Flexible coordination environments of lanthanide complexes grown from chloride-based ionic liquids

Hydrated lanthanide(III) chlorides, LnCl(3)center dot xH(2)O (Ln = La, Pr, Nd, Sm, Eu, Gd; x = 6-7) readily dissolve in the low melting ionic liquid 1-ethyl-3-methylimidazolium chloride ([C(2)mim]Cl) in an open vessel at 110 degrees C, and upon cooling crystallize as the anhydrous [C(2)mim](3)[LnCl(6)]. The crystal structures exhibit a face-centered packing arrangement of the [LnCl(6)](3-) anions, with the cations located as slip aligned pairs in the void spaces which participate in hydrogen-bonding to chlorides. A second crystalline form of the Gd3+ complex, GdCl3(OH2)(4)center dot 2([C(2)mim]Cl), was isolated when the above reaction was conducted in a sealed system. For comparison, a third Gd3+ compound was grown from the ionic liquid 1-butyl-3-methylimidazolium chloride ([C(4)mim]Cl) using the same unsealed conditions as above, and was found to be [C(4)mim](3)[GdCl6]. This compound exhibits a different packing arrangement to that observed for the [C(2)mim](+) analogs. Based on these findings, ILs would appear to offer new crystallization process options based on their often high thermal stabilities and low to negligible vapor pressures.