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

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.