This invention relates to using a guanidinium-based ionic liquid as an absorbent material in an absorption chiller. The invention provides an absorption chiller comprising a mixture of a refrigerant and an absorbent, and the absorbent is a guanidinium-based ionic liquid. A preferred refrigerant is water. This invention also provides a method for synthesizing N,N,N′,N′,N″,N″-hexamethylguanidinium acetate.