Functionalization of nine-atom deltahedral Zintl ions with organic substituents: detailed studies of the reactions.

Presented are the results of a systematic investigation of the reactions of nine-atom deltahedral clusters of germanium (Zintl ions, Ge(9)(n-)) with alkynes and alkyl halides that result in alkenylation and alkylation of the clusters, respectively. The reaction pathways have been probed in depth using various, appropriately substituted alkynes and organic halides, including some typical mechanistic probes and radical clocks. The regioselectivity and stereoselectivity of the reaction with alkynes was examined by systematically varying the steric and electronic nature of the substituents. The studies showed that the Zintl clusters act as strong, anionic nucleophiles toward the alkynes and primary and secondary alkyl halides but, most likely, as electron donors in reactions with tertiary alkyl halides and halogenated olefins. The pentenyl and methylcyclopropyl functionalized clusters, [Ge(9)(C(5)H(9))](3-) and [Ge(9)(CH(2)CH(CH(2))(2))](2-), respectively, were crystallographically characterized in compounds with [K-crypt](+) countercations. All compounds were also analyzed by NMR and electrospray mass spectrometry.

Chemical analysis of Hg0-containing Hindu religious objects.

Parad items used in Hindu practices and Ayurvedic medicines contain elemental mercury (Hg0) and have traditionally been used in prayer and to treat a variety of diseases including diabetes, heart conditions, and sexual dysfunction. These items are often referred to as amalgams of silver, and take the form of shivlings, statues of gods, necklaces, and other jewelry. Fourteen parad items were purchased from online vendors in India and the United States and analyzed. All items produced copious amounts of Hg0 vapor, with Hg0 concentrations exceeding 1,000,000 ng/m3 as measured using a Mercury Instruments Mercury Tracker 3000 IP atomic absorption spectrometer. Measured concentrations were highly variable, so a simple qualitative experiment employing a UV-C light source and a thin-layer chromatography plate impregnated with a fluorescent dye that glows green when irradiated at 254 nm allowed for the indirect visualization of the Hg0 being evolved. In addition, all items were screened using a hand-held X-ray fluorescence analyzer to estimate the concentration of Hg, Sn, Pb, As, and Cd on the surface of the item. Select samples were then digested in aqua regia and analyzed for Hg content using a direct mercury analyzer. All samples were found to exceed 20% by mass Hg. The digestates were analyzed using inductively-coupled plasma-optical emission spectrometry and were determined to be between 10-55% by mass Pb and contain up to 0.3% by mass As. While Article 4 of the Minamata Convention on Mercury specifically requires parties to stop importing, exporting, and manufacturing Hg-added products, products used in traditional and religious practices are excluded.

Time-dependence in mixture toxicity prediction.

The value of time-dependent toxicity (TDT) data in predicting mixture toxicity was examined. Single chemical (A and B) and mixture (A+B) toxicity tests using Microtox(®) were conducted with inhibition of bioluminescence (Vibrio fischeri) being quantified after 15, 30 and 45-min of exposure. Single chemical and mixture tests for 25 sham (A1:A2) and 125 true (A:B) combinations had a minimum of seven duplicated concentrations with a duplicated control treatment for each test. Concentration/response (x/y) data were fitted to sigmoid curves using the five-parameter logistic minus one parameter (5PL-1P) function, from which slope, EC25, EC50, EC75, asymmetry, maximum effect, and r(2) values were obtained for each chemical and mixture at each exposure duration. Toxicity data were used to calculate percentage-based TDT values for each individual chemical and mixture of each combination. Predicted TDT values for each mixture were calculated by averaging the TDT values of the individual components and regressed against the observed TDT values obtained in testing, resulting in strong correlations for both sham (r(2)=0.989, n=25) and true mixtures (r(2)=0.944, n=125). Additionally, regression analyses confirmed that observed mixture TDT values calculated for the 50% effect level were somewhat better correlated with predicted mixture TDT values than at the 25 and 75% effect levels. Single chemical and mixture TDT values were classified into five levels in order to discern trends. The results suggested that the ability to predict mixture TDT by averaging the TDT of the single agents was modestly reduced when one agent of the combination had a positive TDT value and the other had a minimal or negative TDT value.

Water compatibility and organic transformations of organo-Zintl deltahedral clusters.

We report the remarkable stability of di-substituted organo-Zintl deltahedral clusters in the presence of water. This has been exploited in a reaction at the organic substituents of the cluster which produces water as a by-product. Also reported are the synthesis, characterization, and crystal structure of [K-krypt](2)[Ge(9)-(CH=CH-CH(2)NH(2))(2)] involved in the reaction.

Organo-Zintl clusters soluble in conventional organic solvents: setting the stage for organo-Zintl cluster chemistry.

Organo-Zintl cluster ions were synthesized by reactions of alkynes with Ge94- clusters in ethylenediamine. The triple bonds are hydrogenated to double bonds during the process. The resulting dial-kenylated species [RHC=CHGe9CH=CHR]2- have lower charge, their alkali-metal cations can be exchanged for tetralkylammonium cations, and the resulting compounds are soluble in nonpolar solvents. This was demonstrated with [H2C=CHGe9CH=CH2]2-, which was structurally characterized with [K-(18-crown-6)]+, [Me4N]+, and [Pr4N]+ as countercations. The solubility of its salt with [Oc4N]+ in various conventional organic solvents was studied.

Heteroatomic deltahedral clusters: synthesis and structures of closo-[Bi3Ni(4)(CO)6]3-, closo-[Bi4Ni4(CO)6]2-, the open cluster [Bi3Ni6(CO)9]3-, and the intermetalloid closo-[Nix@[Bi6Ni6(CO)8)]4-.

Reactions of ethylenediamine solutions of K4Bi5 with Ni(PPh3)2(CO)2 yielded four novel hetero-atomic Bi/Ni deltahedral clusters. Three of them, the 7-atom pentagonal bipyramidal [Bi3Ni4(CO)6]3-, the 8-atom dodecahedral [Bi4Ni4(CO)6]2-, and the Ni-centered or empty 12-atom icosahedral [Nix@[Bi6Ni6(CO)8]4-, are closo-species according to both electron count and shape. The centered icosahedral cluster resembles packing in intermetallic compounds and belongs to the emerging class of intermetalloid clusters. The shape of the fourth cluster, [Bi3Ni6(CO)9]3-, can be derived from the icosahedral Ni-centered [Ni@[Bi6Ni6(CO)8]4- by removal of three Bi- and one Ni-atoms of two neighboring triangular faces. The clusters were structurally characterized by single-crystal X-ray diffraction in compounds with potassium cations sequestered by 2,2,2-crypt or 18-crown-6 ether. They were also characterized in solution by electrospray mass spectrometry.

Alkylation of Deltahedral Zintl clusters: synthesis of [R-Ge9-Ge9-R]4- (R = tBu, sBu, nBu, tAm and structure of [tBu-Ge9-Ge9-tBu]4-.

Reactions of nine-atom deltahedral clusters (Zintl ions) of germanium, Ge9n- (n = 2, 3, 4), with alkyl chlorides, RCl (R = tBu, nBu, sBu, tAm), yielded the corresponding dialkylated dimers of Ge9 clusters [R-Ge9-Ge9-R]4-. The tBu derivative with [K(2,2,2-crypt)]+ countercations was characterized in the solid state by single-crystal X-ray diffraction as [K(2,2,2-crypt)]4[tBu-Ge9-Ge9-tBu].7en (monoclinic, C2/c, a = 35.0914(10) A, b = 24.8161(6) A, and c = 16.8782(5) A, beta = 94.0136(17) degrees , V = 14662.0(7) A3, and Z = 4) and in solution by 1H and 13C NMR. All species were also characterized in solution by electrospray mass spectrometry in the negative-ion mode. These are the first main group deltahedral clusters functionalized with purely organic substituents.

Electronic dissymmetry in chiral recognition.

The pi-bonding of the beta-diketonate ligands in C2-symmetric (dike)2TiX2 complexes engenders a significant electronic dissymmetry, with the LUMO of the complex resembling a "tipped" dz2 orbital whose tilt with respect to the plane containing the metal and the two X groups is determined by the configuration at titanium. The ability of this electronic dissymmetry to promote chiral recognition has been probed in 1,1'-bi-2-naphtholate complexes (RCOCHCOR)2Ti(BINOL) (R = CH3, Ph, or tBu). The complexes show exclusively one diastereomer by NMR, which has been established as the one predicted on electronic grounds by crystallography of the dibenzoylmethane and 2,2,6,6-tetramethylheptanedione complexes. Confirmation that the selectivity is due to electronic rather than steric factors is given by the behavior of the tin analogues, which are structurally similar but show much smaller diastereoselectivities.