Reactivity studies of 2,3,5,6‐Tetra(2‐pyridyl) pyrazine (tppz) with first‐row transition metal ions

Reactions of 2,3,5,6‐tetra(2‐pyridyl) pyrazine (tppz) with [ML6][X]2 (L = CH3CN, H2O;X = [BF4]−, [ClO4]−, [NO3]− [BArF]−(BArF ‐ B[3,5‐C6H3(CF3)2]4) lead to the high‐yield formation of mononuclear [M(tppz)2]2+, (M = MnII, FeII, CoII, and NiII) and dinuclear [Ni2(tppz)(CH3CN)6]4+ species. The new compounds were fully characterized by X‐ray crystallographic, spectroscopic, and magnetic susceptibility measurements. Surprisingly, the 2:1 M:tppz reactions did not lead to isolation of the dinuclear species except in the case of Ni(II). It was further noted that even in the case of the Ni reactions, the nuclearity of the product depends on the choice of anions and the reaction conditions. Magnetic measurements of the mononuclear species [Co(tppz)2]2+ revealed thermally induced spin‐crossover behavior from a high‐spin S = 3/2 at higher temperatures to a low‐spin S = 1/2 complex at lower temperatures. The dinuclear compound [Ni2(tppz)(CH3CN)6]4+ exhibits a weak anti‐ferromagnetic interaction through the bridging tppz ligand.