.013(1) Å, c = 25.611(2) Å, α = 89.02(1)°, β = 104.76(2)°, γ = 111.78(1)°, and Z = 2. Complex 2·4Me2CO crystallizes in the monoclinic space group C2/c with (at 25 °C) a = 19.085(3) Å, b = 20.142(3) Å, c = 22.574(4) Å, β = 103.30(1)°, and Z = 4. The NiII assemblies of 1 and 2 are composed of a tetrahedral arrangement of four six-coordinate metal ions centered on the fifth. Each of the five η1:η1:η1:μ3 benzotriazolate ligands spans an edge of the Ni4 tetrahedron. The OH- ion bridges three NiII ions and spans the sixth edge of the tetrahedron. A chelating acac- ion and a terminal H2O molecule complete the coordination sphere of each peripheral metal. Variable-temperature magnetic susceptibility data (5.0−295 K), obtained for 1 and 2, show antiferromagnetic interactions for both of them. The data are interpreted using a five-J model, which is based upon the hierarchy of algebras approach. Least-squares fitting of the data gives exchange parameters J for the interactions between the benzotriazolate-bridged peripheral NiII ions in the range from −3.9 to −10.7 cm-1, and for those between the central ion and the peripheral ones in the range from −3.1 to −6.1 cm-1; the J value for the interaction between the O-bridged peripheral nickels is −39.6 cm-1 for 1 and −43.2 cm-1 for 2. Magnetization data are in line with an intermediate spin ground state [S = 0, S = 1] for both clusters. An orbital interpretation of the coupling is proposed.