Studies of the reactivity of {[Ni(tren)]2[Sn2S6]}n: Synthesis and crystal structures of two new thiostannates prepared at room temperature

Abstract

The reactions of {[Ni(tren)]2[Sn2S6]}n (tren=tris(2-aminoethyl)amine, C6H18N4) at room temperature in aqueous solutions of tren or 2amp (2amp=2-(aminomethyl)pyridine, C6H8N2) lead to crystallization of the new compounds [Ni(tren)2]2[Sn2S6]·8H2O (1) and [Ni(tren)(2amp)]2[Sn2S6] (2). For the formation of these compounds the two NiS bonds in {[Ni(tren)]2[Sn2S6]}n are broken during the chemical reactions and the free coordination sites at Ni2+ are occupied by N-donor atoms of the amine molecules. Interestingly, in the structure of 1 the two tren ligands both coordinate in a tridentate mode while in the educt {[Ni(tren)]2[Sn2S6]}n tren acts tetradentately. Hence, in this case not only the two NiS bonds are broken but also one NiN bond. The eight H2O molecules form an octamer by strong OH⋯O hydrogen bonds. In the structure of 2 the two free coordination sites at the Ni2+ after NiS bond breakage are occupied by the two N atoms of the 2amp ligand. The two compounds can be transferred reversibly into the starting compound by heating the reaction slurry. The minimum conversion temperature depends on the amine concentration of the reaction mixture. Investigations of the thermal behavior of compound 1 verify that the water and amine molecules are removed step wise during the heating process leading to the formation of a water free thiostannate, and finally results in the formation of the precursor {[Ni(tren)]2[Sn2S6]}n.