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Changing the Reactivity of Zero- and Mono-Valent Germanium with a Redox Non-Innocent Bis(silylenyl)carborane Ligand.

ABSTRACT: Using the chelating C,C'-bis(silylenyl)-ortho-dicarborane ligand, 1,2-(RSi)₂ -1,2-C₂ B₁₀ H₁₀ [R=PhC(NtBu)₂ ], leads to the monoatomic zero-valent Ge complex ("germylone") 3. The redox non-innocent character of the carborane scaffold has a drastic influence on the reactivity of 3 towards reductants and oxidants. Reduction of 3 with one molar equivalent of potassium naphthalenide (KC₁₀ H₈ ) causes facile oxidation of Ge⁰ to Ge^I along with a two-electron reduction of the C₂ B₁₀ cluster core and subsequent Ge^I -Ge^I coupling to form the dianionic bis(silylene)-supported Ge₂ complex 4. In contrast, oxidation of 3 with one molar equivalent of [Cp₂ Fe][B{C₆ H₃ (CF₃ )₂ }₄ ] as a one-electron oxidant furnishes the dicationic bis(silylene)-supported Ge₂ complex 5. The Ge⁰ atom in 3 acts as donor towards GeCl₂ to form the trinuclear mixed-valent Ge⁰ →Ge^II ←Ge⁰ complex 6, from which dechlorination with KC₁₀ H₈ affords the neutral Ge₂ complex 7 as a diradical species.

SUBMITTER: Yao S

PROVIDER: S-EPMC8252802 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:BackgroundIonic and molecular carriers of dissolved (filter-passing) zero-valent sulfur (S0) in anaerobic natural waters include polysulfides, Sn2-, molecular S8(aq), organic macromolecules and certain higher valent thioanions. Because S0 is rapidly transferred among these various carriers, its biogeochemical roles in such processes as dehalogenation of organic compounds, chelation of trace metals, and anaerobic microbial metabolism are not determined solely by one ionic or molecular species. Here, S0 is treated collectively as a virtual thermodynamic component, and computational as well as graphical methods for quantifying its activity (aS0) in natural waters are presented. From aS0, concentrations of the ionic and molecular carriers of S0 can be calculated easily.ResultsConcentration ratios of any two polysulfide ions define aS0 (Method I). Unfortunately these concentrations are often too low in nature for accurate quantification with current methods. Measurements of total divalent sulfur (ΣS-II), zero-valent sulfur (ΣS0) and pH provide a more widely applicable approach (Method II). Systematic errors in ΣS0 measurements are the main limit to accuracy of this method at the present time. Alternative methods based on greigite solubility and potentiometry are discussed. A critical comparison of Methods I and II reveals inconsistencies at low ΣS0/ΣS-II that imply errors in the thermodynamic data for HS2- and S2-. For samples having low ΣS0/ΣS-II, an interim remedy is recommended: letting pKa2 = 6.3 for all HSn- ions.ConclusionsNewly assembled data for aS0 in a selection of anaerobic natural waters indicate that S0 is always metastable in the surveyed samples with respect to disproportionation to sulfide and sulfate. In all the surveyed environments, sulfur-rich minerals, such as greigite, covellite and orpiment, are stable in preference to their sulfur-poor cohorts, mackinawite, chalcocite and realgar. The aS0 values in the dataset span conditions favoring Hg-polysulfide complexes vs. Hg-sulfide complexes, implying that aS0 could affect Hg-methylation rates in nature. No support is found for the common assumption that aS0 = 1 in reducing natural waters. This paper calls attention to an urgent need for improved measurement methods, especially for total zero-valent sulfur, as well as new determinations of ionization constants for all HSn- species.

Dataset Information

Changing the Reactivity of Zero- and Mono-Valent Germanium with a Redox Non-Innocent Bis(silylenyl)carborane Ligand.

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