19 research outputs found
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 TiF<sub>4</sub> (with starting <i>n</i>(AF):<i>n</i>(TiF<sub>4</sub>) molar ratios in
the range from 3:1 to 1:3) in anhydrous hydrogen fluoride yield [TiF<sub>6</sub>]<sup>2–</sup>, [TiF<sub>5</sub>]<sup>−</sup>, [Ti<sub>4</sub>F<sub>19</sub>]<sup>3–</sup>, [Ti<sub>2</sub>F<sub>9</sub>]<sup>−</sup>, and [Ti<sub>6</sub>F<sub>27</sub>]<sup>3–</sup> salts. With the exception of the A<sub>2</sub>TiF<sub>6</sub> compounds, which consist of A<sup>+</sup> cations
and octahedral [TiF<sub>6</sub>]<sup>2–</sup> anions, all of
these materials arise from the condensation of TiF<sub>6</sub> units.
The anionic part in the crystal structures of A[TiF<sub>5</sub>] (A
= K, Cs) and A[TiF<sub>5</sub>]·HF (A = Na, K, Rb) is composed
of infinite ([TiF<sub>5</sub>]<sup>−</sup>)<sub>∞</sub> chains built of TiF<sub>6</sub> octahedra sharing joint vertices.
Each structure shows a slightly different geometry of the ([TiF<sub>5</sub>]<sup>−</sup>)<sub>∞</sub> chains. The crystal
structure of Na[Ti<sub>2</sub>F<sub>9</sub>]·HF is constructed
from polymeric ([Ti<sub>2</sub>F<sub>9</sub>]<sup>−</sup>)<sub>∞</sub> anions that appear as two parallel infinite zigzag
chains comprising TiF<sub>6</sub> units, where each TiF<sub>6</sub> unit of one chain is connected to a TiF<sub>6</sub> unit of the
other chain through a shared fluorine vertex. Slow decomposition of
single crystals of K<sub>4</sub>[Ti<sub>8</sub>F<sub>36</sub>]·8HF
and Rb<sub>4</sub>[Ti<sub>8</sub>F<sub>36</sub>]·6HF (Shlyapnikov, I. M.; et al. Chem. Commun. 2013, 49, 2703) leads to the
formation of [Ti<sub>2</sub>F<sub>9</sub>]<sup>−</sup> (Rb)
and [Ti<sub>6</sub>F<sub>27</sub>]<sup>3–</sup> (K, Rb) salts.
The former displays the same ([Ti<sub>2</sub>F<sub>9</sub>]<sup>−</sup>)<sub>∞</sub> double chain as in Na[Ti<sub>2</sub>F<sub>9</sub>]·HF, while the anionic part in the latter, ([Ti<sub>6</sub>F<sub>27</sub>]<sup>3–</sup>)<sub>∞</sub>, represents
the first example of a three-dimensional network built of TiF<sub>6</sub> octahedra. The ([Ti<sub>6</sub>F<sub>27</sub>]<sup>3–</sup>)<sub>∞</sub> anion was also found in [H<sub>3</sub>O]<sub>3</sub>[Ti<sub>6</sub>F<sub>27</sub>]. The crystal structure determination
of Cs<sub>3</sub>[Ti<sub>4</sub>F<sub>19</sub>] revealed a new type
of polymeric fluoridotitanate(IV) anion, ([Ti<sub>4</sub>F<sub>19</sub>]<sup>3–</sup>)<sub>∞</sub>. Similar to the ([Ti<sub>2</sub>F<sub>9</sub>]<sup>−</sup>)<sub>∞</sub> anion,
it is also built of zigzag double chains comprising TiF<sub>6</sub> units. However, in the former there are fewer connections between
TiF<sub>6</sub> units of two neighboring chains than in the latter
Finite-temperature fluid–insulator transition of strongly interacting 1D disordered bosons
Crystal Structures and Raman Spectra of Imidazolium Poly[perfluorotitanate(IV)] Salts Containing the [TiF<sub>6</sub>]<sup>2–</sup>, ([Ti<sub>2</sub>F<sub>9</sub>]<sup>−</sup>)<sub><i>∞</i></sub>, and [Ti<sub>2</sub>F<sub>11</sub>]<sup>3–</sup> and the New [Ti<sub>4</sub>F<sub>20</sub>]<sup>4–</sup> and [Ti<sub>5</sub>F<sub>23</sub>]<sup>3–</sup> Anions
Reactions between imidazole (Im,
C<sub>3</sub>H<sub>4</sub>N<sub>2</sub>) and TiF<sub>4</sub> in anhydrous
hydrogen fluoride (aHF) in different molar ratios have yielded [ImH]<sub>2</sub>[TiF<sub>6</sub>]·2HF, [ImH]<sub>3</sub>[Ti<sub>2</sub>F<sub>11</sub>], [ImH]<sub>4</sub>[Ti<sub>4</sub>F<sub>20</sub>],
[ImH]<sub>3</sub>[Ti<sub>5</sub>F<sub>23</sub>], and [ImH][Ti<sub>2</sub>F<sub>9</sub>] upon crystallization. All five structures were
characterized by low-temperature single-crystal X-ray diffraction.
The single-crystal Raman spectra of [ImH]<sub>4</sub>[Ti<sub>4</sub>F<sub>20</sub>], [ImH]<sub>3</sub>[Ti<sub>5</sub>F<sub>23</sub>],
and [ImH][Ti<sub>2</sub>F<sub>9</sub>] were also recorded and assigned.
In the crystal structure of [ImH]<sub>2</sub>[TiF<sub>6</sub>]·2HF,
two HF molecules are coordinated to each [TiF<sub>6</sub>]<sup>2–</sup> anion by means of strong F–H···F hydrogen
bonds. The [Ti<sub>2</sub>F<sub>11</sub>]<sup>3–</sup> anion
of [ImH]<sub>3</sub>[Ti<sub>2</sub>F<sub>11</sub>] results from association
of two TiF<sub>6</sub> octahedra through a common fluorine vertex.
Three crystallographically independent [Ti<sub>2</sub>F<sub>11</sub>]<sup>3–</sup> anions, which have distinct geometries and
orientations, are hydrogen-bonded to the [ImH]<sup>+</sup> cations.
The [ImH]<sub>4</sub>[Ti<sub>4</sub>F<sub>20</sub>] salt crystallized
in two crystal modifications at low (α-phase, 200 K) and ambient
(β-phase, 298 K) temperatures. The tetrameric [Ti<sub>4</sub>F<sub>20</sub>]<sup>4–</sup> anion of [ImH]<sub>4</sub>[Ti<sub>4</sub>F<sub>20</sub>] consists of rings of four TiF<sub>6</sub> octahedra,
which each share two <i>cis</i>-fluorine vertices, whereas
the pentameric [Ti<sub>5</sub>F<sub>23</sub>]<sup>3–</sup> anion
of [ImH]<sub>3</sub>[Ti<sub>5</sub>F<sub>23</sub>] results from association
of five TiF<sub>6</sub> units, where four of the TiF<sub>6</sub> octahedra
share two <i>cis</i>-vertices, forming a tetrameric ring
as in [Ti<sub>4</sub>F<sub>20</sub>]<sup>4–</sup>, and the
fifth TiF<sub>6</sub> unit shares three fluorine vertices with three
TiF<sub>6</sub> units of the tetrameric ring. The [ImH][Ti<sub>2</sub>F<sub>9</sub>] salt also crystallizes in two crystal modifications
at low (α-phase, 200 K) and high (β-phase, 298 K) temperatures
and contains polymeric ([Ti<sub>2</sub>F<sub>9</sub>]<sup>−</sup>)<sub>∞</sub> anions, which appear as two parallel infinite
zigzag chains comprised of TiF<sub>6</sub> units, where each TiF<sub>6</sub> unit of one chain is connected to a TiF<sub>6</sub> 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 [Ti<sub>4</sub>F<sub>20</sub>]<sup>4–</sup> and [Ti<sub>5</sub>F<sub>23</sub>]<sup>3–</sup> 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 [TiF<sub>6</sub>]<sup>2–</sup>, ([Ti<sub>2</sub>F<sub>9</sub>]<sup>−</sup>)<sub><i>∞</i></sub>, and [Ti<sub>2</sub>F<sub>11</sub>]<sup>3–</sup> and the New [Ti<sub>4</sub>F<sub>20</sub>]<sup>4–</sup> and [Ti<sub>5</sub>F<sub>23</sub>]<sup>3–</sup> Anions
Reactions between imidazole (Im,
C<sub>3</sub>H<sub>4</sub>N<sub>2</sub>) and TiF<sub>4</sub> in anhydrous
hydrogen fluoride (aHF) in different molar ratios have yielded [ImH]<sub>2</sub>[TiF<sub>6</sub>]·2HF, [ImH]<sub>3</sub>[Ti<sub>2</sub>F<sub>11</sub>], [ImH]<sub>4</sub>[Ti<sub>4</sub>F<sub>20</sub>],
[ImH]<sub>3</sub>[Ti<sub>5</sub>F<sub>23</sub>], and [ImH][Ti<sub>2</sub>F<sub>9</sub>] upon crystallization. All five structures were
characterized by low-temperature single-crystal X-ray diffraction.
The single-crystal Raman spectra of [ImH]<sub>4</sub>[Ti<sub>4</sub>F<sub>20</sub>], [ImH]<sub>3</sub>[Ti<sub>5</sub>F<sub>23</sub>],
and [ImH][Ti<sub>2</sub>F<sub>9</sub>] were also recorded and assigned.
In the crystal structure of [ImH]<sub>2</sub>[TiF<sub>6</sub>]·2HF,
two HF molecules are coordinated to each [TiF<sub>6</sub>]<sup>2–</sup> anion by means of strong F–H···F hydrogen
bonds. The [Ti<sub>2</sub>F<sub>11</sub>]<sup>3–</sup> anion
of [ImH]<sub>3</sub>[Ti<sub>2</sub>F<sub>11</sub>] results from association
of two TiF<sub>6</sub> octahedra through a common fluorine vertex.
Three crystallographically independent [Ti<sub>2</sub>F<sub>11</sub>]<sup>3–</sup> anions, which have distinct geometries and
orientations, are hydrogen-bonded to the [ImH]<sup>+</sup> cations.
The [ImH]<sub>4</sub>[Ti<sub>4</sub>F<sub>20</sub>] salt crystallized
in two crystal modifications at low (α-phase, 200 K) and ambient
(β-phase, 298 K) temperatures. The tetrameric [Ti<sub>4</sub>F<sub>20</sub>]<sup>4–</sup> anion of [ImH]<sub>4</sub>[Ti<sub>4</sub>F<sub>20</sub>] consists of rings of four TiF<sub>6</sub> octahedra,
which each share two <i>cis</i>-fluorine vertices, whereas
the pentameric [Ti<sub>5</sub>F<sub>23</sub>]<sup>3–</sup> anion
of [ImH]<sub>3</sub>[Ti<sub>5</sub>F<sub>23</sub>] results from association
of five TiF<sub>6</sub> units, where four of the TiF<sub>6</sub> octahedra
share two <i>cis</i>-vertices, forming a tetrameric ring
as in [Ti<sub>4</sub>F<sub>20</sub>]<sup>4–</sup>, and the
fifth TiF<sub>6</sub> unit shares three fluorine vertices with three
TiF<sub>6</sub> units of the tetrameric ring. The [ImH][Ti<sub>2</sub>F<sub>9</sub>] salt also crystallizes in two crystal modifications
at low (α-phase, 200 K) and high (β-phase, 298 K) temperatures
and contains polymeric ([Ti<sub>2</sub>F<sub>9</sub>]<sup>−</sup>)<sub>∞</sub> anions, which appear as two parallel infinite
zigzag chains comprised of TiF<sub>6</sub> units, where each TiF<sub>6</sub> unit of one chain is connected to a TiF<sub>6</sub> 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 [Ti<sub>4</sub>F<sub>20</sub>]<sup>4–</sup> and [Ti<sub>5</sub>F<sub>23</sub>]<sup>3–</sup> anions, which aided in the assignment
of the experimental vibrational frequencies of the anion series