Enhanced mercury reduction in the South Atlantic Ocean during carbon remineralization

Highlights • Dissolved gaseous mercury can be calculated from modeled dissolved inorganic carbon. • Modeled dissolved gaseous mercury agrees well with worldwide observations. • Dissolved gaseous mercury is related to depth and macronutrients concentrations. Mercury (Hg) in seawater is subject to interconversions via (photo)chemical and (micro)biological processes that determine the extent of dissolved gaseous mercury (DGM) (re)emission and the production of monomethylmercury. We investigated Hg speciation in the South Atlantic Ocean on a GEOTRACES cruise along a 40°S section between December 2011 and January 2012 (354 samples collected at 24 stations from surface to 5250 m maximum depth). Using statistical analysis, concentrations of methylated mercury (MeHg, geometric mean 35.4 fmol L−1) were related to seawater temperature, salinity, and fluorescence. DGM concentrations (geometric mean 0.17 pmol L−1) were related to water column depth, concentrations of macronutrients and dissolved inorganic carbon (DIC). The first-ever observed linear correlation between DGM and DIC obtained from high-resolution data indicates possible DGM production by organic matter remineralization via biological or dark abiotic reactions. DGM concentrations projected from literature DIC data using the newly discovered DGM–DIC relationship agreed with published DGM observations

Increasing Structural Dimensionality of Alkali Metal Fluoridotitanates(IV)

Reactions between AF (A = Li, Na, K, Rb, Cs) and TiF₄ (with starting <i>n</i>(AF):<i>n</i>(TiF₄) molar ratios in the range from 3:1 to 1:3) in anhydrous hydrogen fluoride yield [TiF₆]^2–, [TiF₅]⁻, [Ti₄F₁₉]^3–, [Ti₂F₉]⁻, and [Ti₆F₂₇]^3– salts. With the exception of the A₂TiF₆ compounds, which consist of A⁺ cations and octahedral [TiF₆]^2– anions, all of these materials arise from the condensation of TiF₆ units. The anionic part in the crystal structures of A­[TiF₅] (A = K, Cs) and A­[TiF₅]·HF (A = Na, K, Rb) is composed of infinite ([TiF₅]⁻)_∞ chains built of TiF₆ octahedra sharing joint vertices. Each structure shows a slightly different geometry of the ([TiF₅]⁻)_∞ chains. The crystal structure of Na­[Ti₂F₉]·HF is constructed from polymeric ([Ti₂F₉]⁻)_∞ anions that appear as two parallel infinite zigzag chains comprising TiF₆ units, where each TiF₆ unit of one chain is connected to a TiF₆ unit of the other chain through a shared fluorine vertex. Slow decomposition of single crystals of K₄[Ti₈F₃₆]·8HF and Rb₄[Ti₈F₃₆]·6HF (Shlyapnikov, I. M.; et al. Chem. Commun. 2013, 49, 2703) leads to the formation of [Ti₂F₉]⁻ (Rb) and [Ti₆F₂₇]^3– (K, Rb) salts. The former displays the same ([Ti₂F₉]⁻)_∞ double chain as in Na­[Ti₂F₉]·HF, while the anionic part in the latter, ([Ti₆F₂₇]^3–)_∞, represents the first example of a three-dimensional network built of TiF₆ octahedra. The ([Ti₆F₂₇]^3–)_∞ anion was also found in [H₃O]₃[Ti₆F₂₇]. The crystal structure determination of Cs₃[Ti₄F₁₉] revealed a new type of polymeric fluoridotitanate­(IV) anion, ([Ti₄F₁₉]^3–)_∞. Similar to the ([Ti₂F₉]⁻)_∞ anion, it is also built of zigzag double chains comprising TiF₆ units. However, in the former there are fewer connections between TiF₆ units of two neighboring chains than in the latter

Crystal Structures and Raman Spectra of Imidazolium Poly[perfluorotitanate(IV)] Salts Containing the [TiF₆]^2–, ([Ti₂F₉]⁻)_<i>∞</i>, and [Ti₂F₁₁]^3– and the New [Ti₄F₂₀]^4– and [Ti₅F₂₃]^3– Anions

Reactions between imidazole (Im, C₃H₄N₂) and TiF₄ in anhydrous hydrogen fluoride (aHF) in different molar ratios have yielded [ImH]₂[TiF₆]·2HF, [ImH]₃[Ti₂F₁₁], [ImH]₄[Ti₄F₂₀], [ImH]₃[Ti₅F₂₃], and [ImH]­[Ti₂F₉] upon crystallization. All five structures were characterized by low-temperature single-crystal X-ray diffraction. The single-crystal Raman spectra of [ImH]₄[Ti₄F₂₀], [ImH]₃[Ti₅F₂₃], and [ImH]­[Ti₂F₉] were also recorded and assigned. In the crystal structure of [ImH]₂[TiF₆]·2HF, two HF molecules are coordinated to each [TiF₆]^2– anion by means of strong F–H···F hydrogen bonds. The [Ti₂F₁₁]^3– anion of [ImH]₃[Ti₂F₁₁] results from association of two TiF₆ octahedra through a common fluorine vertex. Three crystallographically independent [Ti₂F₁₁]^3– anions, which have distinct geometries and orientations, are hydrogen-bonded to the [ImH]⁺ cations. The [ImH]₄[Ti₄F₂₀] salt crystallized in two crystal modifications at low (α-phase, 200 K) and ambient (β-phase, 298 K) temperatures. The tetrameric [Ti₄F₂₀]^4– anion of [ImH]₄[Ti₄F₂₀] consists of rings of four TiF₆ octahedra, which each share two <i>cis</i>-fluorine vertices, whereas the pentameric [Ti₅F₂₃]^3– anion of [ImH]₃[Ti₅F₂₃] results from association of five TiF₆ units, where four of the TiF₆ octahedra share two <i>cis</i>-vertices, forming a tetrameric ring as in [Ti₄F₂₀]^4–, and the fifth TiF₆ unit shares three fluorine vertices with three TiF₆ units of the tetrameric ring. The [ImH]­[Ti₂F₉] salt also crystallizes in two crystal modifications at low (α-phase, 200 K) and high (β-phase, 298 K) temperatures and contains polymeric ([Ti₂F₉]⁻)_∞ anions, which appear as two parallel infinite zigzag chains comprised of TiF₆ units, where each TiF₆ unit of one chain is connected to a TiF₆ unit of the second chain through a shared fluorine vertex. Quantum-chemical calculations at the B3LYP/SDDALL level of theory were used to arrive at the gas-phase geometries and vibrational frequencies of the [Ti₄F₂₀]^4– and [Ti₅F₂₃]^3– anions, which aided in the assignment of the experimental vibrational frequencies of the anion series

Crystal Structures and Raman Spectra of Imidazolium Poly[perfluorotitanate(IV)] Salts Containing the [TiF₆]^2–, ([Ti₂F₉]⁻)_<i>∞</i>, and [Ti₂F₁₁]^3– and the New [Ti₄F₂₀]^4– and [Ti₅F₂₃]^3– Anions

Reactions between imidazole (Im, C₃H₄N₂) and TiF₄ in anhydrous hydrogen fluoride (aHF) in different molar ratios have yielded [ImH]₂[TiF₆]·2HF, [ImH]₃[Ti₂F₁₁], [ImH]₄[Ti₄F₂₀], [ImH]₃[Ti₅F₂₃], and [ImH]­[Ti₂F₉] upon crystallization. All five structures were characterized by low-temperature single-crystal X-ray diffraction. The single-crystal Raman spectra of [ImH]₄[Ti₄F₂₀], [ImH]₃[Ti₅F₂₃], and [ImH]­[Ti₂F₉] were also recorded and assigned. In the crystal structure of [ImH]₂[TiF₆]·2HF, two HF molecules are coordinated to each [TiF₆]^2– anion by means of strong F–H···F hydrogen bonds. The [Ti₂F₁₁]^3– anion of [ImH]₃[Ti₂F₁₁] results from association of two TiF₆ octahedra through a common fluorine vertex. Three crystallographically independent [Ti₂F₁₁]^3– anions, which have distinct geometries and orientations, are hydrogen-bonded to the [ImH]⁺ cations. The [ImH]₄[Ti₄F₂₀] salt crystallized in two crystal modifications at low (α-phase, 200 K) and ambient (β-phase, 298 K) temperatures. The tetrameric [Ti₄F₂₀]^4– anion of [ImH]₄[Ti₄F₂₀] consists of rings of four TiF₆ octahedra, which each share two <i>cis</i>-fluorine vertices, whereas the pentameric [Ti₅F₂₃]^3– anion of [ImH]₃[Ti₅F₂₃] results from association of five TiF₆ units, where four of the TiF₆ octahedra share two <i>cis</i>-vertices, forming a tetrameric ring as in [Ti₄F₂₀]^4–, and the fifth TiF₆ unit shares three fluorine vertices with three TiF₆ units of the tetrameric ring. The [ImH]­[Ti₂F₉] salt also crystallizes in two crystal modifications at low (α-phase, 200 K) and high (β-phase, 298 K) temperatures and contains polymeric ([Ti₂F₉]⁻)_∞ anions, which appear as two parallel infinite zigzag chains comprised of TiF₆ units, where each TiF₆ unit of one chain is connected to a TiF₆ unit of the second chain through a shared fluorine vertex. Quantum-chemical calculations at the B3LYP/SDDALL level of theory were used to arrive at the gas-phase geometries and vibrational frequencies of the [Ti₄F₂₀]^4– and [Ti₅F₂₃]^3– anions, which aided in the assignment of the experimental vibrational frequencies of the anion series