Water‐Free Rare‐Earth‐Metal Ionic Liquids/Ionic Liquid Crystals Based on Hexanitratolanthanate(III) Anion

The hexanitratolanthanate anion (La(NO 3 ) 6 3− ) is an interesting symmetric anion suitable to construct the component of water‐free rare‐earth‐metal ionic liquids. The syntheses and structural characterization of eleven lanthanum nitrate complexes, [C n mim] 3 [La(NO 3 ) 6 ] ( n =1, 2, 4, 6, 8, 12, 14, 16, 18), including 1,3‐dimethylimidazolium hexanitratolanthanate ([C 1 mim] 3 [La(NO 3 ) 6 ], 1 ), 1‐ethyl‐3‐methylimidazolium hexanitratolanthanate ([C 2 mim] 3 [La(NO 3 ) 6 ], 2 ), 1‐butyl‐3‐methylimidazolium hexanitratolanthanate ([C 4 mim] 3 [La(NO 3 ) 6 ], 3 ), 1‐isobutyl‐3‐methylimidazolium hexanetratolanthanate ([ iso C 4 mim] 3 [La(NO 3 ) 6 ], 4 ), 1‐methyl‐3‐(3′‐methylbutyl)imidazolium hexanitratolanthanate ([MC 4 mim] 3 [La(NO 3 ) 6 ], 5 ), 1‐hexyl‐3‐methylimidazolium hexanitratolanthanate ([C 6 mim] 3 [La(NO 3 ) 6 ], 6 ), 1‐methyl‐3‐octylimidazolium hexanitratolanthanate ([C 8 mim] 3 [La(NO 3 ) 6 ], 7 ), 1‐dodecyl‐3‐methylimidazolium hexanitratolanthanate ([C 12 mim] 3 [La(NO 3 ) 6 ], 8 ), 1‐methyl‐3‐tetradecylimidazolium hexanitratolanthanate ([C 14 mim] 3 [La‐(NO 3 ) 6 ], 9 ), 1‐hexadecyl‐3‐methylimid‐azolium hexanitratolanthanum ([C 16 dmim] 3 [La(NO 3 ) 6 ], 10 ), and 1‐methyl‐3‐octadecylimidazolium hexanitratolanthanate ([C 18 mim] 3 [La(NO 3 ) 6 ], 11 ) are reported. All new compounds were characterized by 1 H and 13 C NMR, and IR spectroscopy as well as elemental analysis. The crystal structure of compound 1 was determined by using single‐crystal X‐ray diffraction, giving the following crystallographic information: monoclinic; P 2 1 / c ; a =15.3170 (3), b =14.2340 (2), c =13.8954(2) Å; β =94.3453(15)°, V =3020.80(9) Å 3 , Z =4, ρ =1.764 g cm −3 . The coordination polyhedron around the lanthanum ion is rationalized by six nitrate anions with twelve oxygen atoms. No hydrogen‐bonding network or water molecule was found in 1 . The thermodynamic stability of the new complexes was investigated by using thermogravimetric analysis (TGA). The water‐free hexanitratolanthanate ionic liquids are thermal and moisture stable. Four complexes, namely complexes 8 – 11 , were found to be ionic liquid crystals by differential scanning calorimetry (DSC) and polarizing optical microscopy (POM). They all present smectic A liquid‐crystalline phase.