Polymorphous crystals of chlorozincate-choline chloride ionic liquid (IL) in different molar ratios were incubated at 5 degrees C and characterized by X-ray diffraction (XRD), differential scanning calorimeter (DSC) and optical microscope (OM). It is clearly shown that the properties of IL crystal change significantly with A(ZnCl2) (mole fraction of ZnCl2) over the range from 0.67 to 0.40. Crystal (a) (m.p. 45 degrees C) is formed at X(ZnCl2) = 0.67, both crystal (a) and crystal (b) (m.p. 85 degrees C) are observed at X(ZnCl2) = 0.50. However, crystal (c) (m.p. 27 degrees C) and non-coordinated choline chloride are observed at X(ZnCl2) = 0.40. Morphology of the IL crystal also changes greatly with the X(ZnCl2). This investigation reveals that structures and properties of the IL anions vary with the X(ZnCl2) and the molar ratio is a pivotal factor dominating the IL property. (c) 2005 Elsevier B.V. All rights reserved.