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(O2CMe)(2)center dot 4H(2)O or NiCl2 center dot 6H(2)O, 4-amino-3,5bis(pyridin-2-yl)-1,2,4-triazole (abpt) and NaN3 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 mu:eta(1):eta(2):eta(1) coordination mode of the deprotonated [abpt-H]- ligand. Structural analysis reveals that a pair of [Ni-2(mu(1),(1)-N-3)(mu-OAc)] motifs in [Ni-4(abpt)(2)(abpt-H)(N-3)(5)(O2CMe)(2)]center dot 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)(H2O)(2)]center dot 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 (mu(1),(1)-N-3)2(mu-OAc) and (mu(1),(1)-N-3)(mu,(1,1)-NHabpt-H)(mu-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. ((C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)