Cysteamine and Its Homoleptic Complexes with Group 12 Metal Ions. Differences in the Coordination Chemistry of Zn^II, Cd^II, and Hg^II with a Small N,S-Donor Ligand

Abstract

2-Ammoniumethanethiolate, (-)SCH(2)CH(2)NH(3)(+), the first structurally characterized zwitterionic ammoniumthiolate, is the stable form of cysteamine (HL) in the solid state and in aqueous solution. Reactions of ZnCl(2), Cd(Oac)(2), and HgCl(2) with cysteamine and NaOH in a 1:2:2 ratio, respectively, lead to the homoleptic complexes ML(2). Their single-crystal X-ray structures demonstrate basic differences in the coordination chemistry of Zn(II), Cd(II), and Hg(II). While chelating N,S-coordination modes are found for all metal ions, Zn(II) forms a mononuclear complex with a distorted tetrahedral Zn(N(2)S(2)) coordination mode, whereas Hg(II) displays a dimer with Hg(N(2)S(2)) coordinated monomers being connected by two long Hg...S contacts. Solid-state (199)Hg NMR spectra of HgL(2) and [Hg(HL)(2)]Cl(2) reveal a low-field shift of the signals with increasing coordination number. Strong and nearly symmetric Cd-S-Cd bridges in solid CdL(2) lead to a chain structure, Cd(II) displaying a distorted square pyramidal Cd(N(2)S(3)) coordination mode. The ab initio [MP2/LANL2DZ(d,f)] structures of isolated ML(2) show a change from a distorted tetrahedral to bisphenoidal coordination mode in the sequence Zn(II)-Cd(II)-Hg(II). A natural bond orbital analysis showed a high ionic character for the M-S bonds and suggests that the S-M-S fragment is best described by a 3c4e bond. The strength of the M...N interactions and the stability of ML(2) toward decomposition to M and L-L decreases in the sequence Zn > Cd > Hg. Ab initio calculations further suggest that a tetrahedral S-M-S angle stabilizes Zn(II) against substitution by Cd(II) and Hg(II) in a M(N(2)S(2)) environment. Such geometry is provided in zinc-finger proteins, as was found by a database survey.

Solution behavior of Hg(II)-cystamine by Uv-Vis and199Hg NMR

“…The peak due to six-coordinate Hg 2þ in 1 is observed at 71144 ppm (figure 2). Addition of base to 1 resulted in a shift to 7591 ppm (1Nu 7 ), which is comparable to the shift observed for 2 (7659 ppm) [21]. The significant difference in the shift can be attributed to the fact that 199 Hg NMR is highly solvent-and concentration-dependent [22].…”

Simple synthesis of highly selective and fast Hg(II) removal polymer from aqueous solution

“…The double peaks of S-H were found at 2312 and 2381 cm −1 . [21] The absorption bands that lie below 1000 cm −1 are the characteristics of substituted benzene. The same finding has been reported earlier.…”

“…[21] Recently, Mahmoud Firouzzare et al [22] used this compound for synthesizing N-Methacryloyl-2-mercaptoethylamine (MMEA) and then complexing the mercury ion. The produced complex monomer copolymerized with methacrylic acid and ethylene glycol.…”

Cation-induced assembly of Zn(II), Cd(II) and Hg(II) coordination complexes and DFT calculations to evaluate weak interactions between the helical chains

“…Group 12 metals (Zn, Cd, and Hg) are regarded to be particularly promising not only due to interesting luminescent properties [9] and broad applications in biological area [10][11][12][13][14] but their wide variety of coordination numbers and geometries provided by the d 10 configuration of the metal center [15][16][17][18]. This structural diversity is closely dependent on factors such as the dimension of the metal ions and halides, nature of ligands, and the availability of other structure controlling interactions, such as hydrogen bonding and charge transfer [19].…”