Unlocking Thermal Flexibility in Ni-Based Fluorinated Square-Pillared MOFs: Insights into Pore Transitions and Node-Linker Dynamics

The thermally responsive behavior of metal–organic frameworks offer a pathway to materials capable of adapting their internal architecture to external stimuli. In this study, we elucidate how fluorinated AlF5 pillars, together with linker-dependent internal motions, govern the distinctive thermoresponsive behavior of ALFFIVE-Ni frameworks. Using molecular simulations, we examine the temperature-induced structural evolution across three linkers of increasing rigidity and length and show that linker tilting, mediated through node–linker dynamics, drives the transformation from large-pore (lp) to narrow-pore (np) states. The magnitude and onset of this transition are finely tuned by linker chemistry, while all systems display pronounced negative thermal expansion arising from coordinated internal vibrations. Water interactions further modulate this response by stabilizing the framework under humid conditions and partially suppressing thermal contraction. By clarifying the microscopic mechanisms underlying flexibility in fluorinated MOFs, this work provides a foundation for designing thermally adaptive materials with tailored pore behavior, structural responsiveness, and application-specific performance.