New Reactivity of 4‐Amino‐3,5‐bis(pyridin‐2‐yl)‐1,2,4‐triazole: Synthesis and Structure of a Mononuclear Species, a Dinuclear Species, and a Novel Tetranuclear Nickel(II) Rectangle Box, and Magnetic Properties of the Dinuclear and Tetranuclear Complexes

Reactions of Ni(O 2 CMe) 2 · 4H 2 O or NiCl 2 · 6H 2 O, 4‐amino‐3,5‐bis(pyridin‐2‐yl)‐1,2,4‐triazole (abpt) and NaN 3 or KSCN in different molar ratios heated under reflux or hydrothermal conditions generate a mononuclear species with dimorphous phases, a dinuclear species incorporating an in situ deaminated [bpt‐H] – ligand and a tetranuclear rectangle box incorporating an unprecedented μ:η 1 :η 2 :η 1 coordination mode of the deprotonated [abpt‐H] – ligand. Structural analysis reveals that a pair of [Ni 2 (μ 1,1 ‐N 3 )(μ‐OAc)] motifs in [Ni 4 (abpt) 2 (abpt‐H)(N 3 ) 5 (O 2 CMe) 2 ] · 5H 2 O ( 1 ) are bridged by two abpt and one [abpt‐H] – units into a rectangle box. [Ni 2 (bpt‐H) 2 (SCN) 2 (H 2 O) 2 ] · 2H 2 O ( 2 ) is a neutral centrosymmetric dinuclear Ni II complex doubly bridged by abpt ligands. The complex [Ni(abpt) 2 (N 3 ) 2 ] ( 3 ) is a neutral centrosymmetric mononuclear Ni II complex and crystallizes in polymorphous phases, showing an interesting example of temperature‐induced polymorphism. Variable‐temperature magnetic susceptibility measurements reveal that the ferromagnetic interaction via the (μ 1,1 ‐N 3 ) 2 (μ‐OAc) and (μ 1,1 ‐N 3 )(μ 1,1 ‐NH abpt–H )(μ‐OAc) bridges slightly dominates over the antiferromagnetic interaction via the abpt bridges, therefore indicative of an overall ferromagnetic coupling between Ni II centers in 1 , and a moderate antiferromagnetic interaction occurs in 2 . (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)