The thermal-engine behaviour of 1 is driven by changes in k with temperature. Notably, the temperature at which the crystal becomes most bendable (265 K in Figure ) is close to the boundary between the HT phase and MT state (~270 K in Figure ), indicating that softening is correlated with its structural changes. The following bending mechanism can be proposed based on the elongation of the crystal upon cooling (Figure ). ( ) The weight causes the elastic crystal to arc. The outer arc is stretched, whereas the inner arc is compressed. That is, the mechanical force elongates the a-axis in the outer arc and compresses the a-axis in the inner arc. (2) When the crystal is cooled to approximately 270 K, the outer-arc region preferentially changes to the MT state with a preference for a long a-axis, whereas the inner-arc region remains in the HT phase with a preference for a short a-axis. Such an inhomogeneous structural phase transition renders the outer arc longer and the inner arc shorter, resulting in the bending of the crystal, which appears as softening, upon cooling. (3) Further decreases in temperature convert the crystal into an entirely