Hydrophobicity directly depends on the charge density of anion. since in [NTf2] charge is more delocalized than [PF6], former is more hydrphobic than latter.

Hi to all,

before reading of my explanation, please visit http://chemwiki.ucdavis.edu/Physical_Chemistry/Physical_Properties_of_Matter/Atomic_and_Molecular_Properties/Intermolecular_Forces/Hydrophobic_interaction, and

http://en.wikipedia.org/wiki/Hydrophobic_effect

  It is clear from thermodynamics that hydrophobic interaction is depend on molecular volume (because larger fragments replace more water), polarity and polaraizability of chemical groups. Hydrophobic properties induced by presence (and number) of low-polar and low polarizable atoms and groups.

Looking at Shashi example, we can see that [NTf2] is much larger than [PF6]. This is main reason of his greater hydrophobicity. No delocalization exist in (CF3SO2)2N' - becase in contrary to -N-CO- pair, delocalization in -N-SO2- is negligible . Often, possibility of delocalization by heteroatoms is indication, that molecule is easy polarazable and is "bed hydrophobe". Check guanidinium (Log P= -4.09) and isopropylammonium (Log P= -0,08) cations - with practically same volume and form, charge is distributed in first and localized in second cation.

could you please tell , what  is the force of interaction between these anion and cations especially in Magnetic ionic liquids? is that electrostatic or ionic bond formation between cation and anions in these ionic liquids ?