16 research outputs found
Structural Studies of Lithium 4,5-Dicyanoimidazolate–Glyme Solvates. 2. Ionic Aggregation Modes in Solution and PEO Matrix
In this paper, we present complementary
spectroscopic analyses
of lithium 2-trifluoromethyl-4,5-dicyanoimidazole adducts with aprotic
solvents like dimethyl ethers of poly(ethylene glycols) (i.e., glymes)
and crown ethers. Comparing the XRD structures with Raman spectra
we have found fingerprints of various structural motifs such as ionic
pairs, dimers, “free ions”, and higher aggregates. Comprehensive
analysis of crystalline materials has been performed to correlate
molecular structures with spectroscopic data, which give valuable
information about the coordination preferences of substituted 4,5-dicyanoimidazolato
anions and provide the basis for further developing a model for poly(ethylene
oxide) electrolytes. Complementary and systematic X-ray studies of
glyme adducts enable precise interpretation of the anion–cation
and cation–solvent interactions from experimental Raman spectra.
This information provides a convenient tool for the characterization
of the ionic association interactions within electrolytes
Snapshots of the Hydrolysis of Lithium 4,5-Dicyanoimidazolate–Glyme Solvates. Impact of Water Molecules on Aggregation Processes in Lithium-Ion Battery Electrolytes
Despite
that 4,5-dicyano-2-(trifluoromethyl)imidazole lithium salt
(LiTDI) exhibits several interesting features in aprotic solvents
such as glymes or carbonate esters, little is known about its structural
rearrangement after exposure to water. Since the LiTDI salt has been
verified as an effective moisture scavenger able to suppress degradation
of the LiPF<sub>6</sub>-based electrolyte, comprehensive knowledge
of coordination modes in the LiTDI–H<sub>2</sub>O system, as
well as information about the structure of formed hydrates, is desirable.
In the present study, we report the impact of water on the LiTDI glyme-based
electrolytes investigated by means of the single-crystal X-ray diffraction
technique and Raman spectroscopy. We have found that the exposure
of lithium 4,5-dicyanoimidazolate–glyme solvates to humid air
gives rise to the hydrolysis products arising from stepwise addition
of water molecules to the lithium coordination sphere. Several structural
motifs have been distinguished as preferred coordination modes in
the LiTDI–H<sub>2</sub>O system. A high number of available
ether oxygen donor center water molecules cause dissociation of ionic
contact pairs and aggregation of cationic species stabilized by crown
ethers. Low O:Li molar ratio leads to the formation of LiTDI–glyme–water
solvates and LiTDI hydrates. The air-stable LiTDI trihydrate comprises
ionic pairs formed by a lithium cation coordinated to an imidazole
nitrogen of TDI. A lithium cation coordinated via nitrile groups and
bearing water molecules is a basic motif constituting dimeric species
of formula [Li(H<sub>2</sub>O)<sub>2</sub>TDI]<sub>2</sub> which are
present in aggregated [Li(H<sub>2</sub>O)TDI]<i><sub>n</sub></i> chains making up the structure of a monohydrate. The discovered
motifs have been proved to occur in both the solid and melted hydrated
systems of LiTDI. They will be helpful for conducting molecular dynamic
calculations and for obtaining information how to manipulate the structure
of a Li<sup>+</sup>-solvation sheath in both hydrated and liquid aqueous
electrolytes based on heterocyclic anions
Structural Studies of Lithium 4,5-Dicyanoimidazolate–Glyme Solvates. 1. From Isolated Free Ions to Conductive Aggregated Systems
We present complementary series of
crystal structures of lithium
salts containing 4,5-dicyanoimidazolato anions substituted with perfluoroalkyl
groups. Single-crystal X-ray analysis of 10 adducts with aprotic solvents,
glymes (dimethyl ethers of poly(ethylene glycols)) and crown ethers,
have been performed to correlate their molecular structures and properties
with spectroscopic and thermal data. Comprehensive structure analysis
of crystalline materials reveals valuable information about the coordination
ability of substituted 4,5-dicyanoimidazolato anions and provides
the basis for developing the model of poly(ethylene oxide) electrolytes
and liquid systems. Presented results reveal new aggregation modes
at high concentrations of lithium salts involving the release of cations
by self-assembly of an anionic subnetwork and provide some insight
into the electrochemical performance of TDI anions
Effect of In–C<sub>NHC</sub> Bonds on the Synthesis, Structure, and Reactivity of Dialkylindium Alkoxides: How Indium Compares to Gallium
The investigation
of the reactivity of dialkylindium alkoxides
toward N-heterocyclic carbenes (NHCs) has shown that both the character
of the In–C<sub>NHC</sub> bond and alkyl and alkoxide substituents
have a significant effect on the formation of R<sub>2</sub>InOR(NHC)
complexes and the distribution of products. The reactions of simple
dimethylindium alkoxides with the N-heterocyclic carbenes 1,3-bis(2,4,6-trimethylphenyl)imidazolin-2-ylidene
(SIMes) and 1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene (IMes)
lead to the monomeric complexes Me<sub>2</sub>InOR(NHC), as shown
by the isolation of Me<sub>2</sub>InOMe(NHC) (NHC = IMes (<b>3</b>), SIMes (<b>4</b>)). Compounds Me<sub>2</sub>InOR(NHC) are
unstable in solution and instantly disproportionate, which can be
associated with a weaker In–C<sub>NHC</sub> bond in comparison
with stable gallium analogues. As a result, Me<sub>3</sub>In(NHC)
(NHC = IMes (<b>1</b>), SIMes (<b>2</b>)) adducts, as
well as Mitsubishi-type methylindium alkoxides, are formed. The exchange
of a simple alkoxy group with chelating (<i>S</i>)-methyl
lactate (<i>S-melac</i>) has resulted in the more stable
Me<sub>2</sub>In(OCH(Me)CO<sub>2</sub>Me)(NHC) complexes. The use
of the bulky alkoxide ligand OCPh<sub>2</sub>Me allows for the synthesis
of stable Me<sub>2</sub>In(OCPh<sub>2</sub>Me)(NHC) (NHC = IMes (<b>6</b>), SIMes (<b>7</b>)) from [Me<sub>2</sub>In(μ-OCPh<sub>2</sub>Me)]<sub>2</sub> (<b>5</b>). While the strongest In–C<sub>NHC</sub> bond, among the characterized Me<sub>2</sub>In(OR)(NHC)
complexes, is crucial for the stability of <b>6</b> and <b>7</b>, it is still weaker in comparison with Ga–C<sub>NHC</sub> bonds in the analogous gallium complexes Me<sub>2</sub>Ga(OCPh<sub>2</sub>Me)(NHC) (NHC = IMes (<b>8</b>), SIMes (<b>9</b>)). For [<sup><i>t</i></sup>Bu<sub>2</sub>In(μ-OCH<sub>2</sub>CH<sub>2</sub>OMe)]<sub>2</sub>, the introduction of a bulky <i>tert</i>-butyl group has resulted in a lack of reactivity toward
NHCs. However, the structure of <sup><i>t</i></sup>Bu<sub>2</sub>In(OCPh<sub>2</sub>Me)(IMes) has confirmed the substantial
effect of bulky alkyl substituents on the strength of the In–C<sub>NHC</sub> bond. The structures of <b>1</b>, <b>2</b>, <b>4</b>–<b>6</b>, and <b>8</b> have been determined
using both spectroscopic methods in solution and X-ray diffraction
studies. Similarly to their gallium analogues, Me<sub>2</sub>In(OCH(Me)CO<sub>2</sub>Me)(NHC) complexes are highly active in the ring-opening polymerization
of <i>rac</i>-lactide already at −20 °C, leading
to isotactically enriched PLA (<i>P</i><sub>m</sub> = 0.67–0.76).
However, in contrast to the gallium complexes Me<sub>2</sub>GaOR(NHC),
the noninnocent role of an NHC ligand, resulting in the formation
of cyclic PLA, has been demonstrated for <b>6</b> and <b>7</b>
Dialkylgallium Complexes with Alkoxide and Aryloxide Ligands Possessing N‑Heterocyclic Carbene Functionalities: Synthesis and Structure
Methods for the synthesis
of dialkylgalium compounds with alkoxide
or aryloxide ligands possessing N-heterocyclic carbene functionalities
have been established. As a result, the synthesis of a series of dialkylgallium
complexes Me<sub>2</sub>Ga(O,C) (<b>1</b>, <b>3</b>–<b>5</b>), and Me<sub>2</sub>Ga(O,C)·Me<sub>3</sub>Ga (<b>2</b>, <b>6</b>) is described, where (O,C) represents an
alkoxide or aryloxide monoanionic chelate ligand with an N-heterocyclic
carbene functionality. All complexes have been fully characterized
using spectroscopic and X-ray techniques. The presence of a strongly
basic NHC functionality in alkoxide or aryloxide ligands resulted
in the formation of monomeric Me<sub>2</sub>Ga(O,C) species. The reaction
of those complexes with the Lewis acid Me<sub>3</sub>Ga leads to Me<sub>2</sub>Ga(O,C)·Me<sub>3</sub>Ga adducts (<b>2</b> and <b>6</b>) with a strong Me<sub>3</sub>Ga–O dative bond. The
effect of (O,C) ligands with various steric and electronic properties
on the structure of obtained Me<sub>2</sub>Ga(O,C) and Me<sub>2</sub>Ga(O,C)·Me<sub>3</sub>Ga has been discussed on the basis of
spectroscopic data. Finally, the bond valence vector model has been
used to estimate the effect of a chelating (O,C) ligand on strains
in complexes <b>1</b>–<b>6</b> on the basis of
X-ray data
Dialkylgallium Complexes with Alkoxide and Aryloxide Ligands Possessing N‑Heterocyclic Carbene Functionalities: Synthesis and Structure
Methods for the synthesis
of dialkylgalium compounds with alkoxide
or aryloxide ligands possessing N-heterocyclic carbene functionalities
have been established. As a result, the synthesis of a series of dialkylgallium
complexes Me<sub>2</sub>Ga(O,C) (<b>1</b>, <b>3</b>–<b>5</b>), and Me<sub>2</sub>Ga(O,C)·Me<sub>3</sub>Ga (<b>2</b>, <b>6</b>) is described, where (O,C) represents an
alkoxide or aryloxide monoanionic chelate ligand with an N-heterocyclic
carbene functionality. All complexes have been fully characterized
using spectroscopic and X-ray techniques. The presence of a strongly
basic NHC functionality in alkoxide or aryloxide ligands resulted
in the formation of monomeric Me<sub>2</sub>Ga(O,C) species. The reaction
of those complexes with the Lewis acid Me<sub>3</sub>Ga leads to Me<sub>2</sub>Ga(O,C)·Me<sub>3</sub>Ga adducts (<b>2</b> and <b>6</b>) with a strong Me<sub>3</sub>Ga–O dative bond. The
effect of (O,C) ligands with various steric and electronic properties
on the structure of obtained Me<sub>2</sub>Ga(O,C) and Me<sub>2</sub>Ga(O,C)·Me<sub>3</sub>Ga has been discussed on the basis of
spectroscopic data. Finally, the bond valence vector model has been
used to estimate the effect of a chelating (O,C) ligand on strains
in complexes <b>1</b>–<b>6</b> on the basis of
X-ray data
Dialkylgallium Alkoxides Stabilized with <i>N</i>‑Heterocyclic Carbenes: Opportunities and Limitations for the Controlled and Stereoselective Polymerization of <i>rac</i>-Lactide
The structure of a series of Me<sub>2</sub>GaOR(NHC) complexes
with <i>N</i>-heterocyclic carbenes (1,3-bis(2,4,6-trimethylphenyl)imidazolin-2-ylidene
(SIMes) and 1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene (IMes))
have been characterized using spectroscopic and X-ray techniques and
discussed in view of their reactivity in the polymerization of <i>rac</i>-lactide (<i>rac</i>-LA). Both structure studies
and density functional theory (DFT) calculations show the significant
influence of NHC and OR on the structure of investigated complexes
and has indicated that the Ga–C<sub>NHC</sub> bond (32.6–39.6
kcal mol<sup>–1</sup>) is strong enough to form stable Me<sub>2</sub>GaOR(NHC) complexes in the form of monomeric species. The
reactivity of Me<sub>2</sub>Ga((<i>S</i>)-OCH(Me)CO<sub>2</sub>Me)(SIMes) (<b>1</b>) and Me<sub>2</sub>Ga((<i>S</i>)-OCH(Me)CO<sub>2</sub>Me)(IMes) (<b>5</b>) toward
Lewis acids such as CO<sub>2</sub> and GaMe<sub>3</sub> has resulted
in breaking of the Ga–C<sub>NHC</sub> bond with the formation
of (NHC)CO<sub>2</sub> and Me<sub>3</sub>Ga(NHC) (<b>8</b> and <b>10</b>) and [Me<sub>2</sub>Ga(μ-(<i>S</i>)-OCH(Me)CO<sub>2</sub>Me)]<sub>2</sub>. Different results have been obtained for
l,3-bis(2,6-diisopropylphenyl)-imidazolin-2-ylidene (SIPr), which
coordinates more weakly to gallium, as demonstrated by the Ga–C<sub>NHC</sub> bond strength for model Me<sub>3</sub>GaSIMes, Me<sub>3</sub>GaIMes (<b>8</b>), and Me<sub>3</sub>GaSIPr (<b>10</b>) adducts. The reaction of SIPr with [Me<sub>2</sub>Ga(μ-OR)]<sub>2</sub> has not allowed for the breaking of Ga<sub>2</sub>O<sub>2</sub> bridges and the formation of monomeric Me<sub>2</sub>GaOR(SIPr)
complexes, contrary to SIMes and IMes. In the case of the reaction
with [Me<sub>2</sub>Ga(μ-(<i>S</i>)-OCH(Me)CO<sub>2</sub>Me)]<sub>2</sub>, the ionic compound [Me<sub>2</sub>Ga(OCH(Me)CO<sub>2</sub>)]<sup>−</sup>[SIPrH]<sup>+</sup> (<b>9</b>)
has been isolated. The investigated Me<sub>2</sub>GaOR(NHC) complexes
are highly active and stereoselective in the ring-opening polymerization
of <i>rac</i>-lactide from −20 °C to room temperature,
due to the insertion of <i>rac</i>-LA exclusively into the
Ga–O<sub>alkoxide</sub> bond, leading to isotactically enriched
polylactide (PLA) (<i>P</i><sub>m</sub> = 0.65–0.78).
It has been shown that the polymerization of lactide at low temperature
is influenced by the chelate interaction of (<i>S</i>)-OCH(Me)CO<sub>2</sub>Me or (OCH(Me)C(O))<sub>2</sub>OR resulting from the primary
insertion of <i>rac</i>-LA into the Ga–O<sub>alkoxide</sub> bond, with the Ga center, which can be responsible for the low control
over the molecular weight of the obtained PLA. The latter effect can
be eliminated by the initial synthesis of Me<sub>2</sub>Ga((PLA)<sub><i>n</i></sub>OR)(NHC) with short PLA chains, which allows
for controlled polymerization. Although the adverse chelate effect
can be also eliminated by the polymerization of <i>rac</i>-LA at room temperature, the stereoselectivity of <i>rac</i>-LA polymerization is strongly affected by transesterification reactions.
Out of investigated Me<sub>2</sub>GaOR(SIMes) and Me<sub>2</sub>GaOR(IMes)
complexes, only the latter allowed for the immortal ring opening polymerization
of <i>rac</i>-LA in the presence of <sup><i>i</i></sup>PrOH
Dialkylgallium Alkoxides Stabilized with <i>N</i>‑Heterocyclic Carbenes: Opportunities and Limitations for the Controlled and Stereoselective Polymerization of <i>rac</i>-Lactide
The structure of a series of Me<sub>2</sub>GaOR(NHC) complexes
with <i>N</i>-heterocyclic carbenes (1,3-bis(2,4,6-trimethylphenyl)imidazolin-2-ylidene
(SIMes) and 1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene (IMes))
have been characterized using spectroscopic and X-ray techniques and
discussed in view of their reactivity in the polymerization of <i>rac</i>-lactide (<i>rac</i>-LA). Both structure studies
and density functional theory (DFT) calculations show the significant
influence of NHC and OR on the structure of investigated complexes
and has indicated that the Ga–C<sub>NHC</sub> bond (32.6–39.6
kcal mol<sup>–1</sup>) is strong enough to form stable Me<sub>2</sub>GaOR(NHC) complexes in the form of monomeric species. The
reactivity of Me<sub>2</sub>Ga((<i>S</i>)-OCH(Me)CO<sub>2</sub>Me)(SIMes) (<b>1</b>) and Me<sub>2</sub>Ga((<i>S</i>)-OCH(Me)CO<sub>2</sub>Me)(IMes) (<b>5</b>) toward
Lewis acids such as CO<sub>2</sub> and GaMe<sub>3</sub> has resulted
in breaking of the Ga–C<sub>NHC</sub> bond with the formation
of (NHC)CO<sub>2</sub> and Me<sub>3</sub>Ga(NHC) (<b>8</b> and <b>10</b>) and [Me<sub>2</sub>Ga(μ-(<i>S</i>)-OCH(Me)CO<sub>2</sub>Me)]<sub>2</sub>. Different results have been obtained for
l,3-bis(2,6-diisopropylphenyl)-imidazolin-2-ylidene (SIPr), which
coordinates more weakly to gallium, as demonstrated by the Ga–C<sub>NHC</sub> bond strength for model Me<sub>3</sub>GaSIMes, Me<sub>3</sub>GaIMes (<b>8</b>), and Me<sub>3</sub>GaSIPr (<b>10</b>) adducts. The reaction of SIPr with [Me<sub>2</sub>Ga(μ-OR)]<sub>2</sub> has not allowed for the breaking of Ga<sub>2</sub>O<sub>2</sub> bridges and the formation of monomeric Me<sub>2</sub>GaOR(SIPr)
complexes, contrary to SIMes and IMes. In the case of the reaction
with [Me<sub>2</sub>Ga(μ-(<i>S</i>)-OCH(Me)CO<sub>2</sub>Me)]<sub>2</sub>, the ionic compound [Me<sub>2</sub>Ga(OCH(Me)CO<sub>2</sub>)]<sup>−</sup>[SIPrH]<sup>+</sup> (<b>9</b>)
has been isolated. The investigated Me<sub>2</sub>GaOR(NHC) complexes
are highly active and stereoselective in the ring-opening polymerization
of <i>rac</i>-lactide from −20 °C to room temperature,
due to the insertion of <i>rac</i>-LA exclusively into the
Ga–O<sub>alkoxide</sub> bond, leading to isotactically enriched
polylactide (PLA) (<i>P</i><sub>m</sub> = 0.65–0.78).
It has been shown that the polymerization of lactide at low temperature
is influenced by the chelate interaction of (<i>S</i>)-OCH(Me)CO<sub>2</sub>Me or (OCH(Me)C(O))<sub>2</sub>OR resulting from the primary
insertion of <i>rac</i>-LA into the Ga–O<sub>alkoxide</sub> bond, with the Ga center, which can be responsible for the low control
over the molecular weight of the obtained PLA. The latter effect can
be eliminated by the initial synthesis of Me<sub>2</sub>Ga((PLA)<sub><i>n</i></sub>OR)(NHC) with short PLA chains, which allows
for controlled polymerization. Although the adverse chelate effect
can be also eliminated by the polymerization of <i>rac</i>-LA at room temperature, the stereoselectivity of <i>rac</i>-LA polymerization is strongly affected by transesterification reactions.
Out of investigated Me<sub>2</sub>GaOR(SIMes) and Me<sub>2</sub>GaOR(IMes)
complexes, only the latter allowed for the immortal ring opening polymerization
of <i>rac</i>-LA in the presence of <sup><i>i</i></sup>PrOH
Coordination Abilities of 4,5-Dicyano-2-(trifluoromethyl)imidazolate Anion toward Sodium Cation: Structural and Spectroscopic Studies of Solid and Liquid Glyme-Solvated Electrolyte Systems
Comprehensive
structural analysis of sodium 4,5-dicyano-2-(trifluoromethyl)imidazolate
(NaTDI) solvates with glymes (1–4), tetrahydrofuran, and crown
ethers has been performed. Several structural motifs obtained from
single-crystal X-ray analysis of complementary series of crystalline
adducts with varying O:Na ratios were correlated with spectroscopic
and thermal data to provide new information about the coordination
ability of heterocyclic anions toward sodium cations. Presented results
provide a basis for developing models of poly(ethylene oxide) electrolytes
and liquid systems for sodium ion battery electrolytes. We have found
a wide variety of anion–cation coordination types which allow
us to compare them with analogous lithium solvates in terms of Brown’s
valence-matching principle and Lewis acid strength (<i>S</i><sub>a</sub>) parameters. Noticed aggregation modes of sodium salts
confirm the occurrence of a solvate disproportionation conductivity
mechanism at high salt concentrations which can be used for developing
new heterocyclic salt systems for sodium batteries
Dialkylgallium Complexes with Alkoxide and Aryloxide Ligands Possessing N‑Heterocyclic Carbene Functionalities: Synthesis and Structure
Methods for the synthesis
of dialkylgalium compounds with alkoxide
or aryloxide ligands possessing N-heterocyclic carbene functionalities
have been established. As a result, the synthesis of a series of dialkylgallium
complexes Me<sub>2</sub>Ga(O,C) (<b>1</b>, <b>3</b>–<b>5</b>), and Me<sub>2</sub>Ga(O,C)·Me<sub>3</sub>Ga (<b>2</b>, <b>6</b>) is described, where (O,C) represents an
alkoxide or aryloxide monoanionic chelate ligand with an N-heterocyclic
carbene functionality. All complexes have been fully characterized
using spectroscopic and X-ray techniques. The presence of a strongly
basic NHC functionality in alkoxide or aryloxide ligands resulted
in the formation of monomeric Me<sub>2</sub>Ga(O,C) species. The reaction
of those complexes with the Lewis acid Me<sub>3</sub>Ga leads to Me<sub>2</sub>Ga(O,C)·Me<sub>3</sub>Ga adducts (<b>2</b> and <b>6</b>) with a strong Me<sub>3</sub>Ga–O dative bond. The
effect of (O,C) ligands with various steric and electronic properties
on the structure of obtained Me<sub>2</sub>Ga(O,C) and Me<sub>2</sub>Ga(O,C)·Me<sub>3</sub>Ga has been discussed on the basis of
spectroscopic data. Finally, the bond valence vector model has been
used to estimate the effect of a chelating (O,C) ligand on strains
in complexes <b>1</b>–<b>6</b> on the basis of
X-ray data