What Are Ionic Liquids? Core Concepts, Application Map, and a Selection Workflow (with a Summary Table of Representative Aladdin Product Categories)

Ionic liquids: salts that can flow at room temperature—and a “designable” solvent platform

Ionic liquids (ILs) are often described as “salts that can flow at relatively low temperatures.” Their importance is not only that they can be used as solvents, but that many of their properties can be tuned through structural combinations—making them a genuinely designable platform.

1) Start from the basics: what is an ionic liquid?

(1) Key definition points

• An ionic liquid is a salt-like liquid whose major components are ions (ions dominate the composition). In most single-salt ILs, overall charge neutrality is maintained by the cation/anion pair; however, in some systems there may be multiple ionic species and/or residual neutral components.

(2) A practical “boundary” commonly used in research

• As a working convention, salts with melting points (Tm) below 100 °C are often classified as ionic liquids. Those that are liquids at room temperature (~25 °C) or near room temperature are commonly called RTILs (room-temperature ionic liquids). Some systems can form supercooled liquids or glassy states; Tg is used to describe low-temperature behavior, but Tg is not the primary classification criterion.
• This also explains a common confusion: not every “ionic liquid” must be liquid at room temperature—it depends on the definition boundary used and on the specific ion structures involved.

2) Draw the boundaries: don’t mix these concepts up

(1) Molten salts

• "Molten salt" is a broader category. For example, NaCl only melts at high temperature. Ionic liquids typically refer to the low-melting subset of molten salts.

(2) Deep eutectic solvents (DES)

• DES are typically multicomponent eutectic mixtures, and the components can include neutral (non-ionic) molecules. They are not equivalent to ionic liquids in which ions are the primary constituents.

3) Why can a “salt” flow like a liquid near room temperature?

The low melting points of ionic liquids are not “mysterious”—they follow from structure and packing:

(1) Larger, more asymmetric, more flexible ions → poorer packing, weaker crystallization driving force

• Note: Low melting points usually arise from multiple factors acting together: shape mismatch, conformational freedom, anisotropy of interionic interactions, and (in some systems) hydrogen bonding/π interactions that make it difficult to form long-range ordered crystals.

(2) Anions often show charge delocalization / weak coordination → reduced lattice energy

(3) Net result：Ions are less easily “locked” into a rigid lattice, so the material more readily remains liquid at lower temperatures and allows ion migration and structural rearrangement.

4) Why did ionic liquids become a “designable platform”?

(1) 1914

• Walden reported low-melting ionic systems such as ethylammonium nitrate, often regarded as early representatives of ionic liquids.

(2) Mid–late 20th century

• Electrochemistry-related “room-temperature molten salt” systems drove application exploration, but many were sensitive to water/air.

(3) Since the 1990s

• More stable and user-friendly systems emerged, enabling ionic liquids to evolve from “special molten salts” into a systematically designable and screenable toolbox for solvents, catalysis, electrolytes, separations, and materials.

Typical features of ionic liquids: a quick pros/cons comparison

Typical feature	Advantages	Common drawbacks / limitations	How to address (selection & operational tips)
Low volatility (low vapor pressure)	Vapor pressures are typically very low at ambient conditions; minimal evaporative loss; can reduce solvent evaporation and VOC emissions	“Low volatility” ≠ “absolutely non-volatile”; at high temperature/high vacuum or under decomposition conditions, loss and/or decomposition products may still occur	Check property data vs operating temperature and decomposition limits; for high-T systems, prioritize more thermally stable ion combinations and design recovery/purification workflows
Tunability (structure is adjustable)	By varying cation/anion combinations, viscosity, hydrophobicity, coordination ability, solvation power, conductivity, etc. can be tuned systematically	“Designable” ≠ “any combination will work”; properties often change nonlinearly and require screening	Use a workflow of “application target → choose anion to set direction → fine-tune with cation”; run small-scale screening of ~3–5 candidates
Strong dissolution/solvation capability	Unique solubility for certain difficult systems (e.g., some cellulose/biomass, inorganic salts, organic substrates)	Highly dependent on the specific ion pair; water content can strongly alter dissolution/swelling and reaction selectivity	Define the exact target to dissolve; choose an anion system with literature support; control water (Karl Fischer) and record water content and pretreatment methods
Higher viscosity (common)	High ionic strength and strong interactions can create a stable solvent environment; sometimes helps suppress evaporation and improve handling safety	High viscosity slows mass transfer, complicates stirring, and can slow kinetics; viscosity varies widely across ILs	Check viscosity–temperature curves; moderately increase temperature; add an inert cosolvent/diluent if compatible; or choose lower-viscosity ion pairs
Potentially wide electrochemical window (system-dependent)	Some systems offer broad electrochemical stability windows suitable for electrolytes, electrodeposition, electrochemical synthesis	Window is highly sensitive to water, halides, dissolved oxygen, and metal impurities; electrode choice and test protocol also matter	For electrochemical uses, prioritize specs for water (KF), halides, and metal impurities; standardize electrode materials and test conditions; include blank controls
Adjustable hydrophilicity/hydrophobicity	Anion and cation side chains can tune miscibility with water or phase separation, enabling biphasic reactions/extractions	Hydrophilicity is not determined by only one ion; temperature and water content can shift phase behavior	For phase-separating systems: consult/measure phase diagrams or miscibility first; verify phase split, viscosity, and extraction efficiency in small-scale tests
Chemical/thermal stability (system-dependent)	Many ILs are stable and convenient within certain temperature ranges	Not all are stable: some anions may hydrolyze in water/acid or upon heating; strong Lewis-acid systems can be more sensitive and highly corrosive	Select anions appropriate to the medium (water/acid/base/temperature); handle sensitive systems under dry/inert conditions; evaluate material compatibility
“Low volatility” safety perception (often misread as “green”)	Low volatility can reduce inhalation exposure and direct emissions	Low volatility ≠ non-toxic/biodegradable; ecotoxicity and biodegradability depend strongly on structure; exposure routes may shift (less inhalation risk but more skin contact/residue pollution and higher waste-treatment burden)	Still require toxicology/environmental assessment; prioritize systems with a better-known environmental profile where possible, and implement strict recovery and waste management
Strong batch/impurity effects on reproducibility	With controlled purity, ILs can provide stable, repeatable solvent environments	Trace water, halides, and metal impurities can strongly shift viscosity, conductivity, electrochemical window, and catalytic selectivity	Require a CoA; re-check water content on receipt (at least by KF); for electrochemistry/catalysis, establish “batch acceptance criteria”

Application map: what roles do ionic liquids usually play in a system?

Role / application module	Primary function of the ionic liquid	What to prioritize in selection	Reminder	Typical product examples
Reaction medium (solvent / reaction environment)	Provides a tunable solvation microenvironment; can form biphasic systems for separation/recycling	Solvation power, viscosity/mass transfer, phase behavior (biphasic or not), compatibility, water content	High viscosity → slower mass transfer; water uptake can shift properties/selectivity	1-Butyl-3-methylimidazolium hexafluorophosphate ([C4mim][PF6]); 1-Butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide ([C4mim][NTf2])
Catalysis platform (Lewis-acid/coordination; e.g., chloroaluminate systems)	Provides both solvent and catalytic sites (often more sensitive/corrosive)	Acidity/coordination strength, water tolerance, corrosivity, material compatibility, impurities	More sensitive to water/air; corrosion and compatibility must be evaluated	1-Ethyl-3-methylimidazolium chloride–AlCl3 system ([C2mim]Cl–AlCl3); 1-Butyl-3-methylimidazolium chloride–AlCl3 system ([C4mim]Cl–AlCl3). Note: These are composition-variable systems; acidity/speciation depends strongly on ratio and water content.
Separation/extraction (organics; metals/rare earths, etc.)	Serves as extraction phase or additive to tune partitioning; TSILs embed ligating groups to increase selectivity	Selectivity, phase split/emulsification behavior, viscosity (kinetics), regenerability/recovery, water content	Emulsions/unstable phase separation; water/impurities alter coordination and distribution	Trioctylmethylammonium nitrate (A336[NO3], alkyl chains are a mixture); Trihexyl(tetradecyl)phosphonium bis(2-ethylhexyl)phosphate ([P66614][DEHP])
Electrochemistry & energy storage (electrolyte / additive)	Low-volatility electrolyte environment; some systems offer wider windows	Electrochemical window, conductivity/viscosity, water (KF), halides/metal impurities, low-temperature flow; note the window is a combined “system–electrode–impurity–method” outcome, not a single fixed constant of an IL	Higher water content can sharply narrow the window; strong viscosity–conductivity trade-off	1-Ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide ([C2mim][NTf2]); N-Methyl-N-propylpyrrolidinium bis(fluorosulfonyl)imide ([Pyr13][FSI])
Biomass/polymer processing (cellulose/lignocellulose, etc.)	Dissolution–regeneration, pretreatment, separation/modification	Literature support for target component, water sensitivity, viscosity, recovery pathway, material compatibility	Not all ILs dissolve cellulose; scale-up often bottlenecked by recovery/reuse	1-Ethyl-3-methylimidazolium acetate ([C2mim][OAc]); 1-Butyl-3-methylimidazolium chloride ([C4mim]Cl)
Materials: poly(ionic liquid)s (PILs) / membranes	Polymerizes IL motifs for membranes, ion conduction, sensing, etc.	Mechanical strength/swelling, ionic conductivity, selectivity/permeability, long-term stability, processability	Swelling–strength trade-off; microstructure governs performance	poly(1-vinyl-3-ethylimidazolium) bis(trifluoromethanesulfonyl)imide (poly([VEIm][NTf2])); poly(1-vinyl-3-alkylimidazolium) bromide (poly([VAmIm]Br))
Engineering intensification: SILP (supported ionic liquid phase)	Forms a thin IL film on porous supports; immobilizes homogeneous catalysts for continuous flow/fixed-bed operation	IL film stability, catalyst retention, support pore structure, mass transfer, leaching	Too much IL can block pores; long-term operation must address loss/regeneration	Silica-supported [C4mim][PF6] ([C4mim][PF6]@SiO2); Silica-supported [C4mim][BF4] ([C4mim][BF4]@SiO2)
CO₂ capture/separation (extended module)	Physical absorption or functionalized chemical absorption; also used in membrane absorption systems	Loading/selectivity, viscosity/mass transfer, regeneration energy, water effect, stability	High viscosity can limit mass transfer; regeneration/energy cost must be quantified	1-Butyl-3-methylimidazolium tetrafluoroborate ([C4mim][BF4], commonly used for physical absorption); 1-(3-Aminopropyl)-3-methylimidazolium tetrafluoroborate ([apmim][BF4])
Analytical chemistry (extended module: GC stationary phases, etc.)	Used as chromatographic stationary phases/coatings or as method-tuning media	Thermal stability/bleed, background interference, selectivity, coating consistency	Not a “universal additive”; structural differences are large—validation is required	1-Butyl-3-methylimidazolium trifluoromethanesulfonate ([C4mim][TfO]); [NTf2]-type IL stationary phases

Main ionic-liquid product categories and selection tips (quick reference)

Note:

PIL = protic ionic liquid

PolyIL = poly(ionic liquid)(s)

Product category	Typical composition / form	Primary role in a system	Key selection keywords	Typical cautions
Aprotic ionic liquids (APIL / aprotic ILs)	Imidazolium / pyrrolidinium / quaternary ammonium / quaternary phosphonium + various anions	Solvent, additive, base electrolyte fluid, separation phase	Viscosity, hydrophilicity/hydrophobicity, coordination/nucleophilicity, thermal stability, electrochemical stability	Water/halides/metal impurities strongly affect reproducibility and electrochemical window (CoA recommended)
Protic ionic liquids (PILs)	Brønsted acid–base proton transfer (often equimolar neutralization; transfer may be incomplete)	Acid catalysis, proton conduction, hydrogen-bond-network medium	Acid strength / ΔpKa, proton mobility, water sensitivity, volatile bycomponents	Strong coupling with water/impurities; may contain residual neutral components—control purity and water
Lewis-acid / metal halide complex / halo-metalate ILs (incl. chloroaluminates)	[Cnmim]Cl–MClx (systems); composition determines speciation such as [MCl₄]⁻ / [M₂Cl₇]⁻	Lewis-acid catalysis, electrodeposition/electrochemistry, hydrocarbon conversion, etc.	Acidity (composition ratio), water sensitivity, corrosivity, material compatibility	Strongly hygroscopic/corrosive; usually requires dry inert handling; acidity can shift dramatically with composition
Task-specific / functionalized ionic liquids (TSILs)	Functional groups covalently built into cation/anion (coordination, acid/base, reactivity, recognition, etc.)	“Solvent + function” in one: extraction/capture/catalysis/material compatibility	Selectivity, compatibility, recyclability, stability	More complex structures and higher cost; screen on small scale before scale-up
Electrolyte-grade ionic liquids / electrolyte formulations	Low-water, low-halide ILs; or IL + lithium salts/additives	Battery/capacitor/electrodeposition electrolytes	Electrochemical window, conductivity–viscosity balance, low-temperature performance, water (KF)	Water content strongly affects the window; specifications should distinguish electrolyte-grade vs general-grade
Solvate ionic liquids (SILs)	Typical [Li(glyme)]X (1:1 complex; “behaves more like an IL than a concentrated solution”)	High Li⁺ transference-number electrolytes; suppresses side reactions	Coordination strength, anion type, viscosity, conductivity, stability	Must be understood as a “solvation structure,” not treated like ordinary diluted solutions
PolyIL (poly(ionic liquid), materials)	Polymers obtained by polymerizing IL monomers (for membranes/adsorption/conduction materials)	Membrane separation, ion conduction, adsorption, sensing	Tg/mechanical strength, swelling, conductivity, long-term stability	Functions more like a material than a solvent; processing and swelling control are critical
Ionic-liquid membranes / gels (SILM / ionogel)	IL immobilized in porous supports (SILM); IL immobilized in polymer networks (ionogel)	Gas separation, flexible electrolytes, ionic conductors	Permeability/selectivity, resistance to IL loss, mechanical strength, temperature window	Watch IL leakage and long-term stability; fabrication strongly affects performance
SILP / supported ionic liquid phase (engineering)	Thin IL film on porous solids dissolving homogeneous catalysts for continuous flow	Fixed-bed/continuous-flow catalysis; easier recovery	Support pore structure, IL film stability, mass transfer, leaching	Excess IL can block pores; lifetime and regeneration strategy must be verified

Practical selection: a workflow that “back-solves structure from the application need”

Step 1 — Clarify the role first: what do you want it to be?

1. As a solvent / reaction medium: prioritize solvation power, viscosity, compatibility with substrates/catalysts, and whether biphasic separation is needed.
2. As an electrolyte: prioritize electrochemical window, ionic conductivity, viscosity, low-temperature flow, and tolerance to water/halides.
3. As an extraction/separation phase: prioritize distribution coefficient, selectivity, viscosity, phase behavior, and regenerability.
4. As a biomass solvent: prioritize cellulose/lignin dissolution ability, viscosity and water sensitivity, and the regeneration route.

Step 2 — Use the anion to set the main direction (often governs hydrophobicity/coordination/stability)

1. Strongly coordinating / highly nucleophilic (e.g., Cl⁻): strong dissolution potential but may interfere with catalysis/materials and can be more corrosive.
2. Weakly coordinating, charge-delocalized (e.g., NTf2⁻): often better for electrochemistry and stability; typically more hydrophobic.
3. BF4⁻ / PF6⁻: widely used, but pay close attention to hydrolysis boundaries—risk increases in aqueous media, under acidic conditions, or at elevated temperature.

Step 3 — Use the cation family to fine-tune handling and engineering properties

1. Longer side chains generally increase hydrophobicity and may increase viscosity. Different families (imidazolium / quaternary ammonium / quaternary phosphonium / pyrrolidinium, etc.) differ in thermal stability, reductive stability, and viscosity–conductivity balance. (Use supplier data sheets plus small-scale screening.)

Step 4 — Lock in reproducibility with grade and impurity specs

Prioritize checking:

1. Water content (Karl Fischer)
2. Halides / acidity-basicity (especially for electrochemistry, metal catalysis, and corrosion-sensitive systems)
3. Metal impurities (ppm levels can matter in both electrochemistry and catalysis)
4. Whether there is a clear CoA and batch consistency statement

Experimental and Safety Notes

1. Water control: Strong hygroscopicity is common for ionic liquids. Water content can significantly change viscosity, conductivity, solvation power, and the electrochemical window.
2. Corrosion prevention & compatibility: Halides and strong Lewis-acid systems are more demanding on equipment and construction materials.
3. Be cautious about hydrolysis of fluorinated anions under water/acid/high-temperature conditions—especially BF₄⁻ and PF₆⁻ systems. Do not treat them as “unconditionally water-stable.”
4. Recovery and reuse: “Recyclability” often holds for ionic liquids, but it must be designed in advance: e.g., extraction / distillation (often impractical for low-volatility systems) / adsorption-based purification / re-drying, etc. Use key performance indicators to confirm no performance drift after recycling.

Frequently Asked Questions (FAQ)

Q1: Are ionic liquids “green solvents”?

• A: They are typically low-volatility and may reduce VOC emissions, but “green” cannot be judged by volatility alone. Many commonly used ionic liquids can be toxic to aquatic/soil organisms and/or poorly biodegradable. Toxicology and life-cycle assessment should be performed case-by-case based on the application.

Q2: Why did my reaction become slower when using an ionic liquid?

• A: The most common reason is high viscosity, which slows mass transfer; another is that the ionic liquid may interact strongly with the catalyst/substrate and shift the reaction pathway. Try raising temperature, choosing a lower-viscosity ion pair, adding an inert cosolvent, or changing the anion.

Q3: Why is the electrochemical window of my ionic-liquid electrolyte not as wide as reported in the literature?

• A: The electrochemical window is highly sensitive to water, halides, dissolved oxygen, and metal impurities. Electrode materials and test methods also affect results. Prioritize low-impurity grades, and measure and record water content (e.g., Karl Fischer) rather than assuming it.

Q4: Can ionic liquids be used together with water?

• A: Many can, but it depends on the system: some are water-miscible, others phase-separate. More importantly, some anions can hydrolyze in water or otherwise alter the chemical environment. Perform a stability check first.

Q5: How do I choose between ionic liquids and DES?

• A: DES are often easier to prepare and potentially lower in cost, but they differ in fundamentals, stability, and compositional complexity. Clarify whether you value a designable ionic microenvironment (IL) or a simple, mix-and-use eutectic system (DES).

Summary Table of Representative Aladdin Ionic-Liquid Product Categories

(Electrochemistry · Extraction/Interfaces · Hydrophilic Polar Systems · Precursors · Dissolution · Acidic Systems)

Category directory:

Electrochemistry / hydrophobic weakly coordinating (TFSI/FSI/PF₆/SbF₆) ｜ Long-chain interfaces / biphasic (C8 imidazolium) ｜ Halide precursors (Cl/Br) ｜ Acetate dissolution (OAc⁻) ｜ Hydrophilic polar anions (OMs/OTf/alkyl sulfate/p-TsO/NO₃⁻) ｜ Phosphate esters (DEP/DBP) ｜ Strongly coordinating anions (DCA/SCN) ｜ Acidic ILs (HSO₄⁻ / cation sulfonic functionalization) ｜ Extraction/phase-transfer quaternary ammonium & phosphonium (A336, P66614, etc.) ｜ DES/biological-system components (ChCl)

Classification	CAS No.	Aladdin Cat. No.	Name	Grade / Purity	Application notes (product features / role, selection tips)
DES / “green” system component | choline salts (Chol⁺) | Cl⁻ (not an IL per se; often used as a DES HBA)	67-48-1	C108897	Choline chloride	For cell culture, for insect cell culture, ≥99%	Choline salts are common hydrogen-bond acceptors (HBAs) in DES and additives in biological systems; typically not used as a “room-temperature ionic liquid” by itself. Hydrophilic and hygroscopic—pay attention to water content and cleanliness.
Extraction / phase transfer | quaternary ammonium (A336, mixed alkyl) | Cl⁻	63393-96-4	A101026	Methyltrioctylammonium chloride (R = C8–C10)	≥90%	Classic phase-transfer/extraction quaternary ammonium salt (mixture); used for anion exchange, extraction of metal complex anions, and phase-transfer catalysis. Record batch number and run blank controls when needed.
Extraction / phase transfer (hydrophobic viscous phase) | phosphonium (P66614⁺) | Cl⁻	258864-54-9	T303251	Trihexyl(tetradecyl)phosphonium chloride	≥97%	Strongly hydrophobic and thermally stable; commonly used for extraction/phase transfer/ion exchange. High viscosity—watch mass transfer and phase-separation behavior.
Hydrophobic functional phase / extraction / (can be used in electrochemistry) | phosphonium (P66614⁺) | TFSI⁻	460092-03-9	T282162	Trihexyl(tetradecyl)phosphonium bis(trifluoromethanesulfonyl)imide	≥95%	Super-hydrophobic, thermally stable, low volatility; used for metal extraction/ion exchange, lubricant additives, and hydrophobic functional phases. Viscosity can be high—consider temperature and mass transfer.
Electrochemistry / hydrophobic weakly coordinating | pyrrolidinium (PYR14⁺) | TFSI⁻	223437-11-4	B463040	1-Butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide	≥99%, H₂O ≤ 500 ppm	Typical electrolyte IL: weakly coordinating, hydrophobic, thermally stable. Low water content helps expand the window and improves reproducibility.
Electrochemistry / low viscosity, high conductivity | pyrrolidinium (PYR13⁺) | FSI⁻	852620-97-4	M304773	1-Methyl-1-propylpyrrolidinium bis(fluorosulfonyl)imide	≥98%	FSI⁻ systems often reduce viscosity and improve conductivity and low-temperature performance. Sensitive to water/acid/impurities—control water and acidity.
Electrochemistry / low viscosity, high conductivity | pyrrolidinium (PYR14⁺) | FSI⁻	1057745-51-3	B302146	1-Butyl-1-methylpyrrolidinium bis(fluorosulfonyl)imide	≥98%	Common FSI⁻ system for batteries/electrochemistry; control water, halides, and metal impurities to maintain the electrochemical window.
Electrochemistry / hydrophobic weakly coordinating | imidazolium (EMIM⁺) | TFSI⁻	174899-82-2	E359386	1-Ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide	≥99%	Classic hydrophobic electrolyte/solvent-type IL; water content affects both electrochemical window and conductivity.
Electrochemistry / low viscosity, high conductivity | imidazolium (EMIM⁺) | FSI⁻	235789-75-0	E404458	3-Ethyl-1-methyl-1H-imidazol-3-ium bis(fluorosulfonyl)imide (EMIMFSI)	≥98%	FSI⁻ is often used to improve conductivity and low-temperature behavior. Impurity-sensitive—control water.
Hydrophobic solvent / electrochemistry (water control needed) | imidazolium (EMIM⁺) | PF₆⁻	155371-19-0	E101504	1-Ethyl-3-methylimidazolium hexafluorophosphate (EMIMPF₆)	≥98%	PF₆⁻ systems are hydrophobic and often used as solvents/electrochemical media; water control and sealed storage are critical.
Electrochemistry / hydrophobic weakly coordinating | imidazolium (BMIM⁺) | TFSI⁻	174899-83-3	B101513	1-Butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide (BMIMTFSI)	≥98%	Classic electrolyte/hydrophobic solvent IL; suitable for batteries, electrodeposition, and separation phases. Water control improves reproducibility.
Hydrophobic solvent / electrochemistry (water control needed) | imidazolium (BMIM⁺) | PF₆⁻	174501-64-5	B107646	1-Butyl-3-methylimidazolium hexafluorophosphate	≥97%	Classic PF₆⁻ system; controlling water reduces hydrolysis risk and improves repeatability.
Strongly hydrophobic / weakly coordinating | imidazolium (BMIM⁺) | SbF₆⁻	174645-81-9	B305181	1-Butyl-3-methylimidazolium hexafluoroantimonate (BMIMSbF₆)	≥98%	Extremely hydrophobic and weakly coordinating; suitable for hydrophobic phases and some electrochemical/separation systems. Watch impurities and water content.
Hydrophobic / interfaces & extraction (also usable as electrolyte medium) | imidazolium (HMIM⁺) | TFSI⁻	382150-50-7	H157060	1-Hexyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide	≥98% (HPLC)	C6 chain increases hydrophobicity and viscosity; often used for hydrophobic extraction/interface systems and can serve as an electrolyte medium. Watch mass transfer.
Hydrophobic solvent / (can be used in electrochemistry) | pyridinium (BPy⁺) | PF₆⁻	186088-50-6	B101511	N-Butylpyridinium hexafluorophosphate	≥98%	Hydrophobic pyridinium PF₆⁻; used as solvent/separation/electrochemistry reference. PF₆⁻ requires strict water control.
Electrochemistry / hydrophobic weakly coordinating | quaternary ammonium (N1114⁺) | TFSI⁻	258273-75-5	B405164	Butyltrimethylammonium bis(trifluoromethanesulfonyl)imide	≥98%	Quaternary ammonium + TFSI⁻ electrolyte reference system; useful for comparing interfacial/reductive stability vs imidazolium. Control water and impurities.
Long-chain interfaces / biphasic extraction | imidazolium (OMIM⁺) | BF₄⁻	244193-52-0	M101530	1-Methyl-3-octylimidazolium tetrafluoroborate	≥98%	C8 chain enhances hydrophobicity and interfacial activity; used in extraction/separation, micelle/interface studies, and phase behavior. Water control improves consistency.
Long-chain interfaces / biphasic extraction | imidazolium (OMIM⁺) | PF₆⁻ (water control needed)	304680-36-2	M102652	1-Octyl-3-methylimidazolium hexafluorophosphate	≥95%	Classic long-chain PF₆⁻ biphasic system; PF₆⁻ hydrolysis risk must be addressed explicitly (water/acid/heating).
Medium polarity (often water-miscible/partially miscible) | imidazolium (EMIM⁺) | BF₄⁻	143314-16-3	E120493	1-Ethyl-3-methylimidazolium tetrafluoroborate (EMIMBF₄)	≥98%	BF₄⁻ system often used as a solvation/electrochemistry/separation reference; watch water control and hydrolysis boundaries.
Medium polarity (often water-miscible/partially miscible) | imidazolium (BMIM⁺) | BF₄⁻	174501-65-6	B359377	1-Butyl-3-methylimidazolium tetrafluoroborate (BMIMBF₄)	≥98%	Higher polarity and broad compatibility; used in catalysis/separation/electrochemistry reference work. Water control reduces hydrolysis-related risks.
Medium polarity | pyridinium (BPy⁺) | BF₄⁻	203389-28-0	B120504	1-Butylpyridinium tetrafluoroborate	≥98%	Can be used as solvent/electrolyte/extraction-media reference; water control remains important.
Medium polarity (more hydrophobic with longer chain) | pyridinium (HPy⁺) | BF₄⁻	474368-70-2	H303779	1-Hexylpyridinium tetrafluoroborate	≥98%	C6 chain increases hydrophobicity and viscosity; suitable for extraction/interface and solvent systems. Watch mass transfer.
Polymerizable / post-modifiable monomer | imidazolium (allyl) | BF₄⁻	851606-63-8	A304770	1-Allyl-3-methylimidazolium tetrafluoroborate	≥98%	Allyl group enables polymerization/crosslinking/post-modification; suitable for PIL/membrane materials. Water/impurities affect polymerization consistency.
Halide precursor / strongly coordinating, hydrophilic | imidazolium (EMIM⁺) | Cl⁻	65039-09-0	E120488	1-Ethyl-3-methylimidazolium chloride	≥98%	Common precursor for anion exchange and for cellulose/polysaccharide systems. Cl⁻ is strongly coordinating—evaluate impacts in electrochemistry/metal catalysis.
Halide precursor / strongly coordinating, hydrophilic | imidazolium (EMIM⁺) | Br⁻	65039-08-9	E101503	1-Ethyl-3-methylimidazolium bromide	≥98%	Common precursor (for preparing BF₄⁻/PF₆⁻/TFSI⁻, etc.); halides can strongly affect catalysis/electrochemistry.
Halide precursor / strongly coordinating, hydrophilic | imidazolium (BMIM⁺) | Cl⁻	79917-90-1	B359327	1-Butyl-3-methylimidazolium chloride (BMIMCl)	≥98%	Strong H-bond acceptor/strongly coordinating; widely used for cellulose/biomass dissolution and anion exchange. Highly hygroscopic—control water.
Halide precursor / strongly coordinating, hydrophilic | imidazolium (BMIM⁺) | Br⁻	85100-77-2	B107644	1-Butyl-3-methylimidazolium bromide	≥97%	General-purpose precursor; halides are strongly coordinating—evaluate impacts and batch impurities for electrochemistry/catalysis.
Halide precursor (more hydrophobic with longer chain) | imidazolium (HMIM⁺) | Cl⁻	171058-17-6	H101522	1-Hexyl-3-methylimidazolium chloride (HMIMCl)	≥98%	Longer-chain halides are more viscous and more hydrophobic; used for interfacial/surface systems or further anion exchange. Watch solubility and mass transfer.
Polymerizable monomer / halide precursor | imidazolium (AMIM⁺) | Cl⁻	65039-10-3	A101536	1-Allyl-3-methylimidazolium chloride (AMIMCl)	≥96%	Polymerizable/post-modifiable precursor; used for PIL/membrane materials or anion exchange. Cl⁻ is strongly coordinating—evaluate impacts.
Pyridinium halide precursor | pyridinium | Cl⁻	1124-64-7	B102663	1-Butylpyridinium chloride	≥98%	Strongly hygroscopic; often used as a precursor or reaction medium. Water content affects viscosity and the practical reaction window.
Strong dissolution / strong H-bond acceptor | imidazolium (EMIM⁺) | OAc⁻	143314-17-4	W131887	1-Ethyl-3-methylimidazolium acetate	≥97%	Common for cellulose/biomass dissolution and CO₂ absorption; strongly hygroscopic—water strongly affects viscosity and dissolving power.
Strong dissolution / strong H-bond acceptor | imidazolium (BMIM⁺) | OAc⁻	284049-75-8	B169261	1-Butyl-3-methylimidazolium acetate	≥95%	Same family, typically more viscous and slightly more hydrophobic; dissolution/swelling is highly water-dependent—record KF water content.
Hydrophilic, strongly polar | imidazolium (EMIM⁺) | methanesulfonate (OMs⁻)	145022-45-3	E121211	1-Ethyl-3-methylimidazolium methanesulfonate	≥99%	Highly polar and hydrophilic; used for polar reaction media, solvation, and salt-effect control. Not ideal as the main solvent when the widest hydrophobic electrochemical window is required.
Hydrophilic, strongly polar | imidazolium (EMIM⁺) | ethyl sulfate (EtSO₄⁻) (alkyl sulfate)	342573-75-5	E120491	1-Ethyl-3-methylimidazolium ethyl sulfate	≥99%	Typical hydrophilic alkyl-sulfate IL; strongly hygroscopic—water affects viscosity and outcomes.
Hydrophilic, strongly polar | imidazolium (EMIM⁺) | methyl sulfate (MeSO₄⁻) (alkyl sulfate)	516474-01-4	E170730	1-Ethyl-3-methylimidazolium methyl sulfate	≥98% (HPLC)	Highly polar, hydrophilic, strong solvation platform; used for dissolution/extraction in polar systems. Control water content.
Hydrophilic, strongly polar | imidazolium (BMIM⁺) | methyl sulfate (MeSO₄⁻) (alkyl sulfate)	401788-98-5	B138798	1-Butyl-3-methylimidazolium methyl sulfate	≥97%	Similar but more viscous; suitable for polar reactions/extractions. Record water content for consistency.
Hydrophilic, strongly polar | imidazolium (BMIM⁺) | p-toluenesulfonate (p-TsO⁻)	410522-18-8	B138815	1-Butyl-3-methylimidazolium p-toluenesulfonate	≥97%	Aromatic sulfonate system: high polarity, often used as solvent/catalytic medium; more viscous and hygroscopic—watch mass transfer and drying.
Medium polarity / weakly coordinating sulfonate | imidazolium (BMIM⁺) | triflate (OTf⁻ / TfO⁻)	174899-66-2	B111364	1-Butyl-3-methylimidazolium trifluoromethanesulfonate	≥97%	OTf⁻ is relatively weakly coordinating and widely used; for reaction media/catalysis and electrochemistry reference. Hygroscopic—control water.
Strong solvation / biomass systems | imidazolium (EMIM⁺) | diethyl phosphate (DEP⁻)	848641-69-0	W196197	1-Ethyl-3-methylimidazolium diethyl phosphate (EMIMDEP)	≥98%	Common platform for biomass/cellulose dissolution and strong solvation; hygroscopic—water affects viscosity and dissolution performance.
Phosphate ester anion (more hydrophobic) | imidazolium (BMIM⁺) | dibutyl phosphate (DBP⁻)	663199-28-8	B101519	1-Butyl-3-methylimidazolium dibutyl phosphate	≥96%	More hydrophobic phosphate ester system; used in phase behavior/extraction/interfaces and materials processing. Watch water content and viscosity.
Coordinating / low-viscosity system | imidazolium (EMIM⁺) | DCA⁻ (dicyanamide)	370865-89-7	E121213	1-Ethyl-3-methylimidazolium dicyanamide (EMIMDCA)	≥98%	DCA⁻ often yields low viscosity and higher conductivity; may coordinate metals/affect catalysis—run comparative controls.
Coordinating / low-viscosity system | imidazolium (BMIM⁺) | DCA⁻ (dicyanamide)	448245-52-1	B102303	1-Butyl-3-methylimidazolium dicyanamide	≥97%	Same family, coordinating anion; suitable for fast mass-transfer systems and as an electrochemistry/electrodeposition reference. Watch impurity effects.
Strongly coordinating / complexation system | imidazolium (EMIM⁺) | SCN⁻ (thiocyanate)	331717-63-6	W136549	1-Ethyl-3-methylimidazolium thiocyanate	≥98%	SCN⁻ is strongly complexing/coordinating; used for metal complexation, extraction, electrodeposition, and separations. Can strongly alter catalytic coordination environments.
Strongly coordinating / complexation system | imidazolium (BMIM⁺) | SCN⁻ (thiocyanate)	344790-87-0	B102306	1-Butyl-3-methylimidazolium thiocyanate	≥95%	Same family with a strongly coordinating anion; water/impurities can change complexation and partition behavior.
Hydrophilic, strongly polar | imidazolium (BMIM⁺) | NO₃⁻ (nitrate)	179075-88-8	B102304	1-Butyl-3-methylimidazolium nitrate (BMIMNO₃)	≥95%	Strongly polar and hydrophilic; suitable for polar solvent environments and some separations. Check compatibility with strongly reducing or sensitive systems.
Brønsted-acidic IL | imidazolium (EMIM⁺) | HSO₄⁻	412009-61-1	E121210	1-Ethyl-3-methylimidazolium hydrogen sulfate	≥98%	Acidic medium for acid catalysis/biomass processing/extraction; hydrophilic and hygroscopic—watch corrosion and water content.
Brønsted-acidic IL | imidazolium (BMIM⁺) | HSO₄⁻	262297-13-2	B101514	1-Butyl-3-methylimidazolium hydrogen sulfate	≥95%	HSO₄⁻ acidic IL; used for esterification/condensation/hydrolysis, etc. Watch material compatibility and water content.
Brønsted-acidic IL (SO₃H-functionalized cation) | imidazolium | HSO₄⁻	827320-59-2	S304729	1-Butylsulfonic acid-3-methylimidazolium hydrogen sulfate	≥98%	Typical strong Brønsted-acidic IL; suitable for esterification/condensation/biomass conversion. More viscous and hygroscopic—watch corrosion and mass transfer.

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