Three isomers in a (hydrogen L-Cysteinato)-thallium(I): Crystal structure, spectroscopic and thermal properties

The isolation of thallium(I) complexes [Tl₂(HCys)₂]_n (1) and [Tl₄(HCys)₄]_n (2) {H₂Cys = l-Cysteine} from aqueous solution by means of crystallization is reported herein. Polar crystals of 1 and 2 were crystallized in P2₁ and P2₁2₁2₁ space groups respectively. Elemental analysis, XRD, IR, UV–Vis, TG-DSC and a single crystal X-ray diffraction were applied for characterizing the compounds. Linkage isomers 1 and 2 have 1D and 2D coordination polymeric structures respectively. The lone pair electrons of thallium(I) in 1–2 are stereo-chemically active. In 1, each of two independent Tl⁺ ions is coordinated by three HCys⁻ ions forming TlS₃O irregular polyhedron that is linked to each other by vertexes in an infinite chain. In 2, four independent Tl⁺ ions are coordinated by HCys⁻ ions through S and O atoms, forming Tl1S₃O₂, Tl2S₄, Tl3S₃, Tl4S₃ irregular polyhedrons. The crystallographic independent HCys⁻ ions are linked to the metal ion differently, two are μ₃-S,S,S-, one is μ₄-O,S,S,S-, and one is μ₄-O,O',S,S,S-coordinated ligands. The amine group of compounds 1 and 2 is in the form of an ammonium ion (–NH₃⁺). The structures of 1–2 are stabilized by NH⋯O hydrogen bonds, thallophilic Tl⋯Tl and anagostic Tl⋯HC interactions. The spectroscopic and thermal properties of compounds were analyzed.