Bipolar Molecular Torque Wrench Modulates the Stacking of Two-Dimensional Metal-Organic Framework Nanosheets

The precise modulation of nanosheet stacking modes introduces unforeseen properties and creates momentous applications but remains a challenge. Herein, we proposed a strategy using bipolar molecules as torque wrenches to control the stacking modes of 2-D Zr-1,3,5-(4-carboxylphenyl)-benzene metal-organic framework (2-D Zr-BTB MOF) nanosheets. The bipolar phenyl-alkanes, phenylmethane (P-C₁) and phenyl ethane (P-C₂), predominantly instigated the rotational stacking of Zr-BTB-P-C₁ and Zr-BTB-P-C₂, displaying a wide angular distribution. This included Zr-BTB-P-C₁ orientations at 0, 12, 18, and 24° and Zr-BTB-P-C₂ orientations at 0, 6, 12, 15, 24, and 30°. With reduced polarity, phenyl propane (P-C₃) and phenyl pentane (P-C₅) introduced steric hindrance and facilitated alkyl hydrophobic interactions with the nanosheets, primarily resulting in the modulation of eclipsed stacking for Zr-BTB-P-C₃ (64.8%) and Zr-BTB-P-C₅ (93.3%) nanosheets. The precise angle distributions of four Zr-BTB-P species were in agreement with theoretical calculations. The alkyl induction mechanism was confirmed by the sequential guest replacement and 2-D ¹³C-¹H heteronuclear correlation (HETCOR). In addition, at the single-particle level, we first observed that rotational stacked pores exhibited similar desorption rates for xylene isomers, while eclipsed stacked pores showed significant discrepancy for xylenes. Moreover, the eclipsed nanosheets as stationary phases exhibited high resolution, selectivity, repeatability, and durability for isomer separation. The universality was proven by another series of bipolar acetate-alkanes. This bipolar molecular torque wrench strategy provides an opportunity to precisely control the stacking modes of porous nanosheets.