Neutral polar hybrid perovskites of [(CH3)2SO][RE(HCOO)3] (RE = Lu and Y): Phase transitions driven by transformation of weak C–H⋯O interactions

Two iso-structural hybrid perovskites of [(CH3)2SO][RE(HCOO)3] for RE3+ = Lu3+ and Y3+ are polar and possess neutral rare earth formate frameworks incorporating dimethyl sulfoxide locating in the framework cavities and coordinating to the RE3+ ions. The materials display reversible phase transitions at 172 K and 138 K for Lu and Y, respectively. The phase transitions are driven by the transformations of weak C–H⋯O interactions and the gradual twists of the constituents in low temperature, which control the order–disorder states of dimethyl sulfoxide and account for different anisotropic thermal expansion behaviors for the two phases and the characters of dielectric responses.