Mohan S. Bharara

Linear coordination of Hg(II) by cysteamine

Combination of the hydrochloride salt of cysteamine (1) with HgCl2 in water affords the unique compound, [Hg{S(CH2)2NH3}2](Cl)2 (2) in which the SHgS angle is nearly linear. The ammonium portion of the molecule forms short hydrogen bonding contacts with the sulfur atoms. A related S···H bond is observed in the structure of the free ligand 1 indicating that such bonding does not require the presence of a metal. The compounds were characterized with spectroscopic ( 1 H NMR, IR) and physical techniques (Mp, CH-analysis) as well as X-ray diffractometry.

Solution behavior of Hg(II)-cystamine by Uv-Vis and 199Hg NMR

The combination of HgCl2 with the disulfide salt of 2-aminoethanethiol (cystamine dihydrogen dichloride) in water yields a two-dimensional chain {[HgCl4][(NH3CH2CH2S[sbnd])2]}n (1). It consists of six-coordinate Hg in [HgCl4]n units with bridging and termainal Cl atoms. The disulfide groups, (NH3CH2CH2S[sbnd])2 are held between the [HgCl4]n chain with weak S[sbnd]S interactions. The chlorides in the [HgCl4]n units are involved in intermolecular hydrogen bonding to yield a three-dimensional network. A similar reaction with the reduced form of cystamine (2-amino ethanethiol) yields a linear Hg(II)-bis-thiolate, [Hg(SCH2CH2NH3]2+ (2). When compound 1 is combined with two equivalents of NaOH it rearranges to 2 as indicated by 199Hg NMR and Uv-Vis.

Mercurophilic interaction in novel polynuclear Hg(II)–2-aminoethanethiolates

The reaction of 2-aminoethanethiol hydrochloride with Hg(2)Cl(2) in water yielded elemental mercury and one-dimensional polynuclear compounds [{Hg(3)Cl(5)(SCH(2)CH(2)NH(3))(3)}Cl](n) and [HgCl(SCH(2)CH(2)NH(2))(H(2)O)(2)](n) (2). The coordination environment around Hg in 1 and 2 is quite variable despite similar reaction conditions. The formation of a five-membered S/N chelate in 2 can be attributed to the use of base to produce a neutral ligand. Three independent types of Hg atoms, both three- and four-coordinate are observed in 1, whereas in 2, the Hg atom is tetracoordinate with S, N and Cl atoms in the primary coordination sphere. Despite distinct structural chemistry, the coordination environments in 1 and 2 are fairly similar with repeating units connected with bridged thiolate S atoms in addition to a terminal Cl attached to Hg. Intermolecular hydrogen-bonding involving amine protons, Cl and water molecules are responsible for a three-dimensional network in both 1 and 2. A short Hg...Hg distance of 3.564 A, indicates the presence of a mercurophilic interaction in 1. The compounds have been characterized by (1)H and (13)C NMR, UV-Vis, FT-IR, Raman, mass spectrometry, TGA and single X-ray crystallography.

Actinide Selective Systems for Environmental Extraction and Sensing Applications

The potential environmental and health concerns surrounding actinides and the use of nuclear fuels limits the acceptance of nuclear power by the public. This in turn, hinders the capability of this country to take advantage of nuclear power. Expanding our fundamental knowledge of actinide coordination chemistry will allow for the development of improved actinide sensors, new separations methods, or new means of radioactive waste remediation. We have designed and optimized a solution-phase parallel method for the synthesis of a library of symmetrical 2-quinoxalinol salens, Schiff-base type ligands with a 2-quinoxalinol incorporated into the salen backbone. This combines the rigid salen coordination framework with the quinoxaline properties that impart properties for use in colorimetric or fluorescent sensors. These have now been incorporated into organic soluble resins for metal extraction. (authors)