Trinuclear Complexes of Nickel(II) and 4-Amino-1,2,4-triazoleстатья
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Дата последнего поиска статьи во внешних источниках: 18 марта 2017 г.
Аннотация:Nickel(II) tetrafluoroborate is capable of forming a variety of complexes with 4-amino-1,2,4-triazole (NH2trz), as NH2trz can coordinate to one, two, or three Ni2+ ions and thus can give rise in particular to polynuclear compounds of “infinite” dimensions. From rather concentrated solutions in the presence of an excess of Ni2+, however, crystallization of the trinuclear compound [Ni3(NH2trz)6(H2O)6](BF4)6·4H2O is observed. In this complex, adjacent nickel ions are connected with three bridging NH2trz ligands, and three water molecules are bound to each of the terminal nickel atoms. The Ni–N distances at the central Ni2+ ion were found to exceed those at the terminal Ni2+ ions, in account with the trans influence of the involved ligands. The distances between the nickel atoms (3.72–3.73 Å) are too large to enable considerable Ni–Ni bonds. Remarkably, over longer periods hydrolyzed BF4– reacted with the glass vessel, in which the synthesis was conducted, to yield SiF62– ions. In the resulting mixture, a BF4–/SiF62– complex developed reproducibly, of the structure [Ni3(NH2trz)6(H2O)6](BF4)4(SiF6)·4H2O. Although both the BF4– and the BF4–/SiF62– complexes are characterized by trinuclear units and exhibit similar Ni–N and Ni–O bond lengths as well as Ni–Ni distances, in the BF4– crystal there are two symmetrically inequivalent trinuclear units, while in the BF4–/SiF62– crystal the two Ni–Ni subunits in a trinuclear unit differ from each other, in particular with respect to the angles between mean planes of the triazole molecules.