High-spin Ni(II) clusters: triangles and planar tetranuclear complexes

The exploration of the NiX2/py(2)CO/Et3N ( X= F, Cl, Br, I; py(2)CO = di-2-pyridyl ketone; Et3N = triethylamine) reaction system led to the tetranuclear [Ni4Cl2{py(2)C(OH)O}(2){py(2)C(OMe)O}(2)(MeOH)(2)]Cl-2 center dot 2Et(2)O (1 center dot 2Et(2)O) and [Ni4Br2{py(2)C(OH)O}(2){py(2)C(OMe)O}(2)(MeOH)(2)]Br-2 center dot 2Et(2)O (2 center dot 2Et(2)O) and the trinuclear [Ni-3{py(2)C(OMe)O}(4)]I-2 center dot 2.5MeOH (3 center dot 2.6MeOH), [Ni-3{py(2)C(OMe)O}(4)](NO3)(0.65)I-1.35 center dot 2MeOH (4 center dot 2MeOH) and [Ni-3{py(2)C(OMe)O}(4)](SiF6)(0.8)F-0.4 center dot 3.5MeOH (5 center dot 3.5MeOH) aggregates. The presence of the intermediate size Cl- and Br- anions resulted in planar tetranuclear complexes with a dense hexagonal packing of cations and donor atoms (tetramolybdate topology) where the X-anions participate in the core acting as bridging ligands. The F- and I- anions do not favour the above arrangement resulting in triangular complexes with an isosceles topology. The magnetic properties of 1-3 have been studied by variable-temperature dc, variable-temperature and variable-field ac magnetic susceptibility techniques and magnetization measurements. All complexes are high-spin with ground states S = 4 for 1 and 2 and S = 3 for 3.