). While heating, the XRD pattern of IL@CuBTC starts from a pattern similar to that of CuBTC, with narrowly split (220), ( ) and (440) peaks. Approaching 100 °C, the initially weak, gradual split transforms into a pronounced, stable state up to the transition temperature of 220 °C, at which the CuBTC pattern is recovered and the split disappears. Obviously, the low-temperature state represents a distorted polymorph of CuBTC.