Ionic Liquids

JCOSMO provides native support for ionic liquids (ILs).

In normal use, ionic liquids should be defined as a single pseudo-compound (ion pair) using bracket notation, for example:

[BMIM][BF4]

This is the recommended and default approach.

Working with individual ions is possible, but is intended only for advanced electrolyte modeling.

In JCOSMO, ionic liquids are normally handled as neutral ion pairs using the bracket notation:

[ CATION ][ ANION ]

Example:

[BMIM][BF4]

Internally, JCOSMO:

  • Searches the database for BMIM+1
  • Searches the database for BF4-1
  • Validates charge balance
  • Automatically constructs the neutral pseudo-compound

The resulting ionic liquid behaves as a single compound in the mixture.

This approach:

  • Ensures automatic electroneutrality
  • Prevents charge imbalance errors
  • Keeps the mixture definition simple
  • Is appropriate for most IL–solvent systems

Adding an Ionic Liquid (Graphical Interface)

To add an ionic liquid:

  1. Click “Add Salt…”
  2. Select the desired cation
  3. Select the desired anion
  4. Click Accept

JCOSMO automatically creates the pseudo-compound and adds it to the selected compounds list.

This method avoids naming errors and is strongly recommended.

Direct Name Entry

Instead of using Add Salt…, you may type the full ion pair directly:

[BMIM][BF4]

If both ions exist in the database, JCOSMO will construct the pseudo-compound automatically.

Multivalent Ions

If charges are not +1 and −1, stoichiometry is reflected explicitly in the name.

Example:

  • DEA+1
  • CO3-2

The ionic liquid becomes:

[DEA]2[CO3]

JCOSMO automatically enforces charge neutrality when constructing pseudo-compounds.

Advanced Use Only: Explicit Ion Representation

It is possible to add the ions separately:

  • BMIM+1
  • BF4-1

In this case, the system becomes a multicomponent ionic mixture.

⚠️ Important — Manual Electroneutrality Required

When working with explicit ions, the user must manually ensure that the total mixture charge is zero:

Σ (zi · xi) = 0

where:

  • zi is the ionic charge
  • xi is the mole fraction

JCOSMO does not automatically enforce electroneutrality in explicit-ion mode.

This makes the explicit-ion approach significantly more error-prone.

For standard ionic liquid–solvent systems, the pseudo-compound notation (e.g., [BMIM][BF4]) should always be preferred.

Abbreviated Names for Ions

JCOSMO uses standardized abbreviated names for ionic liquid species.

Common cations:

  • EMIM — 1-ethyl-3-methylimidazolium
  • BMIM — 1-butyl-3-methylimidazolium
  • HMIM — 1-hexyl-3-methylimidazolium

Common anions:

  • BF4 — tetrafluoroborate
  • PF6 — hexafluorophosphate
  • BTI — bis(trifluoromethylsulfonyl)imide
  • DCA — dicyanamide

The internal database stores the charged forms (e.g., BMIM+1, BF4-1), but users should normally work with the neutral ion pair notation.

Database Behavior

When an ionic liquid is defined as a pseudo-compound:

  • JCOSMO searches for the charged species
  • Verifies charge balance
  • Constructs the neutral ion pair
  • Adds it to the mixture as a single compound

If one of the required ions is missing from the database, the ionic liquid cannot be constructed.

Recommendation

For nearly all ionic liquid applications:

  • Use the ion pair pseudo-compound notation
  • Prefer the “Add Salt…” dialog
  • Avoid explicit-ion mode unless performing electrolyte-specific modeling

The pseudo-compound approach is safer, simpler, and less prone to modeling errors.