Zero in-Plane Thermal Expansion in Guest-Tunable 2D Coordination Polymers

Zero in-plane thermal expansion (TE) in a two-dimensional (2D) coordination polymer is demonstrated. The combination of components that expand and those that shrink into zigzag layers results in no net area change in the 2D materials with temperature. Single crystals of [Mn(salen)]2[Mn(N)(CN)4(guest)] (salen = N,N′-ethylenebis(salicylideneaminato), guest = MeOH and MeCN) were prepared, and variable-temperature single-crystal X-ray structural analyses demonstrated that these compounds exhibited both anisotropic positive and negative thermal expansion depending on the guest species. The TE behavior results from distortions of the octahedral coordination geometry of [Mn(salen)]+ units in the zigzag layers. When both guests MeOH and MeCN were incorporated into one material, [Mn(salen)]2[Mn(N)(CN)4(MeOH)0.25(MeCN)0.75], zero in-plane TE resulted in a range of temperature between 380 and 440 K.