Solid State Machinery of Multiple Dynamic Elements in a Metal-Organic Framework.

Area of Science:

• Materials Science
• Supramolecular Chemistry
• Nanotechnology

Background:

• Metal-Organic Frameworks (MOFs) offer tunable porous architectures.
• Engineering molecular machines in solids requires precise control over motion.
• Flexible MOFs can host and manipulate mobile guest molecules.

Purpose of the Study:

• To design and investigate a flexible, interpenetrated MOF capable of coordinated molecular motion.
• To explore the dynamics of guest molecules and framework components under external stimuli.
• To establish structure-dynamics relationships in MOF-based molecular machinery.

Main Methods:

• Synthesis of a two-fold interpenetrated pillared MOF.
• Characterization using multinuclear solid-state NMR, synchrotron radiation XRD, and gas sorption.
• Computational modeling to elucidate rotor-structure interplay.
• Stimulation of dynamics using iodine vapor and pressurized CO2.

Main Results:

• The MOF precisely organizes bicyclopentane (BCP), pyridyl rotors, and an azo group.
• Chemical stimuli induce reciprocal sub-network sliding, altering channel sizes and dynamics.
• Iodine adsorption triggers piston-like motion, increasing BCP mobility to ultra-fast regimes at low temperatures.
• Pyridyl rotors exhibit differential dynamics, and the azo group facilitates crank-like motion.
• Pressurized CO2 modulates BCP dynamics based on site occupation.

Conclusions:

• The engineered MOF functions as a sophisticated molecular machine in the solid state.
• Framework flexibility is intrinsically coupled to the observed rotary dynamics.
• This work demonstrates a pathway for designing dynamic functional materials based on coordinated molecular motion.