The ability to tune physical properties is attractive for the development of new materials for myriad applications. Understanding and controlling the structural dynamics in complicated network structures like coordination polymers (CPs) is particularly challenging. We report a series of two-dimensional CPs [Mn(salen)][M(CN)]· xHO (M = Pt (1), PtI (2), and MnN (3)) incorporating zigzag cyano-network layers that display composition-dependent anisotropic thermal expansion properties. Variable-temperature single-crystal X-ray structural analyses demonstrated that the thermal expansion behavior is caused by double structural distortions involving [Mn(salen)] units incorporated into the zigzag layers. Thermal relaxations produce structural transformations resulting in positive thermal expansion for 2·HO and negative thermal expansion for 3. In the case of 1·HO, the relaxation does not occur and zero thermal expansion results in the plane between 200 to 380 K. The present study proposes a new strategy based on structural distortions in coordination networks to control thermal responsivities of frameworks.

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)][Mn(N)(CN)(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)][Mn(N)(CN)(MeOH)(MeCN)], zero in-plane TE resulted in a range of temperature between 380 and 440 K.

Consecutive oxidative additions of iodine on the undulating 2D coordination polymer produced unprecedented anisotropic structures.