3 research outputs found
Structural Characterization of 1,1,3,3-Tetramethylguanidinium Chloride Ionic Liquid by Reversible SO<sub>2</sub> Gas Absorption
A unique
new ionic liquid–gas adduct solid state compound formed between
1,1,3,3-tetramethylguanidinium chloride ([tmgH]ÂCl) and sulfur dioxide
has been characterized by X-ray diffraction and Raman spectroscopy.
The structure contains SO<sub>2</sub> molecules of near normal structure
kept at their positions by Cl–S interactions. The crystals
belong in the orthorhombic system, space group <i>Pbcn</i>, with unit cell dimensions of <i>a</i> = 15.6908(10) Ă…, <i>b</i> = 9.3865(6) Ă…, and <i>c</i> = 14.1494(9)
Å, angles α = β = γ = 90°, and <i>Z</i> = 8 at 120 K. The [tmgH]Cl has a very high absorption
capacity of nearly 3 mol of SO<sub>2</sub> per mol of [tmgH]Cl at
1 bar of SO<sub>2</sub> and at room temperature. However, part of
the absorbed SO<sub>2</sub> was liberated during the crystallization,
probably because the crystal only accommodates one molecule of SO<sub>2</sub> per [tmgH]ÂCl. The nature of the high absorption capacity
of [tmgH]Cl as well as of the homologous compounds with bromide and
iodide are discussed. Some of these salts may prove useful as reversible
absorbents of SO<sub>2</sub> in industrial flue gases
Structural Characterization of 1,1,3,3-Tetramethylguanidinium Chloride Ionic Liquid by Reversible SO<sub>2</sub> Gas Absorption
A unique
new ionic liquid–gas adduct solid state compound formed between
1,1,3,3-tetramethylguanidinium chloride ([tmgH]ÂCl) and sulfur dioxide
has been characterized by X-ray diffraction and Raman spectroscopy.
The structure contains SO<sub>2</sub> molecules of near normal structure
kept at their positions by Cl–S interactions. The crystals
belong in the orthorhombic system, space group <i>Pbcn</i>, with unit cell dimensions of <i>a</i> = 15.6908(10) Ă…, <i>b</i> = 9.3865(6) Ă…, and <i>c</i> = 14.1494(9)
Å, angles α = β = γ = 90°, and <i>Z</i> = 8 at 120 K. The [tmgH]Cl has a very high absorption
capacity of nearly 3 mol of SO<sub>2</sub> per mol of [tmgH]Cl at
1 bar of SO<sub>2</sub> and at room temperature. However, part of
the absorbed SO<sub>2</sub> was liberated during the crystallization,
probably because the crystal only accommodates one molecule of SO<sub>2</sub> per [tmgH]ÂCl. The nature of the high absorption capacity
of [tmgH]Cl as well as of the homologous compounds with bromide and
iodide are discussed. Some of these salts may prove useful as reversible
absorbents of SO<sub>2</sub> in industrial flue gases
Molybdenum(VI) Oxosulfato Complexes in MoO<sub>3</sub>–K<sub>2</sub>S<sub>2</sub>O<sub>7</sub>–K<sub>2</sub>SO<sub>4</sub> Molten Mixtures: Stoichiometry, Vibrational Properties, and Molecular Structures
The structural and vibrational properties of molybdenumÂ(VI)
oxosulfato
complexes formed in MoO<sub>3</sub>–K<sub>2</sub>S<sub>2</sub>O<sub>7</sub> and MoO<sub>3</sub>–K<sub>2</sub>S<sub>2</sub>O<sub>7</sub>–K<sub>2</sub>SO<sub>4</sub> molten mixtures
under an O<sub>2</sub> atmosphere and static equilibrium conditions
were studied by Raman spectroscopy at temperatures of 400–640
°C. The corresponding composition effects were explored in the <i>X</i><sub>MoO<sub>3</sub></sub><sup>0</sup> = 0–0.5 range. MoO<sub>3</sub> undergoes a dissolution
reaction in molten K<sub>2</sub>S<sub>2</sub>O<sub>7</sub>, and the
Raman spectra point to the formation of molybdenumÂ(VI) oxosulfato
complexes. The Moî—»O stretching region of the Raman spectrum
provides sound evidence for the occurrence of a dioxo MoÂ(î—»O)<sub>2</sub> configuration as a core. The stoichiometry of the dissolution
reaction MoO<sub>3</sub> + <i>n</i>S<sub>2</sub>O<sub>7</sub><sup>2–</sup> → C<sup>2<i>n</i>–</sup> was inferred by exploiting the Raman band intensities, and it was
found that <i>n</i> = 1. Therefore, depending on the MoO<sub>3</sub> content, monomeric MoO<sub>2</sub>(SO<sub>4</sub>)<sub>2</sub><sup>2–</sup> and/or associated [MoO<sub>2</sub>(SO<sub>4</sub>)<sub>2</sub>]<sub><i>m</i></sub><sup>2<i>m</i>–</sup> complexes are formed in the binary MoO<sub>3</sub>–K<sub>2</sub>S<sub>2</sub>O<sub>7</sub> molten system, and
pertinent structural models are proposed in full consistency with
the Raman data. A 6-fold coordination around Mo is inferred. Adjacent
MoO<sub>2</sub><sup>2+</sup> cores are linked by bidentate bridging
sulfates. With increasing temperature at concentrated melts (i.e.,
high <i>X</i><sub>MoO<sub>3</sub></sub><sup>0</sup>), the observed spectral changes can be explained
by partial dissociation of [MoO<sub>2</sub>(SO<sub>4</sub>)<sub>2</sub>]<sub><i>m</i></sub><sup>2<i>m</i>–</sup> by detachment of S<sub>2</sub>O<sub>7</sub><sup>2–</sup> and
formation of a MoOMo bridge. Addition of K<sub>2</sub>SO<sub>4</sub> in MoO<sub>3</sub>–K<sub>2</sub>S<sub>2</sub>O<sub>7</sub> results in a “follow-up” reaction and
formation of MoO<sub>2</sub>(SO<sub>4</sub>)<sub>3</sub><sup>4–</sup> and/or associated [MoO<sub>2</sub>(SO<sub>4</sub>)<sub>3</sub>]<sub><i>m</i></sub><sup>4<i>m</i>–</sup> complexes
in the ternary MoO<sub>3</sub>–K<sub>2</sub>S<sub>2</sub>O<sub>7</sub>–K<sub>2</sub>SO<sub>4</sub> molten system. The 6-fold
Mo coordination comprises two oxide ligands and four O atoms linking
to coordinated sulfate groups in various environments of reduced symmetry.
The most characteristic Raman bands for the molybdenumÂ(VI) oxosulfato
complexes pertain to the MoÂ(î—»O)<sub>2</sub> stretching modes:
(1) at 957 (polarized) and 918 (depolarized) cm<sup>–1</sup> for the ν<sub>s</sub> and ν<sub>as</sub> MoÂ(î—»O)<sub>2</sub> modes of MoO<sub>2</sub>(SO<sub>4</sub>)<sub>2</sub><sup>2–</sup> and [MoO<sub>2</sub>(SO<sub>4</sub>)<sub>2</sub>]<sub><i>m</i></sub><sup>2<i>m</i>–</sup> and
(2) at 935 (polarized) and 895 (depolarized) cm<sup>–1</sup> for the respective modes of MoO<sub>2</sub>(SO<sub>4</sub>)<sub>3</sub><sup>4–</sup> and [MoO<sub>2</sub>(SO<sub>4</sub>)<sub>3</sub>]<sub><i>m</i></sub><sup>4<i>m</i>–</sup>. The results were tested and found to be in accordance with ab initio
quantum chemical calculations carried out on [MoO<sub>2</sub>(SO<sub>4</sub>)<sub>3</sub>]<sup>4–</sup> and [{MoO<sub>2</sub>}<sub>2</sub>(SO<sub>4</sub>)<sub>4</sub>(μ-SO<sub>4</sub>)<sub>2</sub>]<sup>8–</sup> ions, in assumed isolated gaseous free states,
at the DFT/B3LYP (HF) level and with the 3-21G basis set. The calculations
included determination of vibrational infrared and Raman spectra,
by use of force constants in the Gaussian 03W program