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Solution and Solid-State Study of Heteroleptic Hg(II)-Thiolates:  Crystal Structures of [Hg4I4(SCH2CH2NH2)4] and [Hg4I8(SCH2CH2NH3)2]n·nH2O

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posted on 2006-03-06, 00:00 authored by Mohan S. Bharara, Sean Parkin, David A. Atwood
Combination of 2-aminoethanethiol hydrochloride and HgI2 in water in the presence of a base yielded a cyclic molecular structure, [Hg4I4(SCH2CH2NH2)4] (1). For the same reaction in the absence of the base, a similar structure with protonated amines was expected; however, polymeric [Hg4I8(SCH2CH2NH3)2]n·nH2O(2) was formed instead. The structures are quite variable despite similar reaction conditions. For instance, there is an additional Hg−N interaction in 1 due to the use of base. The environment around tetracoordinate Hg in 1 is comprised of S, N, and I atoms, with the ligand forming a five-membered chelate and the I atoms present alternate to each other. In the repeating unit of 2, three independent types of Hg atoms are observed, with HgSI3, HgS2I2, and HgI4 bonding environments that have both bridging and terminal I atoms. A simple mechanistic pathway for the formation of 1 and 2 is proposed that includes the presence of three- and four-coordinate Hg intermediates in the solution. Intermolecular hydrogen bonding involving N, I, and S in 1 and N, I, and O atoms in 2 create extended three-dimensional networks. The shortest Hg··· Hg distances are found to be intrachain in the range 3.938−3.962 Å and indicate no interaction between these atoms. The solution studies (UV−vis and NMR) along with solid-state (IR, Raman, and X-ray) studies for 1 and 2 confirm retention of the structural configuration in the solution. The thermal study of 2 indicates that degradation of the complex occurs in a single step, in contrast to 1, which takes a more complicated decomposition pathway.