Molecular interaction between mercury and selenium in neurotoxicity

Weak interionic interactions in 2-bromoimidazolium derivatives

The 3 centre-4 electrons (3c-4e) and the donor/acceptor or charge-transfer models for the description of the chemical bond in linear three-body systems, such as I3– and related electron-rich (22 shell electrons) systems, are comparatively discussed on the grounds of structural data from a search of the Cambridge Structural Database (CSD). Both models account for a total bond order of 1 in these systems, and while the former fits better symmetric systems, the latter describes better strongly asymmetric situations. The 3c-4e MO scheme shows that any linear system formed by three aligned closed-shell species (24 shell electrons overall) has reason to exist provided that two electrons are removed from it to afford a 22 shell electrons three-body system: all combinations of three closed-shell halides and/or chalcogenides are considered here. A survey of the literature shows that most of these three-body systems exist. With some exceptions, their structural features vary continuously from the symmetric situation showing two equal bonds to very asymmetric situations in which one bond approaches to the value corresponding to a single bond and the second one to the sum of the van der Waals radii of the involved atoms. This indicates that the potential energy surface of these three-body systems is fairly flat, and that the chemical surrounding of the chalcogen/halogen atoms can play an important role in freezing different structural situations; this is well documented for the I3– anion. The existence of correlations between the two bond distances and more importantly the linearity observed for all these systems, independently on the degree of their asymmetry, support the state of hypervalency of the central atom.

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The nature of the chemical bond in linear three-body systems: from i3- to mixed chalcogen/halogen and trichalcogen moieties.

The synthesis and comprehensive characterisation of a series of 1,2,5-selenadiazolium salts, which were generated from the direct reaction between the neutral bidentate ligand tert-butyl-DAB and a variety of heavy chalcogen halides, are reported. The formation of the cationic heterocycle from the reaction of SeX4 (X = Cl, Br) and the ligand results in a two electron redox process where the chalcogen undergoes a two electron reduction concomitant with the elimination of X2, the oxidation by-product. A reaction pathway for this chemistry has been proposed necessitating several key intermediates. These species have been synthesized and used in a stepwise series of transformations that strongly supports this very unusual reactivity for the chalcogens. In contrast, the reaction between tert-butyl DAB and TeX4 (X = Cl, Br, I), does not result in redox, rather an octahedral Te(IV)·DAB complex is formed or no reaction was observed.

Synthesis and characterization of cationic selenium–nitrogen heterocycles from tert-butyl-DAB (DAB = 1,4-di-tert-butyl-1,3-diazabutadiene) and SeX4via the reductive elimination of X2 (X = Cl, Br): a distinct contrast with tellurium

Halogenation of tellurium by SO2Cl2. Formation and crystal structures of (H3O)[Te3Cl13]·1/2SO2, [(C4H8O)2H][TeCl5]·(C4H8O), [(Me2SO)2H]2[TeCl6], and [Ni(NCCH3)6][Te2Cl10]

Tiefrote Kristalle der Zusammensetzung [H3O][TeBr5] · 3 C4H8O2 (1) wurden aus einer gesattigten Losung von TeBr4 in wasserhaltigem 1,4-Dioxan dargestellt. In der Verbindung (Raumgruppe P21/m, a = 8.922(4) A, b = 13.204(7) A, c = 9.853(5) A, β = 91.82(4)° bei 150 K) konnte erstmals ein quadratisch-pyramidales [TeBr5]− -Anion isoliert werden. Dessen Koordinationspolyeder wird durch eine schwache Wechselwirkung mit einem 1,4-Dioxan-Molekul zu einem verzerrten Oktaeder vervollstandigt. Die [H3O]+-Kationen sind durch 1,4-Dioxan-Molekule zu Ketten verknupft. Die Saure ist bei Raumtemperatur nur in ihrer Mutterlauge stabil. [H3O]2[SeBr6] (2) (Raumgruppe Fm3m, a = 10.421(1) A bei 170 K) ist eine hochsymmetrisch kristallisierende Bromoselen(IV)-saure, mit der es gelang, ein nur sehr schwach durch Br-Atome des Anions koordiniertes [H3O]+-Ion zu isolieren. Die anionische Einheit besteht aus freien, unverzerrt oktaedrischen [SeBr6]2−-Ionen. Die Kristallstruktur ist isotyp zu K2[PtCl6]. Die Verbindung zeigt eine fur Halogenochalkogen(IV)-sauren bemerkenswerte thermische Stabilitat. Beide Oxoniumsalze wurden durch vollstandige Rontgenstrukturanalysen charakterisiert. Uber schwingungsspektroskopische Untersuchungen an 2 wird berichtet.



New Oxonium Bromochalcogenates(IV) — Synthesis, Structure, and Properties of [H3O][TeBr5] · 3 C4H8O2 and [H3O]2[SeBr6]



Dark red crystals of the composition [H3O][TeBr5] · 3 C4H8O2 (1) were isolated from a saturated solution of TeBr4 in 1,4-dioxane containing a small amount of water. In this compound (space group P21/m, a = 8.922(4) A, b = 13.204(7) A, c = 9.853(5) A, β = 91.82(4)° at 150 K) a square pyramidal [TeBr5]− anion has been isolated for the first time. The coordination sphere of the anion is completed to a distorted octahedron by weak interaction with a dioxane molecule of the cationic system. The [H3O]+ cations are connected to chains by dioxane molecules. At room temperature the compound is stable only in its mother liquor. Crystalline [H3O]2[SeBr6] (2) (space group Fm3m, a = 10.421(1) A at 170 K) is a bromoselenous acid of high symmetry. The [H3O]+ ion is only weakly coordinated by Br atoms of the anion. The anions are isolated octahedral [SeBr6]2− units. The structure is isotypic to the K2[PtCl6] structure. Despite being a halogenochalcogen(IV) acid, 2 exhibits a remarkable thermal stability. Both oxonium compounds were characterized by single-crystal X-ray structure analyses. Vibrational spectra of 2 are reported.

K. Büscher

Papers

Neue Oxonium‐Bromochalkogenate(IV) — Darstellung, Struktur und Eigenschaften von [H3O][TeBr5] · 3C4H8O2 und [H3O]2[SeBr6]